Study on the Influence Mechanism of the Organic Matter Components on Phosphorus Adsorption-Release Kinetics in Lake Sediment

Study on the Influence Mechanism of the Organic Matter Components on Phosphorus Adsorption-Release Kinetics in Lake Sediment | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Study on the Influence Mechanism of the Organic Matter Components on Phosphorus Adsorption-Release Kinetics in Lake Sediment Haichao Zhao, Songtao Liu, Haixiang Zhao, Zhihong Huang, Lixin Jiao, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6640256/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Organic matter (OM) components in sediments play a significant role in influencing phosphorus (P) adsorption and release behavior at the sediment-water interface. However, the underlying mechanisms remain unclear. This study examines the relationship between OM components and P adsorption-release kinetics across various sediment types. Results show that as the OM content in sediments increases, both the maximum P adsorption capacity and the maximum P release capacity exhibit a linear increase. The release intensity of P follows an initial increase and subsequent decrease in an exponential pattern (Exp3P2). Similarly, P adsorption intensity first decreases and then increases in an exponential manner (Exp3P2), while the equilibrium concentration of P adsorption-desorption shows an exponential increase followed by a decrease (Exp3P2). At low OM content, an increase in OM leads to greater P release intensity, reduced adsorption intensity, and an increase in equilibrium concentration. At high OM content, however, the P release intensity decreases, adsorption intensity increases, and the equilibrium concentration decreases. The activity of OM plays a key role: low OM activity reduces the P release-adsorption potential, whereas high activity enhances it. When OM degradation is low, it inhibits P release and promotes P adsorption, while high OM degradation facilitates P release and inhibits adsorption. The changes in the quality and quantity of OM in lake sediments significantly affect the physical and chemical mechanisms of P adsorption and release, thereby regulating P behavior at the sediment-water interface. Organic matter phosphorus exponential variations P adsorption-desorption Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 1. Introduction Eutrophication is one of the most pressing environmental issues affecting lakes worldwide. To better understand the mechanisms behind lake water blooms and to support effective control measures, extensive research has been conducted on the causes of lake eutrophication (Dokulil and Teubner, 2000 ; Kong and Gao, 2005 ). Excess phosphorus (P) in water bodies is a primary driver of eutrophication, leading to significant environmental consequences (Long et al., 2021 ). As P concentrations rise, blue-green algae often dominate the phytoplankton community (Steiberg and Hartmann, 1988 ). Lake sediments act as both a "source" and "sink" of P for the overlying water. When external P inputs increase, the sediment adsorbs P; conversely, when external P inputs decrease, the sediment releases P, thus making sediment an important source of nutrients contributing to eutrophication (Huang et al., 2011 ). When P concentrations in the lake water are low, accumulated P in the sediment is released, further contributing to eutrophication (O'Neil et al., 2012 ). The concentration of endogenous P in the overlying water results from the dynamic balance of P adsorption-release at the sediment-water interface. The nutrient level of lake water is largely determined by this adsorption-release equilibrium between the sediment and the overlying water (Peng et al., 2007 ). Determining the kinetics of P release-adsorption in sediments under controlled laboratory conditions can provide insights into the maximum adsorption capacity, maximum release capacity, release intensity, and adsorption intensity of P (Wang et al., 2009 ; Wang et al., 2006 ). The thermodynamic process of P adsorption can further reveal the adsorption-desorption equilibrium concentration at the sediment-water interface (Wang et al., 2006 ). Therefore, studying the kinetics of P adsorption and release in sediments is crucial to understanding the mechanisms governing P dynamics at the sediment-water interface in lakes. Many studies have shown that sediment composition is directly related to its P adsorption capacity (Wang et al., 2009 ). Organic matter (OM), a significant component of sediment, plays a key role in the transport of nitrogen (N) and P. For example, Wang et al. ( 2007 ) observed a positive correlation between OM content and P adsorption in sediments. Previous research has shown that the P adsorption-release capacity increases with higher total organic matter (TOM) content, while the equilibrium adsorption-desorption concentration decreases with greater OM activity in the sediments of Erhai Lake (Zhao et al., 2014 ). Low-molecular-weight organic acids can compete with P for adsorption sites through direct physical or electrostatic interactions (Weyers et al., 2017 ). Humic substances, which are macromolecular in nature, can form organic-inorganic complexes with Fe and Al, providing additional adsorption sites for inorganic P and enhancing P adsorption (Gerke and Hermann, 1992 ). Furthermore, OM has chemical binding effects such as valence ion adsorption and molecular coupling; H + released from OM can protonate mineral surface groups, thereby facilitating P adsorption (Zhao et al., 2014 ). OM can also react with Ca²⁺ to form P-Ca-OM complexes (Lei et al., 2018 ). Through the processes of degradation and polymerization, OM components regulate P adsorption and release at the sediment-water interface by altering the physical, chemical, and biological properties of the sediment. The influence of OM on P adsorption and release is complex, and the specific mechanisms by which OM composition affects P adsorption-release kinetics are not fully understood. Thus, exploring the relationship between OM components and P adsorption-release dynamics in lake sediments is crucial for understanding the processes driving lake eutrophication. This study investigates the OM characteristics in sediments of different layers from one sampling point in Erhai Lake, as well as from surface sediments across various regions of the lake and from sediments in different lakes. Using P release kinetics, adsorption kinetics, and thermodynamic models, the study aims to uncover the P adsorption-release kinetics in lake sediments. The study also analyzes the relationship between OM components in sediment and the P adsorption-release kinetics, focusing on the impact of OM degradation and composition on P dynamics at the sediment-water interface. This will help clarify the regulatory mechanisms of OM on P release from lake sediments. 2. Materials and methods 2.1. Study area and sample collection Erhai Lake (25°35′N − 25°58′N; 100°05′E − 100°17′E) is the largest fault lake in the Yunnan Plateau. The average depth of the lake is approximately 10 m, with the deepest point reaching 20 m at the center (Fig. 1 ). The water surface area spans about 249 km², and its volume is approximately 2.8 × 10⁹ m³. For this study, surface sediment samples (at a depth of 10 cm) were collected from 10 sampling points, selected based on variations in organic matter (OM) deposition, water depth, hydrodynamics, and aquatic vegetation distribution across different areas of Erhai Lake. Additionally, a 30 cm sediment core was taken from the central platform in the southern part of the lake. The samples were layered every 2 cm in the field, placed into plastic bags, and stored in an incubator at 4°C. After transport to the laboratory, the samples were freeze-dried, ground through a 100-mesh sieve, and stored in the dark for subsequent analysis. 2.2 Determination method The kinetic test of phosphorus (P) release from sediment was conducted as described by Zhang et al. ( 2012 ) and Zhao et al. ( 2014 ). Accurately weighed 0.5 g dry sediment samples were added to a series of 100 mL centrifuge tubes, each containing 50 mL of 0.02 mol·L⁻¹ KCl solution. The tubes were then incubated (200 rpm) in a dark shaker for 24 hours at 25°C ± 1°C. At specified time intervals (0.5, 1.5, 3, 5.5, 9, 15, 24, 36, and 48 hours), the centrifuge tubes were removed, and the samples were centrifuged at 5000 × g for 15 minutes. The supernatant was passed through a 0.45 µm GF/C filter membrane, and the filtrate was analyzed for soluble reactive phosphorus (SRP) using the molybdenum blue/ascorbic acid colorimetric method with a dual-beam ultraviolet/visible spectrometer (TU-1900, Beijing Purkinje General Instrument Co., Ltd, Beijing, China). P release kinetics were simulated using a first-order kinetic model, as shown in Eq. (1): C t = C 0 (1-e − Krt ) (1) Where C 0 is the maximum P release capacity from sediment (Qr-max, mg·kg⁻¹), and K r is the reaction constant that represents the P release intensity from the sediment. The kinetic test for P adsorption by sediment followed the procedures of Zhang et al. ( 2012 ) and Zhao et al. ( 2014 ). A 0.5 g dry sediment sample was accurately weighed and placed into a 100 mL acid-washed centrifuge tube. Then, 50 mL of 10 mg·L⁻¹ KH 2 PO 4 solution was added to the tube, which was subsequently covered and shaken (250 rpm) at 25°C ± 1°C in the dark. Samples were taken at 0.5, 1.5, 2.5, 5, 9, 13, 18, and 24 hours. The tubes were then centrifuged at 5000 rpm for 10 minutes in a constant temperature (25°C ± 1°C) centrifuge. The supernatant was filtered through a 0.45 µm GF/C filter membrane for P concentration analysis. All experiments were performed in triplicate under the same conditions, with relative mean deviations of less than 5%. The P adsorption kinetics were modeled using the modified Elovich equation (Eq. 2): q = a + K a ln t (2) Where q is the amount of P adsorbed (mg·kg⁻¹), a is the initial adsorption amount, K a is the adsorption rate constant, and t is the time. The maximum adsorption capacity, Qa-max, was calculated at 12 hours using Eq. (3): Q a−max =a+K a ln(12) (3) Q a−Max reflects the maximum adsorption capacity of the sediment, indicating the number of available adsorption sites for P. The thermodynamic test for P adsorption by sediment was carried out as described by Zhang et al. ( 2012 ) and Zhao et al. ( 2014 ). A 0.5 g dry sediment sample was weighed and placed into a 100 mL centrifuge tube containing 50 mL of KH 2 PO 4 solution at concentrations of 0, 0.01, 0.02, 0.05, 0.08, 0.10, 0.15, and 0.20 mg·L⁻¹. The solution was then incubated (250 rpm) at 25°C ± 1°C for 24 hours in the dark. The tubes were centrifuged at 5000 rpm for 10 minutes, and the supernatant was filtered through a 0.45 µm filter membrane for P concentration analysis. P adsorption was fitted using the following equation (Eq. 4): Q = Q max ×k× C e (1 + k C e ) (4) Where Q is the amount of P adsorbed (mg·kg⁻¹), Q max is the maximum adsorption capacity (mg·kg⁻¹), k is the adsorption constant, and C e is the P adsorption-desorption equilibrium concentration (mg·L⁻¹). Total organic matter (TOM) was determined using the K 2 Cr 2 O 7 -H 2 SO 4 external heating method (Zhao et al., 2014 ). Active sediment organic matter (ASOM) was measured using the KMnO 4 oxidation method at 333 nmol·L⁻¹ (Lefroy and Blair, 1993). Light fraction organic matter (LFOM) was determined using the NaI specific gravity method (Janzen et al., 1992 ). 2.3 Data analysis Data on organic matter (OM) components in the surface sediment of Erhai Lake and lakes located in the Mid-lower reaches of the Yangtze River were obtained from Zhao et al. ( 2013 ) (Figure S1) and Yi et al. ( 2008 ) (Figure S2), respectively. Data on phosphorus (P) release kinetics in other lakes in the Mid-lower reaches of the Yangtze River were sourced from Jin et al. ( 2007 ) (Figure S2). Additionally, P adsorption kinetics data for other lakes in this region were collected from Yi ( 2008 ) and Wang et al. ( 2006 ) (Figure S2). The P adsorption-release kinetic model, kinetic parameters, and OM component models for the lake sediments were analyzed using Origin 9 software. 3. Results 3.1 Effect of OM Components on Phosphorus (P) Adsorption-Release in Stratified Sediments at a Sampling Point in Erhai Lake 3.1.1 Vertical Variation of OM Components and P Adsorption-Release Kinetics in Erhai Lake Sediments P burial process of lake sediments is the result of the constant adsorption and release. The transformation of various forms of P in sediments may also occur in the biogeochemical process of continuous change. With the increase of sedimentary depth in Erhai Lake, TOM, ASOM, and LFOM showed a rapid downward trend in the 0–10 cm layers, and then basically stabilized below 10 cm. The minimum value of TOM appeared at 10 cm layer (Fig. 2 (a, b)). The ASOM/TOM and LFOM/TOM showed a fluctuating downward trend with the increase of sedimentary depth, and the highest value appeared at 8–10 cm layers. The activity and decomposition degree of OM were the highest at 8–10 cm layers of the sediment. The OM components in the upper layer (0–10 cm) of sediment were affected by the deposition and degradation of exogenous substances, and in the lower layer (below 10 cm) of sediment was affected by the upward release and burial of active substances, so the inflection point of action appeared at 10 cm layer of sediment. With the increase of sediment depth, the Q r−max and the K r showed a downward trend, the Q a−max and the K a showed a fluctuating upward trend, the EPC 0 showed a fluctuating downward trend (Fig. 2 (c, d, e)). In the 0–10 cm sedimentary layer, Q r−Max decreased rapidly, while Q a−Max and K a increase rapidly. At the same time, the peak values of EPC 0 and K r occurred in the 4–6 cm sedimentary layer. In the sedimentary layer below 10 cm, the variation of Q r−Max , Q a−Max , K r and EPC 0 tended to be stable, while the variation of K a had no obvious rule. According to the OM composition and the P adsorption-release kinetic process, the deposition process of lake sediments can be divided into two stages: one of was 0–10 cm stage, this stage was the main active layer of benthos and mainly occurred the deposition and degradation of exogenous substances (Zhao et al, 2020 ). In this stage, the OM and its components showed a downward trend, the activity intensity and degradation degree of OM showed an upward trend, the maximum release amount of P in lake sediments showed a rapid downward trend, and the maximum adsorption amount and adsorption strength of P showed an upward trend. This stage can be further divided into two sub layers. At the upper layer (0–4 cm), the K r and EPC 0 showed an upward trend, this layer was dominated by newly deposited OM, and a large amount of exogenous deposited P were gradually released. The lower layer was 6–10 cm, the K r and EPC 0 showed a downward trend, this layer was the stage of P release by the decline of deposited OM. The other stage was below 10 cm, the sediments were in anaerobic state, the activities of benthos were weakened, and the sediments were gradually buried and stabilized (Zhao et al, 2020 ). The kinetic process of material burial and material migration up and down through interstitial water were mainly occurs. The adsorption-release of P at the interface between sedimentary phase and interstitial water was mainly affected by the source and composition of sediments, which could reflect the characteristics of lake ecological environment in the sedimentary age (Zhao et al, 2020 ). Therefore, the dynamic characteristics of P adsorption-release in the sediments showed a fluctuating variation. The burial process of phosphorus (P) in lake sediments is driven by continuous adsorption and release. The transformation of various P forms within sediments may also occur as part of dynamic biogeochemical processes. In the case of Erhai Lake, OM components, including TOM, ASOM, and LFOM, exhibited a sharp decline in the upper 0–10 cm sediment layers, after which they stabilized at greater depths (Fig. 2 a, b). The minimum TOM value was observed at the 10 cm layer. The ratios of ASOM/TOM and LFOM/TOM showed a fluctuating downward trend with increasing sediment depth, reaching their highest values between the 8–10 cm layers. The highest activity and decomposition rates of OM were observed within this 8–10 cm zone. In the upper sediment layers (0–10 cm), OM was influenced by the deposition and degradation of exogenous substances, while in the lower layers (below 10 cm), OM dynamics were shaped by the upward release and burial of active substances. The inflection point marking this transition occurred at 10 cm. Regarding P adsorption-release kinetics, several key parameters exhibited depth-dependent trends. Specifically, the maximum desorption (Qr-max) and the rate constant of desorption (Kr) showed a downward trend with increasing depth. In contrast, the maximum adsorption (Qa-max) and the adsorption rate constant (Ka) demonstrated fluctuating upward trends, while the equilibrium phosphorus concentration (EPC 0 ) fluctuated downward (Fig. 2 c, d, e). In the 0–10 cm sediment layer, Qr-max decreased rapidly, whereas Qa-max and Ka increased significantly. The peak values of EPC₀ and Kr were observed at the 4–6 cm sedimentary layer. In sediments deeper than 10 cm, P adsorption-release parameters (Qr-max, Qa-max, Kr, and EPC₀) stabilized, while Ka showed no clear pattern. Based on the OM composition and P adsorption-release kinetics, the sedimentary deposition process can be divided into two main stages, including 0–10 cm layer and below 10 cm. In 0–10 cm layer represents the primary active zone for benthic organisms, where both deposition and degradation of exogenous substances are dominant (Zhao et al., 2020 ). During this stage, OM and its components decrease in quantity, while the activity and decomposition of OM increase. The release of P from the sediments decreases, whereas P adsorption strength and capacity show an upward trend. This stage can be further subdivided into two sublayers, including upper layer (0–4 cm) and lower layer (6–10 cm). In 0–10 cm layer, Kr and EPC 0 increase, indicating that newly deposited OM is releasing a significant amount of exogenous P. In 6–10 cm layer, here, Kr and EPC 0 decrease, reflecting a phase of P release as the OM degradation slows. In below 10 cm depths, sediments enter an anaerobic state, benthic activity weakens, and the sediments gradually stabilize through burial (Zhao et al., 2020 ). During this stage, the burial and migration of materials occur primarily through interstitial water. The P adsorption-release dynamics at the sediment-water interface are primarily influenced by sediment composition and source, reflecting the ecological characteristics of the lake environment during the sediment’s age (Zhao et al., 2020 ). Thus, the dynamic behavior of P adsorption and release within the sediments shows a complex, fluctuating pattern, strongly influenced by both the vertical distribution of OM and biogeochemical processes. 3.1.2 Effect of OM components on P adsorption-release in stratified sediments at a sampling point in Erhai Lake Organic matter (OM) plays a central role in the cycling of nitrogen (N) and phosphorus (P) in sediments. The migration and transformation of OM during sediment deposition and burial are crucial factors affecting P kinetics in these sediments (Zhao et al., 2014 ). Therefore, studying the impact of OM components at different sediment depths on P adsorption-release characteristics at a single lake sampling point provides insight into the regulatory mechanisms of sedimentary OM on P dynamics.The dynamic relationship between OM components and P adsorption-release during OM deposition in the sediment is illustrated in Fig. 3 . Several trends were observed for the relationship between OM content and P adsorption-release parameters. The relationship between TOM content and Q r−Max in the sediment was linear (y = ax + b, R 2 = 0.9119), with Q r−Max increasing as TOM content increased.The TOM content and the Q a−Max in sediments was a linear relationship (y = -ax + b, R 2 = 0.2917), with Qa-Max decreasing as TOM content increased. The TOM content in lake sediment and the K r followed an exponential variation (Exp3P2) (y = exp (a + bx + cx 2 ), R 2 = 0.6415). Kr initially increased with TOM content at low levels but decreased as TOM content became high. The TOM content and the K a in the sediment showed an exponential (Exp3P1Md) decline variation (y = exp [(a + b)/(x + c)], R 2 = 0.4466). At low TOM content, Ka decreased rapidly, with the rate of decrease slowing as TOM content increased, eventually stabilizing. The TOM content and EPC 0 in lake sediment showed the increased first and then decreased exponential variations (Exp3P2) (R 2 = 0.7670). At low TOM content, EPC 0 increased with increasing TOM, while at high TOM content, EPC 0 decreased as TOM content rose. Similar trends were observed for the relationship between the contents of ASOM and LFOM and P adsorption-release parameters, as seen with TOM content. These results suggest that as OM deposits in the sediment, more P becomes available, increasing the maximum P release. During OM deposition, large amounts of exogenous P occupy adsorption sites, which reduces the sediment’s P adsorption capacity (Weyers et al., 2017 ). When OM content is low, the OM-P binding is weak, leading to rapid increases in P release intensity. In this scenario, OM and P compete for adsorption sites on inorganic particles in the sediment, resulting in a sharp decrease in P adsorption capacity (Hiradate and Uchida, 2004 ), and EPC 0 increases rapidly. However, when OM content is high, the binding capacity of OM to P strengthens, reducing P release intensity. At this point, OM provides stable organic adsorption sites for P (Lin et al., 2017 ), stabilizing the adsorption capacity of sediment for P, while EPC 0 declines rapidly. When OM content was low, its weak binding to P led to an increased intensity of P release. During this phase, OM and P competed for adsorption sites on inorganic particles in the sediment, causing a rapid reduction in P adsorption capacity (Hiradate and Uchida, 2004 ). This resulted in a sharp rise in the equilibrium phosphorus concentration EPC 0 ) of the sediment. On the other hand, at higher OM concentrations, the binding capacity of OM to P was enhanced, which rapidly decreased P release intensity. At this point, OMr provided stable organic adsorption sites for P (Lin et al., 2017 ), which stabilized the P adsorption intensity and caused EPC 0 to rapidly decrease. Previous studies have shown that the ratios of ASOM/TOM and LFOM/TOM can reflect the activity intensity and decomposition degree of OM in sediments (Zhao et al., 2014 ). In Fig. 4 , the relationships between ASOM/TOM and the P adsorption-release parameters—Qr-Max, Qa-Max, Kr, and Ka—exhibited irregular patterns. However, the relationship between EPC 0 and ASOM/TOM followed an exponential variation, increasing initially and then decreasing (Exp3P2) (R²= 0.3427). When EPC 0 was low, it increased with higher ASOM/TOM values; when EPC 0 was high, it decreased as ASOM/TOM increased. The relationship between LFOM/TOM and Qr-Max showed an exponential increase (Exp3P2) (R² = 0.6053), but data from the 8–10 cm and 10–12 cm sediment layers were excluded due to their position at the inflection point of sediment deposition. These layers were influenced by both the sedimentation of upper layers and the release from lower layers, leading to more complex patterns. LFOM/TOM and Qa-Max followed an exponential trend of increase followed by decrease (Exp3P2) (R²= 0.3413), while LFOM/TOM and Kr showed a decrease followed by an increase (Exp3P2) (R²= 0.4763). LFOM/TOM and Ka also showed an exponential increase followed by a decrease (Exp3P2) (R²= 0.5900). The correlation between LFOM/TOM and EPC 0 mirrored that of ASOM/TOM and EPC 0 . These findings indicate that as the decomposition of OM in sediment increases, both the maximum release amount and intensity of P exhibit an exponential increase. When OM decomposition is at a lower level, the sediment’s P adsorption capacity and intensity increase. Conversely, at higher levels of OM decomposition, the P adsorption capacity and intensity decrease. During the decomposition of humus into smaller molecular organic matter, such as fulvic acid, the binding capacity of OM to P weakens, which results in an exponential increase in both P release capacity and intensity. This process also increases the available adsorption sites in the sediment, which enhances P adsorption intensity. However, as OM further decomposes into small molecular organic compounds, such as proteins, these smaller molecules occupy adsorption sites, reducing the maximum P adsorption capacity and intensity exponentially. When OM activity and decomposition intensity are high, the adsorption-desorption equilibrium concentration of P in the sediments reaches its highest value. 3.2 Effects of OM components on P adsorption-release in sediment at different sampling points of Erhai Lake The influence of OM components on P behavior in sediment is strongly influenced by the source of the OM (Zhao et al., 2014 ). In Erhai Lake, the source of OM varies across different sampling regions, leading to a non-linear relationship between the proportion and content of OM components and total phosphorus (TP) (Zhao et al., 2013 ). Figure 5 illustrates the relationship between OM content in the 0–10 cm sediment layer at various sampling points and the dynamic characteristics of P adsorption-release.The TOM content in the sediment exhibited a non-linear relationship with the maximum release amount (Qr-Max) and the release rate constant (Kr), showing exponential variations (Exp3P2), initially decreasing and then increasing. Conversely, TOM content showed a linear relationship with the maximum adsorption amount (Qa-Max) and adsorption rate constant (Ka), though with opposite trends. Both ASOM and LFOM contents in the sediment showed a linear increase in Qr-Max and Qa-Max. However, the relationship between ASOM content and Kr and Ka followed a logarithmic variation (y = aln(x) - b). LFOM content, on the other hand, exhibited an exponential relationship (Exp3P2) with both Kr and Ka. Moreover, the contents of TOM, ASOM, and LFOM all showed an exponential decrease in equilibrium phosphorus concentration (EPC 0 ). These results indicate that increasing OM in the sediments of Erhai Lake enhances the number of adsorption sites available for P, thereby increasing both P adsorption capacity and intensity. However, the OM in sediments with low TOM content was predominantly of endogenous origin. Due to its high degree of humification and strong binding affinity for P, the maximum release capacity and intensity of P decreased with increasing OM content in these sediments. In contrast, the OM in sediments with high TOM content was mainly derived from aquatic plant residues or exogenous organic pollutants, which are richer in P content (Zhao et al., 2020 ). As a result, as TOM content increased, the maximum release capacity and intensity of P exhibited an upward trend. The relationship between TOM, ASOM, and EPC 0 in the sediments from different sampling points of Erhai Lake can be considered as the latter half of the "exponential model" presented in Fig. 3 . This is primarily because the TOM and ASOM contents in the sediments of Erhai Lake are relatively high, influencing the P dynamics accordingly. In Fig. 6 , the relationship between LFOM/TOM and the adsorption rate constant (Ka) at different sampling points in Erhai Lake sediments exhibited an exponential trend, increasing initially and then decreasing (Exp3P2) (R² = 0.6310). However, this trend generally mirrored the first half of the model presented in Fig. 4 . Furthermore, the correlation between ASOM/TOM, LFOM/TOM, and key phosphorus dynamics parameters—Qr-Max, Qa-Max, Kr, Ka, and EPC₀—was not statistically significant across the sediment layers. This lack of significant correlation can be attributed to the varying sources of OM across different sampling points in Erhai Lake. The activity intensity, decomposition degree, and component content of OM differ among these sources. Consequently, the P adsorption-release process in the sediments is driven by the combined influence of both the quality (e.g., decomposition degree, activity intensity) and quantity (e.g., component content) of OM. While a strong regularity exists between the quality and quantity of OM within sediments from the same sampling point, the varying sources of OM at different sampling locations result in lower consistency, leading to a weaker regularity in their influence on P behavior. 3.3 Effect of OM components on P adsorption-release in the sediment of several lakes The extent to which OM components influence P behavior in sediments is shaped by various biogeochemical and environmental factors (Yang et al., 2019 ). Additionally, the characteristics of OM components in the sediments of different lakes can have distinct impacts on their respective biogeochemical cycles. In Fig. 7 , both the maximum P release (Qr-Max) and maximum adsorption (Qa-Max) exhibited a linear upward trend with increasing TOM and ASOM content in the sediment. However, the linear relationship between ASOM content and Qa-Max was not significant (n = 9, R² = 0.0635). As TOM content increased, the release rate constant (Kr) first decreased and then increased, following an exponential variation (Exp3P2), while the adsorption rate constant (Ka) showed a similar trend: an initial increase followed by a decrease (Exp3P2). Furthermore, with increasing TOM content, the equilibrium phosphorus concentration (EPC₀) showed an exponential increase (Exp3P2), aligning closely with the first half of the model in Fig. 3 . Similarly, with increasing LFOM content, EPC 0 exhibited an exponential increase followed by a decrease (Exp3P2), mirroring the pattern observed in Fig. 3 . These findings suggest that the maximum P release capacity and the maximum P adsorption capacity in sediments increased with higher TOM and ASOM content. At low TOM content, increasing TOM reduced the P release intensity while enhancing the P adsorption strength in the sediment. However, as TOM content became higher, the P release intensity increased, and the adsorption strength gradually decreased. The EPC 0 in sediments from different lakes also exhibited an exponential increase with rising TOM content, resembling the first half of the model in Fig. 3 . The relationship between LFOM content and EPC 0 followed a similar pattern to that seen in sediments from various sampling points. In Fig. 8 , the ratio of ASOM/TOM in sediments from various lakes displayed a pattern of initial increase followed by a decrease in both the maximum phosphorus release (Qr-Max) and maximum adsorption (Qa-Max), following an exponential variation (Exp3P2). It showed a linear decrease with the release rate constant (Kr) and adsorption rate constant (Ka), and an exponential decrease with the equilibrium phosphorus concentration (EPC 0 ). On the other hand, the LFOM/TOM ratio in sediments exhibited an initial decrease followed by an increase in Qr-Max, following an exponential variation (Exp3P2), while it showed an exponential downward trend with Kr, Ka, and EPC 0 . These findings suggest that when the activity intensity of organic matter (OM) in the sediment is low, the binding capacity to P gradually strengthens as the activity intensity of OM increases. However, when OM activity intensity is high, the bulk density of the sediment decreases, and its porosity increases. This change in sediment structure promotes the release of P, while the increase in organic adsorption sites enhances the total P adsorption capacity. In this context, the increasing activity of OM strengthens the exchange of adsorption and release of P in the sediment (Zhao et al., 2014 ). As the degree of OM decomposition increases in lake sediments, small molecular organic compounds in the sediment compete with P for adsorption sites. Consequently, the binding capacity of OM to P decreases, leading to a reduction in both the adsorption and release strength of P in the sediment. Notably, the ASOM/TOM and LFOM/TOM ratios in sediments from other lakes were higher than those in the different sediment layers of Erhai Lake. The relationship between ASOM/TOM and EPC 0 can be interpreted as the latter half of the model depicted in Fig. 4 . 4. Discussion 4.1 The effect model of OM content in the sediment on P adsorption and release In this study, the contents of TOM, ASOM, and LFOM in the sediment were found to exhibit a linear dynamic relationship (Y = ax + b) with the maximum phosphorus release (Qr-Max) in the sediment. OM is the primary source of unstable P in sediments (Whalen & Chang, 2001 ). As the OM content in the sediment increases, the phosphorus contained within the OM is gradually released during its degradation process. High molecular weight organic compounds in ASOM, such as humic acids, can form complexes with iron and other metals, preventing these complexes from forming with P (Antelo et al., 2007 ). In contrast, low molecular weight organic acids in LFOM can compete with P for adsorption sites through direct physical or electrostatic competition (Weng et al., 2008 ; Weyers et al., 2017 ), thereby promoting the release of P from the sediment. However, P release from sediments occurs primarily during OM degradation. When OM in the sediment is not fully decomposed and consists mainly of plant residues, it can inhibit the release of P. For instance, at sampling point No. 4 in Erhai Lake, located in the Huwankou area, OM is predominantly composed of plant residues, influenced by the decay of submerged plants (Zhao et al., 2013 ). At this location, the maximum release of P is relatively low, and the sediment in Erhai Lake is significantly affected by plant residues, causing the Qr-Max to decrease with the increasing OM content (Fig. 3 ). The relationship between OM content, ASOM, LFOM, and the maximum phosphorus adsorption capacity (Qa-Max) also follows a linear dynamic trend (Y = ax + b). OM and its interaction with sediments can increase the number of adsorption sites for P, thereby enhancing the P adsorption capacity. Additionally, OM reacts with Ca 2+ ions, facilitating the formation of P-Ca-OM complexes (Lei et al., 2018 ). The negatively charged functional groups of organic substances, such as carboxyl and phenol groups, can interact with positively charged minerals, such as iron oxides, influencing P adsorption (Liu et al., 1999 ). The P bound to organic-functional groups on iron oxide surfaces can promote the adsorption of phosphate (PO 4 2− ) to form P-Fe-OM complexes through cation bridges (Al 3+ and Fe 3+ ), though P-Fe-OM complexes are unstable and highly sensitive to environmental conditions (Jessé et al., 2016 ). Iron oxide can be dissolved through reduction or ligand complexation, which promotes the release of iron-bound P into the soil solution (Ruiz-Agudo et al., 2009 ). In the sediment column samples from Erhai Lake, which have a high Fe/Al-P content, the maximum P adsorption capacity decreased with increasing OM content (Zhao et al., 2020 ), consistent with the findings of Andrade et al. ( 2003 ) and Antelo et al. ( 2007 ). However, in sediments from different sampling points in Erhai Lake and other lakes, the maximum P adsorption capacity increased with increasing OM content (Figs. 5 and 7 ). This increase can be attributed to the fact that OM increases the specific surface area and porosity of sediment particles, thereby enhancing the adsorption of P by the sediments (Lehmann, 2007 ). The curve-fitting equations and trends of OM components and the kinetic characteristics of P adsorption-release in sediments are summarized in Table 1 . Table 1 Curve fitting equation and trend of the relationship between OM components of sediment and P adsorption-release kinetic characteristics Relational model Q r−max Q a−max K r K a EPC 0 TOM Fitted equation y = ax + b y = ax + b Y = exp(a + bx + cx 2 ) Y = exp(a + bx + cx 2 ) Y = exp(a + bx + cx 2 ) Trend Increased Increased Increased and then decreased Decreased and then increased Increased and then decreased ASOM Fitted equation y = ax + b y = ax + b Y = exp(a + bx + cx 2 ) Y = exp(a + bx + cx 2 ) Y = exp(a + bx + cx 2 ) Trend Increased Increased Increased and then decreased Decreased and then increased Increased and then decreased LFOM Fitted equation y = ax + b y = ax + b Y = exp(a + bx + cx 2 ) Y = exp(a + bx + cx 2 ) Y = exp(a + bx + cx 2 ) Trend Increased Increased Increased and then decreased Decreased and then increased Increased and then decreased ASOM/TOM Fitted equation Y = exp(a + bx + cx 2 ) Y = exp(a + bx + cx 2 ) y = ax + b y = ax + b Y = exp(a + bx + cx 2 ) Trend Decreased and then increased Decreased and then increased Decreased Decreased —— LFOM/TOM Fitted equation Y = exp(a + bx + cx 2 ) Y = exp(a + bx + cx 2 ) Y = exp(a + bx + cx 2 ) Y = exp(a + bx + cx 2 ) Y = exp(a + bx + cx 2 ) Trend Decreased and then increased Increased and then decreased Decreased and then increased Increased and then decreased —— 4.2 The effect mechanism of OM content on the kinetic characteristics of P adsorption-release in the sediments EPC 0 represents the dynamic equilibrium between P adsorption and release in the sediment. The influence of sedimentary OM on EPC 0 is a process governed by the balance of these two opposing mechanisms (Zhao et al., 2014 ). In this study, as the content of OM, ASOM, and LFOM in the sediment increased, EPC 0 exhibited an initial increase followed by a decrease (Exp3P2). Similarly, the P release intensity first increased and then decreased (Exp3P2), while the P adsorption intensity showed the opposite trend, first decreasing and then increasing (Exp3P2). When OM content was low, the increase in small molecular OM led to competition with P for adsorption sites, which resulted in higher P release intensity than P adsorption intensity. Consequently, the rate of P release from the sediment was greater than the rate of adsorption, and the P release dominated at the sediment-water interface. However, as OM content increased beyond a certain threshold, OM contributed to the expansion of P adsorption sites and an increase in the specific surface area of the sediment. At the same time, the degradation rate of OM slowed, and the adsorption intensity of P on OM exceeded the release intensity. In this scenario, P became predominantly adsorbed at the sediment-water interface. Thus, at low OM content, a competitive relationship exists between OM and P, where small molecular OM outcompetes P for adsorption sites. In contrast, at high OM content, OM provides a significant number of adsorption sites, becoming the main factor controlling P migration in the sediment. 4.3 The effect mechanism of OM components characteristics on P adsorption-release kinetics in the sediment The release and adsorption of P in sediment involve both physical and chemical mechanisms, with the activity and degradation intensity of OM playing a crucial role in influencing these processes. When the activity intensity of OM in the sediment is high, it indicates a large number of active sites, resulting in stronger chemical binding effects on P, such as surface adsorption, bond ion adsorption, and molecular coupling. In contrast, when the decomposition degree of OM is low—indicating a high proportion of macromolecular organic matter—the porosity in the sediment increases, facilitating physical fixation mechanisms, such as encapsulation of P. As the activity intensity and decomposition degree of OM increase, both the maximum release capacity (Qr-Max) and maximum adsorption capacity (Qa-Max) of P in the sediment follow a pattern of initial decrease, followed by an increase, exhibiting exponential variations (Exp3P2). This trend suggests that at lower activity and decomposition stages, P competes with other ions due to fewer adsorption sites, such as adsorption valence bonds and encapsulated voids, as well as low P content in OM. As the activity and decomposition of OM intensify, the number of available adsorption sites, including valence bonds and encapsulated voids, increases, thereby enhancing both P adsorption and release capacities. Moreover, the equilibrium phosphorus concentration (EPC 0 ) in the sediment also follows a similar pattern, initially decreasing and then increasing exponentially (Exp3P2) with the increasing activity and decomposition degree of OM. As the OM activity in the sediment rises, the chemical binding effects strengthen, leading to surface adsorption, bond ion adsorption, and molecular coupling with OM (Weyers et al., 2017 ; Zhao et al., 2014 ). Consequently, the adsorption and release intensities of P show a linear increase with increased OM activity, following the equation Y = ax + b. When the decomposition degree of OM in the sediment increases, the encapsulation voids and adsorption-release dynamics of P in the sediment exhibit a pattern of first decreasing, then increasing exponentially (Exp3P2). At lower levels of decomposition, the release and adsorption intensity of P decrease because small molecular organic matter from OM competes with P for adsorption sites on the sediment parent material. The strong coupling effect between macromolecular OM and P reduces the release of P. In contrast, when the decomposition degree of OM is high, a larger portion of macromolecular OM is degraded into small molecular organic matter. Small molecule dissolved organic matter (DOM) has a weaker fixation ability on P, leading to an increase in both adsorption and release intensities with the higher decomposition of OM. 4.4 The effect mechanism of OM on P adsorption-release in the sediment The increase in N and P content in water bodies leads to lake eutrophication, which is accompanied by a range of environmental issues, including water quality degradation (Long et al., 2021 ). Sediments serve as both the source and sink of nutrients in aquatic systems, with the phosphorus (P) dynamics at the sediment-water interface being a critical endogenous factor contributing to eutrophication (Huang et al., 2011 ). The organic matter (OM) components in sediment play a significant role in P adsorption and release processes, influencing P kinetics at the sediment-water interface. The mechanisms through which OM affects P adsorption-release kinetics in sediment can be broadly categorized into two aspects.On the one hand, direct influence of OM characteristics on P adsorption-release kinetics, which is primarily driven by the release of P contained in OM during its degradation. The interaction between OM and P is complex, as the degradation of OM leads to the release of P, influencing the overall P behavior in sediments. The specific mechanisms through which OM content and its various components (e.g., TOM, ASOM, LFOM) affect P adsorption and release kinetics are illustrated in Fig. 9 . On the other hand, influence of OM-sediment interaction on P adsorption-release kinetics, which mechanism arises from the interaction between OM and sediment during deposition. The combined effects of OM components and sediment characteristics dictate the dynamics of P adsorption and release. The dominant mechanism of OM action may vary between different sediment types, depending on factors such as the OM content, composition, and the presence of minerals in the sediment. In this study, the OM content in the 0–10 cm sediment layer at a specific sampling point in Erhai Lake showed continuous degradation (Fig. 2 ). This suggests that at this depth, P behavior was predominantly influenced by the characteristics of the OM. In contrast, below the 10 cm sediment layer, OM and sediments interacted to form organic-inorganic colloids during the deposition process. This indicates that P behavior at greater depths was primarily governed by the interaction between OM and the underlying sediments. The source of OM varies across different regions of Erhai Lake (Zhao et al., 2013 ). In regions where the OM is mainly derived from aquatic plants and other external sources, P behavior is strongly influenced by the intrinsic properties of OM. However, in other regions with different OM sources, such as those dominated by microbial and sedimentary OM, P dynamics are more heavily influenced by the interactions between OM and the sediment. Similarly, P behavior in sediments from different lakes is affected by differences in OM composition and sediment characteristics (Yi et al., 2008 ), with the interaction between OM and sediments playing a more dominant role in determining P dynamics. The influence of OM components in sediment on P adsorption-release kinetics is a complex process, shaped by the characteristics of OM, the sediment matrix itself, and the morphology of P in the sediment. In this study, the mechanism by which OM composition characteristics affect P adsorption-release kinetics was explored across three levels: different layers within a single sampling point, different regions of a lake, and across different lakes. The results revealed that the content of OM exhibited a linear relationship with the P adsorption-release kinetic parameters in sediment, while the characteristics of OM composition and the P adsorption-release kinetics followed exponential variations. To further quantify the inflection points of OM composition characteristics in regulating P adsorption-release kinetics, and to elucidate the release mechanisms of endogenous P in sediments, a substantial dataset is required for comprehensive quantitative analysis. Additionally, it is necessary to consider the coupling effects of other factors present in sediments to enable a more systematic understanding of P behavior. The findings of this study provide deeper insights into the mechanisms by which OM and its components influence P adsorption and release in sediments. 5. Conclusions The content and composition of OM in sediments are key factors influencing the kinetics of P release and adsorption. As the OM content increases, both the maximum adsorption capacity and the maximum release capacity of P in sediments exhibit a linear increase. The release intensity of P shows an initial increase followed by a subsequent decrease, while the adsorption intensity of P follows a trend of first decreasing and then increasing. The equilibrium concentration of P in adsorption and desorption also follows a pattern of increasing initially, then decreasing. The activity intensity and decomposition degree of OM in the sediment are critical factors in determining the chemical interactions and physical fixation of P by OM. As the activity intensity of OM increases, the maximum adsorption capacity, maximum release capacity, and equilibrium concentration of adsorption and desorption in the sediment initially decrease and then increase. In contrast, the adsorption and release intensity of P shows a consistent linear increase. Moreover, with the increase in the decomposition degree of OM, the maximum release capacity, adsorption and release intensity, and equilibrium concentration of P in sediments follow a pattern of first decreasing and then increasing. Meanwhile, the maximum adsorption capacity of P initially increases and then decreases. Declarations Ethical Approval: Not Applicable. Consent to Participate The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Consent to Publish All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organization, or those of the publisher. Any product that may be evaluated in this ariticle,is not guaranteed or endorsed by the publishee. Competing Interests The authors declare that they have no conflict of interest. Furthermore, the founding sponsors had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, and in the decision to publish the results. Funding This research is supported by National Major Science and Technology Program for Water Pollution Control and Treatment [No. 2012ZX07102-004], and School level project of Hebei North University [No. D2022405001]. Author Contribution Conceptualization, H.Z., S.L. and H.Z.; Data curation, H.Z., S.L., H.Z., Z.H., L.J., S.W. and S.D.; Formal analysis, H.Z., S.L., H.Z., Z.H.,and S.D.; Funding acquisition, H.Z.; Investigation, H.Z., S.L., H.Z., Z.H., L.J., S.W. and S.D.; Methodology,H.Z., S.L. and H.Z.; Project administration, H.Z.; Resources, H.Z.; Software, S.L.; Supervision, H.Z.; Validation, H.Z., S.L., H.Z., Z.H., L.J., S.W. and S.D.; Visualization,H.Z. and S.L.; Writing – original draft, H.Z. and S.L.; Writing – review & editing, H.Z., S.L., H.Z., Z.H., L.J., S.W. and S.D. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6640256","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":469518509,"identity":"94c34b85-0d6f-4437-ab21-f744363d8864","order_by":0,"name":"Haichao Zhao","email":"","orcid":"","institution":"Hebei North University","correspondingAuthor":false,"prefix":"","firstName":"Haichao","middleName":"","lastName":"Zhao","suffix":""},{"id":469518514,"identity":"b41a4d07-afb5-4041-a681-9a5c0390fcdd","order_by":1,"name":"Songtao 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Sciences","correspondingAuthor":false,"prefix":"","firstName":"Shuai","middleName":"","lastName":"Ding","suffix":""}],"badges":[],"createdAt":"2025-05-11 14:53:15","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6640256/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6640256/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":84402287,"identity":"2d07f029-2b12-4c88-9d6e-530331a30c48","added_by":"auto","created_at":"2025-06-11 13:40:59","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":2936773,"visible":true,"origin":"","legend":"\u003cp\u003eSampling point map of Erhai Lake. ▲ representssampling points of the surface sediment samples of Erhai Lake, □ represents columned sediment sample point of Erhai Lake.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-6640256/v1/241a5cebc541a39ff77961d8.png"},{"id":84401299,"identity":"3b407de4-27a4-490e-ad7d-02e08b70fde6","added_by":"auto","created_at":"2025-06-11 13:32:59","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":352634,"visible":true,"origin":"","legend":"\u003cp\u003eVertical variation of OM components and P adsorption-release characteristics in Erhai Lake sediment.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-6640256/v1/24c78cf121395ceaa7c7fc4a.png"},{"id":84401295,"identity":"e57b3026-c2d6-49d7-8c22-b70950378772","added_by":"auto","created_at":"2025-06-11 13:32:59","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":103556,"visible":true,"origin":"","legend":"\u003cp\u003eThe effect trend of OM content on P adsorption-release kinetic parameters in stratified sediments at one sampling point of Erhai Lake\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-6640256/v1/d4c52024880b68f828bab80a.png"},{"id":84402606,"identity":"088222ac-5ca6-4e5a-9547-f3777d2d1100","added_by":"auto","created_at":"2025-06-11 13:48:59","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":59412,"visible":true,"origin":"","legend":"\u003cp\u003eThe \u003cstrong\u003eeffects\u003c/strong\u003e trend of the characteristics of OM composition on the P adsorption-release kinetic parameters in stratified sediments at one sampling point of Erhai Lake\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-6640256/v1/52513f66609a88f3693283d2.png"},{"id":84401296,"identity":"2c7c1690-fa5a-4065-a12b-fda0d5a5e4fa","added_by":"auto","created_at":"2025-06-11 13:32:59","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":79807,"visible":true,"origin":"","legend":"\u003cp\u003eThe effects trend of OM component content on P adsorption-release kinetic parameters in the sediment at the different sampling points of Erhai Lake.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-6640256/v1/8b593f19d39e90d17473003e.png"},{"id":84402289,"identity":"40dfda39-e83d-40ac-8e6b-bca758592ef9","added_by":"auto","created_at":"2025-06-11 13:40:59","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":62007,"visible":true,"origin":"","legend":"\u003cp\u003eThe effect trend of the characteristics of OM components on P adsorption-release kinetic parameters in sediments at different sampling points of Erhai Lake.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-6640256/v1/8ca6f085bb1777e889f6e46d.png"},{"id":84401303,"identity":"870b9f47-976b-404b-ac8c-5cf76dd0db43","added_by":"auto","created_at":"2025-06-11 13:32:59","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":80877,"visible":true,"origin":"","legend":"\u003cp\u003eThe effect trends of OM components content on P adsorption-release kinetic parameters in sediments of different lakes.\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-6640256/v1/53e4d6647319fac9a81520c3.png"},{"id":84401309,"identity":"14596614-e704-46d9-af79-ee8dc7ddb9d9","added_by":"auto","created_at":"2025-06-11 13:32:59","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":56638,"visible":true,"origin":"","legend":"\u003cp\u003eThe effect trends of OM components characteristics on P adsorption-release kinetic parameters in sediments of different lakes sediment.\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-6640256/v1/cf2e29406bd5c0cee75b0309.png"},{"id":84402608,"identity":"32f72b08-9586-4415-bf17-11058ed12d45","added_by":"auto","created_at":"2025-06-11 13:48:59","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":104785,"visible":true,"origin":"","legend":"\u003cp\u003eThe influence models of OM composition in sediments on P adsorption-release kinetics.\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-6640256/v1/b397a7850e5fbec59f95039b.png"},{"id":107488063,"identity":"7d42ebc6-2f3f-4419-90d3-ff9d6c24eb06","added_by":"auto","created_at":"2026-04-22 02:43:24","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":6353157,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6640256/v1/a15575d7-0598-45a3-a038-f146ab06eeeb.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Study on the Influence Mechanism of the Organic Matter Components on Phosphorus Adsorption-Release Kinetics in Lake Sediment","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eEutrophication is one of the most pressing environmental issues affecting lakes worldwide. To better understand the mechanisms behind lake water blooms and to support effective control measures, extensive research has been conducted on the causes of lake eutrophication (Dokulil and Teubner, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2000\u003c/span\u003e; Kong and Gao, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2005\u003c/span\u003e). Excess phosphorus (P) in water bodies is a primary driver of eutrophication, leading to significant environmental consequences (Long et al., \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). As P concentrations rise, blue-green algae often dominate the phytoplankton community (Steiberg and Hartmann, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e1988\u003c/span\u003e). Lake sediments act as both a \"source\" and \"sink\" of P for the overlying water. When external P inputs increase, the sediment adsorbs P; conversely, when external P inputs decrease, the sediment releases P, thus making sediment an important source of nutrients contributing to eutrophication (Huang et al., \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). When P concentrations in the lake water are low, accumulated P in the sediment is released, further contributing to eutrophication (O'Neil et al., \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2012\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe concentration of endogenous P in the overlying water results from the dynamic balance of P adsorption-release at the sediment-water interface. The nutrient level of lake water is largely determined by this adsorption-release equilibrium between the sediment and the overlying water (Peng et al., \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2007\u003c/span\u003e). Determining the kinetics of P release-adsorption in sediments under controlled laboratory conditions can provide insights into the maximum adsorption capacity, maximum release capacity, release intensity, and adsorption intensity of P (Wang et al., \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Wang et al., \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2006\u003c/span\u003e). The thermodynamic process of P adsorption can further reveal the adsorption-desorption equilibrium concentration at the sediment-water interface (Wang et al., \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2006\u003c/span\u003e). Therefore, studying the kinetics of P adsorption and release in sediments is crucial to understanding the mechanisms governing P dynamics at the sediment-water interface in lakes.\u003c/p\u003e \u003cp\u003eMany studies have shown that sediment composition is directly related to its P adsorption capacity (Wang et al., \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). Organic matter (OM), a significant component of sediment, plays a key role in the transport of nitrogen (N) and P. For example, Wang et al. (\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2007\u003c/span\u003e) observed a positive correlation between OM content and P adsorption in sediments. Previous research has shown that the P adsorption-release capacity increases with higher total organic matter (TOM) content, while the equilibrium adsorption-desorption concentration decreases with greater OM activity in the sediments of Erhai Lake (Zhao et al., \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). Low-molecular-weight organic acids can compete with P for adsorption sites through direct physical or electrostatic interactions (Weyers et al., \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Humic substances, which are macromolecular in nature, can form organic-inorganic complexes with Fe and Al, providing additional adsorption sites for inorganic P and enhancing P adsorption (Gerke and Hermann, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e1992\u003c/span\u003e). Furthermore, OM has chemical binding effects such as valence ion adsorption and molecular coupling; H\u0026thinsp;+\u0026thinsp;released from OM can protonate mineral surface groups, thereby facilitating P adsorption (Zhao et al., \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). OM can also react with Ca\u0026sup2;⁺ to form P-Ca-OM complexes (Lei et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Through the processes of degradation and polymerization, OM components regulate P adsorption and release at the sediment-water interface by altering the physical, chemical, and biological properties of the sediment.\u003c/p\u003e \u003cp\u003eThe influence of OM on P adsorption and release is complex, and the specific mechanisms by which OM composition affects P adsorption-release kinetics are not fully understood. Thus, exploring the relationship between OM components and P adsorption-release dynamics in lake sediments is crucial for understanding the processes driving lake eutrophication.\u003c/p\u003e \u003cp\u003eThis study investigates the OM characteristics in sediments of different layers from one sampling point in Erhai Lake, as well as from surface sediments across various regions of the lake and from sediments in different lakes. Using P release kinetics, adsorption kinetics, and thermodynamic models, the study aims to uncover the P adsorption-release kinetics in lake sediments. The study also analyzes the relationship between OM components in sediment and the P adsorption-release kinetics, focusing on the impact of OM degradation and composition on P dynamics at the sediment-water interface. This will help clarify the regulatory mechanisms of OM on P release from lake sediments.\u003c/p\u003e"},{"header":"2. Materials and methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1. Study area and sample collection\u003c/h2\u003e \u003cp\u003eErhai Lake (25\u0026deg;35\u0026prime;N \u0026minus;\u0026thinsp;25\u0026deg;58\u0026prime;N; 100\u0026deg;05\u0026prime;E \u0026minus;\u0026thinsp;100\u0026deg;17\u0026prime;E) is the largest fault lake in the Yunnan Plateau. The average depth of the lake is approximately 10 m, with the deepest point reaching 20 m at the center (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e1\u003c/span\u003e). The water surface area spans about 249 km\u0026sup2;, and its volume is approximately 2.8 \u0026times; 10⁹ m\u0026sup3;. For this study, surface sediment samples (at a depth of 10 cm) were collected from 10 sampling points, selected based on variations in organic matter (OM) deposition, water depth, hydrodynamics, and aquatic vegetation distribution across different areas of Erhai Lake. Additionally, a 30 cm sediment core was taken from the central platform in the southern part of the lake. The samples were layered every 2 cm in the field, placed into plastic bags, and stored in an incubator at 4\u0026deg;C. After transport to the laboratory, the samples were freeze-dried, ground through a 100-mesh sieve, and stored in the dark for subsequent analysis.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Determination method\u003c/h2\u003e \u003cp\u003eThe kinetic test of phosphorus (P) release from sediment was conducted as described by Zhang et al. (\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2012\u003c/span\u003e) and Zhao et al. (\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). Accurately weighed 0.5 g dry sediment samples were added to a series of 100 mL centrifuge tubes, each containing 50 mL of 0.02 mol\u0026middot;L⁻\u0026sup1; KCl solution. The tubes were then incubated (200 rpm) in a dark shaker for 24 hours at 25\u0026deg;C\u0026thinsp;\u0026plusmn;\u0026thinsp;1\u0026deg;C. At specified time intervals (0.5, 1.5, 3, 5.5, 9, 15, 24, 36, and 48 hours), the centrifuge tubes were removed, and the samples were centrifuged at 5000 \u0026times; g for 15 minutes. The supernatant was passed through a 0.45 \u0026micro;m GF/C filter membrane, and the filtrate was analyzed for soluble reactive phosphorus (SRP) using the molybdenum blue/ascorbic acid colorimetric method with a dual-beam ultraviolet/visible spectrometer (TU-1900, Beijing Purkinje General Instrument Co., Ltd, Beijing, China).\u003c/p\u003e \u003cp\u003eP release kinetics were simulated using a first-order kinetic model, as shown in Eq.\u0026nbsp;(1):\u003c/p\u003e \u003cp\u003e \u003cem\u003eC\u003c/em\u003e \u003csub\u003et\u003c/sub\u003e=\u003cem\u003eC\u003c/em\u003e\u003csub\u003e0\u003c/sub\u003e(1-e\u003csup\u003e\u0026minus;\u0026thinsp;Krt\u003c/sup\u003e) (1)\u003c/p\u003e \u003cp\u003eWhere \u003cem\u003eC\u003c/em\u003e\u003csub\u003e0\u003c/sub\u003e is the maximum P release capacity from sediment (Qr-max, mg\u0026middot;kg⁻\u0026sup1;), and K\u003csub\u003er\u003c/sub\u003e is the reaction constant that represents the P release intensity from the sediment.\u003c/p\u003e \u003cp\u003eThe kinetic test for P adsorption by sediment followed the procedures of Zhang et al. (\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2012\u003c/span\u003e) and Zhao et al. (\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). A 0.5 g dry sediment sample was accurately weighed and placed into a 100 mL acid-washed centrifuge tube. Then, 50 mL of 10 mg\u0026middot;L⁻\u0026sup1; KH\u003csub\u003e2\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e solution was added to the tube, which was subsequently covered and shaken (250 rpm) at 25\u0026deg;C\u0026thinsp;\u0026plusmn;\u0026thinsp;1\u0026deg;C in the dark. Samples were taken at 0.5, 1.5, 2.5, 5, 9, 13, 18, and 24 hours. The tubes were then centrifuged at 5000 rpm for 10 minutes in a constant temperature (25\u0026deg;C\u0026thinsp;\u0026plusmn;\u0026thinsp;1\u0026deg;C) centrifuge. The supernatant was filtered through a 0.45 \u0026micro;m GF/C filter membrane for P concentration analysis. All experiments were performed in triplicate under the same conditions, with relative mean deviations of less than 5%. The P adsorption kinetics were modeled using the modified Elovich equation (Eq.\u0026nbsp;2):\u003c/p\u003e \u003cp\u003e \u003cem\u003eq\u003c/em\u003e\u0026thinsp;=\u0026thinsp;a\u0026thinsp;+\u0026thinsp;K\u003csub\u003ea\u003c/sub\u003eln\u003cem\u003et\u003c/em\u003e (2)\u003c/p\u003e \u003cp\u003eWhere \u003cem\u003eq\u003c/em\u003e is the amount of P adsorbed (mg\u0026middot;kg⁻\u0026sup1;), a is the initial adsorption amount, K\u003csub\u003ea\u003c/sub\u003e is the adsorption rate constant, and \u003cem\u003et\u003c/em\u003e is the time. The maximum adsorption capacity, Qa-max, was calculated at 12 hours using Eq.\u0026nbsp;(3):\u003c/p\u003e \u003cp\u003eQ\u003csub\u003ea\u0026minus;max\u003c/sub\u003e=a+K\u003csub\u003ea\u003c/sub\u003eln(12) (3)\u003c/p\u003e \u003cp\u003eQ\u003csub\u003ea\u0026minus;Max\u003c/sub\u003e reflects the maximum adsorption capacity of the sediment, indicating the number of available adsorption sites for P.\u003c/p\u003e \u003cp\u003eThe thermodynamic test for P adsorption by sediment was carried out as described by Zhang et al. (\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2012\u003c/span\u003e) and Zhao et al. (\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). A 0.5 g dry sediment sample was weighed and placed into a 100 mL centrifuge tube containing 50 mL of KH\u003csub\u003e2\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e solution at concentrations of 0, 0.01, 0.02, 0.05, 0.08, 0.10, 0.15, and 0.20 mg\u0026middot;L⁻\u0026sup1;. The solution was then incubated (250 rpm) at 25\u0026deg;C\u0026thinsp;\u0026plusmn;\u0026thinsp;1\u0026deg;C for 24 hours in the dark. The tubes were centrifuged at 5000 rpm for 10 minutes, and the supernatant was filtered through a 0.45 \u0026micro;m filter membrane for P concentration analysis. P adsorption was fitted using the following equation (Eq.\u0026nbsp;4):\u003c/p\u003e \u003cp\u003e \u003cem\u003eQ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;\u003cem\u003eQ\u003c/em\u003e\u003csub\u003emax\u003c/sub\u003e\u0026times;k\u0026times;\u003cem\u003eC\u003c/em\u003e\u003csub\u003ee\u003c/sub\u003e(1\u0026thinsp;+\u0026thinsp;k\u003cem\u003eC\u003c/em\u003e\u003csub\u003ee\u003c/sub\u003e) (4)\u003c/p\u003e \u003cp\u003eWhere \u003cem\u003eQ\u003c/em\u003e is the amount of P adsorbed (mg\u0026middot;kg⁻\u0026sup1;), \u003cem\u003eQ\u003c/em\u003e\u003csub\u003emax\u003c/sub\u003e is the maximum adsorption capacity (mg\u0026middot;kg⁻\u0026sup1;), k is the adsorption constant, and \u003cem\u003eC\u003c/em\u003e\u003csub\u003ee\u003c/sub\u003e is the P adsorption-desorption equilibrium concentration (mg\u0026middot;L⁻\u0026sup1;).\u003c/p\u003e \u003cp\u003eTotal organic matter (TOM) was determined using the K\u003csub\u003e2\u003c/sub\u003eCr\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e-H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e external heating method (Zhao et al., \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). Active sediment organic matter (ASOM) was measured using the KMnO\u003csub\u003e4\u003c/sub\u003e oxidation method at 333 nmol\u0026middot;L⁻\u0026sup1; (Lefroy and Blair, 1993). Light fraction organic matter (LFOM) was determined using the NaI specific gravity method (Janzen et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e1992\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Data analysis\u003c/h2\u003e \u003cp\u003eData on organic matter (OM) components in the surface sediment of Erhai Lake and lakes located in the Mid-lower reaches of the Yangtze River were obtained from Zhao et al. (\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2013\u003c/span\u003e) (Figure S1) and Yi et al. (\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2008\u003c/span\u003e) (Figure S2), respectively. Data on phosphorus (P) release kinetics in other lakes in the Mid-lower reaches of the Yangtze River were sourced from Jin et al. (\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2007\u003c/span\u003e) (Figure S2). Additionally, P adsorption kinetics data for other lakes in this region were collected from Yi (\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2008\u003c/span\u003e) and Wang et al. (\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2006\u003c/span\u003e) (Figure S2).\u003c/p\u003e \u003cp\u003eThe P adsorption-release kinetic model, kinetic parameters, and OM component models for the lake sediments were analyzed using Origin 9 software.\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results","content":"\u003cp\u003e \u003cb\u003e3.1 Effect of OM Components on Phosphorus (P) Adsorption-Release in Stratified Sediments at a Sampling Point in Erhai Lake\u003c/b\u003e \u003c/p\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e3.1.1 Vertical Variation of OM Components and P Adsorption-Release Kinetics in Erhai Lake Sediments\u003c/h2\u003e \u003cp\u003eP burial process of lake sediments is the result of the constant adsorption and release. The transformation of various forms of P in sediments may also occur in the biogeochemical process of continuous change. With the increase of sedimentary depth in Erhai Lake, TOM, ASOM, and LFOM showed a rapid downward trend in the 0\u0026ndash;10 cm layers, and then basically stabilized below 10 cm. The minimum value of TOM appeared at 10 cm layer (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e2\u003c/span\u003e(a, b)). The ASOM/TOM and LFOM/TOM showed a fluctuating downward trend with the increase of sedimentary depth, and the highest value appeared at 8\u0026ndash;10 cm layers. The activity and decomposition degree of OM were the highest at 8\u0026ndash;10 cm layers of the sediment. The OM components in the upper layer (0\u0026ndash;10 cm) of sediment were affected by the deposition and degradation of exogenous substances, and in the lower layer (below 10 cm) of sediment was affected by the upward release and burial of active substances, so the inflection point of action appeared at 10 cm layer of sediment. With the increase of sediment depth, the Q\u003csub\u003er\u0026minus;max\u003c/sub\u003e and the K\u003csub\u003er\u003c/sub\u003e showed a downward trend, the Q\u003csub\u003ea\u0026minus;max\u003c/sub\u003e and the K\u003csub\u003ea\u003c/sub\u003e showed a fluctuating upward trend, the EPC\u003csub\u003e0\u003c/sub\u003e showed a fluctuating downward trend (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e2\u003c/span\u003e(c, d, e)). In the 0\u0026ndash;10 cm sedimentary layer, Q\u003csub\u003er\u0026minus;Max\u003c/sub\u003e decreased rapidly, while Q\u003csub\u003ea\u0026minus;Max\u003c/sub\u003e and K\u003csub\u003ea\u003c/sub\u003e increase rapidly. At the same time, the peak values of EPC\u003csub\u003e0\u003c/sub\u003e and K\u003csub\u003er\u003c/sub\u003e occurred in the 4\u0026ndash;6 cm sedimentary layer. In the sedimentary layer below 10 cm, the variation of Q\u003csub\u003er\u0026minus;Max\u003c/sub\u003e, Q\u003csub\u003ea\u0026minus;Max\u003c/sub\u003e, K\u003csub\u003er\u003c/sub\u003e and EPC\u003csub\u003e0\u003c/sub\u003e tended to be stable, while the variation of K\u003csub\u003ea\u003c/sub\u003e had no obvious rule. According to the OM composition and the P adsorption-release kinetic process, the deposition process of lake sediments can be divided into two stages: one of was 0\u0026ndash;10 cm stage, this stage was the main active layer of benthos and mainly occurred the deposition and degradation of exogenous substances (Zhao et al, \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). In this stage, the OM and its components showed a downward trend, the activity intensity and degradation degree of OM showed an upward trend, the maximum release amount of P in lake sediments showed a rapid downward trend, and the maximum adsorption amount and adsorption strength of P showed an upward trend. This stage can be further divided into two sub layers. At the upper layer (0\u0026ndash;4 cm), the K\u003csub\u003er\u003c/sub\u003e and EPC\u003csub\u003e0\u003c/sub\u003e showed an upward trend, this layer was dominated by newly deposited OM, and a large amount of exogenous deposited P were gradually released. The lower layer was 6\u0026ndash;10 cm, the K\u003csub\u003er\u003c/sub\u003e and EPC\u003csub\u003e0\u003c/sub\u003e showed a downward trend, this layer was the stage of P release by the decline of deposited OM. The other stage was below 10 cm, the sediments were in anaerobic state, the activities of benthos were weakened, and the sediments were gradually buried and stabilized (Zhao et al, \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). The kinetic process of material burial and material migration up and down through interstitial water were mainly occurs. The adsorption-release of P at the interface between sedimentary phase and interstitial water was mainly affected by the source and composition of sediments, which could reflect the characteristics of lake ecological environment in the sedimentary age (Zhao et al, \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Therefore, the dynamic characteristics of P adsorption-release in the sediments showed a fluctuating variation.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe burial process of phosphorus (P) in lake sediments is driven by continuous adsorption and release. The transformation of various P forms within sediments may also occur as part of dynamic biogeochemical processes. In the case of Erhai Lake, OM components, including TOM, ASOM, and LFOM, exhibited a sharp decline in the upper 0\u0026ndash;10 cm sediment layers, after which they stabilized at greater depths (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e2\u003c/span\u003ea, b). The minimum TOM value was observed at the 10 cm layer.\u003c/p\u003e \u003cp\u003eThe ratios of ASOM/TOM and LFOM/TOM showed a fluctuating downward trend with increasing sediment depth, reaching their highest values between the 8\u0026ndash;10 cm layers. The highest activity and decomposition rates of OM were observed within this 8\u0026ndash;10 cm zone. In the upper sediment layers (0\u0026ndash;10 cm), OM was influenced by the deposition and degradation of exogenous substances, while in the lower layers (below 10 cm), OM dynamics were shaped by the upward release and burial of active substances. The inflection point marking this transition occurred at 10 cm.\u003c/p\u003e \u003cp\u003eRegarding P adsorption-release kinetics, several key parameters exhibited depth-dependent trends. Specifically, the maximum desorption (Qr-max) and the rate constant of desorption (Kr) showed a downward trend with increasing depth. In contrast, the maximum adsorption (Qa-max) and the adsorption rate constant (Ka) demonstrated fluctuating upward trends, while the equilibrium phosphorus concentration (EPC\u003csub\u003e0\u003c/sub\u003e) fluctuated downward (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e2\u003c/span\u003ec, d, e). In the 0\u0026ndash;10 cm sediment layer, Qr-max decreased rapidly, whereas Qa-max and Ka increased significantly. The peak values of EPC₀ and Kr were observed at the 4\u0026ndash;6 cm sedimentary layer.\u003c/p\u003e \u003cp\u003eIn sediments deeper than 10 cm, P adsorption-release parameters (Qr-max, Qa-max, Kr, and EPC₀) stabilized, while Ka showed no clear pattern. Based on the OM composition and P adsorption-release kinetics, the sedimentary deposition process can be divided into two main stages, including 0\u0026ndash;10 cm layer and below 10 cm. In 0\u0026ndash;10 cm layer represents the primary active zone for benthic organisms, where both deposition and degradation of exogenous substances are dominant (Zhao et al., \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). During this stage, OM and its components decrease in quantity, while the activity and decomposition of OM increase. The release of P from the sediments decreases, whereas P adsorption strength and capacity show an upward trend. This stage can be further subdivided into two sublayers, including upper layer (0\u0026ndash;4 cm) and lower layer (6\u0026ndash;10 cm). In 0\u0026ndash;10 cm layer, Kr and EPC\u003csub\u003e0\u003c/sub\u003e increase, indicating that newly deposited OM is releasing a significant amount of exogenous P. In 6\u0026ndash;10 cm layer, here, Kr and EPC\u003csub\u003e0\u003c/sub\u003e decrease, reflecting a phase of P release as the OM degradation slows.\u003c/p\u003e \u003cp\u003eIn below 10 cm depths, sediments enter an anaerobic state, benthic activity weakens, and the sediments gradually stabilize through burial (Zhao et al., \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). During this stage, the burial and migration of materials occur primarily through interstitial water. The P adsorption-release dynamics at the sediment-water interface are primarily influenced by sediment composition and source, reflecting the ecological characteristics of the lake environment during the sediment\u0026rsquo;s age (Zhao et al., \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2020\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThus, the dynamic behavior of P adsorption and release within the sediments shows a complex, fluctuating pattern, strongly influenced by both the vertical distribution of OM and biogeochemical processes.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003e3.1.2 Effect of OM components on P adsorption-release in stratified sediments at a sampling point in Erhai Lake\u003c/b\u003e \u003c/p\u003e \u003cp\u003eOrganic matter (OM) plays a central role in the cycling of nitrogen (N) and phosphorus (P) in sediments. The migration and transformation of OM during sediment deposition and burial are crucial factors affecting P kinetics in these sediments (Zhao et al., \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). Therefore, studying the impact of OM components at different sediment depths on P adsorption-release characteristics at a single lake sampling point provides insight into the regulatory mechanisms of sedimentary OM on P dynamics.The dynamic relationship between OM components and P adsorption-release during OM deposition in the sediment is illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e3\u003c/span\u003e. Several trends were observed for the relationship between OM content and P adsorption-release parameters. The relationship between TOM content and Q\u003csub\u003er\u0026minus;Max\u003c/sub\u003e in the sediment was linear (y\u0026thinsp;=\u0026thinsp;ax\u0026thinsp;+\u0026thinsp;b, R\u003csup\u003e2\u003c/sup\u003e\u0026thinsp;=\u0026thinsp;0.9119), with Q\u003csub\u003er\u0026minus;Max\u003c/sub\u003e increasing as TOM content increased.The TOM content and the Q\u003csub\u003ea\u0026minus;Max\u003c/sub\u003e in sediments was a linear relationship (y = -ax\u0026thinsp;+\u0026thinsp;b, R\u003csup\u003e2\u003c/sup\u003e\u0026thinsp;=\u0026thinsp;0.2917), with Qa-Max decreasing as TOM content increased. The TOM content in lake sediment and the K\u003csub\u003er\u003c/sub\u003e followed an exponential variation (Exp3P2) (y\u0026thinsp;=\u0026thinsp;exp (a\u0026thinsp;+\u0026thinsp;bx\u0026thinsp;+\u0026thinsp;cx\u003csup\u003e2\u003c/sup\u003e), R\u003csup\u003e2\u003c/sup\u003e\u0026thinsp;=\u0026thinsp;0.6415). Kr initially increased with TOM content at low levels but decreased as TOM content became high. The TOM content and the K\u003csub\u003ea\u003c/sub\u003e in the sediment showed an exponential (Exp3P1Md) decline variation (y\u0026thinsp;=\u0026thinsp;exp [(a\u0026thinsp;+\u0026thinsp;b)/(x\u0026thinsp;+\u0026thinsp;c)], R\u003csup\u003e2\u003c/sup\u003e\u0026thinsp;=\u0026thinsp;0.4466). At low TOM content, Ka decreased rapidly, with the rate of decrease slowing as TOM content increased, eventually stabilizing. The TOM content and EPC\u003csub\u003e0\u003c/sub\u003e in lake sediment showed the increased first and then decreased exponential variations (Exp3P2) (R\u003csup\u003e2\u003c/sup\u003e\u0026thinsp;=\u0026thinsp;0.7670). At low TOM content, EPC\u003csub\u003e0\u003c/sub\u003e increased with increasing TOM, while at high TOM content, EPC\u003csub\u003e0\u003c/sub\u003e decreased as TOM content rose. Similar trends were observed for the relationship between the contents of ASOM and LFOM and P adsorption-release parameters, as seen with TOM content.\u003c/p\u003e \u003cp\u003eThese results suggest that as OM deposits in the sediment, more P becomes available, increasing the maximum P release. During OM deposition, large amounts of exogenous P occupy adsorption sites, which reduces the sediment\u0026rsquo;s P adsorption capacity (Weyers et al., \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). When OM content is low, the OM-P binding is weak, leading to rapid increases in P release intensity. In this scenario, OM and P compete for adsorption sites on inorganic particles in the sediment, resulting in a sharp decrease in P adsorption capacity (Hiradate and Uchida, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2004\u003c/span\u003e), and EPC\u003csub\u003e0\u003c/sub\u003e increases rapidly. However, when OM content is high, the binding capacity of OM to P strengthens, reducing P release intensity. At this point, OM provides stable organic adsorption sites for P (Lin et al., \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2017\u003c/span\u003e), stabilizing the adsorption capacity of sediment for P, while EPC\u003csub\u003e0\u003c/sub\u003e declines rapidly.\u003c/p\u003e \u003cp\u003eWhen OM content was low, its weak binding to P led to an increased intensity of P release. During this phase, OM and P competed for adsorption sites on inorganic particles in the sediment, causing a rapid reduction in P adsorption capacity (Hiradate and Uchida, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2004\u003c/span\u003e). This resulted in a sharp rise in the equilibrium phosphorus concentration EPC\u003csub\u003e0\u003c/sub\u003e ) of the sediment. On the other hand, at higher OM concentrations, the binding capacity of OM to P was enhanced, which rapidly decreased P release intensity. At this point, OMr provided stable organic adsorption sites for P (Lin et al., \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2017\u003c/span\u003e), which stabilized the P adsorption intensity and caused EPC\u003csub\u003e0\u003c/sub\u003e to rapidly decrease.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003ePrevious studies have shown that the ratios of ASOM/TOM and LFOM/TOM can reflect the activity intensity and decomposition degree of OM in sediments (Zhao et al., \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). In Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e4\u003c/span\u003e, the relationships between ASOM/TOM and the P adsorption-release parameters\u0026mdash;Qr-Max, Qa-Max, Kr, and Ka\u0026mdash;exhibited irregular patterns. However, the relationship between EPC\u003csub\u003e0\u003c/sub\u003e and ASOM/TOM followed an exponential variation, increasing initially and then decreasing (Exp3P2) (R\u0026sup2;= 0.3427). When EPC\u003csub\u003e0\u003c/sub\u003e was low, it increased with higher ASOM/TOM values; when EPC\u003csub\u003e0\u003c/sub\u003e was high, it decreased as ASOM/TOM increased. The relationship between LFOM/TOM and Qr-Max showed an exponential increase (Exp3P2) (R\u0026sup2; = 0.6053), but data from the 8\u0026ndash;10 cm and 10\u0026ndash;12 cm sediment layers were excluded due to their position at the inflection point of sediment deposition. These layers were influenced by both the sedimentation of upper layers and the release from lower layers, leading to more complex patterns. LFOM/TOM and Qa-Max followed an exponential trend of increase followed by decrease (Exp3P2) (R\u0026sup2;= 0.3413), while LFOM/TOM and Kr showed a decrease followed by an increase (Exp3P2) (R\u0026sup2;= 0.4763). LFOM/TOM and Ka also showed an exponential increase followed by a decrease (Exp3P2) (R\u0026sup2;= 0.5900). The correlation between LFOM/TOM and EPC\u003csub\u003e0\u003c/sub\u003e mirrored that of ASOM/TOM and EPC\u003csub\u003e0\u003c/sub\u003e. These findings indicate that as the decomposition of OM in sediment increases, both the maximum release amount and intensity of P exhibit an exponential increase. When OM decomposition is at a lower level, the sediment\u0026rsquo;s P adsorption capacity and intensity increase. Conversely, at higher levels of OM decomposition, the P adsorption capacity and intensity decrease.\u003c/p\u003e \u003cp\u003eDuring the decomposition of humus into smaller molecular organic matter, such as fulvic acid, the binding capacity of OM to P weakens, which results in an exponential increase in both P release capacity and intensity. This process also increases the available adsorption sites in the sediment, which enhances P adsorption intensity. However, as OM further decomposes into small molecular organic compounds, such as proteins, these smaller molecules occupy adsorption sites, reducing the maximum P adsorption capacity and intensity exponentially. When OM activity and decomposition intensity are high, the adsorption-desorption equilibrium concentration of P in the sediments reaches its highest value.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003e3.2 Effects of OM components on P adsorption-release in sediment at different sampling points of Erhai Lake\u003c/b\u003e \u003c/p\u003e \u003cp\u003eThe influence of OM components on P behavior in sediment is strongly influenced by the source of the OM (Zhao et al., \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). In Erhai Lake, the source of OM varies across different sampling regions, leading to a non-linear relationship between the proportion and content of OM components and total phosphorus (TP) (Zhao et al., \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). Figure\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e5\u003c/span\u003e illustrates the relationship between OM content in the 0\u0026ndash;10 cm sediment layer at various sampling points and the dynamic characteristics of P adsorption-release.The TOM content in the sediment exhibited a non-linear relationship with the maximum release amount (Qr-Max) and the release rate constant (Kr), showing exponential variations (Exp3P2), initially decreasing and then increasing. Conversely, TOM content showed a linear relationship with the maximum adsorption amount (Qa-Max) and adsorption rate constant (Ka), though with opposite trends. Both ASOM and LFOM contents in the sediment showed a linear increase in Qr-Max and Qa-Max. However, the relationship between ASOM content and Kr and Ka followed a logarithmic variation (y\u0026thinsp;=\u0026thinsp;aln(x) - b). LFOM content, on the other hand, exhibited an exponential relationship (Exp3P2) with both Kr and Ka. Moreover, the contents of TOM, ASOM, and LFOM all showed an exponential decrease in equilibrium phosphorus concentration (EPC\u003csub\u003e0\u003c/sub\u003e). These results indicate that increasing OM in the sediments of Erhai Lake enhances the number of adsorption sites available for P, thereby increasing both P adsorption capacity and intensity. However, the OM in sediments with low TOM content was predominantly of endogenous origin. Due to its high degree of humification and strong binding affinity for P, the maximum release capacity and intensity of P decreased with increasing OM content in these sediments. In contrast, the OM in sediments with high TOM content was mainly derived from aquatic plant residues or exogenous organic pollutants, which are richer in P content (Zhao et al., \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). As a result, as TOM content increased, the maximum release capacity and intensity of P exhibited an upward trend. The relationship between TOM, ASOM, and EPC\u003csub\u003e0\u003c/sub\u003e in the sediments from different sampling points of Erhai Lake can be considered as the latter half of the \"exponential model\" presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e3\u003c/span\u003e. This is primarily because the TOM and ASOM contents in the sediments of Erhai Lake are relatively high, influencing the P dynamics accordingly.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e6\u003c/span\u003e, the relationship between LFOM/TOM and the adsorption rate constant (Ka) at different sampling points in Erhai Lake sediments exhibited an exponential trend, increasing initially and then decreasing (Exp3P2) (R\u0026sup2; = 0.6310). However, this trend generally mirrored the first half of the model presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e4\u003c/span\u003e. Furthermore, the correlation between ASOM/TOM, LFOM/TOM, and key phosphorus dynamics parameters\u0026mdash;Qr-Max, Qa-Max, Kr, Ka, and EPC₀\u0026mdash;was not statistically significant across the sediment layers. This lack of significant correlation can be attributed to the varying sources of OM across different sampling points in Erhai Lake. The activity intensity, decomposition degree, and component content of OM differ among these sources. Consequently, the P adsorption-release process in the sediments is driven by the combined influence of both the quality (e.g., decomposition degree, activity intensity) and quantity (e.g., component content) of OM. While a strong regularity exists between the quality and quantity of OM within sediments from the same sampling point, the varying sources of OM at different sampling locations result in lower consistency, leading to a weaker regularity in their influence on P behavior.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e3.3 Effect of OM components on P adsorption-release in the sediment of several lakes\u003c/h2\u003e \u003cp\u003eThe extent to which OM components influence P behavior in sediments is shaped by various biogeochemical and environmental factors (Yang et al., \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Additionally, the characteristics of OM components in the sediments of different lakes can have distinct impacts on their respective biogeochemical cycles. In Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e7\u003c/span\u003e, both the maximum P release (Qr-Max) and maximum adsorption (Qa-Max) exhibited a linear upward trend with increasing TOM and ASOM content in the sediment. However, the linear relationship between ASOM content and Qa-Max was not significant (n\u0026thinsp;=\u0026thinsp;9, R\u0026sup2; = 0.0635). As TOM content increased, the release rate constant (Kr) first decreased and then increased, following an exponential variation (Exp3P2), while the adsorption rate constant (Ka) showed a similar trend: an initial increase followed by a decrease (Exp3P2). Furthermore, with increasing TOM content, the equilibrium phosphorus concentration (EPC₀) showed an exponential increase (Exp3P2), aligning closely with the first half of the model in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e3\u003c/span\u003e. Similarly, with increasing LFOM content, EPC\u003csub\u003e0\u003c/sub\u003e exhibited an exponential increase followed by a decrease (Exp3P2), mirroring the pattern observed in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e3\u003c/span\u003e. These findings suggest that the maximum P release capacity and the maximum P adsorption capacity in sediments increased with higher TOM and ASOM content.\u003c/p\u003e \u003cp\u003eAt low TOM content, increasing TOM reduced the P release intensity while enhancing the P adsorption strength in the sediment. However, as TOM content became higher, the P release intensity increased, and the adsorption strength gradually decreased. The EPC\u003csub\u003e0\u003c/sub\u003e in sediments from different lakes also exhibited an exponential increase with rising TOM content, resembling the first half of the model in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e3\u003c/span\u003e. The relationship between LFOM content and EPC\u003csub\u003e0\u003c/sub\u003e followed a similar pattern to that seen in sediments from various sampling points.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e8\u003c/span\u003e, the ratio of ASOM/TOM in sediments from various lakes displayed a pattern of initial increase followed by a decrease in both the maximum phosphorus release (Qr-Max) and maximum adsorption (Qa-Max), following an exponential variation (Exp3P2). It showed a linear decrease with the release rate constant (Kr) and adsorption rate constant (Ka), and an exponential decrease with the equilibrium phosphorus concentration (EPC\u003csub\u003e0\u003c/sub\u003e). On the other hand, the LFOM/TOM ratio in sediments exhibited an initial decrease followed by an increase in Qr-Max, following an exponential variation (Exp3P2), while it showed an exponential downward trend with Kr, Ka, and EPC\u003csub\u003e0\u003c/sub\u003e. These findings suggest that when the activity intensity of organic matter (OM) in the sediment is low, the binding capacity to P gradually strengthens as the activity intensity of OM increases. However, when OM activity intensity is high, the bulk density of the sediment decreases, and its porosity increases. This change in sediment structure promotes the release of P, while the increase in organic adsorption sites enhances the total P adsorption capacity. In this context, the increasing activity of OM strengthens the exchange of adsorption and release of P in the sediment (Zhao et al., \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). As the degree of OM decomposition increases in lake sediments, small molecular organic compounds in the sediment compete with P for adsorption sites. Consequently, the binding capacity of OM to P decreases, leading to a reduction in both the adsorption and release strength of P in the sediment. Notably, the ASOM/TOM and LFOM/TOM ratios in sediments from other lakes were higher than those in the different sediment layers of Erhai Lake. The relationship between ASOM/TOM and EPC\u003csub\u003e0\u003c/sub\u003e can be interpreted as the latter half of the model depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e4\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"4. Discussion","content":"\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e4.1 The effect model of OM content in the sediment on P adsorption and release\u003c/h2\u003e \u003cp\u003eIn this study, the contents of TOM, ASOM, and LFOM in the sediment were found to exhibit a linear dynamic relationship (Y\u0026thinsp;=\u0026thinsp;ax\u0026thinsp;+\u0026thinsp;b) with the maximum phosphorus release (Qr-Max) in the sediment. OM is the primary source of unstable P in sediments (Whalen \u0026amp; Chang, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2001\u003c/span\u003e). As the OM content in the sediment increases, the phosphorus contained within the OM is gradually released during its degradation process. High molecular weight organic compounds in ASOM, such as humic acids, can form complexes with iron and other metals, preventing these complexes from forming with P (Antelo et al., \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2007\u003c/span\u003e). In contrast, low molecular weight organic acids in LFOM can compete with P for adsorption sites through direct physical or electrostatic competition (Weng et al., \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2008\u003c/span\u003e; Weyers et al., \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2017\u003c/span\u003e), thereby promoting the release of P from the sediment. However, P release from sediments occurs primarily during OM degradation. When OM in the sediment is not fully decomposed and consists mainly of plant residues, it can inhibit the release of P. For instance, at sampling point No. 4 in Erhai Lake, located in the Huwankou area, OM is predominantly composed of plant residues, influenced by the decay of submerged plants (Zhao et al., \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). At this location, the maximum release of P is relatively low, and the sediment in Erhai Lake is significantly affected by plant residues, causing the Qr-Max to decrease with the increasing OM content (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e3\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe relationship between OM content, ASOM, LFOM, and the maximum phosphorus adsorption capacity (Qa-Max) also follows a linear dynamic trend (Y\u0026thinsp;=\u0026thinsp;ax\u0026thinsp;+\u0026thinsp;b). OM and its interaction with sediments can increase the number of adsorption sites for P, thereby enhancing the P adsorption capacity. Additionally, OM reacts with Ca\u003csup\u003e2+\u003c/sup\u003e ions, facilitating the formation of P-Ca-OM complexes (Lei et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). The negatively charged functional groups of organic substances, such as carboxyl and phenol groups, can interact with positively charged minerals, such as iron oxides, influencing P adsorption (Liu et al., \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e1999\u003c/span\u003e). The P bound to organic-functional groups on iron oxide surfaces can promote the adsorption of phosphate (PO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2\u0026minus;\u003c/sup\u003e) to form P-Fe-OM complexes through cation bridges (Al\u003csup\u003e3+\u003c/sup\u003e and Fe\u003csup\u003e3+\u003c/sup\u003e), though P-Fe-OM complexes are unstable and highly sensitive to environmental conditions (Jess\u0026eacute; et al., \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). Iron oxide can be dissolved through reduction or ligand complexation, which promotes the release of iron-bound P into the soil solution (Ruiz-Agudo et al., \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2009\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIn the sediment column samples from Erhai Lake, which have a high Fe/Al-P content, the maximum P adsorption capacity decreased with increasing OM content (Zhao et al., \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2020\u003c/span\u003e), consistent with the findings of Andrade et al. (\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2003\u003c/span\u003e) and Antelo et al. (\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2007\u003c/span\u003e). However, in sediments from different sampling points in Erhai Lake and other lakes, the maximum P adsorption capacity increased with increasing OM content (Figs.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e5\u003c/span\u003e and \u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e7\u003c/span\u003e). This increase can be attributed to the fact that OM increases the specific surface area and porosity of sediment particles, thereby enhancing the adsorption of P by the sediments (Lehmann, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2007\u003c/span\u003e). The curve-fitting equations and trends of OM components and the kinetic characteristics of P adsorption-release in sediments are summarized in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eCurve fitting equation and trend of the relationship between OM components of sediment and P adsorption-release kinetic characteristics\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"7\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003eRelational model\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eQ\u003csub\u003er\u0026minus;max\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eQ\u003csub\u003ea\u0026minus;max\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eK\u003csub\u003er\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eK\u003csub\u003ea\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eEPC\u003csub\u003e0\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eTOM\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eFitted equation\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003ey\u0026thinsp;=\u0026thinsp;ax\u0026thinsp;+\u0026thinsp;b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003ey\u0026thinsp;=\u0026thinsp;ax\u0026thinsp;+\u0026thinsp;b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eY\u0026thinsp;=\u0026thinsp;exp(a\u0026thinsp;+\u0026thinsp;bx\u0026thinsp;+\u0026thinsp;cx\u003csup\u003e2\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eY\u0026thinsp;=\u0026thinsp;exp(a\u0026thinsp;+\u0026thinsp;bx\u0026thinsp;+\u0026thinsp;cx\u003csup\u003e2\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eY\u0026thinsp;=\u0026thinsp;exp(a\u0026thinsp;+\u0026thinsp;bx\u0026thinsp;+\u0026thinsp;cx\u003csup\u003e2\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTrend\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eIncreased\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eIncreased\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eIncreased and then decreased\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eDecreased and then increased\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eIncreased and then decreased\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eASOM\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eFitted equation\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003ey\u0026thinsp;=\u0026thinsp;ax\u0026thinsp;+\u0026thinsp;b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003ey\u0026thinsp;=\u0026thinsp;ax\u0026thinsp;+\u0026thinsp;b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eY\u0026thinsp;=\u0026thinsp;exp(a\u0026thinsp;+\u0026thinsp;bx\u0026thinsp;+\u0026thinsp;cx\u003csup\u003e2\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eY\u0026thinsp;=\u0026thinsp;exp(a\u0026thinsp;+\u0026thinsp;bx\u0026thinsp;+\u0026thinsp;cx\u003csup\u003e2\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eY\u0026thinsp;=\u0026thinsp;exp(a\u0026thinsp;+\u0026thinsp;bx\u0026thinsp;+\u0026thinsp;cx\u003csup\u003e2\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTrend\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eIncreased\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eIncreased\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eIncreased and then decreased\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eDecreased and then increased\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eIncreased and then decreased\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eLFOM\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eFitted equation\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003ey\u0026thinsp;=\u0026thinsp;ax\u0026thinsp;+\u0026thinsp;b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003ey\u0026thinsp;=\u0026thinsp;ax\u0026thinsp;+\u0026thinsp;b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eY\u0026thinsp;=\u0026thinsp;exp(a\u0026thinsp;+\u0026thinsp;bx\u0026thinsp;+\u0026thinsp;cx\u003csup\u003e2\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eY\u0026thinsp;=\u0026thinsp;exp(a\u0026thinsp;+\u0026thinsp;bx\u0026thinsp;+\u0026thinsp;cx\u003csup\u003e2\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eY\u0026thinsp;=\u0026thinsp;exp(a\u0026thinsp;+\u0026thinsp;bx\u0026thinsp;+\u0026thinsp;cx\u003csup\u003e2\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTrend\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eIncreased\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eIncreased\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eIncreased and then decreased\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eDecreased and then increased\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eIncreased and then decreased\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eASOM/TOM\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eFitted equation\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eY\u0026thinsp;=\u0026thinsp;exp(a\u0026thinsp;+\u0026thinsp;bx\u0026thinsp;+\u0026thinsp;cx\u003csup\u003e2\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eY\u0026thinsp;=\u0026thinsp;exp(a\u0026thinsp;+\u0026thinsp;bx\u0026thinsp;+\u0026thinsp;cx\u003csup\u003e2\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003ey\u0026thinsp;=\u0026thinsp;ax\u0026thinsp;+\u0026thinsp;b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003ey\u0026thinsp;=\u0026thinsp;ax\u0026thinsp;+\u0026thinsp;b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eY\u0026thinsp;=\u0026thinsp;exp(a\u0026thinsp;+\u0026thinsp;bx\u0026thinsp;+\u0026thinsp;cx\u003csup\u003e2\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTrend\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eDecreased and then increased\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eDecreased and then increased\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eDecreased\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eDecreased\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e\u0026mdash;\u0026mdash;\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eLFOM/TOM\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eFitted equation\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eY\u0026thinsp;=\u0026thinsp;exp(a\u0026thinsp;+\u0026thinsp;bx\u0026thinsp;+\u0026thinsp;cx\u003csup\u003e2\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eY\u0026thinsp;=\u0026thinsp;exp(a\u0026thinsp;+\u0026thinsp;bx\u0026thinsp;+\u0026thinsp;cx\u003csup\u003e2\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eY\u0026thinsp;=\u0026thinsp;exp(a\u0026thinsp;+\u0026thinsp;bx\u0026thinsp;+\u0026thinsp;cx\u003csup\u003e2\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eY\u0026thinsp;=\u0026thinsp;exp(a\u0026thinsp;+\u0026thinsp;bx\u0026thinsp;+\u0026thinsp;cx\u003csup\u003e2\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eY\u0026thinsp;=\u0026thinsp;exp(a\u0026thinsp;+\u0026thinsp;bx\u0026thinsp;+\u0026thinsp;cx\u003csup\u003e2\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTrend\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eDecreased and then increased\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eIncreased and then decreased\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eDecreased and then increased\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eIncreased and then decreased\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e\u0026mdash;\u0026mdash;\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003e4.2 The effect mechanism of OM content on the kinetic characteristics of P adsorption-release in the sediments\u003c/b\u003e \u003c/p\u003e \u003cp\u003eEPC\u003csub\u003e0\u003c/sub\u003e represents the dynamic equilibrium between P adsorption and release in the sediment. The influence of sedimentary OM on EPC\u003csub\u003e0\u003c/sub\u003e is a process governed by the balance of these two opposing mechanisms (Zhao et al., \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). In this study, as the content of OM, ASOM, and LFOM in the sediment increased, EPC\u003csub\u003e0\u003c/sub\u003e exhibited an initial increase followed by a decrease (Exp3P2). Similarly, the P release intensity first increased and then decreased (Exp3P2), while the P adsorption intensity showed the opposite trend, first decreasing and then increasing (Exp3P2). When OM content was low, the increase in small molecular OM led to competition with P for adsorption sites, which resulted in higher P release intensity than P adsorption intensity. Consequently, the rate of P release from the sediment was greater than the rate of adsorption, and the P release dominated at the sediment-water interface. However, as OM content increased beyond a certain threshold, OM contributed to the expansion of P adsorption sites and an increase in the specific surface area of the sediment. At the same time, the degradation rate of OM slowed, and the adsorption intensity of P on OM exceeded the release intensity. In this scenario, P became predominantly adsorbed at the sediment-water interface. Thus, at low OM content, a competitive relationship exists between OM and P, where small molecular OM outcompetes P for adsorption sites. In contrast, at high OM content, OM provides a significant number of adsorption sites, becoming the main factor controlling P migration in the sediment.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e4.3 The effect mechanism of OM components characteristics on P adsorption-release kinetics in the sediment\u003c/h2\u003e \u003cp\u003eThe release and adsorption of P in sediment involve both physical and chemical mechanisms, with the activity and degradation intensity of OM playing a crucial role in influencing these processes. When the activity intensity of OM in the sediment is high, it indicates a large number of active sites, resulting in stronger chemical binding effects on P, such as surface adsorption, bond ion adsorption, and molecular coupling. In contrast, when the decomposition degree of OM is low\u0026mdash;indicating a high proportion of macromolecular organic matter\u0026mdash;the porosity in the sediment increases, facilitating physical fixation mechanisms, such as encapsulation of P.\u003c/p\u003e \u003cp\u003eAs the activity intensity and decomposition degree of OM increase, both the maximum release capacity (Qr-Max) and maximum adsorption capacity (Qa-Max) of P in the sediment follow a pattern of initial decrease, followed by an increase, exhibiting exponential variations (Exp3P2). This trend suggests that at lower activity and decomposition stages, P competes with other ions due to fewer adsorption sites, such as adsorption valence bonds and encapsulated voids, as well as low P content in OM. As the activity and decomposition of OM intensify, the number of available adsorption sites, including valence bonds and encapsulated voids, increases, thereby enhancing both P adsorption and release capacities.\u003c/p\u003e \u003cp\u003eMoreover, the equilibrium phosphorus concentration (EPC\u003csub\u003e0\u003c/sub\u003e) in the sediment also follows a similar pattern, initially decreasing and then increasing exponentially (Exp3P2) with the increasing activity and decomposition degree of OM. As the OM activity in the sediment rises, the chemical binding effects strengthen, leading to surface adsorption, bond ion adsorption, and molecular coupling with OM (Weyers et al., \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Zhao et al., \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). Consequently, the adsorption and release intensities of P show a linear increase with increased OM activity, following the equation Y\u0026thinsp;=\u0026thinsp;ax\u0026thinsp;+\u0026thinsp;b.\u003c/p\u003e \u003cp\u003eWhen the decomposition degree of OM in the sediment increases, the encapsulation voids and adsorption-release dynamics of P in the sediment exhibit a pattern of first decreasing, then increasing exponentially (Exp3P2). At lower levels of decomposition, the release and adsorption intensity of P decrease because small molecular organic matter from OM competes with P for adsorption sites on the sediment parent material. The strong coupling effect between macromolecular OM and P reduces the release of P. In contrast, when the decomposition degree of OM is high, a larger portion of macromolecular OM is degraded into small molecular organic matter. Small molecule dissolved organic matter (DOM) has a weaker fixation ability on P, leading to an increase in both adsorption and release intensities with the higher decomposition of OM.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e4.4 The effect mechanism of OM on P adsorption-release in the sediment\u003c/h2\u003e \u003cp\u003eThe increase in N and P content in water bodies leads to lake eutrophication, which is accompanied by a range of environmental issues, including water quality degradation (Long et al., \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Sediments serve as both the source and sink of nutrients in aquatic systems, with the phosphorus (P) dynamics at the sediment-water interface being a critical endogenous factor contributing to eutrophication (Huang et al., \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). The organic matter (OM) components in sediment play a significant role in P adsorption and release processes, influencing P kinetics at the sediment-water interface. The mechanisms through which OM affects P adsorption-release kinetics in sediment can be broadly categorized into two aspects.On the one hand, direct influence of OM characteristics on P adsorption-release kinetics, which is primarily driven by the release of P contained in OM during its degradation. The interaction between OM and P is complex, as the degradation of OM leads to the release of P, influencing the overall P behavior in sediments. The specific mechanisms through which OM content and its various components (e.g., TOM, ASOM, LFOM) affect P adsorption and release kinetics are illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e9\u003c/span\u003e. On the other hand, influence of OM-sediment interaction on P adsorption-release kinetics, which mechanism arises from the interaction between OM and sediment during deposition. The combined effects of OM components and sediment characteristics dictate the dynamics of P adsorption and release. The dominant mechanism of OM action may vary between different sediment types, depending on factors such as the OM content, composition, and the presence of minerals in the sediment.\u003c/p\u003e \u003cp\u003eIn this study, the OM content in the 0\u0026ndash;10 cm sediment layer at a specific sampling point in Erhai Lake showed continuous degradation (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e2\u003c/span\u003e). This suggests that at this depth, P behavior was predominantly influenced by the characteristics of the OM. In contrast, below the 10 cm sediment layer, OM and sediments interacted to form organic-inorganic colloids during the deposition process. This indicates that P behavior at greater depths was primarily governed by the interaction between OM and the underlying sediments.\u003c/p\u003e \u003cp\u003eThe source of OM varies across different regions of Erhai Lake (Zhao et al., \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). In regions where the OM is mainly derived from aquatic plants and other external sources, P behavior is strongly influenced by the intrinsic properties of OM. However, in other regions with different OM sources, such as those dominated by microbial and sedimentary OM, P dynamics are more heavily influenced by the interactions between OM and the sediment. Similarly, P behavior in sediments from different lakes is affected by differences in OM composition and sediment characteristics (Yi et al., \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2008\u003c/span\u003e), with the interaction between OM and sediments playing a more dominant role in determining P dynamics.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe influence of OM components in sediment on P adsorption-release kinetics is a complex process, shaped by the characteristics of OM, the sediment matrix itself, and the morphology of P in the sediment. In this study, the mechanism by which OM composition characteristics affect P adsorption-release kinetics was explored across three levels: different layers within a single sampling point, different regions of a lake, and across different lakes. The results revealed that the content of OM exhibited a linear relationship with the P adsorption-release kinetic parameters in sediment, while the characteristics of OM composition and the P adsorption-release kinetics followed exponential variations.\u003c/p\u003e \u003cp\u003eTo further quantify the inflection points of OM composition characteristics in regulating P adsorption-release kinetics, and to elucidate the release mechanisms of endogenous P in sediments, a substantial dataset is required for comprehensive quantitative analysis. Additionally, it is necessary to consider the coupling effects of other factors present in sediments to enable a more systematic understanding of P behavior. The findings of this study provide deeper insights into the mechanisms by which OM and its components influence P adsorption and release in sediments.\u003c/p\u003e \u003c/div\u003e"},{"header":"5. Conclusions","content":"\u003cp\u003eThe content and composition of OM in sediments are key factors influencing the kinetics of P release and adsorption. As the OM content increases, both the maximum adsorption capacity and the maximum release capacity of P in sediments exhibit a linear increase. The release intensity of P shows an initial increase followed by a subsequent decrease, while the adsorption intensity of P follows a trend of first decreasing and then increasing. The equilibrium concentration of P in adsorption and desorption also follows a pattern of increasing initially, then decreasing. The activity intensity and decomposition degree of OM in the sediment are critical factors in determining the chemical interactions and physical fixation of P by OM. As the activity intensity of OM increases, the maximum adsorption capacity, maximum release capacity, and equilibrium concentration of adsorption and desorption in the sediment initially decrease and then increase. In contrast, the adsorption and release intensity of P shows a consistent linear increase. Moreover, with the increase in the decomposition degree of OM, the maximum release capacity, adsorption and release intensity, and equilibrium concentration of P in sediments follow a pattern of first decreasing and then increasing. Meanwhile, the maximum adsorption capacity of P initially increases and then decreases.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e \u003ch2\u003eEthical Approval:\u003c/h2\u003e \u003cp\u003eNot Applicable.\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003eConsent to Participate\u003c/strong\u003e \u003cp\u003eThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003eConsent to Publish\u003c/strong\u003e \u003cp\u003eAll claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organization, or those of the publisher. Any product that may be evaluated in this ariticle,is not guaranteed or endorsed by the publishee.\u003c/p\u003e \u003c/p\u003e\u003cp\u003e \u003ch2\u003eCompeting Interests\u003c/h2\u003e \u003cp\u003eThe authors declare that they have no conflict of interest. Furthermore, the founding sponsors had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, and in the decision to publish the results.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eFunding\u003c/h2\u003e \u003cp\u003eThis research is supported by National Major Science and Technology Program for Water Pollution Control and Treatment [No. 2012ZX07102-004], and School level project of Hebei North University [No. D2022405001].\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eConceptualization, H.Z., S.L. and H.Z.; Data curation, H.Z., S.L., H.Z., Z.H., L.J., S.W. and S.D.; Formal analysis, H.Z., S.L., H.Z., Z.H.,and S.D.; Funding acquisition, H.Z.; Investigation, H.Z., S.L., H.Z., Z.H., L.J., S.W. and S.D.; Methodology,H.Z., S.L. and H.Z.; Project administration, H.Z.; Resources, H.Z.; Software, S.L.; Supervision, H.Z.; Validation, H.Z., S.L., H.Z., Z.H., L.J., S.W. and S.D.; Visualization,H.Z. and S.L.; Writing \u0026ndash; original draft, H.Z. and S.L.; Writing \u0026ndash; review \u0026amp; editing, H.Z., S.L., H.Z., Z.H., L.J., S.W. and S.D.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eAndrade FV, Mendon\u0026ccedil;a ES, Alvarez VVH, Novais RF (2003) Adi\u0026ccedil;\u0026atilde;o de \u0026aacute;cidos org\u0026acirc;nicos e h\u0026uacute;micosem Latossolos e adsor\u0026ccedil;\u0026atilde;o de fosfato. 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Environ Sci Pollut Res 27:19901\u0026ndash;19914. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s11356-020-08120-9\u003c/span\u003e\u003cspan address=\"10.1007/s11356-020-08120-9\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAttached drawings\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Organic matter, phosphorus, exponential variations, P adsorption-desorption","lastPublishedDoi":"10.21203/rs.3.rs-6640256/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6640256/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eOrganic matter (OM) components in sediments play a significant role in influencing phosphorus (P) adsorption and release behavior at the sediment-water interface. However, the underlying mechanisms remain unclear. This study examines the relationship between OM components and P adsorption-release kinetics across various sediment types. Results show that as the OM content in sediments increases, both the maximum P adsorption capacity and the maximum P release capacity exhibit a linear increase. The release intensity of P follows an initial increase and subsequent decrease in an exponential pattern (Exp3P2). Similarly, P adsorption intensity first decreases and then increases in an exponential manner (Exp3P2), while the equilibrium concentration of P adsorption-desorption shows an exponential increase followed by a decrease (Exp3P2). At low OM content, an increase in OM leads to greater P release intensity, reduced adsorption intensity, and an increase in equilibrium concentration. At high OM content, however, the P release intensity decreases, adsorption intensity increases, and the equilibrium concentration decreases. The activity of OM plays a key role: low OM activity reduces the P release-adsorption potential, whereas high activity enhances it. When OM degradation is low, it inhibits P release and promotes P adsorption, while high OM degradation facilitates P release and inhibits adsorption. The changes in the quality and quantity of OM in lake sediments significantly affect the physical and chemical mechanisms of P adsorption and release, thereby regulating P behavior at the sediment-water interface.\u003c/p\u003e","manuscriptTitle":"Study on the Influence Mechanism of the Organic Matter Components on Phosphorus Adsorption-Release Kinetics in Lake Sediment","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-06-11 13:32:54","doi":"10.21203/rs.3.rs-6640256/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"cd0f616e-9450-49d9-b34a-039bf5f45e94","owner":[],"postedDate":"June 11th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2026-04-21T07:12:37+00:00","versionOfRecord":[],"versionCreatedAt":"2025-06-11 13:32:54","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-6640256","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6640256","identity":"rs-6640256","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}