Heavy metal pollution in the Yongjiang Estuary, China and their relations to environmental factors

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The results found that the change concentrations of heavy metals and environmental factors were high, which had obvious spatial distribution and seasonal dynamic characteristics. In the aspect of spatial distribution, the concentrations of heavy metals and the physical and chemical indexes were higher at the points near the industrial area. In the aspect of seasonal dynamics, the concentrations of Pb, total phosphorus and ammonia nitrogen were the highest in winter. In the aspect of tidal change, the change rules of different indicators were different, among which, the concentrations of Cd, Ni and total nitrogen in the rising tide and ebb tide were quite different. The concentration of dissolved organic carbon, total nitrogen, pH, salinity, ammonia nitrogen and chlorophyll a were positively correlated with target heavy metals. This study explored the relationship between the concentrations of heavy metals and environmental parameters, which is beneficial to future heavy metals research in estuaries. Heavy metals environmental factors tidal effect Yongjiang Estuary Figures Figure 1 Figure 2 Figure 3 Figure 4 1. Introduction Heavy metal pollution was one of the most concerned environmental problems in recent years, which had the characteristics of environmental concealment, persistence and un-degradability (Yuan et al., 2021 ; Tam and Wong, 2000 ). At the same time, due to the gradual amplification of heavy metals with the food chain, they posed a great threat to human health (Liu et al., 2022 ; Stankovic and Jovic, 2012 ). For example, Minamata disease and Itai-itai disease in Japan in the 1930s were typical heavy metal pollution events. These serious environmental pollution events have awakened people's awareness of environmental protection (Mubiana et al., 2005 ). In recent years, with the continuous development of the coastal estuary in China, the problem of heavy metal pollution has become increasingly prominent (Liu et al., 2020; O’Mara et al., 2016). The main sources of heavy metals in the estuary were the discharge of domestic sewage and industrial wastewater and the use of pesticides and fertilizers (Masson et al., 2006 ). Due to the tidal and salinity gradient characteristics of the estuary, the water quality fluctuated greatly, which was significantly different from the river and marine environment (Kibria et al., 2016 ). In the water environment, the concentration of heavy metals was affected by many environmental factors. Heavy metals can continuously migrated in water, sediments and suspended solid particles (Liu et al., 2020; Fu et al., 2014 ). Generally, when heavy metals were imported into the water body, they can be adsorbed and settled into the seabed sediments by suspended solids under the dilution of water. Under the change of some environmental factors such as pH and salinity, the heavy metals in the sediments can enter the water body again through a series of chemical and biological processes, which makes the content of heavy metals in the water body with a dynamic balance (Chaturvedi et al., 2021 ; Boyle et al., 1974 ). The dynamic changes of physical and chemical properties of estuarine water in coastal cities were fierce (Omar et al., 2019 ; Chen et al., 2013 ). In addition, the impact of human activities has increased in recent years, and the normal balance of water quality has been broken. The migration and transformation mechanism of heavy metals and their relationship with environmental factors also tend to be complex and difficult to predict (Rivera et al., 2019 ). Ningbo is one of the core cities in China's Yangtze River Delta Urban Agglomeration. In recent decades, due to the rapid economic development, urban rivers have been polluted by heavy metals and nutrients in varying degrees. There are three main rivers in Ningbo, including Fenghua River, Yuyao River and Yongjiang River (Zhao and Yang, 2009 ). Among them, Yongjiang River is formed by the confluence of Fenghua River and Yuyao River, which is the throat connecting inland river and open sea. Yongjiang River is 26 km in length with a drainage area of 361 km 2 . The runoff of Yongjiang River carried industrial and agricultural wastewater of the upstream township into the estuary, especially the discharge of nutrients, organic matter and heavy metals, which is easy to cause a series of ecological and environmental problems. Some scholars have studied water quality, algae, etc. in the Yongjiang River (Zheng et al., 2021 ; Simpson et al., 2002 ). However, there were relatively few studies on heavy metals and water quality in the Yongjiang Estuary. In this research, we took Yongjiang Estuary as the research object to study the content level and distribution of typical heavy metals and environmental factors in water bodies in different seasons during high tide and low tide. 8 heavy metals and 11 environmental parameters were investigated at five sites. Revealing the distribution level of typical heavy metals and physicochemical indicators and discussing the relationship between heavy metals and physicochemical factors, can clarify the temporal and spatial distribution law of heavy metals and physicochemical factors. The results will be useful to understand the relationships between heavy metals and environment parameters during two tidal processes, which provide background data for assessing the ecological risks and managing heavy metals in the Yongjiang Estuary. 2. Materials And Methods 2.1 Sample collection Four sampling events at the tide rising and tide ebbing over tidal cycles were conducted from September 2017 to June 2018. Five sampling sites were selected along the Yongjiang Estuary, among which A, B and C were located in the center of urban area and D and E were located in the Zhenhai industrial zone (Fig. 1 ). The fundamental properties of water samples such as pH, temperature, salinity and dissolved oxygen (DO) were measured in situ. All water samples were collected from the center of the river (0–0.5m below the water surface) and stored in pre-cleaned amber glass bottles (5L) and plastic bottles (5L), which had been enrinsed 2–3 times before the final sample was collected. The water samples passed 0.45 µm cellulose acetate filter membrane and were stored at 4℃ to prevent degradation. The determination of heavy metals and related physical and chemical indexes was completed within 1 week from the time of collection. 2.2 Sample determination The contents of heavy metals (Pb, Cd, Mn, Ni, Cr, Fe, Cu and As) in water samples were determined by inductively coupled plasma mass spectrometry (ICP-MS). 5 blank repetitions were set for each batch of samples to eliminate the influence of different batches on the experimental data between treatments and during the test process. The standard curve was drawn with the standard reagent produced by the national reference material research center, and the deionized water was used as the blank to eliminate the systematic error. Detection limit of instrument method(µg L − 1 ) were Pb 0.004, Cd 0.003, Mn 0.044, Ni 0.019, Cr 0.017, Fe 0.507, Cu 0.005 and As 0.079, respectively. Other physical and chemical indexes included total suspended solids (TSS), total nitrogen (TN), total phosphorus (TP), chlorophyll a (Chla), nitrate nitrogen (NO 3 − -N), ammonia nitrogen (NH 4 + -N), nitrous nitrogen (NO 2 − -N) and dissolved organic carbon (DOC) were measured according to the environmental quality standard for surface water (GB 3838 − 2002). NO 3 − -N and NO 2 − -N were determined by ion chromatography. TP was determined by ammonium molybdate spectrophotometry. DOC and TN were measured by total organic carbon analyzer. NH 4 + -N was determined by flow analyzer and Chla was determined by hot ethanol method. 2.3 Statistical analysis The data of heavy metals and physical and chemical indexes were preprocessed by Excel 2013, and the significance of the data was analyzed by SPSS 16.0. Originpro 9.1 was used to display the distribution characteristics of heavy metals and physical and chemical indexes. Canoco 5 software was applied to map redundancy analysis (RDA) for exploring the relationship between heavy metals and physical and chemical factors by using the maximum and minimum data standardization method. The significance level was calculated by linear region analysis and the results were considered as statistically significant as p < 0.05. 3. Results 3.1 Distribution characteristics of heavy metal concentrations The concentration variation of heavy metals at each sampling point in Yongjiang Estuary was shown in Fig. 2 . In general, the content of heavy metals in water were affected by the location of sampling points, rising tide and ebb tide, and seasons. Each heavy metal had a significant difference level at different sampling points, but the variation laws of different heavy metals were inconsistent. The variation range of Cd concentrations were from not detected to 4.90 µg L − 1 and the concentrations at sites D and E were high. The variation range of Cr concentrations were from not detected to 11.6 µg L − 1 and the concentration of D and E were high in March and June at the rising tide, while the concentration of other sampling points were relatively low. Different seasons had a significant impact on the Cr content. For example, although the Cr content of D were high in March and June, it was not detected in September and December. The variation range of Mn content in water body were not detected to 562 µg L − 1 and the concentration of A, B and C were high in June, while the content level of E were low. The variation range of Pb content level were not detected to 4.68 µg L − 1 , in general, the content of E were relatively high in December, while the content of A, B and C remained relatively low. The variation range of Cu content level were 0.11 ~ 16.9 µg L − 1 , the content of E were higher in March and June, and the content of various points were relatively low in September and December. The seasonal variation of Fe content were obvious. For example, it was higher in September and December at A, B and C, and the overall variation law of rising tide and ebb tide were basically the same. It can be seen that different heavy metals were affected by different sampling points, seasons and rising tide and ebb tide, and the variation range was large. In general, the concentration of heavy metals were generally low, which were the level of µg L − 1 (Table 1 ). 3.2 Distribution characteristics of water quality The physical and chemical indexes of water quality were jointly affected by sampling points, seasons, rising tide and ebb tide, and different sampling points had reached a significant difference level. The range of temperature was from 8.8 to 30.1 ℃, the concentration range of DO was from 1.24 to 14.9 mg L − 1 . The range of pH was from 6.31 to 7.95. It can be seen from Fig. 3 that pH showed obvious seasonal variation law at both upstream and downstream sample points, and reached the lowest in December. The salinity increased significantly from A to E, and the increase multiple was more than 50 times. The concentration of TSS were high in March and December, which reached the highest at D and E, and its highest content reached more than 700 mg L − 1 . The content of Chla was higher at A and reached the peak in September. Contrary to salinity, the content of Chla decreased from upstream to downstream. The content of TN had a certain increasing trend with seasons at A, B and C, and reached the highest in December, while D and E reached the peak in September. The content of TP reached the peak in December at D and E, while the variation range of A, B and C with seasons was relatively small. The changes of NH 4 + -N and NO 3 − -N in the water body were basically similar. Among them, the content of NH 4 + -N reached the highest at D and E in December, while the content of NO 3 − -N reached the peak at D in March. The content of NH 4 + -N and NO 3 − -N in the upstream sampling points were relatively low and the change were relatively stable. In general, average water quality of five sampling sites at the rising tide and ebb tide were different (Table 2 ). Table 2 Average water quality data of five sampling sites in the Yongjiang Estuary, China Tides Site NO 3 -N (mg/L) NH4+-N (mg/L) TN (mg/L) TP [mg/L] DOC (mg/L) Salinity (‰) DO (mg/L) pH TSS (mg/L) Chla (mg L − 1 ) RT A 4.81 0.34 7.42 0.42 7.41 0.25 7.89 7.04 185.91 9.72 B 5.93 0.28 5.51 0.26 7.89 0.32 7.59 7.51 181.60 2.71 C 3.83 0.31 11.39 0.29 13.02 0.72 6.83 7.37 157.91 3.33 D 8.11 2.94 15.64 2.35 28.28 17.02 7.81 7.62 397.67 0.86 E 3.79 2.47 15.74 2.30 25.57 23.23 8.09 7.65 429.83 0.66 ET A 5.53 0.41 6.70 0.23 6.98 0.26 7.14 7.12 185.64 8.66 B 6.16 0.34 6.48 0.24 7.04 0.30 7.77 7.33 153.90 1.71 C 5.55 0.32 7.53 0.21 9.40 0.34 6.33 7.33 180.73 3.78 D 6.70 1.51 12.15 1.48 15.38 4.99 7.19 6.93 495.08 2.35 E 2.53 2.96 9.97 2.32 20.81 15.56 7.87 7.24 478.58 0.83 RT: rising tide; ET: ebb tide. 3.3 Impact on environmental factors RDA was used to study the correlation between the concentration of heavy metals and environmental factors (Fig. 4 ). The included angle of the arrows between species factors (Pb, Cd, Mn, Ni, Cr, Fe, Cu and As) and environmental factors (pH, salinity, TSS, TN, TP, Chla, NO 3 − N, NH 4 + -N and DOC) indicated the correlation between variables. The results showed that the concentrations of heavy metals and environmental factors among all water samples with RDA1 and RDA2 explained 80.2% and 6.3% variation, respectively. The concentration of Mn and Ni were highly correlated. The concentration of Pb, Cr and As were highly correlated, and there was a good correlation between Fe and Cd. The concentration of DOC and TN were positively correlated with Fe and As. The concentration of Cu was positively correlated with pH, while Pb and Cr were positively correlated with salinity and NH 4 + -N. Chla content had a strong correlation with Cd. It can be seen that the relationship between different heavy metals and different physical and chemical factors was different. 4. Discussion There were some similarities in the distribution of different heavy metals in water. For example, the contents of Mn and Ni were higher in June, which is closely related to the periodic production of industrial enterprises. The concentration of As was relatively high in September, which was only detected in September at E, and it was lower at rising tide than at ebb tide. The reason for this phenomenon is related to the dilution of seawater (Ubando et al., 2021 ; Nedia et al., 2013 ). At the same time, the estuary has a relatively high concentration of suspended solids, which will enhance the adsorption performance of As (Jaishankar et al., 2014 ). As is adsorbed in suspended solids and transported to the lower water body or sediment, resulting in its concentration at the sea inlet was lower than that at the upstream sampling points. In contrast to As, the content of most heavy metals such as Pb, Cr, CD and Cu were generally higher in the downstream. On the one hand, it is related to more heavy industrial enterprises (such as electroplating and machining) in Zhenhai District and Beilun District in the downstream. On the other hand, it is related to the collection of upstream pollutants in the downstream. In general, along the sampling points A to E, the heavy metal pollution in water showed obvious seasonal variation characteristics. For example, Cu and Cr were higher in March and June, while As and Pb were relatively higher in September and December, respectively. This phenomenon indicated that the heavy metals in the water are affected by the synergistic effect of human activities and natural environmental factors, which is consistent with the research results of Sheyang Estuary in Jiangsu Province (Zhao et al., 2018 ). The concentrations of heavy metals in Yongjiang Estuary were generally low and did not exceed the standard. Among them, the concentrations of Fe, Mn, Cr, Ni, Cu and Pb were much lower than those in Hugri Estuary, India (Mitra et al., 2018 ), indicating that the heavy metal pollution in Yongjiang Estuary is controllable. However, the monitoring and control should be strengthened, especially the monitoring of the accumulation area of heavy metals in the downstream area, so as to prevent the pollution of heavy metals in water. The concentrations dynamics of heavy metals and water quality indicators in Yongjiang Estuary showed diversity characteristics by the measurement of water samples at rising tide and ebb tide in four different seasons from 2017 to 2018. This phenomenon was mainly affected by many factors such as estuarine development, management and pollution source input, which was related to natural factors such as estuarine unique tidal cycle, topographic and geomorphic characteristics and hydrology (Chai et al., 2006 ). Estuary is a hot area for the accumulation of materials in the whole basin, and the probability of environmental problems caused by human activities is also high (Fernandes et al., 2019 ). Study showed that the probability of eutrophication and heavy metal pollution in large coastal estuaries was higher than that in small coastal estuaries because the acceptance of pollutants in large coastal estuaries was greater than that in small coastal estuaries (Liu et al., 2021 ). The sample collection area of Yongjiang Estuary included different industrial categories. For example, Haishu District was a typical commercial area with few industries, dense population and developed transportation. Zhenhai District was a gathering place for heavy industry and petrochemical enterprises. Beilun District was a port industrial area, and there were large ports, thermal power plants and electroplating industry in the area. The location characteristics of these potential pollution sources can cause the differences of heavy metal and nutrient pollution in different water bodies of Yongjiang Estuary. In general, NH 4 + -N, NO 3 − N, DOC and TSS in water quality indicators showed obvious downstream accumulation characteristics and obvious seasonal variation law, which was consistent with the research results of Minjiang Estuary (Zheng et al., 2022 ). Seasonal variation may be affected by flow, TSS and estuarine buffer effect. pH was the lowest in December and Chla content was higher in September. This phenomenon is mainly related to the joint action of natural factors and human activities such as water temperature, light, DO and salinity in different seasons (Xia et al., 2021 ; McQuatters-Gollop et al., 2007 ). The factors affecting estuarine element circulation and nutrient characteristics are complex, and the synergistic effects of various comprehensive factors must be considered. There was a certain correlation between heavy metals and water quality indicators, which was mainly related to the different properties of heavy metals in water. 5. Conclusions In the present study, we illustrated the case study of Yongjiang Estuary where the 8 heavy metals and 11 environmental parameters were investigated at five sites across four seasons during the tide rising and ebbing durations. The results indicated that the heavy metals and environmental factors in estuaries showed obvious seasonal and tidal variation characteristics, which were enriched at the points where the main industries were concentrated. The changes of environmental factors caused by the productivity cycle and seasonal changes of industrial enterprises affected the time of the peak of heavy metal content. In general, heavy metals pollution in the Yongjiang Estuary was relatively lightly. The seasonal variation of water quality indexes along the sampling points was very obvious, especially NH 4 + -N, NO 3 -N and TSS were enriched in the downstream. There was nitrogen surplus in the water body of Yongjiang Estuary, so the monitoring should be further strengthened to prevent the occurrence of water eutrophication. Declarations Conflict of interest : The authors declare that there are no conflicts of interest. Data availability : Research data may be obtained from the lead author upon reasonable request. Color should be used for any figures in print. Funding statement: This paper is based upon the grant supports provided by National Natural Science Foundation of China (42167017), the Foundation of Guizhou Educational Committee (QJJ[2022]201), and the Projects of Guizhou Medical University (XBHJZ[2020]034 and 21NSFCP22). Author Contribution statement: Chunli Zheng wrote the main manuscript text and Hongkai Liao prepared figures 1-4. All authors reviewed the manuscript. 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Introduction","content":"\u003cp\u003eHeavy metal pollution was one of the most concerned environmental problems in recent years, which had the characteristics of environmental concealment, persistence and un-degradability (Yuan et al., \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Tam and Wong, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2000\u003c/span\u003e). At the same time, due to the gradual amplification of heavy metals with the food chain, they posed a great threat to human health (Liu et al., \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Stankovic and Jovic, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). For example, Minamata disease and Itai-itai disease in Japan in the 1930s were typical heavy metal pollution events. These serious environmental pollution events have awakened people's awareness of environmental protection (Mubiana et al., \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2005\u003c/span\u003e). In recent years, with the continuous development of the coastal estuary in China, the problem of heavy metal pollution has become increasingly prominent (Liu et al., 2020; O\u0026rsquo;Mara et al., 2016). The main sources of heavy metals in the estuary were the discharge of domestic sewage and industrial wastewater and the use of pesticides and fertilizers (Masson et al., \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2006\u003c/span\u003e). Due to the tidal and salinity gradient characteristics of the estuary, the water quality fluctuated greatly, which was significantly different from the river and marine environment (Kibria et al., \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2016\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIn the water environment, the concentration of heavy metals was affected by many environmental factors. Heavy metals can continuously migrated in water, sediments and suspended solid particles (Liu et al., 2020; Fu et al., \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). Generally, when heavy metals were imported into the water body, they can be adsorbed and settled into the seabed sediments by suspended solids under the dilution of water. Under the change of some environmental factors such as pH and salinity, the heavy metals in the sediments can enter the water body again through a series of chemical and biological processes, which makes the content of heavy metals in the water body with a dynamic balance (Chaturvedi et al., \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Boyle et al., \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1974\u003c/span\u003e). The dynamic changes of physical and chemical properties of estuarine water in coastal cities were fierce (Omar et al., \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Chen et al., \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). In addition, the impact of human activities has increased in recent years, and the normal balance of water quality has been broken. The migration and transformation mechanism of heavy metals and their relationship with environmental factors also tend to be complex and difficult to predict (Rivera et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Ningbo is one of the core cities in China's Yangtze River Delta Urban Agglomeration. In recent decades, due to the rapid economic development, urban rivers have been polluted by heavy metals and nutrients in varying degrees. There are three main rivers in Ningbo, including Fenghua River, Yuyao River and Yongjiang River (Zhao and Yang, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). Among them, Yongjiang River is formed by the confluence of Fenghua River and Yuyao River, which is the throat connecting inland river and open sea. Yongjiang River is 26 km in length with a drainage area of 361 km\u003csup\u003e2\u003c/sup\u003e. The runoff of Yongjiang River carried industrial and agricultural wastewater of the upstream township into the estuary, especially the discharge of nutrients, organic matter and heavy metals, which is easy to cause a series of ecological and environmental problems. Some scholars have studied water quality, algae, etc. in the Yongjiang River (Zheng et al., \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Simpson et al., \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2002\u003c/span\u003e). However, there were relatively few studies on heavy metals and water quality in the Yongjiang Estuary.\u003c/p\u003e \u003cp\u003eIn this research, we took Yongjiang Estuary as the research object to study the content level and distribution of typical heavy metals and environmental factors in water bodies in different seasons during high tide and low tide. 8 heavy metals and 11 environmental parameters were investigated at five sites. Revealing the distribution level of typical heavy metals and physicochemical indicators and discussing the relationship between heavy metals and physicochemical factors, can clarify the temporal and spatial distribution law of heavy metals and physicochemical factors. The results will be useful to understand the relationships between heavy metals and environment parameters during two tidal processes, which provide background data for assessing the ecological risks and managing heavy metals in the Yongjiang Estuary.\u003c/p\u003e"},{"header":"2. Materials And Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Sample collection\u003c/h2\u003e \u003cp\u003eFour sampling events at the tide rising and tide ebbing over tidal cycles were conducted from September 2017 to June 2018. Five sampling sites were selected along the Yongjiang Estuary, among which A, B and C were located in the center of urban area and D and E were located in the Zhenhai industrial zone (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). The fundamental properties of water samples such as pH, temperature, salinity and dissolved oxygen (DO) were measured in situ. All water samples were collected from the center of the river (0\u0026ndash;0.5m below the water surface) and stored in pre-cleaned amber glass bottles (5L) and plastic bottles (5L), which had been enrinsed 2\u0026ndash;3 times before the final sample was collected. The water samples passed 0.45 \u0026micro;m cellulose acetate filter membrane and were stored at 4℃ to prevent degradation. The determination of heavy metals and related physical and chemical indexes was completed within 1 week from the time of collection.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Sample determination\u003c/h2\u003e \u003cp\u003eThe contents of heavy metals (Pb, Cd, Mn, Ni, Cr, Fe, Cu and As) in water samples were determined by inductively coupled plasma mass spectrometry (ICP-MS). 5 blank repetitions were set for each batch of samples to eliminate the influence of different batches on the experimental data between treatments and during the test process. The standard curve was drawn with the standard reagent produced by the national reference material research center, and the deionized water was used as the blank to eliminate the systematic error. Detection limit of instrument method(\u0026micro;g L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) were Pb 0.004, Cd 0.003, Mn 0.044, Ni 0.019, Cr 0.017, Fe 0.507, Cu 0.005 and As 0.079, respectively.\u003c/p\u003e \u003cp\u003eOther physical and chemical indexes included total suspended solids (TSS), total nitrogen (TN), total phosphorus (TP), chlorophyll a (Chla), nitrate nitrogen (NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e-N), ammonia nitrogen (NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e-N), nitrous nitrogen (NO\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e-N) and dissolved organic carbon (DOC) were measured according to the environmental quality standard for surface water (GB 3838\u0026thinsp;\u0026minus;\u0026thinsp;2002). NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e-N and NO\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e-N were determined by ion chromatography. TP was determined by ammonium molybdate spectrophotometry. DOC and TN were measured by total organic carbon analyzer. NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e-N was determined by flow analyzer and Chla was determined by hot ethanol method.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Statistical analysis\u003c/h2\u003e \u003cp\u003eThe data of heavy metals and physical and chemical indexes were preprocessed by Excel 2013, and the significance of the data was analyzed by SPSS 16.0. Originpro 9.1 was used to display the distribution characteristics of heavy metals and physical and chemical indexes. Canoco 5 software was applied to map redundancy analysis (RDA) for exploring the relationship between heavy metals and physical and chemical factors by using the maximum and minimum data standardization method. The significance level was calculated by linear region analysis and the results were considered as statistically significant as \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05.\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results","content":"\u003cdiv class=\"Section2\" id=\"Sec7\"\u003e\n \u003ch2\u003e3.1 Distribution characteristics of heavy metal concentrations\u003c/h2\u003e\n \u003cp\u003eThe concentration variation of heavy metals at each sampling point in Yongjiang Estuary was shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e. In general, the content of heavy metals in water were affected by the location of sampling points, rising tide and ebb tide, and seasons. Each heavy metal had a significant difference level at different sampling points, but the variation laws of different heavy metals were inconsistent. The variation range of Cd concentrations were from not detected to 4.90 \u0026micro;g L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and the concentrations at sites D and E were high. The variation range of Cr concentrations were from not detected to 11.6 \u0026micro;g L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and the concentration of D and E were high in March and June at the rising tide, while the concentration of other sampling points were relatively low. Different seasons had a significant impact on the Cr content. For example, although the Cr content of D were high in March and June, it was not detected in September and December. The variation range of Mn content in water body were not detected to 562 \u0026micro;g L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and the concentration of A, B and C were high in June, while the content level of E were low. The variation range of Pb content level were not detected to 4.68 \u0026micro;g L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, in general, the content of E were relatively high in December, while the content of A, B and C remained relatively low. The variation range of Cu content level were 0.11\u0026thinsp;~\u0026thinsp;16.9 \u0026micro;g L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, the content of E were higher in March and June, and the content of various points were relatively low in September and December. The seasonal variation of Fe content were obvious. For example, it was higher in September and December at A, B and C, and the overall variation law of rising tide and ebb tide were basically the same. It can be seen that different heavy metals were affected by different sampling points, seasons and rising tide and ebb tide, and the variation range was large. In general, the concentration of heavy metals were generally low, which were the level of \u0026micro;g L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e\n \u003cp\u003e\u003cimg 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\"\u003e\u003c/p\u003e\n \u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv class=\"Section2\" id=\"Sec8\"\u003e\n \u003ch2\u003e3.2 Distribution characteristics of water quality\u003c/h2\u003e\n \u003cp\u003eThe physical and chemical indexes of water quality were jointly affected by sampling points, seasons, rising tide and ebb tide, and different sampling points had reached a significant difference level. The range of temperature was from 8.8 to 30.1 ℃, the concentration range of DO was from 1.24 to 14.9 mg L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. The range of pH was from 6.31 to 7.95. It can be seen from Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e that pH showed obvious seasonal variation law at both upstream and downstream sample points, and reached the lowest in December. The salinity increased significantly from A to E, and the increase multiple was more than 50 times. The concentration of TSS were high in March and December, which reached the highest at D and E, and its highest content reached more than 700 mg L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. The content of Chla was higher at A and reached the peak in September. Contrary to salinity, the content of Chla decreased from upstream to downstream. The content of TN had a certain increasing trend with seasons at A, B and C, and reached the highest in December, while D and E reached the peak in September. The content of TP reached the peak in December at D and E, while the variation range of A, B and C with seasons was relatively small. The changes of NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e-N and NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e-N in the water body were basically similar. Among them, the content of NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e-N reached the highest at D and E in December, while the content of NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e-N reached the peak at D in March. The content of NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e-N and NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e-N in the upstream sampling points were relatively low and the change were relatively stable. In general, average water quality of five sampling sites at the rising tide and ebb tide were different (Table \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e).\u0026nbsp;\u003c/p\u003e\n \u003ctable border=\"1\" id=\"Tab2\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eAverage water quality data of five sampling sites in the Yongjiang Estuary, China\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eTides\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSite\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eNO\u003csub\u003e3\u003c/sub\u003e-N\u003c/p\u003e\n \u003cp\u003e(mg/L)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eNH4+-N (mg/L)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eTN\u003c/p\u003e\n \u003cp\u003e(mg/L)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eTP\u003c/p\u003e\n \u003cp\u003e[mg/L]\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eDOC\u003c/p\u003e\n \u003cp\u003e(mg/L)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSalinity\u003c/p\u003e\n \u003cp\u003e(\u0026permil;)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eDO\u003c/p\u003e\n \u003cp\u003e(mg/L)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003epH\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eTSS\u003c/p\u003e\n \u003cp\u003e(mg/L)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eChla\u003c/p\u003e\n \u003cp\u003e(mg L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eRT\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eA\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e4.81\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.34\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e7.42\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.42\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e7.41\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e7.89\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e7.04\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e185.91\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e9.72\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eB\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e5.93\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.28\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e5.51\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.26\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e7.89\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.32\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e7.59\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e7.51\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e181.60\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.71\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e3.83\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.31\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e11.39\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.29\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e13.02\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.72\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e6.83\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e7.37\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e157.91\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e3.33\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eD\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e8.11\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.94\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e15.64\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.35\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e28.28\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e17.02\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e7.81\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e7.62\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e397.67\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.86\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eE\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e3.79\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.47\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e15.74\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.30\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e25.57\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e23.23\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e8.09\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e7.65\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e429.83\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.66\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eET\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eA\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e5.53\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.41\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e6.70\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.23\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e6.98\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.26\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e7.14\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e7.12\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e185.64\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e8.66\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eB\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e6.16\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.34\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e6.48\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.24\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e7.04\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.30\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e7.77\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e7.33\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e153.90\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.71\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e5.55\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.32\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e7.53\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.21\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e9.40\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.34\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e6.33\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e7.33\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e180.73\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e3.78\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eD\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e6.70\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.51\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e12.15\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.48\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e15.38\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e4.99\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e7.19\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e6.93\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e495.08\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.35\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eE\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.53\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.96\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e9.97\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.32\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e20.81\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e15.56\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e7.87\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e7.24\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e478.58\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.83\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003ctfoot\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"12\"\u003eRT: rising tide; ET: ebb tide.\u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tfoot\u003e\n \u003c/table\u003e\n \u003cp\u003e\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv class=\"Section2\" id=\"Sec9\"\u003e\n \u003ch2\u003e3.3 Impact on environmental factors\u003c/h2\u003e\n \u003cp\u003eRDA was used to study the correlation between the concentration of heavy metals and environmental factors (Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e). The included angle of the arrows between species factors (Pb, Cd, Mn, Ni, Cr, Fe, Cu and As) and environmental factors (pH, salinity, TSS, TN, TP, Chla, NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003eN, NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e-N and DOC) indicated the correlation between variables. The results showed that the concentrations of heavy metals and environmental factors among all water samples with RDA1 and RDA2 explained 80.2% and 6.3% variation, respectively. The concentration of Mn and Ni were highly correlated. The concentration of Pb, Cr and As were highly correlated, and there was a good correlation between Fe and Cd. The concentration of DOC and TN were positively correlated with Fe and As. The concentration of Cu was positively correlated with pH, while Pb and Cr were positively correlated with salinity and NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e-N. Chla content had a strong correlation with Cd. It can be seen that the relationship between different heavy metals and different physical and chemical factors was different.\u003c/p\u003e\n\u003c/div\u003e"},{"header":"4. Discussion","content":"\u003cp\u003eThere were some similarities in the distribution of different heavy metals in water. For example, the contents of Mn and Ni were higher in June, which is closely related to the periodic production of industrial enterprises. The concentration of As was relatively high in September, which was only detected in September at E, and it was lower at rising tide than at ebb tide. The reason for this phenomenon is related to the dilution of seawater (Ubando et al., \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Nedia et al., \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). At the same time, the estuary has a relatively high concentration of suspended solids, which will enhance the adsorption performance of As (Jaishankar et al., \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). As is adsorbed in suspended solids and transported to the lower water body or sediment, resulting in its concentration at the sea inlet was lower than that at the upstream sampling points. In contrast to As, the content of most heavy metals such as Pb, Cr, CD and Cu were generally higher in the downstream. On the one hand, it is related to more heavy industrial enterprises (such as electroplating and machining) in Zhenhai District and Beilun District in the downstream. On the other hand, it is related to the collection of upstream pollutants in the downstream. In general, along the sampling points A to E, the heavy metal pollution in water showed obvious seasonal variation characteristics. For example, Cu and Cr were higher in March and June, while As and Pb were relatively higher in September and December, respectively. This phenomenon indicated that the heavy metals in the water are affected by the synergistic effect of human activities and natural environmental factors, which is consistent with the research results of Sheyang Estuary in Jiangsu Province (Zhao et al., \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). The concentrations of heavy metals in Yongjiang Estuary were generally low and did not exceed the standard. Among them, the concentrations of Fe, Mn, Cr, Ni, Cu and Pb were much lower than those in Hugri Estuary, India (Mitra et al., \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2018\u003c/span\u003e), indicating that the heavy metal pollution in Yongjiang Estuary is controllable. However, the monitoring and control should be strengthened, especially the monitoring of the accumulation area of heavy metals in the downstream area, so as to prevent the pollution of heavy metals in water.\u003c/p\u003e \u003cp\u003eThe concentrations dynamics of heavy metals and water quality indicators in Yongjiang Estuary showed diversity characteristics by the measurement of water samples at rising tide and ebb tide in four different seasons from 2017 to 2018. This phenomenon was mainly affected by many factors such as estuarine development, management and pollution source input, which was related to natural factors such as estuarine unique tidal cycle, topographic and geomorphic characteristics and hydrology (Chai et al., \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2006\u003c/span\u003e). Estuary is a hot area for the accumulation of materials in the whole basin, and the probability of environmental problems caused by human activities is also high (Fernandes et al., \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Study showed that the probability of eutrophication and heavy metal pollution in large coastal estuaries was higher than that in small coastal estuaries because the acceptance of pollutants in large coastal estuaries was greater than that in small coastal estuaries (Liu et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). The sample collection area of Yongjiang Estuary included different industrial categories. For example, Haishu District was a typical commercial area with few industries, dense population and developed transportation. Zhenhai District was a gathering place for heavy industry and petrochemical enterprises. Beilun District was a port industrial area, and there were large ports, thermal power plants and electroplating industry in the area. The location characteristics of these potential pollution sources can cause the differences of heavy metal and nutrient pollution in different water bodies of Yongjiang Estuary.\u003c/p\u003e \u003cp\u003eIn general, NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e-N, NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003eN, DOC and TSS in water quality indicators showed obvious downstream accumulation characteristics and obvious seasonal variation law, which was consistent with the research results of Minjiang Estuary (Zheng et al., \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Seasonal variation may be affected by flow, TSS and estuarine buffer effect. pH was the lowest in December and Chla content was higher in September. This phenomenon is mainly related to the joint action of natural factors and human activities such as water temperature, light, DO and salinity in different seasons (Xia et al., \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; McQuatters-Gollop et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2007\u003c/span\u003e). The factors affecting estuarine element circulation and nutrient characteristics are complex, and the synergistic effects of various comprehensive factors must be considered. There was a certain correlation between heavy metals and water quality indicators, which was mainly related to the different properties of heavy metals in water.\u003c/p\u003e"},{"header":"5. Conclusions","content":"\u003cp\u003eIn the present study, we illustrated the case study of Yongjiang Estuary where the 8 heavy metals and 11 environmental parameters were investigated at five sites across four seasons during the tide rising and ebbing durations. The results indicated that the heavy metals and environmental factors in estuaries showed obvious seasonal and tidal variation characteristics, which were enriched at the points where the main industries were concentrated. The changes of environmental factors caused by the productivity cycle and seasonal changes of industrial enterprises affected the time of the peak of heavy metal content. In general, heavy metals pollution in the Yongjiang Estuary was relatively lightly. The seasonal variation of water quality indexes along the sampling points was very obvious, especially NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e-N, NO\u003csub\u003e3\u003c/sub\u003e-N and TSS were enriched in the downstream. There was nitrogen surplus in the water body of Yongjiang Estuary, so the monitoring should be further strengthened to prevent the occurrence of water eutrophication.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eConflict of interest\u003c/strong\u003e: The authors declare that there are no conflicts of interest.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e: Research data may be obtained from the lead author upon reasonable request.\u003c/p\u003e\n\u003cp\u003eColor should be used for any figures in print.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding statement:\u0026nbsp;\u003c/strong\u003eThis paper is based upon the grant supports provided by National Natural Science Foundation of China (42167017), the Foundation of Guizhou Educational Committee (QJJ[2022]201), and the Projects of Guizhou Medical University (XBHJZ[2020]034 and 21NSFCP22).\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003cstrong\u003eAuthor Contribution statement:\u0026nbsp;\u003c/strong\u003eChunli Zheng wrote the main manuscript text and Hongkai Liao prepared figures 1-4. 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Environ Sci Pollut Res 2022; 109.\u003c/li\u003e\n\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":"Heavy metals, environmental factors, tidal effect, Yongjiang Estuary","lastPublishedDoi":"10.21203/rs.3.rs-2593484/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-2593484/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThis study aimed to investigate the relationship between 8 heavy metals (Pb, Cd, Mn, Ni, Cr, Fe, Cu and As) and 11 environmental parameters at five sites during the tide rising and ebbing durations of surface water over four seasons in the Yongjiang Estuary, China. The results found that the change concentrations of heavy metals and environmental factors were high, which had obvious spatial distribution and seasonal dynamic characteristics. In the aspect of spatial distribution, the concentrations of heavy metals and the physical and chemical indexes were higher at the points near the industrial area. In the aspect of seasonal dynamics, the concentrations of Pb, total phosphorus and ammonia nitrogen were the highest in winter. In the aspect of tidal change, the change rules of different indicators were different, among which, the concentrations of Cd, Ni and total nitrogen in the rising tide and ebb tide were quite different. The concentration of dissolved organic carbon, total nitrogen, pH, salinity, ammonia nitrogen and chlorophyll a were positively correlated with target heavy metals. This study explored the relationship between the concentrations of heavy metals and environmental parameters, which is beneficial to future heavy metals research in estuaries.\u003c/p\u003e","manuscriptTitle":"Heavy metal pollution in the Yongjiang Estuary, China and their relations to environmental factors","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2023-02-20 18:03:58","doi":"10.21203/rs.3.rs-2593484/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":"b45922cf-1650-4a8e-9169-218f10f67b67","owner":[],"postedDate":"February 20th, 2023","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2023-02-23T05:29:14+00:00","versionOfRecord":[],"versionCreatedAt":"2023-02-20 18:03:58","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-2593484","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-2593484","identity":"rs-2593484","version":["v1"]},"buildId":"7rjqhiLT3MXkJMwkYKINL","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}