Aquatic Ecological Landscape Planning Based on Numerical Modelling

Aquatic Ecological Landscape Planning Based on Numerical Modelling | 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PDF Article Aquatic Ecological Landscape Planning Based on Numerical Modelling Xianyuan Chen This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5226003/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 Urban waterbody landscape planning necessitates the dual objectives of water quality improvement and landscape optimization to create a favorable aquatic ecological landscape environment. Taking Canghai Lake in Guangxi as a case study, the MIKE 21 hydro-environment simulation software was employed to establish a two-dimensional hydrodynamic and water quality model for the lake area. This model was utilized to simulate the flow and water quality conditions within the lake, and to propose an overall strategy for enhancing hydrodynamics and improving water quality in the lake area. The study findings indicate that incorporating an artificial wetland at the lake inlet within the planning, by appropriately configuring emergent, floating, and submerged plants, can construct an efficient plant ecosystem. This approach is expected to reduce the phosphorus load entering the lake by over 45%, effectively improving the water quality in the lake area, and fundamentally eliminating the risk of large-scale algal bloom outbreaks in Canghai Lake. Additionally, it will create a wetland landscape, thereby achieving an organic unity of water quality enhancement and landscape optimization. An integrated planning method for lake ecological landscapes that combines water quality simulation, aquatic ecosystem restoration, and water landscape planning technologies is proposed, which can serve as a reference for the planning and design of urban waterbody landscapes. Earth and environmental sciences/Environmental sciences Earth and environmental sciences/Hydrology Earth and environmental sciences/Limnology Landscape Architecture Numerical Simulation Canghai Lake Water Environmental Quality Waterbody Landscape Planning Artificial Wetland Figures Figure 1 Figure 2 Figure 3 Figure 4 1. Introduction Waterbody landscapes, as a natural element within urban systems, serve not only to beautify the urban environment but also perform multiple ecological functions such as improving microclimates and enhancing the urban ecological environment. Respecting the natural laws of water bodies, ensuring water quality, and coordinating the relationship between urban construction and urban waterbody landscapes have become fundamental methods and starting points in the process of urban ecological construction [ 1 – 2 ]. The planning of urban waterbody landscapes requires joint research and implementation by professionals in both landscape architecture and environmental science. It should not only focus on visual imagery but also prioritize the ecological needs of water, achieving water quality maintenance and continuous improvement. Therefore, how to conduct ecological design of waterbody landscapes based on scientific calculation and quantitative indicators, realizing the coupling of environmental quality improvement and landscape effect enhancement, has become one of the important topics in the planning and design of current urban landscape water bodies. Restricted by various conditions, urban landscape water bodies are often artificially constructed and differ significantly from natural water bodies, making it difficult to form a complete aquatic ecosystem with poor stability. Additionally, urban landscape water bodies are typically static or have poor flow, characterized by small water areas, limited environmental capacity, and low self-purification capabilities. Insufficient consideration of water quality purification and the self-maintenance of the aquatic ecosystem can lead to water bodies being easily affected by various point and non-point source pollutants, resulting in the loss of waterbody landscape functions, and even the occurrence of black odorous phenomena, severely impacting the surrounding natural environment and the living conditions of residents [ 3 ]. This study takes Canghai Lake in Cangwu County, Guangxi as a case study, employing the MIKE 21 hydro-environment simulation software developed by the Danish Hydraulic Institute (DHI) to establish a coupled hydrodynamic and water quality model of Canghai Lake. The model assesses its water environmental capacity, and within the framework of the overall strategy for water quality maintenance, plans the waterbody landscape to achieve the integration of water quality assurance and landscape optimization. Canghai Lake is located in Cangwu County, Wuzhou City, Guangxi Zhuang Autonomous Region. It is a comprehensive project that integrates flood control and drainage, environmental remediation, urban development of Cangwu County, and leisure tourism. The area within the flood control embankment (with a top elevation of 22 to 22.4 meters) covers an area of 393 hectares. The Xiacao River is situated in the low mountain and hill area on the south bank of the Xunjiang River near Cangwu County, and it is a first-order tributary of the Xunjiang River in the Pearl River system. After the construction of the Guangxin Sluice Dam at the estuary where the Xiacao River flows into the Xunjiang River, the river was retained to form the ecological landscape lake, Canghai Lake (Fig. 1 ). The water quality risks of Canghai Lake primarily stem from two aspects. First, the water quality of the rivers flowing into the lake is poor. Canghai Lake mainly receives water from the Xiacao River and the Gufeng River. According to the monitoring data of river water quality from 2008 to 2011, the exceeding rates of total nitrogen and total phosphorus in most sections of the Xiacao River were both 100%, with the maximum excess multiples being 0.26 and 1.70 times, respectively. The total nitrogen concentration exceeded the Class IV criteria of the Surface Water Environmental Quality Standard, and the total phosphorus concentration exceeded the Class V criteria. The water quality is mainly affected by agricultural non-point source pollution (agricultural irrigation return water) along the banks. The Gufeng River tributary has high concentrations of COD and total nitrogen due to aquaculture pollution, with total nitrogen exceeding the Class V criteria of surface water. Second, Canghai Lake is significantly affected by urban non-point source pollution. The lake is planned to receive rainwater discharge from the surrounding areas. Analysis shows that the pollutant concentration in the initial rainwater is much higher than the planned water quality target of Canghai Lake, which is Class III of the Surface Water Environmental Quality Standard, thus facing higher water quality risks. 2. Hydrodynamic and water quality coupled model for lake area 2.1 Hydrodynamic model The hydrodynamic model of Canghai Lake was constructed using the MIKE 21 software developed by the Danish Hydraulic Institute (DHI). MIKE 21 is a versatile model capable of solving two-dimensional flow problems with a free surface and is well-suited for research related to inland lakes, rivers, and landscape water bodies. MIKE 21 employs a finite volume method based on unstructured grids, which allows for a good fit of complex topographies, ensures mass flux balance, and is computationally efficient. The hydrodynamic model calculates water levels and flow velocities at various grid points over time by solving the continuity equation and the momentum equation, which is used to analyze the flow patterns in the lake under different inflow conditions. The amount of actual data required for the model depends on the precision requirements of the project and the physical phenomena to be described. The hydrodynamic model of Canghai Lake is primarily used to calculate the hydrodynamic field under different inflow conditions, providing hydrodynamic driving conditions for subsequent water quality model research and for the verification of flood control capacity of embankments. Based on the current topography within the 20-meter normal water level of Canghai Lake, the model's generalized lake topography was obtained, considering the dredging scheme (Fig. 2 ). The basic settings of the hydrodynamic model are presented in Table 1 , with the main model parameter being the Manning coefficient, which is related to the roughness of the bed. As a newly formed lake through dredging and excavation in an existing river channel, the Manning coefficient for Canghai Lake can be set at 0.32, referencing the simulation experience of other similar lakes. Table 1 Setting of Canghai lake hydrodynamic model Grid quantity > 10000 Grid scale 5 ~ 25 m Time step 0.5 s Vorticity function Smagorinsky subgrid scale model Smagorinsky coefficient 0.24 Manning coefficient 32 m 1/3 /s Initial water level 20 m Boundary conditions The inflow boundary of Xiaoxia River and Gufeng River, and the outlet boundary of Xiaoxia River estuary 2.2 Water quality model A water quality model was constructed based on the hydrodynamic model. The model includes 14 state variables representing four trophic levels (phytoplankton, zooplankton, benthic plants, and detritus), nutrients, dissolved oxygen, and chemical oxygen demand. The model calculates the concentration of substances at various grid points over time by coupling the solution of the advection-diffusion equation with a system of ordinary differential equations describing the biochemical reaction processes of each substance, which is used to analyze the patterns of water quality changes and eutrophication risks in the Canghai Lake area under different conditions. According to the set hydrodynamic boundary conditions, the corresponding water quality boundary conditions at each boundary are provided to determine the pollutant load entering the lake. The determination of water quality data at each boundary comprehensively considers the monitoring data of the Canghai river system from 2008 to 2011, as shown in Table 2 . Referencing the existing research findings of other similar lakes, the values of the main parameters in the model are listed in Table 3 . The light intensity references the monitoring values for Guangxi region published by the National Meteorological Data Sharing Service. Table 2 Boundary conditions of water quality ( mg/L) Boundary NH 3 -N TN TP DO CODcr Xiaoxia River into the Canghai Lake 0.3 0.86 0.11 8.1 13.0 Gufeng River into the Canghai Lake 1.0 2.60 0.26 8.1 29.1 Table 3 Major parameter Parameters Value Phytoplankton growth rate 1.800 /d The maximum rate at which zooplankton feed on phytoplankton 0.300 /d Phytoplankton death rate 0.100 /d Minimum nitrogen content inside algae cells 0.070 g N/g C Maximum nitrogen content inside algal cells 0.170 g N/g C Minimum phosphorus content in algal cells 0.002 g P/g C Maximum phosphorus content in algal cells 0.030 g P/g C Nitrogen uptake rate of algae under restricted conditions 0.300 g N/g C/d Phosphorus uptake rate of algae under limited conditions 0.050 g P/g C/d Minimum chlorophyll yield coefficient 0.200 1/(E/m 2 /d) Maximum chlorophyll yield coefficient 1.500 1/(E/m 2 /d) 3. Water quality maintenance and landscape design strategy based on mathematical model 3.1 Lake flow field analysis and landscape design strategy Referencing the long-term runoff measurement and analysis results of the Xiaoxia River, the inflow and outflow rates of Canghai Lake were determined to be 12 m³/s during the wet season and 4 m³/s during the dry season. The hydrodynamic conditions of the Canghai Lake area were analyzed under normal conditions, where the lake water level is maintained at the constant level of 20 meters. The findings revealed that the flow velocity in the lake area is generally below 5 cm/s, regardless of whether it is the wet or dry season. Computational simulations of lake currents during the wet season driven by eastward, northward, and southeastward winds with an average annual wind speed of 1.7 m/s, as well as during the dry season driven by northward winds, showed that the wind field has no significant impact on the hydrodynamic characteristics of Canghai Lake. Under the condition of a constant water level of 20 meters, the average hydraulic retention time during the wet and dry seasons is 17 days and 50 days, respectively. The hydraulic retention time of Canghai Lake during the dry season is relatively long, and the hydrodynamic conditions in the lake area are poor. Currently, the water depth at the normal water level of Canghai Lake is primarily between 14 to 16 meters, allowing for appropriate subaqueous topographical design. Different water bodies with varying terrain heights will experience distinct temperatures and flow velocities after being subjected to solar radiation and wind, which can guide the formation of a circulation system with tributary streams, thereby enhancing the hydrodynamics of the lake area. Properly designing artificial islands with elevations between the normal and flood water levels, and covering them with aquatic vegetation, creates a topography that provides habitats for different types of aquatic plants, enriching biodiversity. While improving the fluidity of the lake's water bodies, this approach also creates an ever-changing visual landscape. By increasing the installation of pumps, jet systems, and aeration facilities within the lake area, and designing landscape fountains at the waterfront, the circulation of the water body is accelerated. This increases the dissolved oxygen in the water, accelerating the degradation of pollutants. 3.2 Lake Area Water Quality Analysis and Landscape Design Strategies Model calculations have revealed that the concentrations of COD and NH 3 -N in Canghai Lake meet the Class II standards, while TN and TP basically satisfy the Class III standards. However, the risk of algal blooms is high during the dry season under high temperature conditions (approximately 25°C). As shown in Fig. 3 , after 17 days of sustained high temperatures during the dry season, nearly one-third of the lake area experiences severe algal bloom phenomena, and after 22 days, more than half of the lake area is affected by algal blooms, which could severely damage the ecological environment and landscape function of the lake. The high TP load during the dry season in Canghai Lake makes it difficult for the water to meet the Class III standard and is a key stimulant for algal bloom outbreaks. Therefore, it is essential to strictly control the phosphorus load entering the lake. Since the main pollution source of Canghai Lake is the Xiaoxia River, strict control over the phosphorus load from the Xiaoxia River entering the lake should be implemented. A plan is proposed to establish an artificial wetland at the entrance of the Xiaoxia River where it flows into Canghai Lake, with a wetland area of approximately 40 hectares, to construct an efficient plant ecosystem. This system, based on the creation of deep pools and shallow shoals, integrates surface flow wetlands, subsurface flow wetlands, and substrate modification techniques. It involves selecting and planting various aquatic plants that can efficiently absorb phosphorus to enhance the phosphorus removal effect, improve the water quality of the Xiaoxia River entering Canghai Lake, and form a wetland landscape. Due to the significant correlation between the nitrogen and phosphorus accumulation, concentration, and biomass of plants, biomass can be used as an indicator to select plants for the artificial wetland. Studies indicate that species such as Canna indica, Acorus calamus, Tradescantia virginiana, Spilanthes oleracea, Arundo donax, A. donax 'Variegata', Lolium perenne, and Commelina communis are highly effective at nitrogen absorption; while Acorus calamus, Tradescantia virginiana, Spilanthes oleracea, Arundo donax, Lagenaria siceraria, Lolium perenne, Iris tectorum, and Commelina communis are effective at phosphorus absorption. Considering the morphological characteristics, landscape functions, biodiversity requirements, and the seasonal stability of purification capabilities, the plan involves large-scale planting of tall and colorful emergent plants such as Acorus calamus, Arundo donax, and A. donax 'Variegata', interspersed with herbaceous flowering plants like Tradescantia virginiana and Canna indica. Spilanthes oleracea, Lolium perenne, and Commelina communis are planted as ground cover to control the landscape effect. Floating plants such as Nymphaea alba and Ludwigia sedioides, and submerged plants like Elodea canadensis, Ceratophyllum demersum, and Hydrocharis dubia are selected to achieve water purification and landscape optimization through a reasonable configuration of emergent, floating, and submerged plants (Figs. 4 ). Taking into account the topography and purification effects, and referring to relevant domestic research findings, the expected phosphorus removal efficiency is anticipated to be over 45% [ 5 – 6 ]. Simulation results indicate that the implementation of the wetland project can effectively improve the water quality of Canghai Lake, and the risk of large-scale algal blooms during the dry season is basically eliminated. 4. Discussion Currently, the demand for water quality and hydroecological considerations in the planning and design of urban landscape water bodies is receiving increasing attention. Han Yi et al. [ 7 ] introduced the application of relevant hydrological knowledge in practice through two ongoing planning projects and suggested that the movement characteristics of river flows must be understood before design. The urban river landscape environment should meet various requirements such as aesthetics, leisure, and biodiversity without reducing the river's flood-carrying capacity. However, there are still relatively few planning and design efforts that quantitatively analyze and optimize water quality and hydroecological issues, and such literature is rarely reported. This study aims to construct a two-dimensional dynamic hydrodynamic-water quality coupled model for the planning of Canghai Lake, attempting to find a path for quantitatively assessing the water quality risks of planning schemes and the effectiveness of water quality improvement measures. Hydrodynamic and water quality models contain a large number of parameters, which generally require calibration and validation using relevant measured data. Since it is impossible to have actual measurement data during the planning stage, this inevitably affects the accuracy of the model. Nevertheless, with appropriate experience in hydrodynamic and water quality simulation and by referencing the model research results of similar water bodies, it is still possible to obtain reasonable simulation results that can support planning and design. This work is just a beginning, and whether its conclusions are consistent with reality remains to be tested by the practice after the completion of all projects in Canghai Lake. In any case, using hydrodynamic and water quality models at the initial planning stage to find a more scientific optimization of urban landscape water body planning schemes, integrating lake hydrodynamic enhancement and water quality improvement measures from the field of environmental science with landscape optimization strategies from the field of landscape architecture, and proposing a comprehensive planning method for lake ecological landscapes that integrates water quality simulation, water ecological restoration, and water landscape planning technology, represents a new approach and method for the ecological landscape design of urban rivers and lakes. 5. Conclusion This paper utilizes MIKE 21 water environment simulation software to establish two-dimensional hydrodynamic and water quality models for Canghai Lake, conducting calculation and analysis of the lake's water flow and water quality conditions under different scenarios. Based on this, an overall strategy for enhancing hydrodynamics and improving water quality in the lake area is proposed: by setting up an artificial wetland at the entrance of the Xiaoxia River where it flows into Canghai Lake, using plant floating beds, and rationally configuring emergent plants, floating plants, and submerged plants to construct an efficient plant ecosystem. Through landscape facilities (such as water curtains) that promote water movement, the strategy can effectively reduce the phosphorus load entering the lake, improve the water quality of the lake area, and is expected to basically eliminate the risk of large-scale algal blooms in Canghai Lake. Additionally, it will form a wetland landscape, thereby achieving an organic unity of improved water environmental quality and landscape optimization. Declarations Conflicts of Interest The authors declare that they have no conflicts of interest. Author Contribution Only one author. Acknowledgements This paper is supported by the National Natural Science Foundation of China (Grant Nos. 52408326, 52278335). Data Availability The datasets used and/or analysed during the current study available from the corresponding author on reasonable request. References Chen, Y. & Zhang, B. Urban design based on water environment:A case study of Meilong Lake area in Chunhua Town, Nanjing. Chin. Landsc. Archit. , (4): 16–19. (2014). Zhu, L. Adv. Water Sci. , 16 (6): 784–787. (2005). Li, F. P., Zhang, H. P. & Chen, L. Study on the spatial and temporal distribution and correlation between environmental factors and chlorophyll a in small closed water. Environ. Sci. 34 (10), 3854–3861 (2013). Jiang, Y. P. et al. Contribution of constructed wetland plants to nitrogen and phosphorus removal in ornamental water. Acta Ecol. Sin. 24 (8), 1720–1725 (2004). Yuan, S. F. et al. Ecological engineering restoration and initial water purification effect of Nantiaoxi estuary at the source of Taihu Lake Basin. J. Environ. Sci. 33 (5), 1475–1483 (2013). Q Zhang. Study on phosphorus removal from polluted water in horizontal underflow constructed wetland (Tongji University, 2007). Han, Y., Liu, H. L. & Yang, D. D. Practice of urban river landscape planning and design based on landscape hydrology theory. Chin. Landsc. Archit. , 2014 (1): 23–28 . Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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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-5226003","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":377298226,"identity":"e85b0b2a-2a72-44af-b06a-455fbdeceae3","order_by":0,"name":"Xianyuan Chen","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAxklEQVRIiWNgGAWjYBAC+wPnn3/48MNGTp69gVg9B8+wMc7sSTM27DlArJbDZ9iYedgOJTbcSCBSB2Pb2WMPZ/AcSGyc+XjjDYYam2iCWph5zqUbfLC4Y9wunVZswXAsLbeBkBY2iQMGkjN4nsk2zs4xk2BsOExYC4/8AwNpHrbDjA03zxCpRYLhjBlIi2LDDR4itRgwHEs2hAQy0C8JxPjFgOHwwQeQqDy88caHGhvCWlC0SySQohyihVQdo2AUjIJRMDIAAGFuRsGe+En1AAAAAElFTkSuQmCC","orcid":"","institution":"Shanghai Jiao Tong University","correspondingAuthor":true,"prefix":"","firstName":"Xianyuan","middleName":"","lastName":"Chen","suffix":""}],"badges":[],"createdAt":"2024-10-08 14:08:22","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-5226003/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-5226003/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":70380041,"identity":"9f644a8c-cbbe-4fe0-8160-44637ab63d1e","added_by":"auto","created_at":"2024-12-02 15:53:09","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":223675,"visible":true,"origin":"","legend":"\u003cp\u003eCanghai Lake\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-5226003/v1/15475e00ca3802c62f687ab3.png"},{"id":70380040,"identity":"c62ae870-a6c8-4600-9a5c-430c9dd6b20e","added_by":"auto","created_at":"2024-12-02 15:53:09","extension":"jpeg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":742504,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic diagram of underwater topography within 20m normal water level of Canghai Lake\u003c/p\u003e","description":"","filename":"floatimage2.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-5226003/v1/ad89d9ef7606c22f403d9441.jpeg"},{"id":70380038,"identity":"f70a93cb-e709-4aa1-8cd4-3b1e1e728282","added_by":"auto","created_at":"2024-12-02 15:53:09","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":203682,"visible":true,"origin":"","legend":"\u003cp\u003eThe concentration of chlorophyll-A was predicted after 10, 12, 17 and 22 days at high temperature during dry season in Canghai Lake\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-5226003/v1/5a238e391520bcea494ab847.png"},{"id":70380039,"identity":"0e44f72d-c9f9-4ca3-b883-1b7d962ab696","added_by":"auto","created_at":"2024-12-02 15:53:09","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":2470292,"visible":true,"origin":"","legend":"\u003cp\u003ePlant configuration of constructed wetland cross section at Xiaoxia River into Canghai Lake\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-5226003/v1/cec202b1f5d6ca4540aa1d2c.png"},{"id":76496660,"identity":"5f15e494-5c01-487e-a0f3-ed988936ee13","added_by":"auto","created_at":"2025-02-17 18:31:50","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":4521087,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5226003/v1/bfecfbe3-5e01-4f02-9dd2-fe1ea66952db.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Aquatic Ecological Landscape Planning Based on Numerical Modelling","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eWaterbody landscapes, as a natural element within urban systems, serve not only to beautify the urban environment but also perform multiple ecological functions such as improving microclimates and enhancing the urban ecological environment. Respecting the natural laws of water bodies, ensuring water quality, and coordinating the relationship between urban construction and urban waterbody landscapes have become fundamental methods and starting points in the process of urban ecological construction [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. The planning of urban waterbody landscapes requires joint research and implementation by professionals in both landscape architecture and environmental science. It should not only focus on visual imagery but also prioritize the ecological needs of water, achieving water quality maintenance and continuous improvement. Therefore, how to conduct ecological design of waterbody landscapes based on scientific calculation and quantitative indicators, realizing the coupling of environmental quality improvement and landscape effect enhancement, has become one of the important topics in the planning and design of current urban landscape water bodies.\u003c/p\u003e \u003cp\u003eRestricted by various conditions, urban landscape water bodies are often artificially constructed and differ significantly from natural water bodies, making it difficult to form a complete aquatic ecosystem with poor stability. Additionally, urban landscape water bodies are typically static or have poor flow, characterized by small water areas, limited environmental capacity, and low self-purification capabilities. Insufficient consideration of water quality purification and the self-maintenance of the aquatic ecosystem can lead to water bodies being easily affected by various point and non-point source pollutants, resulting in the loss of waterbody landscape functions, and even the occurrence of black odorous phenomena, severely impacting the surrounding natural environment and the living conditions of residents [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThis study takes Canghai Lake in Cangwu County, Guangxi as a case study, employing the MIKE 21 hydro-environment simulation software developed by the Danish Hydraulic Institute (DHI) to establish a coupled hydrodynamic and water quality model of Canghai Lake. The model assesses its water environmental capacity, and within the framework of the overall strategy for water quality maintenance, plans the waterbody landscape to achieve the integration of water quality assurance and landscape optimization.\u003c/p\u003e \u003cp\u003eCanghai Lake is located in Cangwu County, Wuzhou City, Guangxi Zhuang Autonomous Region. It is a comprehensive project that integrates flood control and drainage, environmental remediation, urban development of Cangwu County, and leisure tourism. The area within the flood control embankment (with a top elevation of 22 to 22.4 meters) covers an area of 393 hectares. The Xiacao River is situated in the low mountain and hill area on the south bank of the Xunjiang River near Cangwu County, and it is a first-order tributary of the Xunjiang River in the Pearl River system. After the construction of the Guangxin Sluice Dam at the estuary where the Xiacao River flows into the Xunjiang River, the river was retained to form the ecological landscape lake, Canghai Lake (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe water quality risks of Canghai Lake primarily stem from two aspects. First, the water quality of the rivers flowing into the lake is poor. Canghai Lake mainly receives water from the Xiacao River and the Gufeng River. According to the monitoring data of river water quality from 2008 to 2011, the exceeding rates of total nitrogen and total phosphorus in most sections of the Xiacao River were both 100%, with the maximum excess multiples being 0.26 and 1.70 times, respectively. The total nitrogen concentration exceeded the Class IV criteria of the Surface Water Environmental Quality Standard, and the total phosphorus concentration exceeded the Class V criteria. The water quality is mainly affected by agricultural non-point source pollution (agricultural irrigation return water) along the banks. The Gufeng River tributary has high concentrations of COD and total nitrogen due to aquaculture pollution, with total nitrogen exceeding the Class V criteria of surface water. Second, Canghai Lake is significantly affected by urban non-point source pollution. The lake is planned to receive rainwater discharge from the surrounding areas. Analysis shows that the pollutant concentration in the initial rainwater is much higher than the planned water quality target of Canghai Lake, which is Class III of the Surface Water Environmental Quality Standard, thus facing higher water quality risks.\u003c/p\u003e"},{"header":"2. Hydrodynamic and water quality coupled model for lake area","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Hydrodynamic model\u003c/h2\u003e \u003cp\u003eThe hydrodynamic model of Canghai Lake was constructed using the MIKE 21 software developed by the Danish Hydraulic Institute (DHI). MIKE 21 is a versatile model capable of solving two-dimensional flow problems with a free surface and is well-suited for research related to inland lakes, rivers, and landscape water bodies. MIKE 21 employs a finite volume method based on unstructured grids, which allows for a good fit of complex topographies, ensures mass flux balance, and is computationally efficient. The hydrodynamic model calculates water levels and flow velocities at various grid points over time by solving the continuity equation and the momentum equation, which is used to analyze the flow patterns in the lake under different inflow conditions. The amount of actual data required for the model depends on the precision requirements of the project and the physical phenomena to be described. The hydrodynamic model of Canghai Lake is primarily used to calculate the hydrodynamic field under different inflow conditions, providing hydrodynamic driving conditions for subsequent water quality model research and for the verification of flood control capacity of embankments. Based on the current topography within the 20-meter normal water level of Canghai Lake, the model's generalized lake topography was obtained, considering the dredging scheme (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). The basic settings of the hydrodynamic model are presented in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, with the main model parameter being the Manning coefficient, which is related to the roughness of the bed. As a newly formed lake through dredging and excavation in an existing river channel, the Manning coefficient for Canghai Lake can be set at 0.32, referencing the simulation experience of other similar lakes.\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\u003eSetting of Canghai lake hydrodynamic model\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"2\"\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 \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGrid quantity\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u0026gt;\u0026thinsp;10000\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGrid scale\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e5\u0026thinsp;~\u0026thinsp;25 m\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTime step\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.5 s\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eVorticity function\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSmagorinsky subgrid scale model\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSmagorinsky coefficient\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.24\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eManning coefficient\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e32 m\u003csup\u003e1/3\u003c/sup\u003e/s\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eInitial water level\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e20 m\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBoundary conditions\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eThe inflow boundary of Xiaoxia River and Gufeng River, and the outlet boundary of Xiaoxia River estuary\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 \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Water quality model\u003c/h2\u003e \u003cp\u003eA water quality model was constructed based on the hydrodynamic model. The model includes 14 state variables representing four trophic levels (phytoplankton, zooplankton, benthic plants, and detritus), nutrients, dissolved oxygen, and chemical oxygen demand. The model calculates the concentration of substances at various grid points over time by coupling the solution of the advection-diffusion equation with a system of ordinary differential equations describing the biochemical reaction processes of each substance, which is used to analyze the patterns of water quality changes and eutrophication risks in the Canghai Lake area under different conditions.\u003c/p\u003e \u003cp\u003eAccording to the set hydrodynamic boundary conditions, the corresponding water quality boundary conditions at each boundary are provided to determine the pollutant load entering the lake. The determination of water quality data at each boundary comprehensively considers the monitoring data of the Canghai river system from 2008 to 2011, as shown in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e.\u003c/p\u003e \u003cp\u003eReferencing the existing research findings of other similar lakes, the values of the main parameters in the model are listed in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. The light intensity references the monitoring values for Guangxi region published by the National Meteorological Data Sharing Service.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eBoundary conditions of water quality ( mg/L)\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBoundary\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eNH\u003csub\u003e3\u003c/sub\u003e-N\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eTN\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eTP\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eDO\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eCODcr\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eXiaoxia River into the Canghai Lake\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.86\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.11\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e8.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e13.0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGufeng River into the Canghai Lake\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2.60\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.26\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e8.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e29.1\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 \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eMajor parameter\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"2\"\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 \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eParameters\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eValue\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePhytoplankton growth rate\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1.800 /d\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eThe maximum rate at which zooplankton feed on phytoplankton\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.300 /d\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePhytoplankton death rate\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.100 /d\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMinimum nitrogen content inside algae cells\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.070 g N/g C\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMaximum nitrogen content inside algal cells\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.170 g N/g C\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMinimum phosphorus content in algal cells\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.002 g P/g C\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMaximum phosphorus content in algal cells\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.030 g P/g C\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNitrogen uptake rate of algae under restricted conditions\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.300 g N/g C/d\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePhosphorus uptake rate of algae under limited conditions\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.050 g P/g C/d\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMinimum chlorophyll yield coefficient\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.200 1/(E/m\u003csup\u003e2\u003c/sup\u003e/d)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMaximum chlorophyll yield coefficient\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1.500 1/(E/m\u003csup\u003e2\u003c/sup\u003e/d)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"3. Water quality maintenance and landscape design strategy based on mathematical model","content":"\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Lake flow field analysis and landscape design strategy\u003c/h2\u003e \u003cp\u003eReferencing the long-term runoff measurement and analysis results of the Xiaoxia River, the inflow and outflow rates of Canghai Lake were determined to be 12 m\u0026sup3;/s during the wet season and 4 m\u0026sup3;/s during the dry season. The hydrodynamic conditions of the Canghai Lake area were analyzed under normal conditions, where the lake water level is maintained at the constant level of 20 meters. The findings revealed that the flow velocity in the lake area is generally below 5 cm/s, regardless of whether it is the wet or dry season. Computational simulations of lake currents during the wet season driven by eastward, northward, and southeastward winds with an average annual wind speed of 1.7 m/s, as well as during the dry season driven by northward winds, showed that the wind field has no significant impact on the hydrodynamic characteristics of Canghai Lake. Under the condition of a constant water level of 20 meters, the average hydraulic retention time during the wet and dry seasons is 17 days and 50 days, respectively. The hydraulic retention time of Canghai Lake during the dry season is relatively long, and the hydrodynamic conditions in the lake area are poor.\u003c/p\u003e \u003cp\u003eCurrently, the water depth at the normal water level of Canghai Lake is primarily between 14 to 16 meters, allowing for appropriate subaqueous topographical design. Different water bodies with varying terrain heights will experience distinct temperatures and flow velocities after being subjected to solar radiation and wind, which can guide the formation of a circulation system with tributary streams, thereby enhancing the hydrodynamics of the lake area. Properly designing artificial islands with elevations between the normal and flood water levels, and covering them with aquatic vegetation, creates a topography that provides habitats for different types of aquatic plants, enriching biodiversity. While improving the fluidity of the lake's water bodies, this approach also creates an ever-changing visual landscape.\u003c/p\u003e \u003cp\u003eBy increasing the installation of pumps, jet systems, and aeration facilities within the lake area, and designing landscape fountains at the waterfront, the circulation of the water body is accelerated. This increases the dissolved oxygen in the water, accelerating the degradation of pollutants.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Lake Area Water Quality Analysis and Landscape Design Strategies\u003c/h2\u003e \u003cp\u003eModel calculations have revealed that the concentrations of COD and NH\u003csub\u003e3\u003c/sub\u003e-N in Canghai Lake meet the Class II standards, while TN and TP basically satisfy the Class III standards. However, the risk of algal blooms is high during the dry season under high temperature conditions (approximately 25\u0026deg;C). As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, after 17 days of sustained high temperatures during the dry season, nearly one-third of the lake area experiences severe algal bloom phenomena, and after 22 days, more than half of the lake area is affected by algal blooms, which could severely damage the ecological environment and landscape function of the lake. The high TP load during the dry season in Canghai Lake makes it difficult for the water to meet the Class III standard and is a key stimulant for algal bloom outbreaks. Therefore, it is essential to strictly control the phosphorus load entering the lake. Since the main pollution source of Canghai Lake is the Xiaoxia River, strict control over the phosphorus load from the Xiaoxia River entering the lake should be implemented.\u003c/p\u003e \u003cp\u003eA plan is proposed to establish an artificial wetland at the entrance of the Xiaoxia River where it flows into Canghai Lake, with a wetland area of approximately 40 hectares, to construct an efficient plant ecosystem. This system, based on the creation of deep pools and shallow shoals, integrates surface flow wetlands, subsurface flow wetlands, and substrate modification techniques. It involves selecting and planting various aquatic plants that can efficiently absorb phosphorus to enhance the phosphorus removal effect, improve the water quality of the Xiaoxia River entering Canghai Lake, and form a wetland landscape.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eDue to the significant correlation between the nitrogen and phosphorus accumulation, concentration, and biomass of plants, biomass can be used as an indicator to select plants for the artificial wetland. Studies indicate that species such as Canna indica, Acorus calamus, Tradescantia virginiana, Spilanthes oleracea, Arundo donax, A. donax 'Variegata', Lolium perenne, and Commelina communis are highly effective at nitrogen absorption; while Acorus calamus, Tradescantia virginiana, Spilanthes oleracea, Arundo donax, Lagenaria siceraria, Lolium perenne, Iris tectorum, and Commelina communis are effective at phosphorus absorption.\u003c/p\u003e \u003cp\u003eConsidering the morphological characteristics, landscape functions, biodiversity requirements, and the seasonal stability of purification capabilities, the plan involves large-scale planting of tall and colorful emergent plants such as Acorus calamus, Arundo donax, and A. donax 'Variegata', interspersed with herbaceous flowering plants like Tradescantia virginiana and Canna indica. Spilanthes oleracea, Lolium perenne, and Commelina communis are planted as ground cover to control the landscape effect. Floating plants such as Nymphaea alba and Ludwigia sedioides, and submerged plants like Elodea canadensis, Ceratophyllum demersum, and Hydrocharis dubia are selected to achieve water purification and landscape optimization through a reasonable configuration of emergent, floating, and submerged plants (Figs.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eTaking into account the topography and purification effects, and referring to relevant domestic research findings, the expected phosphorus removal efficiency is anticipated to be over 45% [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. Simulation results indicate that the implementation of the wetland project can effectively improve the water quality of Canghai Lake, and the risk of large-scale algal blooms during the dry season is basically eliminated.\u003c/p\u003e \u003c/div\u003e"},{"header":"4. Discussion","content":"\u003cp\u003eCurrently, the demand for water quality and hydroecological considerations in the planning and design of urban landscape water bodies is receiving increasing attention. Han Yi et al. [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e] introduced the application of relevant hydrological knowledge in practice through two ongoing planning projects and suggested that the movement characteristics of river flows must be understood before design. The urban river landscape environment should meet various requirements such as aesthetics, leisure, and biodiversity without reducing the river's flood-carrying capacity. However, there are still relatively few planning and design efforts that quantitatively analyze and optimize water quality and hydroecological issues, and such literature is rarely reported. This study aims to construct a two-dimensional dynamic hydrodynamic-water quality coupled model for the planning of Canghai Lake, attempting to find a path for quantitatively assessing the water quality risks of planning schemes and the effectiveness of water quality improvement measures.\u003c/p\u003e \u003cp\u003eHydrodynamic and water quality models contain a large number of parameters, which generally require calibration and validation using relevant measured data. Since it is impossible to have actual measurement data during the planning stage, this inevitably affects the accuracy of the model. Nevertheless, with appropriate experience in hydrodynamic and water quality simulation and by referencing the model research results of similar water bodies, it is still possible to obtain reasonable simulation results that can support planning and design.\u003c/p\u003e \u003cp\u003eThis work is just a beginning, and whether its conclusions are consistent with reality remains to be tested by the practice after the completion of all projects in Canghai Lake. In any case, using hydrodynamic and water quality models at the initial planning stage to find a more scientific optimization of urban landscape water body planning schemes, integrating lake hydrodynamic enhancement and water quality improvement measures from the field of environmental science with landscape optimization strategies from the field of landscape architecture, and proposing a comprehensive planning method for lake ecological landscapes that integrates water quality simulation, water ecological restoration, and water landscape planning technology, represents a new approach and method for the ecological landscape design of urban rivers and lakes.\u003c/p\u003e"},{"header":"5. Conclusion","content":"\u003cp\u003eThis paper utilizes MIKE 21 water environment simulation software to establish two-dimensional hydrodynamic and water quality models for Canghai Lake, conducting calculation and analysis of the lake's water flow and water quality conditions under different scenarios. Based on this, an overall strategy for enhancing hydrodynamics and improving water quality in the lake area is proposed: by setting up an artificial wetland at the entrance of the Xiaoxia River where it flows into Canghai Lake, using plant floating beds, and rationally configuring emergent plants, floating plants, and submerged plants to construct an efficient plant ecosystem. Through landscape facilities (such as water curtains) that promote water movement, the strategy can effectively reduce the phosphorus load entering the lake, improve the water quality of the lake area, and is expected to basically eliminate the risk of large-scale algal blooms in Canghai Lake. Additionally, it will form a wetland landscape, thereby achieving an organic unity of improved water environmental quality and landscape optimization.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e \u003ch2\u003eConflicts of Interest\u003c/h2\u003e \u003cp\u003eThe authors declare that they have no conflicts of interest.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eOnly one author.\u003c/p\u003e\u003ch2\u003eAcknowledgements\u003c/h2\u003e \u003cp\u003eThis paper is supported by the National Natural Science Foundation of China (Grant Nos. 52408326, 52278335).\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eThe datasets used and/or analysed during the current study available from the corresponding author on reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eChen, Y. \u0026amp; Zhang, B. Urban design based on water environment:A case study of Meilong Lake area in Chunhua Town, Nanjing. \u003cem\u003eChin. Landsc. Archit.\u003c/em\u003e, (4): 16\u0026ndash;19. (2014).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhu, L. \u003cem\u003eAdv. Water Sci.\u003c/em\u003e, \u003cb\u003e16\u003c/b\u003e(6): 784\u0026ndash;787. (2005).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLi, F. P., Zhang, H. P. \u0026amp; Chen, L. Study on the spatial and temporal distribution and correlation between environmental factors and chlorophyll a in small closed water. \u003cem\u003eEnviron. Sci.\u003c/em\u003e \u003cb\u003e34\u003c/b\u003e (10), 3854\u0026ndash;3861 (2013).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eJiang, Y. P. et al. Contribution of constructed wetland plants to nitrogen and phosphorus removal in ornamental water. \u003cem\u003eActa Ecol. Sin.\u003c/em\u003e \u003cb\u003e24\u003c/b\u003e (8), 1720\u0026ndash;1725 (2004).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYuan, S. F. et al. Ecological engineering restoration and initial water purification effect of Nantiaoxi estuary at the source of Taihu Lake Basin. \u003cem\u003eJ. Environ. Sci.\u003c/em\u003e \u003cb\u003e33\u003c/b\u003e (5), 1475\u0026ndash;1483 (2013).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eQ Zhang. \u003cem\u003eStudy on phosphorus removal from polluted water in horizontal underflow constructed wetland\u003c/em\u003e (Tongji University, 2007).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHan, Y., Liu, H. L. \u0026amp; Yang, D. D. Practice of urban river landscape planning and design based on landscape hydrology theory. \u003cem\u003eChin. Landsc. Archit.\u003c/em\u003e, \u003cb\u003e2014\u003c/b\u003e(1): 23\u0026ndash;28 .\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":"Landscape Architecture, Numerical Simulation, Canghai Lake, Water Environmental Quality, Waterbody Landscape Planning, Artificial Wetland","lastPublishedDoi":"10.21203/rs.3.rs-5226003/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5226003/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eUrban waterbody landscape planning necessitates the dual objectives of water quality improvement and landscape optimization to create a favorable aquatic ecological landscape environment. Taking Canghai Lake in Guangxi as a case study, the MIKE 21 hydro-environment simulation software was employed to establish a two-dimensional hydrodynamic and water quality model for the lake area. This model was utilized to simulate the flow and water quality conditions within the lake, and to propose an overall strategy for enhancing hydrodynamics and improving water quality in the lake area. The study findings indicate that incorporating an artificial wetland at the lake inlet within the planning, by appropriately configuring emergent, floating, and submerged plants, can construct an efficient plant ecosystem. This approach is expected to reduce the phosphorus load entering the lake by over 45%, effectively improving the water quality in the lake area, and fundamentally eliminating the risk of large-scale algal bloom outbreaks in Canghai Lake. Additionally, it will create a wetland landscape, thereby achieving an organic unity of water quality enhancement and landscape optimization. An integrated planning method for lake ecological landscapes that combines water quality simulation, aquatic ecosystem restoration, and water landscape planning technologies is proposed, which can serve as a reference for the planning and design of urban waterbody landscapes.\u003c/p\u003e","manuscriptTitle":"Aquatic Ecological Landscape Planning Based on Numerical Modelling","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-12-02 15:53:04","doi":"10.21203/rs.3.rs-5226003/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":"eabe73e0-8944-4019-934d-262275a42f8c","owner":[],"postedDate":"December 2nd, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":40168505,"name":"Earth and environmental sciences/Environmental sciences"},{"id":40168506,"name":"Earth and environmental sciences/Hydrology"},{"id":40168507,"name":"Earth and environmental sciences/Limnology"}],"tags":[],"updatedAt":"2025-02-17T18:23:42+00:00","versionOfRecord":[],"versionCreatedAt":"2024-12-02 15:53:04","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-5226003","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5226003","identity":"rs-5226003","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}