Water-level fluctuations in lakes regulate phosphorus transformation and release by cyclically exposing and submerging sediments, potentially worsening eutrophication. However, predicting potential release susceptibility of phosphorus mobilization remains challenging due to complex sediment-hydrology interactions. To address this, in-situ monitoring and analysis of 558 sediment samples was conducted across to three elevation gradients (U: 8.8-9 m; M: 8.6-8.8 m; D: 8.4-8.6 m) in Lake Chaohu to examine the spatiotemporal dynamic. Total phosphorus (TP) varied significantly across flooding depths; Fe/Al-bound P (Fe/Al-P) was generally higher during exposure, particularly in zone M; organic phosphorus (OP) accumulated in frequently exposed sediments, especially in zone U, while inorganic phosphorus (IP) decreased with elevation and calcium-bound phosphorus (Ca-P) was enriched in flooding sediments at zone D. Bulk density negatively affected Fe/Al-P and OP by influencing sediment compaction and structural stability, whereas organic matter (OM) emerged as a key driver of total and IP. Importantly, partial dependence graphs revealed nonlinear thresholds, implying that low bulk density (<1.1 g/cm & sup3;) weakens sediment structural stability, while high OM (>3 %) was associated with increased redox-related instability, thereby facilitating high phosphorus retention while simultaneously increasing the pulse-release susceptibility of OP and Fe/Al-P upon rewetting. These results identify frequently exposed, organic-rich sediments as unstable phosphorus sinks that can release legacy P upon rewetting, particularly under conditions of low bulk density and high OM content. This mechanistic understanding provides a scientific foundation for targeted wetland ecological restoration, emphasizing the importance of stabilizing sediment structure and managing hydrological regimes in these specific zones in reducing eutrophication and promoting aquatic ecosystem recovery.

Littoral sediments serve as dynamic biogeochemical interfaces, yet how exposure-inundation gradients dictate the compositional divergence of sediment dissolved organic matter (DOM) through nested physical-chemical pathways remains poorly understood. In this study, sediment DOM dynamics across a littoral exposure-inundation gradient (upper, middle, and permanently inundated zones) were examined by integrating micro-hydrological zonation, depth-resolved physicochemical properties, and PARAFAC-derived fluorescence components. The results demonstrated a pronounced horizontal and vertical divergence in DOM composition along the gradient. Intermittently exposed upper zones (U) exhibited higher relative contributions of humic-like (45.2%) and fulvic-like (40.4%) components with lower DOC concentrations (0.18-0.81 mg g-1), indicating selective preservation of aromatic structures during oxic-suboxic exposure. Conversely, the permanently inundated zone (D) was dominated by protein-like DOM (43.4%) and elevated DOC (0.25-0.96 mg g-1), coupled with higher spectral slope ratios (SR), reflecting enhanced preservation of lower-molecular-weight, labile organic matter under prolonged anaerobic conditions. Piecewise structural equation modeling (SEM) successfully disentangled the hierarchical environmental controls, explaining 47%, 22%, and 19% of the variances in protein-like (C3), fulvic-like (C2), and humic-like (C1) fractions, respectively. Sediment redox potential exerted a significant negative effect on protein-like DOM (standardized coefficient = -0.35), whereas bulk density imposed strong constraints on both humic- and protein-like fractions. These findings underscore that exposure-inundation gradients govern littoral DOM architecture via divergent redox gating and physical matrix filtering. Our results imply that adaptive lake water-level regulations must account for localized sediment physical-chemical coupling to optimize carbon retention and manage internal nutrient loading under fluctuating hydrological regimes.

Based on zonal management and engineering-ecological synergy, this study innovatively designed and constructed a "pollution absorption zone" (PAZ) system to restore shallow eutrophic lakes, in response to excessive external nitrogen and phosphorus loads and the degradation of aquatic vegetation. Using Lake Changdanghu (China's Yangtze River Basin) as a case study, a functionally synergistic PAZ integrating underwater shoals, bottom traps, prereservoirs, and flow-guiding channels was constructed. Three-year monitoring demonstrated that PAZ effectively attenuated wind wave by 72% via the underwater shoals, significantly reducing the concentration of suspended solids and increasing water transparency. The marked increase in transparency has successfully created a still, clear-water environment conducive to the recovery of aquatic vegetation. Simultaneously, the synergistic effect of the PAZ effectively intercepted and slowed polluted inflows, thereby creating favorable conditions for in situ pollutant purification. With the improved habitat conditions, the area, distribution range, biomass, and coverage of aquatic vegetation within the PAZ have all significantly increased, leading to the effective restoration of the ecosystem structure. These outcomes demonstrate PAZ effectively mitigate external nitrogen, phosphorus loads while restoring degraded habitats. This study provides a replicable, large-scale engineering solution for balancing environmental carrying capacity with nutrient pressure through coupled physical-ecological intervention.

This paper focuses on a typical shallow lake, Lake Changdanghu, which is subject to frequent hydrodynamic disturbances and suspended sediment deposition, resulting in reduced water clarity and the degradation of the grass-type ecosystem. Using a combination of long-term systematic observations and numerical simulations, the impact of terrain modification on the hydrodynamic characteristics of Lake Changdanghu and its resulting environmental improvements are systematically analyzed. The results indicate that there is a significant correlation between the wind wave intensity, suspended solids concentration of the water, and water clarity. The artificial shoal project effectively reduces the local wind wave intensity, increases the water area of the weak waves, and alters the flow structure and transport path of the lake. The wave reduction effect of the artificial shoal significantly improves the transparency of the local water, especially under high wind wave conditions, with a 60% increase in the sheltered area, significantly improving the physical habitat environment. Additionally, the flow resistance and guidance roles of the artificial shoal concentrate the impact of the poor water quality of the inflow in a local area, reducing its adverse effects on the main body of the lake. Our research demonstrates that for shallow lakes, the water transparency can be improved, the physical habitat conditions for aquatic vegetation can be enhanced, and grass-type ecosystems can be gradually restored through artificial intervention and vegetation recovery projects by reducing the wave energy, flow resistance, and guidance through the construction of artificial shoals. This approach achieves long-term maintenance of eutrophication control and water quality improvement in shallow lakes.

Wind waves in shallow lakes is of great significance to the lake ecosystem. Based on the synchronous high-frequency observing results of wind, wind waves and water environment parameters in Lake Chaohu, the evolution characteristics of wind waves under fast-changing wind fields and its impact on the water environment were analyzed in detail in shallow lakes. The significant wave height and wave period of wind waves in shallow lakes had good synchronous response with the rapid increase of wind speed. In the phase of wind speed declining, the wave period has better stability compared with wave height. The wave direction could quickly respond to the change of wind direction in shallow lake. During the rapid growth phase of the wind field, the frequency range of the main energy for the wind wave spectrum gradually widens, and mainly widens for the low-frequency part in shallow lakes. In the attenuation stage, the frequency range of the main energy of the wind wave spectrum became narrower, and the frequency range of the main energy shifted to the low frequency as a whole.

Hydrodynamics are the key factor influencing sediment resuspension, transport and nutrient release in large shallow lakes. However, the hydrodynamic responses of bottom traps during pollutant capture remain unclear. In this study, a large eutrophic shallow lake was selected to carry out a field test of deep traps at the lake bottom. Based on observations of the lake current around the trap, the sedimentation rate of the particles in the trap and the nutrient content of the captured sediments, combined with the numerical simulation of the waves outside the trap, the effects of lake currents and waves on the sediment deposition in the traps were studied, and the response of the nutrient content of the sediments captured in the deep traps to the changes in lake currents and waves was analyzed. The results showed that the strong hydrodynamic force significantly promoted sediment deposition in the trap and enhanced the ability of the trap to capture sediments with high nutrient contents. The influences of waves and lake currents on the bottom trap capture of polluted sediments varied among different periods. Waves played the leading role in winter and spring, accelerating sediment capture in the bottom traps near the southern shore of eastern Lake Chaohu during this period. In summer, the lake current was the main dynamic factor contributing to the rapid deposition of particulate matter and the capture of sediments with high nutrient contents in the bottom traps of western Lake Chaohu. The multiple stepwise linear regression model based on lake current and wave data explained 37.6 % of the sediment deposition in the trap, and the model built for a single bottom trap explained more than 80 % of the deposition. After correcting the sediment deposition thickness in the trap by considering the water content of the sediment, the quantitative relation yield better inversion results for the sediment deposition process, and different thicknesses in the bottom trap were linked to different sediment deposition periods. According to the hydrodynamic strength in 2020, the thickness of the highly contaminated sediments captured by traps CC1-CC5 was calculated to be 1.09-1.93 m, and the corresponding TN and TP were 26.66-68.53 kg and 6.84-19.89 kg, respectively. This study provides a scientific analysis and guidance for the evaluation of endogenous nutrients captured by lake bottom trap methods.

Sediment phosphorus (P) biogeochemical processes impact water quality. Restoration measures and global warming lead to the same outcome, namely that reactive P moves from the sediments to the bottom waters. In this study, a vertical-compressed sediment P transport model was developed and coupled with a three dimensional (3-D) hydrodynamic-ecological model (EcoLake). The proposed model was used to evaluate the effects of two different strategies (external loads reduction and global warming) on sediment P release flux and P concentrations in the water column of Lake Chaohu, the fifth largest shallow lake in China. The results found that the coupled model accurately reflected P transport in the water column, sediment, and dissolved reactive P (SRP) diffusion at the sediment and water interface. The degradable rate of rapidly degradable organic P (vp1) and adsorbed rate (kad) are the most sensitive parameters influencing sediment P release flux. The internal SRP loads caused by diffusion accounted for roughly 5% of the total external P loads, with higher values in heavily polluted lake basins (western and eastern) and during warmer seasons (summer and autumn). Sediment P release may have caused the current lake water SRP concentrations to increase by 31.1, 12.0, and 21.2%, in western, central, and eastern basins, respectively, due to the large difference of sediment SRP concentration between three basins. The SRP concentration in water responded to changing loads and water temperature strategies more in the western basin than in the other two basins. The sediment P release flux showed spatially contrary responses between two strategies. These findings have important implications with respect to the effects of sediment P release on water quality, and will assist water quality managers in developing appropriate P control measures.

Study region: Lake Chaohu is a typically large shallow freshwater lake in China, experiencing long-term eutrophication and a short period of drought. Study focus: This study employs a three-dimensional (3-D) hydrodynamic-ecological model to assess the impacts of water transfer on lake flow, water quality, and their relationship, and then reveals optimal strategies for achieving improved water quality in Lake Chaohu. New hydrological insights for the region: Results indicated that clean water transfer could dramatically increase flow rate and decrease nutrient concentrations near the water transfer inlets, while the grade level of lake water quality is not changed. The degree of improvement in water quality parameters is not always proportional to lake flow rate. A clean water transfer through the eastern route (ZH) has the largest improvement effect on the average flow rate and water quality (total nitrogen (TN) and total phosphorus (TP)) of the entire lake. Winter water transfer improves TN and TP better than summer, while the opposite for ammonia nitrogen (NH3-N). Decrease of wind speed is essential for mitigating nutrient accumulation in western lake’s heavily polluted bay through weakening the reverse circulation and the northwest flow. Water transfer operations are revealed to improve water quality in Lake Chaohu: conduct water transfer through ZH in winter, strictly control NH3-N concentration in the donating water, and combine the effects of the low east wind.

Gaining a deeper understanding of factors that influence changes in phytoplankton community has significant implications for shallow lake management. The present study examined changes in the algae community of three shallow eutrophic lakes of the Taoge water system between 2008 and 2018 and the related factors influencing these changes. The composition of the algal community varied significantly during this period with the relative diatom biomass in lakes Changdanghu and Gehu increasing between 2014 and 2016 and again decreasing after 2017. However, relative cyanobacteria biomass initially decreased and later increased; meanwhile, the proportion of biomass of other phyla decreased continuously in the study period. Lake Zhushanhu showed similar trends, although it eventually returned to its initial state with absolute Microcystis dominance. Furthermore, the analysis of driving factors revealed that the concentrations of total nitrogen (TN), nitrate (NO3), and orthophosphate (PO4) were significantly associated with a significant increase in Microcystis biomass. Meteorological conditions also influenced changes in total algal and diatom biomasses, which were inversely related to the daily mean and daily maximum wind speeds. Monthly cumulative precipitation was only significantly associated with diatom biomass. Meanwhile, rainfall primarily affected the algal community structure between 2013 and 2017; an increase in the relative biomass of diatoms coincided with increased precipitation. Coordinating nitrogen and phosphorous use within the Taoge water system should improve lake habitat management; a broader perspective in attempts to control global and regional climate change may be needed.

The relationship between nitrogen and phosphorus concentrations in rivers and lakes and their influencing factors have been global concerns. However, how air temperature changes affect the nitrogen and phosphorus concentrations in rivers and lakes remains unknown. In this study, we conducted analyses linking the characteristics of air temperature to monthly nitrogen and phosphorus monitoring datasets of the lake and adjacent inflowing rivers in the Lake Chaohu basin from 2014 to 2018. We found that the variations in the mean air temperature of the antecedent 7 days significantly affected the nitrogen and phosphorus concentrations in shallow eutrophic lakes, and the air temperature threshold ranged from 3 to 27 °C. As the air temperature increased, the nitrogen concentrations in Lake Chaohu decreased, but the phosphorus concentrations showed an upwards trend. The lake had a “buffer” function, as indicated by the more pronounced response of nitrogen and phosphorus to increasing air temperature in western Lake Chaohu (TN = − 0.085 mg L−1 °C−1, TP = + 0.004 mg L−1 °C−1) than eastern Lake Chaohu (TN = − 0.034 mg L−1 °C−1, TP = + 0.003 mg L−1 °C−1). The decreasing trend of nitrogen concentrations (average declining rate: 0.090 mg L−1 °C−1) in inflowing rivers with increasing air temperature was even more pronounced than that in Lake Chaohu. However, no significant statistical relationship was found between the phosphorus concentrations and air temperature in most inflowing rivers. Therefore, this study emphasizes the need to further unravel the coupling mechanism between internal nutrient loads and climate factors while reducing external nutrient loads.

浅水湖泊风浪过程对于湖泊生态系统具有重要的意义.基于巢湖风场、风浪和水环境参数同步高频观测结果,详细分析了快速变化风场下的风浪快速变化特征及其对湖泊水环境的影响特征.浅水湖泊风浪的有效波高和平均波周期均随风速的快速变化有较好的同步响应规律.在风速快速衰减阶段,相较有效波高,波周期有更好的稳定性.湖泊水体pH、水温、溶解氧会快速响应风浪的变化,随着风浪强度增强,对水体浊度、总磷浓度以及藻密度和生物量的扰动影响逐渐呈现.强烈的风浪扰动引起水体浊度变化的滞后时间可达3 d.快速变化的风浪场下,风浪的强烈扰动会改变水体固有的理化参数分布特征,扰动藻类常规的水体分布规律,风浪强度是造成差异的主要因子.

Little is known about the distribution and risk levels of nutrients and organic matter(OM) in the surface sediment of shallow submerged macrophyte-dominated lakes. In the current study, sixty surface sediment samples were collected from Xukou Bay, a typical submerged macrophyte-dominated zone in Lake Taihu, China. A 60-day degradation experiment of Potamogeton malaianus, a dominant species in the bay,was done in the laboratory. The results demonstrated that the ranges of total nitrogen(TN) and total phosphorus(TP), alkali-hydrolyzable nitrogen(AN), available phosphorus(AP), and OM in the surface sediment of the bay were 262.2-2,979.6 mg/kg, 41.2-728.7 mg/kg, 8.6-150.0 mg/kg, 4.4-36.4 mg/kg,and 3.7-50.2 g/kg, respectively. The spatial distributions of TN, OM, and AN concentrations showed similar trends: The highest concentrations were present in the northeastern and southwestern zones,while the TP and AP concentrations were high in the northeastern, central, and southwestern zones. The heterogeneity in the spatial distribution of nutrients and OM in the surface sediment of the bay was associated with aquatic vegetation and anthropogenic activities. The comprehensive risk index and organic nitrogen index revealed that the surface sediment was moderately, interactively contaminated by TN and TP and by organic nitrogen. TN and OM in the northeastern zone were mainly derived from endogenous residues due to the decomposition of aquatic plants, while TN in the southwestern zone was primarily derived from agricultural wastewater. Consequently, targeted measures should be implemented to reduce TN and OM in the surface sediment of macrophyte-dominated lakes.

基于长荡湖不同位置的风浪实测资料,对实施水利优化工程后的长荡湖风浪特征进行了分析.结果表明,风速较大时,湖心水域总体风浪强度较大,长荡湖谱峰周期与平均波周期和跨零周期都存在显著线性相关.生态潜堤可以有效削减西湖近岸水域风浪强度,有效波高衰减百分比介于56％～81％,平均周期衰减百分比介于14％～31％.西部近岸水域风浪强度的削减,有利于水体透明度增加,从而为近岸水域水生植被的修复提供较好的生境条件.

Bottom traps capture and preserve nutrient-rich mobile bottom sediments by forming a weak hydrodynamic environment. In this study, Lake Chaohu, a large shallow lake in China, was considered the research object, and the influence of trap at the bottom of the lake on the physical, chemical, and biological characteristics of sediments and water were analysed by combining on-site monitoring and laboratory analysis. The results showed that the hydrodynamic intensity was attenuated by more than 65% at the bottom of the trap compared with that of the upper surface of the water body under different weather conditions, forming an obviously weak hydrodynamic environment. The weak dynamic environment and large sedimentation rate at the bottom of the trap were beneficial to the sedimentation and storage of fine particles that adsorb nutrients, such as nitrogen and phosphorus, in the water. Owing to the increase in local water depth, a low-temperature and low-dissolved oxygen environment was formed inside the trap. The abundance and diversity of microorganisms in the sediments inside the trap were reduced, and the abundance of nitrifying and denitrifying bacteria in the sediment was reduced by approximately 50%, indicating an environment favourable for nitrogen accumulation in the sediment in the trap. Therefore, the environment inside the bottom trap is favourable for capturing the high nutrient-rich particulate matter in the water, which provides theoretical support for use of the lake bottom traps for controlling the endogenous pollution of shallow lakes.

基于研发的湖底陷阱捕获内污染技术,在巢湖进行应用研究.结果表明,湖底陷阱可有效收集叶绿素a、有机质、总氮和总磷等湖底沉积物中内源污染物.不同位置和季节湖底陷阱收集的沉积物厚度差异显著,西巢湖收集的污染物含量最多,湖心区域收集污染物量最少;夏秋季节淤积较快,冬春季节淤积略慢.单位面积(lm2)湖底陷阱年收集叶绿素a、有机质、总氮和总磷可分别达2.37～15.28g、8.96～21.82kg、0.78～1.88kg和0.30～0.93kg.综合考虑湖流场、风浪场、湖底污染物分布及厚度,巢湖湖体内沿湖流汇集区可布置6条11～33km的湖底陷阱,并在7个主要入河口布置湖底陷阱,同时可利用现有航道,进一步加深后形成湖底陷阱,可为巢湖内源控制提供新的治理手段和管理方法.

We investigated the spatial distribution and storage of nitrogen and phosphorus in Lake Chaohu sediments and evaluated the sediment nitrogen and phosphorus pollution index. Results show that the average total nitrogen (TN) and total phosphorus (TP) content in the surface-layer sediments of Lake Chaohu were 1088 mg·kg-1 and 585 mg·kg-1, respectively, and 666 mg·kg-1 and 509 mg·kg-1 in the bottom-layer sediments, respectively. TN content in the surface layer was significantly higher than in the bottom layer (P<0.01). Spatially, TN, TP, and sediment thickness were ranked in the order western lake area > eastern lake area > middle lake area, and the TN and TP contents were significantly different in the surface sediments from the middle and eastern areas of the lake (P<0.05, P<0.01). TN and TP storage in the lake sediments was 1.58×105 t and 0.98×105 t, respectively. TN and TP were significantly correlated in both the western and middle parts of the lake (P<0.01). In addition, TN was significantly correlated with sediment thickness in middle area of the lake, which indicated that TN may have the same pollution sources as TP and both were affected by sediment thickness. TN pollution index (STN), TP pollution index (STP), and comprehensive pollution index (FF) values were 1.09, 1.39, and 1.32, respectively, indicating light-to-moderate levels of pollution. Specifically, the western lake surface sediments were heavily polluted with respect to TP, the eastern lake surface sediments were moderately polluted, and the middle lake surface sediments were slightly polluted. Nutrient pollution varied widely between different areas of the lake, with sediments in the western part of the lake presenting a higher safety risk. Overall, these observations indicate that Lake Chaohu is threatened by internal nutrient loading.

深入认识大型湖泊在不同风速、风向和水位下三维风生流结构特征对于湖泊污染控制、生态恢复及资源的开发利用具有重要意义.本文在构建笛卡尔坐标系下洪泽湖三维水动力模型的基础上,利用2次全湖30个点位流场监测数据验证了模型精度.基于1975 2020年长系列风场观测数据,确定了洪泽湖典型风速风向.在此基础上,模拟了16种不同风向,13种不同风速和20种不同水位工况条件下洪泽湖三维风生流结构.结果表明:水动力模型可以较好地刻画洪泽湖三维湖流变化特征.洪泽湖风生流结构随风向变化呈现出较大空间差异.风生流流速随着风速的升高呈加速上升趋势,其中表层水体流速上升幅度远高于其他水层.在2.4 m/s东风驱动下,溧河洼、成子湖和南部湖区垂向平均流速随着水位上升呈先升高后降低的趋势,3个湖区分别在12.7、12.4和12.2 m水位下流速达到最大值.

The effective removal of internal pollution is of great importance for lake management and eutrophication control in shallow lakes. A new technology for collecting internal pollution was tested in a shallow lake. The surface sediments of shallow lakes have a low density and flow easily. Under the disturbance of wind-induced waves, such sediments will resuspend and enter the water body from the bottom of the lake and move horizontally with lake currents. Based on these characteristics, bottom traps were installed in the bottom of Lake Chaohu, China, to capture the internal pollutants in suspended sediments. Static water environments can be formed inside the traps. The amount of chlorophyll a and organic matter in the sediments inside the traps was approximately 3.0–4.0 times and 1.5–2.0 times greater than in the surrounding sediments, respectively. After long-term collection by traps, the average reduction of chlorophyll a, organic matter, total nitrogen, and total phosphorus in the surrounding sediments were approximately 8–14%, 9–14%, 27–48%, and 0.5–2%, respectively. A trap with a width of 4 m can collect surface sediments within a 400 m wide area (200 m on both sides of the trap). Bottom traps can collect a large amount of surface sediment, which can be treated with desilting, which have little impact on the lake bottom ecosystem and biological community. Compared with ecological dredging, an investment of more than 50% can be saved. It has a broad application potential for the collection and removal of internal pollutants in shallow lakes.

Large hydraulic infrastructures have been constructed globally to address water challenges. Past studies have well documented their effects on downstream aquatic ecosystems, which have included disrupting hydrological regimes as well as nutrient delivery, cycling and mediating processes that affect primary production. However, how these infrastructure operations affect lake ecosystems where the infrastructures are situated remains poorly understood. In the present study, we used a three-dimensional hydrodynamic-biogeochemical lake model to quantify the potential effects of large lake sluice operations under extreme high water levels on current structure and water quality parameters of Lake Chaohu in China. We designed and simulated multiple operation strategies based on actual operation curves during the 2016 extreme rainfall season. The model successfully captured the water quality dynamics of Lake Chaohu during both the calibration and validation phases. Our results indicate that higher lake water release rates led to overall accelerations of the current velocity; however, the deceleration of along-shore current velocity along the shorelines was also evident. Higher release rates also resulted in rapid rises ammonium nitrogen (NH4-N), total nitrogen (TN) and total phosphorous (TP) concentrations in the eastern lake basin, as well as a lake-wide rise of chlorophyll-a (Chla) concentration. When the lake sluice was operated at its full capacity, mean concentrations of these four parameters increased by 5.21%, 5.58%, 9.6% and 7.46%, respectively. Modeling results demonstrate that the effects of lake sluice operations were still quite pronounced for four months after the operations. Modeling results also revealed that higher release rate during the operation phase may help decease TN and TP concentrations during the subsequent period. This study provides a useful perspective on how to support the planning and operation of large infrastructures in the face of climate change induced extreme events.