Maintaining the health of lake ecosystems is an urgent issue. However, eutrophication seriously affects lakes’ ecological functions. Eutrophication is also the main target of lake ecological restoration. It is vital to carry out research on lake eutrophication control and energy flow evaluation in ecosystems scientifically. Based on in situ survey results for the aquatic life data for Lianshi Lake from 2018 to 2019, the Ecopath model was used to establish an evaluation index system for the typical biological chain to screen out the key species in the water ecosystem, and the fuzzy comprehensive evaluation (FCE) method was used to screen all the biological chains controlling algae. A combination of the FCE coupled with the Ecopath screening method for typical biological chains for algal control was applied to the Lianshi Lake area; the results show that the typical biological chain for algal control is phytoplankton (Phyt)–zooplankton (Zoop)–macrocrustaceans (Macc)–other piscivorous (OthP). Upon adjusting the biomass of Zoop and Macc in the typical biological chain for algal control to three times that of the current status, the ecological nutrition efficiency of Phyt was increased from 0.308 to 0.906. The material flow into the second trophic level from primary producers increased from 3043 to 8283 t/km²/year. The amount of detritus flowing into primary producers for sedimentation decreased from 7618 to 2378 t/km²/year. Finally, the total primary production/total respiratory volume (TPP/TR) decreased from 9.224 to 3.403, the Finn’s cycle index (FCI) increased from 13.6% to 17.5%, and the Finn’s average energy flow path length (FCL) increased from 2.854 to 3.410. The results suggest that the problem of eutrophication can be solved by introducing Zoop (an algal predator) and Macc to a large extent, resulting in improved ecosystem maturity. The research results can facilitate decision making for the restoration of urban lake water ecosystems.

With the rapid development of social economy, the development and utilization of water resources is increasing, which leads to the increasing importance of ecological water demand in wetland protection. The study of lake ecological water demand can provide theoretical basis for improving the distribution of water resources and ecosystem balance in lake wetland and establish a solid theoretical basis for the sustainable development of lake wetland ecosystem. Based on the analysis and summary of the relevant literature on wetland ecological water demand, this paper expounded the connotation of lake ecological water demandand summarized the calculation method of ecological water demand of lake type wetland in China. In addition,this paper pointed out that the research focus of lake ecological water demand mainly included the application of hydrologicalhydrodynamic- water quality and the research of water demand based on ecological protection target hydrology demand.

Shallow urban lakes are prone to hydrodynamic stagnation due to limited water exchange, rendering them highly susceptible to eutrophication and algal blooms However, for small urban lakes with weak hydrodynamics, key knowledge gaps remain: whether water diversion can disrupt stagnant zones, what critical flow rate is required to suppress algae, and which regions are most suitable for submerged macrophyte restoration. Focusing on Lianshi Lake-a small shallow urban lake in North China-this study developed a coupled hydrodynamic-water quality-ecology model based on the Environmental Fluid Dynamics Code (EFDC) to quantify how water diversion and submerged macrophyte restoration regulate circulation patterns and algal biomass under weak hydrodynamic conditions. Water diversion induced a pronounced nonlinear response in algae: a critical discharge of approximately 20 m³/s was identified, marking the transition of chlorophyll-a (Chl-a) concentrations from rapid decline to a stable low level. This critical discharge coincided with the minimum number of closed circulation zones, indicating that lake-wide algal suppression is closely linked to the mitigation of hydrodynamic stagnation. High Chl-a concentrations consistently occurred in low-velocity areas across different months, underscoring circulation structure as a key driver of spatial heterogeneity in algal distribution. In contrast, at the tested restoration scale, submerged macrophyte planting did not restructure the lake-wide flow field; its hydrodynamic impacts were confined to local regions. The Chl-a response to macrophyte restoration exhibited spatial heterogeneity, the most significant Chl-a reduction was observed in the western nearshore zone-characterized by weak water exchange and high background Chl-a concentrations-while improvements were limited in areas with favorable exchange conditions. Overall, the findings support the integration of water diversion strategies (to enhance hydrodynamic exchange) and targeted macrophyte restoration to mitigate algal bloom hotspots in eutrophic small shallow urban lakes. However, further validation in larger lake systems is warranted to generalize these conclusions.

Lake Erhai is an important plateau freshwater lake in China. It serves not only as a crucial drinking water source for the local region but also as the core area of the Cangshan Erhai National Nature Reserve. Consequently, Lake Erhai plays an extremely significant role in the local economy, society, and ecology. Since 2000, the water quality of Lake Erhai has continuously deteriorated, showing a eutrophic trend. To identify the primary driving forces behind these water quality changes, this study employed stepwise regression analysis. Climate conditions, socio-economic development within the basin, and implementation of environmental protection measures (IEPMs) were considered influencing factors for a comprehensive and systematic analysis of Lake Erhai’s water quality. The results indicate that rising air temperature may increase total phosphorus (TP) concentration, while rainfall may elevate both TP and total nitrogen (TN) levels. In contrast, higher wind speed may reduce chemical oxygen demand (COD_Mn), TP, and TN concentrations. Socio-economic development, meanwhile, may contribute to increased COD_Mn concentration. Based on these findings, this paper proposes recommendations focusing on formulating more effective non-point source pollution control measures and strengthening water quality monitoring in Lake Erhai during summer. By identifying the key natural and anthropogenic drivers of water quality changes in Lake Erhai, this study provides a scientific basis for the development of targeted pollution control strategies and directly contributes to the protection of clean water sources. Moreover, its revelation of the coupled impacts of climate change and socio-economic activities enhances understanding of plateau lake ecosystem resilience. This insight is critical for ensuring regional ecological security and serves as a model for advancing sustainable development goals in similar lake systems worldwide.

Coupling municipal wastewater treatment plants (WWTPs) with constructed wetlands (CWs) has become an effective strategy for improving effluent quality while providing potential benefits in resource efficiency and environmental sustainability. However, previous studies have predominantly optimized WWTPs and CWs as independent treatment units, whereas coordinated operation of integrated WWTP–CW systems has received comparatively limited attention. This study evaluated a full-scale coupled WWTP–CW system using long-term operational data collected during 2021–2022. Environmental impacts were quantified using scenario-based calculations incorporating electricity consumption, chemical consumption, sludge production, and IPCC-based greenhouse gas accounting. Pollutant removal performance, electricity consumption, chemical consumption, and greenhouse gas (GHG) emissions were comprehensively assessed, and operational scenarios were developed to investigate the environmental benefits of coordinated optimization. The results showed that the WWTP consistently satisfied the Chinese Class 1A discharge standard, whereas the ancillary CW achieved effective polishing for COD and NH₃-N but exhibited relatively low removal efficiencies for TN and TP because of insufficient biodegradable carbon in the influent. Scenario-based simulation demonstrated that moderately relaxing pollutant removal within the WWTP while maintaining compliant effluent quality substantially enhanced the treatment performance of the downstream CW. Under the optimized scenario, the average removal efficiencies of COD, TN, and TP in the CW increased by 28.3%, 17.4%, and 19.8%, respectively. Meanwhile, electricity consumption, sludge production, and dewatering-agent consumption in the WWTP were reduced by approximately 25%. When compared on a harmonized water-volume basis, unit external carbon-source consumption likewise decreased under the optimized scenario. Consequently, overall greenhouse gas emissions decreased by 40.3%, from 527.9 to 315.3 g CO₂-eq·m⁻³ of treated wastewater. These findings demonstrate that coordinated pollutant allocation between engineered and ecological treatment units can substantially improve the environmental sustainability of existing WWTP–CW systems, providing a practical, low-carbon operational strategy without infrastructure expansion.