Yili Ge

Lake water quality is heavily influenced by agricultural activities, hydrological variations, and regional climate extremes, yet holistic assessments of their relative contributions and non-linear thresholds remain limited. We evaluated the water quality variation characteristics of Lake Dongting from 2014 to 2023 and found that total phosphorus (TP), total nitrogen (TN), and dissolved oxygen (DO) decreased significantly, while ammonia nitrogen (NH₃-N) showed no significant temporal trend. CatBoost models identified water level and sediment load as important predictors of TP and DO, whereas TXx and SU25 were important predictors of TN and NH₃-N. The testing R² values were 0.62, 0.51, 0.39, and 0.58 for TP, TN, NH₃-N, and DO, respectively, with testing RMSE values of 0.031, 0.480, 0.200, and 0.790, respectively. GAMs identified indicator-specific nonlinear responses: TP showed a model-estimated response point at WL = 28.36 m (95% CI: 27.74–28.89 m) and a hump-shaped response to Rx1 day, with a model-estimated point at 44.81 mm (95% CI: 40.32–49.45 mm); TN showed a response point at SU25 = 18.38 days (95% CI: 15.21–21.74 days), whereas NH₃-N decreased monotonically with increasing SU25 and no accumulation threshold was inferred. Annual-scale variance partitioning and correlation analyses indicated that decadal nutrient variations co-varied with changes in agricultural activities. Our results indicate that lake water quality is associated with agricultural inputs and hydro-climatic conditions, underscoring the value of integrating agricultural non-point source control with climate-adaptive hydrological regulation for future water environment management.

The presence of submerged plant communities and the restoration of their diversity have critical impacts on aquatic ecosystem function, especially in eutrophic lakes. However, we lack a holistic understanding of how specific species and functional groups and their richness of submerged macrophytes affect the community productivity and water quality in aquatic ecosystems, and how these effects varied across water nutrient gradients. Here, we performed a mesocosm experiment by manipulating species richness and functional richness from a species pool of 22 submerged macrophytes to test what are the ecological implications of shifts in macrophytes diversity under two nutrients levels. The results showed that species richness significantly enhanced community productivity only at low nutrient level, while functional richness had no marked effects on community productivity across nutrient levels. The improvement of water quality by increasing submerged plant diversity (species and functional group richness) is often efficient, despite their context‐dependent effect (e.g. nutrient level, specific parameters). Specifically, our results demonstrated a remarkable role in distinct functional groups (FG). That is, the presence of particular functional group characterized by high leaf dry mass content (LDMC) and small specific leaf area (SLA) significantly enlarged the reduction of total nitrogen (TN) across nutrient levels, as well as the reduction of total phosphorus (TP) and chemical oxygen demand (COD _Mn ) at low nutrient level. Additionally, the presence of FG characterized by long florescence and great SLA significantly affected nitrate reduction at high nutrient level and the reduction of TN, COD _Mn and conductivity at low nutrient level. The presence of FG characterized by low LDMC and short shoot height significantly enhanced the reduction of dissolved oxygen and pH. Our findings highlighted the unique contributions of functional groups of macrophyte communities to water quality improvement should be taken into account when designing restoration strategies.

The main aim of this research was to determine the physiological response of the submerged macrophyte Vallisneria natans (V. natans) to black water with a foul odor. V. natans was chosen as the experimental plant species to investigate the morphological response and ecophysiological adaptation methods in response to varying light depths and black-odorous water. V. natans was planted in tap water (D), two types of black-odorous water (E and F), and under three distinct light conditions (low light, medium light, and high light). In the high-light condition with black-odorous water (E), the biomass content of V. natans declined from 1.78 g on the 14th day to 1.49 g on the 28th day, demonstrating that the black-odorous water inhibited the growth of V. natans. Under the stress of black-odorous water, the chlorophyll content of V. natans increased greatly in the early period but reduced during the latter experimental period. However, on the 21st day, maximum chlorophyll content of 1.30 mg/g (E) and 1.18 mg/g (F) was observed. In addition, the malondialdehyde (MDA), superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) activity was monitored and reported under black-odorous water stress in V. natans. The experimental results of this work demonstrated conclusively that odorous black water exerts a certain stress on the physiological development of V. natans. Future research should incorporate the evaluation of several plant species and vary the process and environmental conditions to produce field-relevant, dependable results.