Zhengrong Huang

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.

Water-level fluctuation (WLF) is a key factor disturbing aquatic ecosystems, particularly aquatic plants (macrophytes in this review). These organisms are exceptionally sensitive to WLF as it profoundly governs their spatial distribution, productivity, species richness, community composition and successional trajectories. In this review, we synthesized recent advances regarding the impacts of WLF on the growth environment, survival strategies, and the integrated morphological, physiological, and reproductive responses of aquatic macrophytes. While existing research has predominantly focused on flooding-related WLF responses and freshwater macrophytes, the ecological consequences of drawdown and the responses of marine macrophytes remain comparatively underexplored. Despite the adverse alterations in sediment dynamics, light availability, hydrostatic pressure, pollutant concentrations, wind and wave exposure, dissolved oxygen levels and nutrient concentration conditions under WLF, aquatic macrophytes can demonstrate remarkable adaptive plasticity. This resilience was mediated through rapid adjustments in survival strategies, coupled with morphological traits, physiological processes and reproductive modifications. While their adaptive capacities were limited, and varied depending on life-forms, species or the WLF amplitudes, fluctuations in water level often precipitated rapid shifts in dominant species or even community succession over short timeframes. Consequently, while moderate WLF might confer ecological benefits, prolonged or extreme WLF posed substantial threats to aquatic vegetation. Synthesizing these findings, we developed a conceptual model diagram integrating the multifaceted responses of aquatic macrophytes to flooding-induced WLF. Future research should prioritize investigating the ecological consequences of drawdown-induced WLF and the responses of marine macrophytes—areas that remain comparatively underexplored. Furthermore, implementing refined water-level-management regimes could help optimize the good functions and services delivered by aquatic ecosystems.

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.