摘要：大型浅水湖泊是区域水资源供给与生态安全的重要载体，其水质长期演变规律对流域治理与生态保护具有重要科学与实践意义。然而，该类湖泊具有高度易扰性与生态脆弱性，在高强度人类活动与持续治理共同作用下，其水质演变过程是否呈阶段性和非线性响应特征仍缺乏系统认识。为此，本研究以中国第五大淡水湖泊—巢湖为研究对象，选取能够综合表征水体光学特征与水质状态的Forel-Ule指数（FUI）作为切入点；基于2000-2024年MODIS长时序遥感数据，采用改进的高精度水色反演模型（验证精度MRE=1.38%，RMSE=3.32°）构建水色序列，系统揭示长期人为扰动背景下湖泊水色的时空演变特征及其驱动机制。结果显示，巢湖多年平均FUI为12-15级，整体呈现绿-黄色水体特征；空间上呈显著的“西高东低”梯度格局，主要受入湖污染负荷差异及湖体自净过程共同影响；季节水色呈“双峰式”波动，夏季最清澈（色度角α：208.74°）、秋季最浑浊（色度角α：214.23°），受气象因子节律性调控。长期趋势上，2000-2024年巢湖年均α总体呈上升趋势（0.15°/年），且东湖区增幅最为明显（0.26°/年）。Mann-Kendall与Pettitt检验共同识别出2014年为关键转折点，水色演变由2000-2014年的下降趋势（?0.13°/年）转变为2014-2024年的上升趋势（0.44°/年），呈现“先改善、后恶化”的阶段性特征。SHAP归因分析表明，人为活动因子对水色年际变化的贡献显著高于自然气候因子，是驱动巢湖长期变化的主导因素。总体而言，前期治理措施成效显著，但后期社会经济压力增速超过治理能力提升，导致“压力-响应”关系失衡；同时，引调水工程和极端气候事件进一步加剧了水色年际波动与短期恶化风险。研究结果揭示了大型浅水湖泊在长期人为扰动下水色演变的阶段性、非线性与空间异质性特征，可为巢湖及同类湖泊的水环境治理与长效调控提供科学依据。

Large shallow lakes are important for regional water supply and ecological security, and their long-term water quality dynamics are of great scientific and practical importance for watershed management and ecological protection. However, these lakes are highly sensitive to external disturbances and ecologically vulnerable. Under the combined effects of intensive human activities and continuous environmental management, the extent to which their water quality exhibits staged and nonlinear responses remains poorly understood. In this study, Lake Chaohu, the fifth-largest freshwater lake in China, was selected as a representative large shallow lake. The Forel-Ule Index (FUI), which provides an integrated measure of water optical properties and water quality status, was used to characterize long-term water quality changes. Based on MODIS long-term remote sensing data from 2000 to 2024, a high-accuracy improved water color inversion model was applied to generate a long-term water color series, with an overall validation mean relative error (MRE) of 1.38% and root mean square error (RMSE) of 3.32°. The spatiotemporal patterns of water color and their driving factors under long-term human disturbance were then systematically examined. The results showed that the multi-year mean FUI of Lake Chaohu ranged from 12 to 15, with a mean hue angle (α) of 211.67° ± 2.58°, indicating an overall green-to-yellow water color. Spatially, a clear west-to-east decreasing gradient was observed, with mean α values of 213.13° ± 2.22°, 211.67° ± 2.58°, and 209.79° ± 2.16° in the western, central, and eastern lake regions, respectively. This spatial pattern was largely consistent with the distribution of major inflowing rivers and their differences in pollution loads. At the seasonal scale, water color showed a distinct bimodal pattern, with the highest α value in autumn (214.23°), indicating the most turbid conditions, and the lowest value in summer (208.74°), indicating the clearest conditions. Seasonal variations in natural factors, particularly wind speed, precipitation, normalized difference vegetation index (NDVI), and temperature, were found to regulate these intra-annual changes. Over the long term, the annual mean α increased at a rate of 0.15° yr?1 from 2000 to 2024, with the largest increase occurring in the eastern lake region (0.26° yr?1). The Mann-Kendall and Pettitt tests jointly identified around 2014 as a key transition point. The decreasing trend during 2000–2014 (?0.13° yr?1) changed to a significant increasing trend during 2014–2024 (0.44° yr?1), indicating a clear shift from an earlier improvement to later deterioration in the water environment. SHAP-based attribution further showed that anthropogenic factors, including gross domestic product (GDP), impervious surface area, nighttime light, and population, contributed substantially more to long-term water color changes than natural climatic factors and were identified as the dominant drivers. Early watershed pollution control and ecological restoration measures effectively reduced environmental pressure and promoted water color improvement. However, as urbanization and socioeconomic activities continued to intensify, management gains gradually weakened, resulting in an imbalance in the lake"s pressure-response relationship and a subsequent rebound in water color deterioration. Meanwhile, the Yangtze-to-Huaihe River Diversion Project and extreme climate events further intensified hydrodynamic disturbances and external pollutant inputs, increasing interannual variability and the risk of short-term water color deterioration. Overall, the results revealed distinct staged, nonlinear, and spatially heterogeneous patterns in the long-term water color evolution of large shallow lakes under sustained human disturbance. These findings provide a scientific basis for long-term water environmental management and adaptive regulation of Lake Chaohu and other large shallow lakes.