Water clarity (Secchi disk depth: SDD), as a proxy of water transparency, provides important information on the light availability to the water or lake ecosystem. Shallow lakes have been experienced dramatic environmental and climatic change. This study demonstrated using combination of long-term MODIS and in-situ measurements to track the dynamics of SDD with these environmental and climate changes in shallow water environments. We selected a typical turbid shallow Lake Taihu as our case study. Based on MODIS-Aqua data, an empirical model for estimating SDD was developed and validated. Subsequently, we employed the proposed model to derive the spatial and temporal SDD distribution patterns of Lake Taihu from 2003 to 2015. Combining MODIS-derived SDD time series of 2003–2015 and long-term in-situ SDD observations dated back to 1993, we elucidated SDD long-term variation trends and driving mechanism. Deteriorating water clarity from the long-term SDD observations indicated that Lake Taihu became more and more turbid and water quality was decreasing. Increasing in cyanobacterial bloom area, as a result of decreasing in wind speed and eutrophication, may partially be responsible for the decreasing trend. A predicted future decrease in the wind speed in Lake Taihu region could enhance the formation of cyanobacterial blooms and consequently lead to a further decrease in water clarity. This study suggested that coupling remote sensing monitoring and long-term in-situ observations could provide robust evidence and new insights to elucidate long-term dynamics in aquatic ecosystem evolution.

水透明度（Secchi盘深度：SDD）作为水透明度的代名词，提供了有关水或湖泊生态系统可用光的重要信息。浅湖经历了剧烈的环境和气候变化。这项研究证明了结合长期MODIS和原位测量来跟踪SDD在浅水环境中随这些环境和气候变化的动态变化。我们选择了一个典型的浑浊浅湖太湖作为我们的案例研究。基于MODIS-Aqua数据，开发并验证了估算SDD的经验模型。随后，我们使用提出的模型来推导2003年至2015年太湖的空间和时间SDD分布模式。结合了MODIS得出的2003-2015年SDD时间序列和可追溯到1993年的长期原位SDD观测，我们阐明了SDD的长期变化趋势和驱动机制。长期的SDD观测表明，水的透明度下降，表明太湖变得越来越浑浊，水质下降。风速和富营养化程度降低的结果是蓝藻开花面积的增加可能是造成这种下降趋势的部分原因。预计太湖地区风速未来的下降可能会增强蓝藻水华的形成，从而导致水的透明度进一步下降。这项研究表明，结合遥感监测和长期就地观​​测可以为阐明水生生态系统演变的长期动态提供有力的证据和新见解。长期的SDD观测表明，水的透明度下降，表明太湖变得越来越浑浊，水质下降。风速和富营养化程度降低的结果是蓝藻开花面积的增加可能是造成这种下降趋势的部分原因。预计太湖地区风速未来将下降，这可能会增强蓝藻水华的形成，从而导致水的透明度进一步下降。这项研究表明，结合遥感监测和长期就地观​​测可以为阐明水生生态系统演变的长期动态提供有力的证据和新见解。长期的SDD观测表明，水的透明度下降，表明太湖变得越来越浑浊，水质下降。风速和富营养化程度降低的结果是蓝藻开花面积的增加可能是造成这种下降趋势的部分原因。预计太湖地区风速未来的下降可能会增强蓝藻水华的形成，从而导致水的透明度进一步下降。这项研究表明，结合遥感监测和长期就地观​​测可以为阐明水生生态系统演变的长期动态提供有力的证据和新见解。风速降低和富营养化的结果可能部分归因于下降趋势。预计太湖地区风速未来的下降可能会增强蓝藻水华的形成，从而导致水的透明度进一步下降。这项研究表明，将遥感监测与长期就地观​​测结合起来，可以为阐明水生生态系统演变的长期动态提供有力的证据和新见解。风速降低和富营养化的结果可能部分归因于下降趋势。预计太湖地区风速未来的下降可能会增强蓝藻水华的形成，从而导致水的透明度进一步下降。这项研究表明，结合遥感监测和长期就地观​​测可以为阐明水生生态系统演变的长期动态提供有力的证据和新见解。