China has made considerable efforts to mitigate the pollution of lakes over the past decade, but the success rate of these restoration actions at a national scale remains unclear. The present study compiled a 13-year (2005-2017) comprehensive dataset consisting of 24,319 records from China's 142 lakes and reservoirs. We developed a novel Water Quality Index (WQI-DET), customized to China's water quality classification scheme, to investigate the spatio-temporal pollution patterns. The likelihood of regime shifts during our study period is examined with a sequential algorithm. Our analysis suggests that China's lake water quality has improved and is also characterized by two WQI-DET abrupt shifts in 2007 and 2010. However, we also found that the eutrophication problems have not been eradicated and heavy metal (HM) pollution displayed an increasing trend. Our study suggests that the control of Cr, Cd and As should receive particular attention in an effort to alleviate the severity of HM pollution. Priority strategies to control HM pollution include the reduction of the contribution from mining activities and implementation of soil remediation in highly polluted areas. The mitigation efforts of lake eutrophication are more complicated due to the increasing importance of internal nutrient loading that can profoundly modulate the magnitude and timing of system response to external nutrient loading reduction strategies. We also contend that the development of a rigorous framework to quantify the socioeconomic benefits from well-functioning lake and reservoir ecosystems is critically important to gain leeway and keep the investments to the environment going, especially if the water quality improvements in many Chinese lakes and reservoirs are not realized in a timely manner.

In comparison to lentic systems, the species composition and community structure of phytoplankton in lotic habitats are still poorly understood. We investigated the spatial and temporal dynamics of the phytoplankton community in a German lowland river, the Kielstau catchment, and the relationships with environmental variables. Among the 125 taxa observed, Desmodesmus communis, Pediastrum duplex and Discostella steligera were dominant species at lentic sites while Tabellaria flocculosa, Euglena sp., Planothidium lanceolatum, Cocconeis placentula and Fragilaria biceps dominated at lotic sites. Remarkable spatial and temporal variations of the phytoplankton community were revealed by non-metric multidimensional scaling. Canonical correspondence analysis indicated that physical factors (e.g. hydrological variables) and major nutrients [e.g. total phosphorus, dissolved inorganic nitrogen (DIN)] were of equal importance controlling the variation in structure of riverine phytoplankton assemblages. Weighted averaging regression and cross-calibration produced strong models for predicting DIN, water temperature (WT) and total suspended solid (TSS), which enabled the selection of algal taxa as potentially sensitive indicators: for DIN, Ulnaria ulna var. acus, U. ulna, D. communis and Euglena sp.; for WT: D. steligera, Scenedesmus dimorphus, D. communis and Euglena sp.; for TSS, Nitzschia sigmoidea, D. communis and Oscillatoria sp. The results from this relatively small survey indicate the need for further monitoring to gain a better understanding of riverine phytoplankton and to capitalize on the environmental indicator capacity of the phytoplankton community.