LAUSR

Abstract Long-term monitoring data, including physical, chemical and biological environmental parameters, were collected every 3 months at 15 sites in Lake Poyang from 2009 to 2015. A cluster analysis divided the 15 sampling sites into four significant spatial groups (Spatial Groups I–IV, respectively) that generally reflected the trends from north to south. The underwater light conditions in the northern spatial group (SG I) were significantly poorer than those in the other areas. All nutrient variables reached relatively higher concentrations in the southern spatial group (SG III) and the northern parts of the lake. At the annual scale, the water quality in Lake Poyang generally worsened during the study period, and the degradation was severe compared with that in the period from 1987 to 1988; the water quality also exhibited strong seasonality. The characteristics of the lake and the freshwater input from the watersheds with high human activity are the main contributors to the spatial heterogeneity in water quality in Lake Poyang. Dredging appears to play an important role in the underwater light conditions and nutrient distributions in Lake Poyang, especially in SG I, and non-point source pollution from industry and upstream mines may contribute to the high nutrient concentrations in SG I and SG III. Because human exploitation of the Lake Poyang Basin has increased, external pollution loads are the likely causes of the generally deteriorating water quality at the annual scale. Additionally, combined with the external loads, substantial fluctuations in water level contribute to a strong seasonality in water quality, especially variable nutrient concentrations. Degradation in Lake Poyang has occurred more rapidly than in the other 4 largest freshwater lakes in China. Our findings may be beneficial for preventing and controlling water pollution in Lake Poyang.