Abstract
As one of the few remaining lakes that are freely connected with the Yangtze River, Poyang Lake exhibits large annual water level (WL) fluctuations. In this study, weekly samples were collected at the north end of Poyang Lake from September 2011 to December 2012, and we investigated the mechanism of limnological responses to fluctuations in the WL. The study covers three seasons that were associated with WL fluctuations ranging from 8 to 19 m. Spearman's rank correlations and multivariate non-metric multidimensional scaling analyses indicated that low and high WL periods differed in a number of water quality characteristics. The low WL period coincided with the non-growing season and was associated with the peak concentrations of nitrogen, the highest turbidity (Turb), and the lowest water temperature. The high WL period was mainly characterized by enhanced chlorophyll a concentration. Spearman's rank correlations revealed positive relationships between the WL and the concentrations of NO3-N and PO4-P and negative relationships between the WL and the Turb, total nitrogen, total phosphorus, NO2-N, and NH4-N concentrations. All results support the conclusion that the large WL fluctuations are the principal drivers for physicochemical variables in this floodplain lake ecosystem.
Highlights
The largest freshwater lake in China, Poyang Lake (28 W220– 29 W450N, 115 W470–116 W450E), which is downstream of the Yangtze River, has a surface area of 3,283.4 km2 and an average depth of 8.4 m
The main aims of the study are as follows: What is the water environment in the Yangtze River–Poyang Lake system? What is the difference between the high and low water level (WL)? What influences would appear in Poyang Lake if the WL of the lake was maintained by a floodgate? The results of this study can be extended to evaluating similar problems in other catchment areas, such as the Dongting Lake to the west of Poyang Lake, and to lake–river systems in other regions and continents
During the study period (2011–2012), the WLs of Poyang Lake at Xingzi station varied from 7.8 m to 19.2 m
Summary
The largest freshwater lake in China, Poyang Lake (28 W220– 29 W450N, 115 W470–116 W450E), which is downstream of the Yangtze River, has a surface area of 3,283.4 km and an average depth of 8.4 m. The lake–river interactions are complicated by surface discharges into Poyang Lake from five sub-tributaries (the Xiushui, Ganjiang, Fuhe, Xinjiang, and Raohe Rivers) in the Poyang basin and by climate variations in the region The outcomes of these interactions determine the lake level and its annual and interannual variations, the expansion and contraction of the lake area and the droughts and floods in the lake basin. Zhang et al ( ) reported that the operation of the TGD intensified the extremes of the wet and dry conditions downstream of Poyang Lake, which, in particular, further reduced the WL over the dry period from late summer to autumn These changes can put serious pressure on communities in the lake basin, e.g., WLs force changes in the water chemistry and biota both directly and indirectly
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