Annual Dynamics Of Nutrients In Water Column And Assessment Of Water Environmental Carrying Capacity In Three Typical Shallow Lakes Adjacent To Poyang Lake

Jiangxi Province boasts a great number of lakes and large freshwater capacity,about 86 lakes that water surface area more than 1 km2 and its total water area 3805km2, located in the middle-lower Yangtze River. Poyang Lake mainly imports the incoming water of five large rivers such as Gan River, Fu River, Xiu River, Raohe and Xinjiang River in Jiangxi Province, and finally the lake water flows into the main branch of Yangtze River after regulating the water volume by Poyang Lake, which is the largest freshwater lake in China and a river-connected huge lake as well. However,in recent years, the clean water of Poyang Lake has became turbid sharply year by year, and the risk of lake eutrophication is accelerating. As a typical huff-and-puff lake, the quality of peripheral inflowing water into Poyang Lake can tightly affect the whole water quality of Poyang Lake. Therefore, managing and impoving the quality of the inflowing water may be an inevitable way to construct the "clear channels" for Poyang Lake.An annual limnological investigation was conducted in the year of 2014-2015 in3 typical shallow lakes(Qingshan Lake, Yaohu Lake and Junshan Lake), adjacent to southwest bank of Poyang Lake at the suburb of Nanchang City, Jiangxi Province.Parameters of the water quality and eutrophic level were time-serially monitored to deeply understand the spatio-temporal eutrophic dynamics, driving mechanism and the water environmental carrying capacity for providing a new angle on the wise goverance and protection of different peripheral lakes around Poyang Lake. The main results and conclusion were as follows:(1) As to spatio-temporal dynamics of water quality in the three lakes, Qingshan Lake and Yaohu Lake have been found polluted by organic compounds, and TP contamination(in the GB3838-2002 standard from class IV to worse than class V)was found more serious in the both lakes above than Junshan lake. However, the water quality of Junshan Lake was general in class III. The water quality of the three lakes in winter and spring was both better than that in autumn and summer. Due to the occurrance of various pollution sources into lake water, the regional differences ofwater quality existed in most lake zones of the three lakes investigated.(2) There was obvious in the gradient of eutrophic level about the three lakes.Both Qingshan Lake and Yaohu Lake were already in steady eutrophic state, while Junshan Lake was in the mesotrophic state. However, with the surrounding environment deterioration and the expanding of breeding scale, the eutrophic level would gradually rise and the risk would be aggravered in the three lakes.As the N/P ratio indicated, the growth of phytoplankton algae be limited by nitrogen nutrient, and the quality of Junshan Lake was complex with fluctuation on the spatio-temporal dynamics, which is effected by different nutrient with different period. Because of special hydrological conditions, there be more rise of eutrophication compared with other shallow lakes in Ynagtze River basin,China.Among the different water quality factors in three lakes, the impact of some factors such as DO, pH, Conductivity, was weak for the contribution to water eutrophication,However, Chl_a, TN, TP were detected as the main driving factors in the progress of eutrophication, especially TN and TP. The continuous import of external contamination would make their eutrophication aggravate. Water temperature was also found as one of the important environmental factors affecting the seasonal trophic fluation of these three subtropic shallow lakes, and trophic states of the three lakes were detected as temperature dependence.(3) Because of the influence of the water volume, the water characteristics and the hydrological conditions, the water environmental capacity of different pollutants in the three lakes is not large. Therefore, as for the government of two eutrophic lakes,contrlling the import of exernal contamination is a effective way prevent further deterioration of water quality, and in recent years, the nitrogen and phosphorus pollutants load is higher than the water environmental capacity in Junshan Lake, so effective reduction of total pollutants amount input should be beneficial to the protection of water quality.(4) Overall, nitrogen in water column was one of the dominant factors affecting the environmental characteristics in these lakes, and phosphorus was the predominant factor affecting two eutrophic lakes(e.g. Qingshan Lake and Yaohu Lake). In the process of nutrient control, effective reduction of the nitrogen input should beconsidered in the eutrophic lakes while lowering the phosphorus discharge, especially,during the period of middle water temperature(15~25℃), and systematical regulation should be conducted in the mesotrophic lake(e.g. Junshan Lake) through the combination of N reduction and P sources control, in particular, during the period of high water temperature at more than 25℃. It would provide a new way to protect and manage water environment of these shallow lakes around Poyang Lake.