Abstract:

 The Dongting Lake located in north of Hunan Province and south bank of middle reaches of the Yangtze River is the 2nd largest freshwater lake in China.It not only is the important fishery water， but also the precious fishery genetic resources center. Over the past few decades， as the human population growth，development of industry and agriculture， and the acceleration of urbanization， the extent of pollution in the Dongting Lake is also increased. Nitrogen （N） and phosphorus （P） are the two most important elements in natural water bodies， because N and P can directly influence the primary productivity of water bodies， then the aquatic community will be changed.This article is based on the 20002011 monitoring data of the Dongting Lake fishery environment to analyze the temporalspatial distribution of total nitrogen（TN）， total phosphorus（TP）， ammonia（NH3-N） and nitrate nitrogen（NO3-N） concentrations in different fishery waters of the Dongting Lake. The results show as follows. （1） In the Dongting Lake， the mean concentration of TN， TP， NH3-N and NO3-N were 143±041 mg/L， 009±003 mg/L， 032±005 mg/L and 063±011mg/L， respectively.The maximum of TN was 480 mg/L， appeared at Lujiao sampling point in May of 2009，and the maximum of TP was 0417 mg/L， appeared at Lujiao sampling point in January of 2008. （2）Oneway ANOVA results of mean annual concentration of nitrogen and phosphorus between 2000 and 2011 showed that the differences were significant （P<005）.Except for TP， mean annual concentration of TN， NH3-N and NO3-N showed the rising trend， and the differences of mean concentration of nitrogen and phosphorus during low water period， wet season and median water period were also significant（P<005）.The mean concentration of TN at median water period and TP at low water period were both the highest.（3） Simultaneously，the differences of mean concentration of nitrogen and phosphorus on spatial distribution were also significant （P<005）.The maximum of mean concentration of TN， TP and NO3-N appeared at SanJiangkou， and the maximum of mean concentration of NH3-N appeared at the East Dongting Lake According to reports in the literature and actuality analysis， the industrial waste water and municipal sewage were the greatest sources of pollution in Sanjiangkou area and the East Dongting Lake.（4） Nonpoint pollutant source which accounted 94%～99% of the total amount of pollutant for the Dongting Lake was the major way， also the main factors to enhance the Dongting Lake water eutrophication. The nonpoint pollutant source mainly included agricultural pollution， urban sewage， animal husbandry and aquaculture pollution.（5）During all of the monitoring years， the water quality，based on Peoples Republic of China Surface Water Environment Quality Standards（GB38382002），was defined as III only in 2000， and defined as IV in most of the other years，and as V in parts of those years. According to The Water Quality Standards of Fisheries and the demands of fish for the environment of water quality， the water environment of the Dongting Lake was in the state of medium pollution，which was not suitable to fish breeding， early development， feeding， wintering and the other life behaviour