Abstract:

Jiangxi province lies in the southern bank of the middle and lower reaches of the Yangtze River in China.It belongs to eastern plain lake area and is the highest one of the provinces for the owing rate of fresh lakes.In addition to the overlarge lake for Poyang Lake,the remaining 90% are small or medium size lakes which area is less than 100 km2.The 25 investigated lakes,where the total area is nearly 800 km2,are distributed in the mainstream of Yangtze River system,Xiu River system and Poyang Lake system.The 175 monitoring points were set in the 25 investigated lakes,and the quarterly water quality indexes including chlorophylla(Chl.a),transparency(SD),permanganate index(CODMn),total phosphorus(TP) and total nitrogen(TN) were monitored and analyzed between March 2010 to February 2011 for 25 small or medium size lakes in Jiangxi province.According to the data analysis of above water quality monitoring indexes,the seasonal and annual trophic state of investigated lakes was evaluated by comprehensive eutrophication state index (TLI) method and the probability of eutrophication was calculated in every season and the whole year.On the basis of annual trophic state,the confidence interval was be found in different trophic state using Bootstrap method,and then the recommended values for eutrophication control indicators were be inferred.The results indicated that the probability of eutrophication for investigated lakes in spring and summer was near,autumn was the highest,and winter was the lowest.In spring,summer and winter,the trophic state of investigated lakes was mainly on mesotropher; in autumn,the proportion of mesotrophic lakes was decreased and the proportion of eutrophic lake was increased.In the whole year,the proportion of eutrophic and mesotrophic lakes were 32% and 68%,respectively.The recommended values for eutrophication control indicators of SD,TP,Chl.a and CODMn for small or medium size lakes in Jiangxi province should be respectively at 044 m,005 mg/L,1000 mg/m3 and 270 mg/L.This research provides basic data and theoretical basis for eutrophication regionalization control in our country