Temporal-spatial Variation Of Chlorophyll A And Eutrophication Evaluation In Five Lakes Of Hanyang

To understand the current situation of eutrophication in Hanyang Lakes,we monitored and investigated the water quality and chlorophyll a of the five Lakes including Houguan Lake,Sanjiao Lake,Nantaizi Lake,Moshui Lake and Longyang Lake.We studied the temporal-spatial variation of chlorophyll a and the relationship with environmental factors,and evaluated the eutrophication states of the five lakes.The study results are expected to provide basic information for pollution control and ecological restoration of lakes in Hanyang region.The main results are as follows:Among the five laks,the water quality of Houguan Lake was best,and that of Longyang Lake was worst.The average transparency of Houguan Lake was 0.55±0.15m,and that of other lakes ranged from 0.35 to 0.42m.The lowest chemical oxygen demand,total nitrogen and total phosphorous were observed in Houguan Lake,with the values were 27.45±10.71mg/L,1.12±0.45mg/L and 0.15±0.13mg/L,respectively.The highest chemical oxygen demand,total nitrogen and total phosphorous were observed in Longyang Lake,with the values were39.21±11.63mg/L,2.96±6.15mg/L,and 1.71±0.79mg/L,respectively.There was no significant difference for these three paramters among other three lakes.The average content of chlorophyll a in Houguan Lake was the lowest(29.01±13.26mg/m~3),and that in Longyang lake was the highest(165.32±86.18mg/m~3).The average content of chlorophyll a in Sanjiao Lake,Nantaizi Lake and Moshui Lake was 81.16±50.48mg/m~3,111.66±56.59mg/m~3 and 127.14±57.69mg/m~3,respectively.The content of chlorophyll a of the five lakes showed significant seasional variation,the peak content of chlorophyll a in four lakes except Houguan Lake was observed in October.Multiple stepwise regression analysis showed that total nitrogen,chemical oxygen demand and transparency were the key factors affecting the spatial distribution of chlorophyll a in the five lakes in Hanyang region.The evaluation based on the content of chlorophyll a showed that Houguan Lake and Sanjiao Lake were eutrophic,and the other three lakes were severely eutrophic.The evaluation based on comprehensive nutrition state index showed that Houguan Lake was in the level of medium eutrophication,with the index of 60.95,and the other lakes in the level of severe eutrophication,with the indices of 70.70,74.62,73.82 and 82.51.