Eutrophication characteristics and variation analysis of estuaries in China
LI Jun-long1,2, ZHENG Bing-hui2, ZHANG Ling-song1,2, JIN Xiao-wei1, HU Xu-peng3, LIU Fang1, SHAO Jun-bo3
1. State Environmental Protection Key Laboratory of Quality Control in Environmental Monitoring, China National Environmental Monitoring Center, Beijing 100012, China;
2. State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China;
3. Zhoushan Marine Ecological Environmental Monitoring Station, Zhoushan 316000, China
Eutrophication characteristics and variations were analyzed using four main statistical methods of box-plot analysis, cluster analysis, correlation analysis and principal component analysis, which were conducted based on natural geographic data and water quality monitoring data of 65 estuaries from 2007 to 2012 years in China. The results showed there was significant difference in eutrophication response indicators between the large-scale estuaries and small-scale estuaries. The eutrophication states of large-scale estuaries were more serious. It was also showed DIN, PO43--P and COD were the first principal component of eutrophication characteristics, followed as DO and Chl-a for second, and Depth, Tidal and Area for third. In addition, there was significant positive correlation between the Chl-a and TN input (P<0.01), DIN (P<0.01), PO43--P (P<0.05), inflow (P<0.01) and temperature (P<0.05), while there was significant negative correlation between chlorophyll a and tidal (P<0.05), salinity (P<0.01) and DO (P<0.01) in estuaries. It indicated the increase in nutrient input was the main factor which resulted in eutrophication symptoms. However, eutrophication state would be adjusted by typological factors and lead to different response characteristics among estuaries. The nutrient conversion efficiencies of estuarine tidal below 2.5m were higher than the ones above 2.5m. It is implied the eutrophication susceptibility to nutrient load could be regulated by changing water residence time, vertical mixing and light conditions. Furthermore, the Chl-a concentration were also influenced by water exchange with offshore area, biological predation and other nutrient forms supply in estuary. The differences and extent of eutrophication among estuaries were determined synthetically by nutrient inputs from human activities, as well as natural attributes of the estuary.
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