Application Of The Phase Ⅱ Coastal Eutrophication Assessment Methods

Eutrophication of coastal area due to anthropogenic nutrient fluxes increase into the sea, has been a threat to the coastal marine ecosystem health and harmful to the normal use of the coastal waters. Therefore, seeking a proper method to evaluate the coastal eutrophication has been one of the focuses for the researchers.In this study, based on the framework of the Pressure-State-Response model (P-S-R), we selected five symptom indicators, such as chlorophyll a, phytoplankton diversity (Shannon-Weaver) index, dissolved oxygen levels, sediment organic carbon and occurrences of red tide, which respond to the coastal eutrophication, to establish a Phase Ⅱ method for the coastal eutrophication assessment in Guangxi area.The established method was applied to assess the trophic status in Qinzhou bay, Fangcheng bay and Tieshan bay located in Guangxi Zhuang Autonomous Region. The assessment can be concluded as follows:The anthropogenic inorganic nitrogen from land source accounted for36.7%share of inorganic nitrogen in Qinzhou Bay, and the impact of the anthropogenic inorganic nitrogen in Qinzhou bay was moderate. Although the chlorophyll a, phytoplankton diversity index, dissolved oxygen levels and occurrences of red tide in this coastal area showed a slight abnormity in Qinzhou bay, the eutrophic condition of Qinzhou bay was assessed to be in lower grade by evaluating the nutrient input pressure, the frequency and area of eutrophic zone and the measures for reducing the nutrients into the sea flux.The anthropogenic inorganic nitrogen from land source accounted for45.7%share of inorganic nitrogen in Fangcheng Bay, and the impact of the anthropogenic inorganic nitrogen in Fangcheng bay was moderate. Although the chlorophyll a and phytoplankton diversity index in this coastal area showed a slight abnormity in Fangcheng bay, the eutrophic condition of Fangcheng bay was assessed to be in low grade by evaluating the nutrient input pressure, the frequency and area of eutrophic zone and the measures for reducing the nutrients into the sea flux.The anthropogenic inorganic nitrogen from land source accounted for23.1%share of inorganic nitrogen in Tieshan Bay, and the impact of the anthropogenic inorganic nitrogen in Tieshan bay was low. Although the chlorophyll a, and phytoplankton diversity index in this coastal area showed a moderate abnormity in Tieshan bay, the eutrophic condition of Tieshan bay was assessed to be in low grade by evaluating the nutrient input pressure, the frequency and area of eutrophic zone and the measures for reducing the nutrients into the sea flux.