Eutrophication Assessment And Discuss The High Nitrite Phenomenon In The Xiaoqing River Estuary

we investigated the nutrients, carbon and other parameters in the Xiaoqing River estuary and adjacent sea waters during 5 cruises in the 2005.11,2006.11, 2007.11, 2008.05and11. Researches and analysis have been made on pollution, eutrophication and the reasons for the high nitrite, and the main conclusions are as follows:1,Xiaoqing River estuary was seriously polluted as a result of direct emissions of untreated sewerage. The permanganate index in the majority of the waters was higher than the limited value(COD≤5mg/L)for the 4th categories of water according to the national seawater quality standard (GB3097-1997).Although the volume of organic matter showed little changes in water, the harm decreased annually according to our analysis.2,The average dissolved organic nitrogen, mainly ammonia, for the survey during the2005.11,2006.11,2007.11,2008.05and11were9.04mg/L,14.70mg/L,7.57mg/L,6.61mg/L,9.29mg/L respectively, which are all higher than the limited value(DIN≤0.5mg/L)for the 4th categories of water. The average phosphate for the surveyduringthe2005.11,2006.11,2007.11,2008.05and11were0.09mg/L,0.94mg/L,0.12mg/L,0.26mg/L,0.20mg/L respectively, above the limited value(PO43-≤0.045mg/L)for the 4th categories of water .except for the higher salinity water in the Laizhou Bay. The ratio of N to P was much higher that the value of the Redfield ratio, while the growth of plankton was not limited by the concentration of P. The average Chla value for the survey during the fall 2005,fall 2006,fall 2007,spring and fall 2008 were 19.01μg/L,11.13μg/L,4.53μg/L,13.17μg/L and 23.16μg/L.3,Xiaoqing River estuary was seriously polluted in terms of eutrophication, with waters of salinity below 20 advanced eutrophication, the majority waters of salinity above 24 intermediate eutrophication and , relatively small area oligotrophic. The degree of eutrophication in the Xiaoqing River estuary can be given as: spring 2008> fall 2008> fall 2006>fall 2007>fall 2005, indicating that eutrophication there has been deteriorated since 2005 and it was more serious in spring than in fall.5,The estuary of the Xiaoqing River existed the hypoxia phenomenon due to oxygen consumption of organic matter degradation in the waters.The level of dissolved oxygen(DO) during different cruises can be presented as: the fall 2008> spring 2008> fall 2005> fall 2007> fall 2006. Xiaoqing River. The nitrite level in Xiaoqing River estuary is slightly high, with the value in much water above0.1mg/L. Nitrite transparently increased in the estuary due to the nitrification occurring under the low level of DO and emission of the nitrite. Nitrite is greatly affected by the level of DO. The DO increase fosters the production of nitrite when the saturation of DO is lower than 70-80%, while the consumption of nitrite may be promoted if the saturation of DO is higher than 80-90%. In addition, the transformation of nitrite might be weaken by the decline of ammonia when the ammonia value is beneath 3-4mg/L.