Study On The Chang Of The Eutrophication At Wenzhou Qujiang River Estuary

The Oujiang River is the second largest river in Zhejiang Province, flowing through the southern region of Zhejiang with fast economic and social development in recent years, the pollutant fluxes from the Oujiang River into the sea increased constantly, resulting in a serious threat to the environment quality of the Oujiang River Estuary, eutrophication is becoming more and more serious. Study on the change of the eutrophication at Oujiang River Estuary has a certain reference function to the management departments to strengthen the pollution management of Oujiang River coast, improve the water quality of Oujiang River Estuary, and restore the ecosystem of the ocean.This essay was based on the three marine researches that the Second Institute of Oceanography of State Oceanic Administration surveyed in April 2010, May 2012 and May 2013, in the Oujiang River Estuary and its adjacent seas. The water quality environment was analyzed, and the eutrophicated level by different eutrophicated methods was evaluated. The main conclusions are as follows:(1) The results of the sea water quality environment investigation and evaluation in Wenzhou Oujiang River Estuary and its adjacent seas.Based on the survey data, evaluating the pH, dissolved oxygen, COD, inorganic nitrogen, active phosphate, oil and heavy metals (Cu、Pb、Zn、Cd) and so on by the means of water quality single factor evaluation method according to the concentration valve of water environmental factors which were list in<sea water quality standard> (GB3097-1997). It can be seen from the evaluation results that inorganic nitrogen and active phosphate exceeded standard severely in these three voyages, and the COD concentration of some stations were out of limits in 2010 and 2012. In the horizontal distribution of water quality parameters, the content of COD, inorganic nitrogen and active phosphate in the water generally decreased from Oujiang River Estuary and coast to seaward side. The annual variation of the three water quality parameters was large. The change trend of COD concentration showed a downward trend year by year; the concentration of inorganic nitrogen had little change from 2010 to 2012, and have a significant rise in 2013; Active phosphate concentration change trend shows "V" type.(2) The eutrophication analysis of Wenzhou Oujiang River Estuary and its adjacent seasThis essay used the eutrophication index method and potential eutrophication assessment method for the eutrophicated level evaluation of Oujiang River Estuary and its adjacent seas, both methods’ evaluation results showed eutrophication. Eutrophication index method is the most widely used evaluation method in domestic, and the results showed the trend that eutrophicated level gradually decreased from estuaries and coastal waters to outward side waters. The potential eutrophication assessment method can be used to draw conclusions on the basis of the eutrophication index method, that which element had a limited impact. The evaluation results demonstrate the characteristics of phosphorus limitation in this sea area.