Study On The Water Pollution Situation And Nitrite Distribution And Its Origin In The Xiaoqing River Estuary

In the last few years, Chinese economy has developed rapidly. Lots of rivers withsmall basin are affected by the emissions of industrial wastewater and sewageseriously. Although the flux of the contaminants of the river mentioned above is lessthan that of the major rivers, the concentration of the contaminants into the sea reach ahigh level and destroy the estuaries and coastal waters. Among them, Xiaoqing Riverin Shandong Province is one typical river of these severely polluted. Plenty of organicmatter and nutrients were carried through Xiaoqing River into the Laizhou Bay,resulted in severe damage of Laizhou Bay water bodies. This contamination causeddamage to the fishery resources and the ecosystem. Local economic developmentswere constrained. Therefore, according to the study, reference data and early warningwere provided to the further management of the pollution status, fisheries andaquaculture production of Xiaoqing River and Laizhou Bay.We investigated the nutrients, carbon and other parameters in the Xiaoqing Riverestuary and adjacent sea waters during2cruises in the2010.5and2010.9, andintegrated the historical data of2005.11,2006.11,2008.5,2008.11and2009.8toanalyse the changes of the water quality and discuss the nitrite distribution and itsinfluencing factors. The main conclusions are obtained as follows:1. Xiaoqing River estuary was seriously polluted as a result of direct emissions ofuntreated sewerage. The average dissolved organic nitrogen （mainly ammonia） comeup to7.98mg/L, which are all higher than the limited value（DIN≤0.5mg/L）for the4th categories of water. The permanganate index in the majority of the waters washigher than the limited value （COD≤5mg/L） for the4th categories of wateraccording to the national seawater quality standard （GB3097-1997）. And thepercentage of labile TOC was about30%. The estuary of the Xiaoqing River showedthe phenomenon of hypoxia and high pCO₂value due to oxygen consumption oforganic matter degradation and nitrification in the waters,which resulted in low pHvalue. Xiaoqing River estuary was seriously polluted in terms of eutrophication, withwaters of salinity below15hyper eutropher. With the increase of the salinity, the levelof eutrophication become slightly, but still above mesotropher. 2. The nitrite concentration in Xiaoqing River estuary is between0.02and0.61mg/L, slightly higher than the average of rivers all around the world. With theraise of salinity, the distribution of NO₂-N became non-conservation.The highconcentration of NH₄-N in the freshwater fell down in the sea water, while theproportion of NO₃-N increased. It indicated that during the mixing process offreshwater and sea water, nitrification happened and NO₂-N was accumulated.Through the relationship between exceeded CO₂and AOU, it can be summed up thatthe main reasons of hypoxia and high pCO₂value in Xiaoqing River estuary were theprocess of partly and completely nitrification, also leaded to high NO₂-Nconcentration.3. The degree of nitrification in Xiaoqing River estuary was closely related to theDO saturation and NH₄-N concentration. When DO%was between30%and90%,NO₂-N concentration raised. Excessive low and high DO%were bad for theaccumulation of NO₂-N. Also low NH₄-N in sea water would hinder nitrification. Inaddition to, temperature, pCO₂and pH can also impact the process of nitrification.4. The regularity of distribution between the rate of NO₂-N accumulation andDO%was showed as follows: when DO%was between15%and75%, the rate offormation was higher than consumption. The rate of NO₂-N accumulation reached apcak when DO%was about45%. Lower than15%did bad to the accumulation, whileexceeded than75%, NO₂-N would be oxidized into NO₃-N, and the rate fell down.To sum up, most pollutional parameters in Xiaoqing River estuary weresubstandard and the annual variation tendency was not shown as decline. Thepollution in Xiaoqing River estuary was still serious. Therefore the departmentconcerned should pay much attention to the pollution prevention and control.