Spatio-temporal Variability Of Principal Pollutants In Laizhou Bay In Nearly30Years And Establishment Of Evaluation Index System In Water Of Xiaoqing River Estuary

In the21st century, the Bohai Sea region becomes hot spot for social and economicdevelopment. Economic development and environmental protection of marine ecosystems havebecome increasingly prominent. Marine ecological and environmental problems take more andmore attention.Based on the project “research on estuary marine environmental quality comprehensiveevaluation method” of State Oceanic Administration, we explore pollution concentration changesin time and space nearly three decades since1980in Laizhou Bay by analysis historical monitoringdata about the Laizhou Bay pollution, taking inorganic nitrogen (DIN), inorganic phosphorus (DIP)and chemical oxygen demand (COD) for example. Meanwhile, duilding evaluation index system forXiaoqing River estuary based on the water quality status and characteristics. Then evaluate thewater quality of this area, in order for the North Sea area environmental quality comprehensiveevaluation methods provide reference.（1） It was shown from the study results that the proportion between high-water period andlow-water period of the three pollutants were1.26,1.07and1.06, considered that they wereproduced by rivers flow. DIN was the principal pollutant in Laizhou Bay, whose concentration is3.2times in1990s compared with1980s, and added38%in2001-2008, and then beyond the classIII of sea-water quality standards after2004. The proportion of NH4-N in DIN decline from70%-85%to20%after90s. While the concentration of DIP and COD up to the class I, but DIP stillhad the rising trend. Shown from regional distribution, Western was a high value area of DIN andDIP influencing by the estuary of yellow River and Xiaoqing River. The water of center and esternarea was better, but concentrations of DIN and DIP in southern area have been far more thanwestern after2004. It should be noticed that the primary pollution source of Laizhou Bay translatedfrom yellow River estuary to the southern rivers.（2） Through the analysis of historical pollution of Laizhou Bay and the current water qualitycharacteristics of Xiaoqing River estuary, combined with the correlation analysis and principalcomponent analysis, screened quality evaluation indicators of Xiaoqing River estuary: total suspended particles (TSS), dissolved oxygen (DO), non-ionic ammonia (NH3), dissolved inorganicnitrogen (DIN), phosphate (PO4-P), COD and petroleum. Established the evaluation criteria andlevels of index weight and water quality evaluation system, and then evaluated the water quality ofXiaoqing River estuary in2011. The results are as follows: In May2011and August, WQI in areaof S≤20are0.24, the level of water quality is poor. In the area of S>20, WQI is0.81and0.66,respectively, the water quality level were excellent and good.（3） In current, the main threat of water quality of Xiaoqing River estuarine is prominentinorganic nitrogen and oil pollution problems; the hypoxia phenomenon of water which salinity isless than20is still more serious, and closely related to the dissolved oxygen content andnitrification; because of the potentially harmful of phosphates, the weight in the evaluation processis larger and small changes will have an impact on water quality evaluation level. So it should betreated with caution.This method not only meet the demand for comprehensive evaluation of thewater quality and at the same time， clear the traceability of the main influencing factors,convenient for management of administrator.