Preliminary Study On The Criteria And Standard Of Dissolved Oxygen In Water Environments Of China

Dissolved oxygen is an important index to measure the environmental quality of surface water.At present,the unified standard of dissolved oxygen in China is likely to lead to "under-protection" or "over-protection" of water bodies in different areas.A more accurate and scientific water environmental standard system is needed.By means of model simulation and long series data analysis,the regional differences of dissolved oxygen background values in surface water in China are quantitatively discussed;the temporal and spatial variation characteristics of dissolved oxygen concentration in surface water and the causes of water pollution in different regions of China in recent years are analyzed;the acute/chronic baseline values of dissolved oxygen in fresh water and seawater in China were calculated by using toxicity percentage sequencing method and species sensitivity distribution curve method.Based on the analysis of the influencing factors and biological effects of dissolved oxygen in China,some suggestions for revising the standard of dissolved oxygen in surface water in China are put forward.The main research conclusions are as follows:(1)The distribution of the background values of dissolved oxygen in the surface water of China shows obvious spatial and temporal changes due to the influence of temperature and altitude.The background value of dissolved oxygen in Chinese surface water varies significantly in seasons,and is high in winter and low in summer.The region presents a band distribution,gradually decreasing from north to south,and the whole country can be divided into three regions: the northern high dissolved oxygen background value region,the southern low dissolved oxygen background value region and the middle dissolved oxygen background value transition region.Moreover,under the background of global warming,the influence of the background value of dissolved oxygen is most obvious in the temperature sensitive northern region.(2)The temporal and spatial variation characteristics of dissolved oxygen and its main influencing factors in different regions of China from 2004 to 2018 were analyzed.Chinese surface water quality began to improve significantly in the second half of 2010,and in 2018,72% and 20.5% of the national controlled sections reached class I water quality standards for dissolved oxygen concentration and saturation,respectively.Dissolved oxygen saturation takes into account the influence of natural factors such as temperature and altitude on the background value of dissolved oxygen,which can better reflect the influence of human factors on dissolved oxygen,except for frozen water in winter.(3)The differences of sensitivity of aquatic organisms to dissolved oxygen in China were preliminarily analyzed.The acute/chronic baseline values of dissolved oxygen in fresh water and seawater in China were calculated by using toxicity percentage ranking method and species sensitivity distribution curve method.Species in freshwater areas of China differ greatly from the north to the south,and fish species,life stages,metabolic activities and oxygen demand are different in different seasons.Therefore,it is suggested to establish a standard of dissolved oxygen according to different regions and seasons.(4)Systematically review the standard setting system for dissolved oxygen in the United States,and analyze the existing deficiencies of the standard for dissolved oxygen in China and the enlightenment of the standard setting for dissolved oxygen in the United States.Based on the comprehensive consideration of the spatiotemporal variation characteristics and biological effects of dissolved oxygen in China,it is suggested to revise the dissolved oxygen standards regionally and seasonally,refine the dissolved oxygen standards corresponding to water body functions,reflect the antidegradation policy,and prevent further degradation of water bodies.