Study On Temporal And Spatial Variation Characteristics Of Iron,Manganese And Water Quality In Shankouyan Reservoir

Water resource is necessary to realize the sustainable development of human society.The water supply of reservoirs has greatly eased the pressure on water use,and water source reservoirs have become an important position for protecting water resources.In view of the lack of research on reservoir water quality stratification and insufficient understanding of the characteristics in reservoir iron and manganese and water quality temporal and spatial changes,this paper took Shankouyan reservoir,the important water source in Pingxiang,as a case study.Research on the characteristics of change,and used different water quality evaluation methods to obtain the comprehensive water quality status of the reservoir,discussed the causes and countermeasures of the temporal and spatial changes of the iron and manganese and water quality of the reservoir,and the results were as follows:(1)There was obvious thermal stratification in the water temperature structure of the reservoir.In areas where the water depth below than 30 m,the water temperature stratification in summer and autumn was a double thermocline structure,and the water temperature stratification gradually weakens in winter and behave a short-term mixed state in spring.There was no obvious water temperature stratification in the reservoir tail and the shallower water depth area.The dissolved oxygen concentration decreased with the increase of water depth.The bottom water below 30 m was in anoxic to anaerobic environment from summer to winter.On the whole,the dissolved oxygen concentration in summer and autumn was lower than that in winter and spring,and the concentration was highest in spring.The pH of the surface water was higher in summer and autumn than in winter and spring,and the bottom water was weakly alkaline to acidic,and the difference in the horizontal direction was small.(2)By analyzing the characteristics of the temporal and spatial changes of iron and manganese in the reservoir,the overall distribution was significant vertical,the bottom water has higher concentration,the iron and manganese concentration exceeded the standard,and the surface water concentration temporarily exceeded the standard in spring.In terms of time changes,the concentrations of iron and manganese were higher in August to October and January to March.In terms of spatial changes,the concentration of iron and manganese in the water increased roughly from the reservoir tail to the dam,and the time and range of the concentration of iron and manganese in front of the dam were longer than those at the reservoir tail.The concentration of iron and manganese in the bottom water in summer and autumn exceeded the standard of level Ⅲ.In winter,the concentration of iron and manganese in the middle of the reservoir to the dam was large,and the exceeding range rose to 24 m,showing a trend of diffusion.The concentration of iron and manganese in the water in the early spring became mixed,and then the concentration decreased.(3)By analyzing the characteristics of the temporal and spatial variation of the nutrient index of the reservoir,in terms of time,the total phosphorus concentration in summer and autumn was higher than that in winter and spring,and it exceeded0.05mg/L(the standard of level Ⅲ)in most periods,and exceeded 0.2mg/L(the standard of level Ⅴ)in the worst case;the change pattern of total nitrogen and ammonia nitrogen concentration was similar,high in spring and summer and low in autumn and winter.The concentration of total nitrogen in summer was between0.8～1mg/L,and the concentration of total nitrogen in spring was the highest value in the whole year,with an average concentration of 1.5mg/L;ammonia nitrogen was below 0.5mg/L(the standard of level Ⅱ)throughout the year and reach the standard of level I.In terms of spatial changes,the overall trend characteristics of the three indicators in all regions except the end of the reservoir were consistent in the horizontal direction.The vertical change characteristics were more obvious in summer but tend to be mixed in winter and spring.(4)The water pollution index method,the improved Nemero index method and the comprehensive water quality identification index method were used to evaluate the comprehensive water quality of the reservoir.The analysis showed that the overall water quality of the Shankouyan reservoir was not optimistic,and the comprehensive water quality was between the standard of level Ⅲ to Ⅳ,and there were great pollution hazards.According to the discrimination of the main pollutants,the main pollutants of the reservoir were total phosphorus,iron,manganese and total nitrogen are seasonally exceeding the standard.The comprehensive water quality in summer and autumn was worse than that in winter and spring,and the end and dam front area was worse than that in the middle area.By comprehensive comparison of the three methods,the improved Nemerow index method has a better applicability in the evaluation of water source reservoirs.(5)Through investigation and experimental research on pollutants,the input of substances in the tail area of the reservoir may be the main source of nitrogen and phosphorus pollutants.The reduction and release of pollutants in the sediment under anoxic or anaerobic environment not only made the nitrogen and phosphorus present a vertical distribution,but was also the main reason why the iron and manganese concentration of the water exceeded the standard.The increase in convection between the upper and lower water bodies in winter and spring may be the cause of the excessive concentrations of iron and manganese on the surface.In response to the causes of water pollution in Shankouyan reservoir,measures should be taken to reduce external source pollution,prevent and control internal source pollution,and strengthen reservoir operation and management methods.