Analysis On Temporal-spatial Variations In Water Quality And Pollution Sources Of Honghu Lake

With the rapid development of economy and the acceleration of urbanization,all kinds of industrial and agricultural waste water and domestic sewage that is untreated or not up to the standards after treating has been discharged into water bodies,resulting in increasingly serious water pollution and threats to people's health.In this paper,taking water pollution status in Honghu as the research base,the water quality of 2016 is investigated in three watershed periods.Spatial and temporal variations characteristics of water quality are analyzed by using water quality spatial analysis,variance analysis,box-plots and principal component analysis.The pollution load of point source and non-point source is estimated and analyzed at the basin level.Finally,according to the characteristics of water pollution and the structure characteristics of pollution sources,scientific and reasonable measures for prevention and control of water pollution are put forward.The main conclusions are as follows:(1)The concentrations and spatial distribution characteristics of TN,TP,and NH3-N are closely related to the upstream water carried by the Four main canal.The concentration of nutrient elements in the Four main canal is hight,which has a significant influence on the concentration of nutrient indexes in Honghu Lake.TN,TP,and NH3-N show a trend of gradual improvement from northwest to southeast in each water period.Due to the shallow water level and the large wind waves,the Four main canal has a weak effect on the lake's DO.And pH value,COD,and Permanganate index are closely related to the lake itself,but the size of water storage affects the concentration of this indexes under the action of sediment agitation,neutralization or dilution.The high value of pH in Honghu is mainly due to the high background value.High concentrations of organic matter are associated with cage culture,sediment agitation,and domestic sewage of fishermen.(2)The one-way ANOVA analysis shows that there,are significant differences among all the indicators.The differences of TN and TP during three water periods are conspicuous.There are 7 indicators(the most)between medium and abundant period,and 4 indicators(the least)between the dry period and abundant period.It can be seen that significant water quality changes may be more likely to occur between medium and abundant period.The water quality during the dry and abundant period may be the closest.When there is too much or too little water storage capacity in Honghu,some indicators have less pollution.When the water volume is medium,the concentration is often higher,because the pollutants in the water can neither be dissolved in time nor diluted enough.The box-plots method analysis results show that the dry and abundant period are more likely to appear outliers.And the indexes with better stability are NH3-N,TN,COD in dry period,pH,SD,DO,TP in medium period,and Permanganate index in abundant period.The results of the principal component analysis show that the main influencing factors for each water period are nutrient indicators,followed by organic indicators.(3)The results of single-factor evaluation showed that,all the indicators cannot meet the class II standard except pH and NH3-N in certain period.TN is the worst with more inferior ?grade,and the highest value occurs in medium period.During the abundant period,the concentration of TP in the entire lake is the highest.The single factor evaluation results of the Permanganate index and COD during each water period in each area were not significantly different.In general,the order from good to bad of the water quality is:dry period(?)>abundant period(?)>medium period(inferior ?).The main pollution factors in dry,medium abundant period are TP,TN,and TP respectively.The results of the improved Nemerow pollution index method shows that the water quality didn't meet the standard of Class ?,and the water quality level was mainly ?-?,The order from good to bad is:dry period(?)>medium period(?)>abundant period(?).(4)The results of pollution load calculation show that the pollutants entering the rive of Honghu Basin was 5,2014.3 t/a for COD,9430.5 t/a for TN,1506.9 t/a for TP,and 4175.3 t/a for NH3-N.The contribution rate of non-point source pollution to each index is absolutely dominant,reaching more than two-thirds.The largest contributor to COD was agricultural non-point source(26%),followed by aquaculture(23%);The largest contributor to TN was agricultural non-point source(29%),followed by livestock(24%);The largest contributor to TP was livestock(47%),followed by agricultural non-point source(24%);The largest contributor to NH3-N was livestock(25%),followed by agricultural non-point source(23%).Agricultural non-point source and livestock breeding are the main sources of pollution.Jianli County is the main output of the four pollution indicators,especially for TP.The main reason is that Jianli County has a large area,large permanent population,and a large amount of sewage from agriculture,livestock,and aquaculture.The output of pollutants in Shashi District and Honghu City should not be ignored.(5)According to the structural characteristics of pollution,the key points are:to strengthen the treatment of industrial waste water and urban domestic sewage in Shashi District,to strengthen the urban sewage treatment in Jingzhou District,and to strengthen the control and governance to agricultural fertilizer and livestock pollution in Jiangling County,to strengthen agricultural fertilizer,livestock farming and urban domestic sewage in Jianli County;and to strengthen agricultural non-point source,aquaculture,livestock breeding management in Honghu City.