Study On The Spatial-temporal Distribution In The Sediment-Water Interface Of Yuehu Lake

During the governance of eutrophic lakes in the past,some studies have found that the internal source is the dominant factor during the process of eutrophication of the lake after effectively controlling the external source of the polluted lake,which maintains nutritional status of the lake for a long time.In this paper,we conducted a study on the typical shallow Yuehu Lake in Wuhan.By sampling and investigating in field and laboratory,we analyzed the characteristics of spatial and temporal variation of nutrients in sediments,pore water,and overlying water in Yuehu Lake.We discussed the migration process of sediment-water interface in Yuehu Lake,and investigated the correlations of nutrients in different media.The purpose of this study is to provide references for the governance of Yuehu Lake.The main results are as follows:(1)The concentration of total nitrogen(TN)in sediments was 1.36-2.10g/kg.With the increase of depth vertically,the concentration of TN decreased gradually.In spring,the concentration of TN was the lowest and the highest was in winter.The concentration of ammonia-nitrogen(NH4+-N)in sediments was much higher than that of nitrate-nitrogen(NO3'-N).As the depth increased,the concentration of NH4+-N increased,but the concentration of NO3--N decreased and the seasonal changes were different.Total phosphorus(TP)in sediment showed extensive accumulation on the surface,and the concentration of TP in autumn was the highest.At that time,sediment was the source of phosphorus.TOC/TN indicated that the source of organic matter on the surface of sediments was dominated by external sources,and the bottom was dominated by internal sources.In general,the nutrient loading of sediment was the highest in the western lake,and the pollution level in the center of the lake was relatively low.(2)The concentration of TN in the pore water was 3.966-10.998mg/l,and the spatial and temporal variation were similar to TN in sediment.The proportion of dissolved nitrogen in pore water was NH4-N>NO3-=N>nitrite nitrogen(NO2--N).The concentration of NH4+-N increased with depth vertically,which was contrary to that of NH4+-N.The concentrations of NO3--N and NO2--N decreased with depth,and the seasonal changes were inconsistent.The TP in pore water of Yuehu Lake showed extensive accumulation on the surface and the characteristic was most obvious in spring.The concentration of TP in pore water was highest in autumn,and the seasonal variation was similar to that of TP in sediment.The spatial and temporal distribution of nutrients in the pore water was greatly affected by sediments.(3)The concentration of TN in the pore water was much higher than that of the overlying water,and it was possible that the TN in sediment diffused in the water of the lake.The directions of diffusion of NH4+-N and NO2--N were from the sediment to the overlying water.The NO3--N in the overlying water diffused to the sediments.In different seasons,the directions of migration and release of TP in pore water and overlying water were not the same.Internal release from sediment is important which affects the water environment of Yuehu Lake.(4)In addition to the NH4+-N in sediment,there were significant correlations between the various forms of carbon,nitrogen,and phosphorus in sediment of Yuehu Lake,and the interactions were strong.The TN and TOC in sediments of Yuehu Lake were positively correlated with the TN in pore water.There is a significantly positive correlation between the NH4+-N in pore water and the NH4+-N in overlying water,and there existed the migration and diffusion trend.The migration of nutrients in the sediment-water interface of Yuehu Lake was determined by the concentration gradient,and the specific situations of various nutrients in different media were influenced by both internal and external factors.