Nitrogen Migration And Transformation In Hyporheic Zone Of Jinghe And Factors On Its Key Process

With the intensification of human activities,nitrogen pollution in surface water and groundwater has been a serious problem to human health and ecological environment.The hyporheic zone is an important transitional area for dynamic mixing of surface water and groundwater,it plays an important role in river ecosystem.More and more attention has been paid to the nitrogen cycle in the hyporheic zone.The study of the migration and transformation of nitrogen in the hyporheic zone and the influencing factors has a great significance for the development and utilization of the hyporheic zone,the prevention and repair of the surface water and the nitrogen pollution of the groundwater.Jinghe River was taken as the research background in this study,and the two periods of winter and summer with different temperature characteristics were selected from four different river sections?four research sites in Ning County,Changwu,Bin county and Jingyang?.On the basis of the field survey and the laboratory experiment,this study revealed the water exchange characteristics of the underflow zone of Jinghe,the law of nitrogen migration and transformation and the factors affecting the main process of nitrogen removal are discussed in the hyporheic zone.The main results are as follows:?1?The temperature varies with the depth of the sediments during the two period on the4 sites.The water exchange mode shows the groundwater recharge rivers in winter and the water supply to the river in the summer.The spatial stratification of water exchange volume various obviously,and the water volume increases with the increase of depth.The exchange volume in winter is 1.99⁴6.89 mm·d^-1,and the exchange volume in summer is 11.89¹03.25 mm·d^-1.?2?The migration of NO₃^--N in the four research areas was consistent in summer and winter,and decreased with the sediment depth.The sediment in the underflow zone can remove NO₃^--N in the river water by denitrification or ammonification,the decrease in summer was obviously than that in winter,NO₃^--N and NH₄⁺-N in Jingyang sediments had become a new N pollution source in Jingjing river.?3?The distribution of NH⁴⁺-N concentration in the four study area was different.The NH⁴⁺-N concentration showed a phenomenon of bottom enrichment in Ning county and Bin County,and the accumulation in winter is more obvious than that in summer.The ammonification of sediments in Changwu and Jingyang was obvious in summer.And the NH₄⁺-N in sediments of the Changwu hyporheic zone was mainly caused by surface water migration.?4?In summer,the pollutants in the water were mainly transport from the sediments,and the nitrification occured in the middle gap water in the process of groundwater recharge rivers in winter.The content of NO₂^--N was not changed in winter for its content was limited.?5?The denitrification process happened in Jingyang,the rate of denitrification was greater in summer than winter.And the rate in Bin County and Jingyang decreased with the increase of soil depth,and it was opposited in Changwu.The denitrification rate of sediment in the subsurface flow zone is affected by a variety of factors,including temperature,sediment pH,soluble organic carbon?DOC?,pH,water redox potential?Eh?and dissolved oxygen?DO?,which have significant effects on denitrification in river sediments.The main factors affecting denitrification rate in winter were temperature and DOC.The most important factors affecting denitrification rate in summer were DO,DOC and NO^3--N contents.pH,Eh,DO of surface water showed a significant negative correlation with denitrification rate in sediment.