Nitrogen Distribution And Its Influencing Factors In Poyang Lake Sediments

In order to study the distribution of sediment nitrogen and its relationship with environmental factors in Poyang Lake,this paper divided Poyang Lake into three parts:the northern lake,the central lake,and the river into the lake.Overlying water and sediment were collected in different areas during wet,normal,and dry seasons.Meanwhile,on-site environmental factors（wind speed,water depth,transparency,water temperature,electrical conductivity,and p H）were recorded.The water quality index of overlying water was determined,and the correlation between environmental factors and water nitrogen was obtained by using Pearson analysis method.The distribution characteristics of different nitrogen contents in water were also discussed.The eutrophication state of overlying water was analyzed by sampling comprehensive nutrition index method,and the source of water pollution was obtained by using principal component method.Secondly,four kinds of convertible nitrogen（IEF-N,WAEF-N,SAEF-N,SOEF-N）were extracted from sediments by fractional leaching method,and some indexes（TP,p H,organic matter,and Chl.a）of sediments were determined.The correlation between the sediment indexes and the physical and chemical indexes of overlying water and TN and four kinds of convertible nitrogen in sediments was analyzed.Then,based on the previous results,three conditions of water temperature,p H and disturbance were selected for nitrogen release intensity test,to explore the variation law of the release intensity of total nitrogen,ammonia nitrogen and nitrate nitrogen in sediments under different factor levels.The main research results are as follows:（1）Water depth,transparency,temperature,dissolved oxygen,wind speed,p H,COD_Mnand TP were closely related to water nitrogen in Poyang Lake.During the wet season,TN content in water body was 1.36mg/L～4.16mg/L,especially in the central lake area.The ammonia nitrogen content was 0.16mg/L～0.30mg/L,and the ammonia nitrogen content was higher in the lake area.The content of nitrate nitrogen is 0.26mg/L～1.29mg/L,and the content is larger in the western region of the central Lake District.In normal water period,the contents of total nitrogen,ammonia nitrogen and nitrate nitrogen ranged from 1.68mg/L to3.67mg/L,0.17mg/L to 0.43mg/L,and 0.81mg/L to 1.52mg/L.TN content was higher in the central lake area,NH₄⁺-N content was higher in the southeastern river flowing into the lake area,and nitrate nitrogen content was higher in the western area of the central Lake area.In dry season,TN content ranges from 2.08mg/L to 3.72mg/L,and is the highest in the central lake area.Ammonia nitrogen and nitrate nitrogen contents range from 0.36mg/L to 0.61mg/L and 1.06mg/L to 1.92mg/L,respectively.Ammonia nitrogen increases from north to south,while nitrate nitrogen increases from south to north.The overall water quality was between mild and moderate eutrophication,and the water pollution mainly came from domestic and agricultural surface pollution.（2）The IEF-N content in the sediments of Poyang Lake is 8.81 mg/kg～263.96 mg/kg during the high water period,with an average content of 87.43 mg/kg,17.02 mg/kg～179.74mg/kg during the normal water period,with an average content of 54.42 mg/kg,and 31.89mg/kg～233.70 mg/kg during the low water period,with an average content of 96.04 mg/kg,with the highest in the low water period;The content of WAEF-N is also the highest during the dry season,and the content of SAEF-N and SOEF-N varies consistently over time,which is the highest during the wet season..The content of convertible nitrogen is high in SOEF-N.Spatially,TN content in sediments of Poyang Lake ranges from 2.06 g/kg to 8.91g/kg in wet season,and TN content in the middle part of the lake is higher,while that in the east and west sides of the lake is lower.The total nitrogen content in normal water period ranges from1.89g/kg to 4.73g/kg,the overall average content is in the following order:river enters lake area,northern lake area,and central lake area.The total nitrogen content in surface sediments of Poyang Lake during dry season ranges from 480.79mg/kg to 3933.00mg/kg,and the central lake area has the highest nitrogen content,followed by the northern lake area and the estuary area.The spatial distribution of IEF-N content was the highest in the northern lake district during the wet season,and higher in the central lake district during the normal and dry seasons.The content of WAEF-N in the sediments of the three periods was higher in the northern lakes,and the SAEF-N was mainly concentrated in the central lakes.The distribution of SOEF-N was the highest in the northern lake area during wet season and normal season,and the highest in the central lake area during dry season.（3）There is a certain correlation between IEF-N,SAEF-N and SOEF-N in sediments and TN,indicating that the variation trend of IEF-N content is consistent with TN.TN and TP are highly correlated and have the same source.IEF-N was positively correlated with WAEF-N and Chl.a,and negatively correlated with p H.WAEF-N was negatively correlated with SAEF-N and SOEF-N.SAEF-N was negatively correlated with organic matter（OM）and p H,while SOEF-N was positively correlated with sediment TP.In addition,water depth,water p H,water temperature,wind speed,transparency,permanganate index,TP,DTN,DTP,NO₃^--N,NO₂^--N and NH₄⁺-N have different degrees of correlation with total sediment nitrogen and four kinds of convertible nitrogen.（4）With the increase of temperature,the release of total nitrogen,ammonia nitrogen and nitrate nitrogen increased significantly.Under acidic condition,the release intensity of ammonia nitrogen is the highest,while under alkaline condition,it is the lowest.The release intensity of total nitrogen and nitrate nitrogen is the highest under alkaline condition.Under different disturbance intensification,the release intensities of ammonia nitrogen,total nitrogen and nitrate nitrogen reached their maximum at 160r/min,indicating that water disturbance had a significant effect on nitrogen release.The fitting curves of the release intensity of TN,NH₄⁺-N and NO₃^--N and p H are quadratic function,first function and cubic function respectively.The fitting curve of the release intensity and temperature of TN and NH₄⁺-N is a quadratic function,while that of NO₃^--N is a quadratic function.The release intensity and perturbation rate of TN and NH₄⁺-N are fitted as cubic functions,while that of NO₃^--N is a linear function.