Study On Nitrification And Denitrification Potential In The Ponds And Bottomland In Chaohu Lakeshore Zone

Chaohu Lake is one of the five largest freshwater lakes in China,with a very serious eutrophication problem.High nitrogen pollution has become one of the problems plagued by the governance of eutrophication in Chaohu Lake.The Chaohu Basin is mostly low-lying hilly land with developed river systems and numerous ponds and bottomland,which plays an important role in controlling non-point source nitrogen pollution.From October2018 to August 2019,three typical ponds and bottomland were selected in Chaohu Lakeshore zone,where surface sediments and overlying water samples were collected simultaneously.And then a set of incubation experiments were conducted to analyze sediment nitrification and denitrification rates and its dynamic characteristics.Moreover,the carbon and nitrogen limitation of denitrification potential were explored and major environmental impact factors were identified.The main research results obtained are as follows:（1）The comprehensive water quality and health assessment method（ETI）shows that the water quality of pond and bottomland are all at a general level;organic pollution evaluation results show that all organic nitrogen mass fractions are at level III;organic index evaluation results show that almost all points are at a level III,with individual sampling points at level II or IV.（2）The TP pollution evaluation results of the sediments show that the TP pollution index of the study section is between 0.53 and 1.00.Except for the sampling point of the pond 2 reed 2 reaching the lower limit of moderate pollution in October 2018,the remaining sampling points are all within the range of light pollution in the sampling period.（3）The overall change pattern of the potential nitrification/areal nitrification rate of the plant communities in the pond and bottomland area was consistent throughout the sampling period,and basically showed the lowest in February and the highest in August.During the entire sampling period,the potential nitrification rates of bottomland,pond 1and pond 2 were（0.006?0.004）,（0.054?0.032）,and（0.049?0.030）?mol?（g?h）^-1,respetively;the areal nitrification rates were（5.649?3.248）,（11.154?5.189）,and（11.247?5.520）?mol?（m²?h）^-1,respetively.（4）The single factor analysis of variance showed that the potential nitrification rate and areal nitrification rate of the sampling points in bottomland,pond 1 and pond 2 did not differ significantly,but there were still some differences in some months.（5）The denitrification rate of the plant communities in the pond and bottomland has a significant change with time,and generally the highest in August and the lowest in February.Among them,the denitrification rate of depression is（7.52?3.48）mg?（kg?h）^-1,and the denitrification rates of pond 1 and pond 2 are（7.55?3.48）and（7.50?2.95）mg?（kg?h）^-1,respetively.The results of single factor analysis of variance showed that there were no significant differences among the sampling points in the pond and bottomland,but there were some differences in individual months.（6）In general,exogenous nitrogen addition could significantly increase denitrification rates of the pond and bottomland sediments.However,with the increase of nitrogen concentration,the rate of denitrification of sediment decreases in a few cases.;Exogenous carbon addition resulted in a significant decrease in the denitrification rates of pond and bottomland sediments,with the depression of the Pucao in bottomland most obvious;Exogenous carbon and nitrogen added simultaneously is more favorable to the process of sediment denitrification than that of carbon or nitrogen alone and almost all cases were higher denitrification rates in high carbon and nitrogen concentration.