| Under the new situation that the non-point source pollution is the main pollution source,the water eutrophication caused by the loss of non-point source nutrients such as nitrogen and phosphorus is the chief water environment problem in many areas.This thesis aimed at two key issues,which are the quantitative identification of nitrogen pollution sources and the uncertainty analysis and the classified calculation of direct runoff non-point nitrogen pollutants export to the river after deduct the in-stream total nitrogen pollution contributed by baseflow source,in the non-point pollution research.Taking Changle River watershed of southeastern coastal area as a case study,this thesis investigated the quantitative pollution sources apportionment and non-point source pollution control by using Monte Carlo water quality assessment model,stable isotope analysis,digital filter algorithm,one-dimensional river water quality equation and export coefficient combination model,and integrated minimum water environmental Gini coefficient model.The main results are as follows:The water quality of Changle River was generally good.The average comprehensive water pollution index（CWQI）of Nanshan Reservoir（S1）,North River（S2）,Tanyuan River（S3）,Shihuang River（S4）,Furun Rive（S5）,Ganlin（S6）,Chongren River（S7）,and Yazhiqiao（S8）were 0.48,0.42,0.64,0.57,0.72,0.56,0.68,and 0.57,respectively.The probability of S1～S8 being at or better than the slightly pollution level were 87.53%,90.38%,69.89%,76.44%,58.80%,78.21%,64.55%,and 78.03%,respectively.Total nitrogen（TN）had the largest Sperman rank correlation coefficient,indicating that TN was the most influential input variable on the CWQI.Therefore,controlling nitrogen pollution is the key to further improve the water environment quality in Changle River watershed.NO3--N is the main form of non-point source nitrogen pollution.In Changle River watershed,manure and sewage contributed the most NO3--N to aquatic systems,accounting for 38.2%during wet season and 45.4%during dry season,followed by soil nitrogen（32.7%and 35.3%for wet and dry seasons,respectively）,chemical nitrogen fertilizer（26.0%and 17.7%for wet and dry seasons,respectively）,and atmospheric deposition（3.1%and 1.6%for wet and dry seasons,respectively）.Furthermore,we constructed an uncertainty index,UI90,to quantitatively characterize the uncertainties inherent in NO3--N source apportionment.The annual average riverine TN loads in Changle River watershed was 1990.72±838.02 t·yr-1,baseflow contributing with an average value of 65.40%.The baseflow driving TN loads showed a significant upward trend at the 99%confidence intervals.These findings suggested that the baseflow delivery of pollutants should be taken into account for prioritizing non-point source pollution management and remediation actions in agricultural watersheds.The average annual export coefficients of paddy field,dry land,residential land and forest in Changle River watershed were 6.89 kg·ha-1·yr-1,28.79 kg·ha-1·yr-1,19.85 kg·ha-1·yr-1,and 3.78 kg·ha-1·yr-1,respectively;the annual average self-purification rate was 21.35±5.04%.From 2003 to 2012,the annual non-point source nitrogen export to the Changle River was 2250.82 t·yr-1,of which via baseflow was 1526.01 t·yr-1 and via direct runoff was 724.81 t·yr-1.The percentage of paddy field,dry land,residential land and forest contributed to the direct runoff TN export loads to river were 13.47%,57.15%,13.78%and 15.60%,respectively.The annual TN export loads to river of Chongren,Ganlin,Changle,Lushan,Shihuang,Tongyuan,Yahuang and Wangyuan were 197.52 t、99.81 t、202.70t、39.01t、58.17t、45.01t、24.93t,and 15.61t,respectively.The river self-purification capacity scenarios simulation results showed that after carrying out a series of measures such as "process interception" and "end treatment",there existed 344.58 t realistic allocatable water environmental capacity when the self-purification capacity of non-point source nitrogen pollution was 50%.Based on the integrated minimum water environmental Gini coefficient model,the TN emissions for Chongren,Ganlin,Changle,Lushan,Shihuang,Tongyuan,Yahuang,and Wangyuan should reduce respectively 112.62 t,36.14 t,99.22 t,21.53 t,27.36 t,24.31t,11.23 t,and 5.78t,accounting for 57.02%,36.20%,48.95%,55.20%,47.03%,54.00%,45.04%,and 37.06%of the total reduction amount in the present situation.Finally,we put forward the control suggestion of non-point source pollution in Changle River watershed. |
