| With the effective treatment of point source pollution,non-point source pollution has become the main reason for exceeding the water quality standards in many areas.Unlike point source pollution,non-point source pollution is affected by many environmental factors,and its occurrence and development process are characterized by variability,randomness,and lag.The quantitative research and effective control of non-point source pollution still face great challenges.Quantitative identification of non-point source pollution nitrogen and phosphorus output and inflow into the river basin is the key foundation for effective control of non-point source pollution.This study took Changle River basin,Shaoxing,Zhejiang Province,as the reaserch object.Based on the hydrological water quality monitoring from 2003 to 2016,the LOADEST model of nitrogen and phosphorus pollution in the Changle River was established to simulate the continuous change trend of nitrogen and phosphorus.The periodic variation of nitrogen and phosphorus load in the river was studied by wavelet analysis.The rainfall factor that drives the occurrence of non-point source pollution and the topographic factor,surface runoff factor,underground infiltration factor and plant interception factor that affected the development process of non-point source pollution in the basin were analyzed systematically and quantitatively.Finally,the coupling equation of one-dimensional water quality equation-export coefficient is improved by using the method of factor correction coefficient to estimate the amount of nitrogen and phosphorus pollutants entering the river in Changle River basin.The main research results are as follows:?1?From 2003 to 2016,the average flow of Changle River was 16.39 m3·s-1,and the water quality of the river was significantly polluted by nitrogen,phosphorus and other nutrients.The multi-year TN monitoring concentration of the river outlet section varied from 0.20 to 13.29 mg·L-1,and the multi-year average concentration was 3.75±0.91mg·L-1,far exceeding the reference value of the region(1.70 mg·L-1).The multi-year monitoring concentration of TP ranged from0.01?0.69mg·L-1,and the average multi-year concentration was 0.14±0.09mg·L-1,which was at the level of surface water Class III.LOADEST model estimation results indicated that the annual TN and TP load from 2003 to 2016 were 2208±862t·yr-1 and 71±32t·yr-1.The TN and TP loads of rivers were highly correlated with runoff,but the correlation with TN and TP concentrations was weak.?2?During 2003?2016,there were obvious periodic changes in the TN and TP loads of Changle River.The time scale of TN and TP load was mainly 18 months,which was subject to the periodic change of multi-frequency,but the change of the TP load strength was weaker than the change of TN load intensity.Moreover,the similarity between the frequency contour map of the wavelet coefficients and the river flow was large,and the time scale and the date of the oscillation were the same.Furture analysis of the wavelet variance of TN and TP load revealed that the periodic change of TN and TP load was caused by the periodic change of river flow,but had little correlation with the change of TN and TP concentration.?3?A systematic quantitative analysis of the rainfall factor driving the occurrence of non-point source pollution,as well as the topographic factor,surface runoff factor,underground storage factor and plant retention factor that affected the development processes of non-point source pollution showed that all five factors performed a certain spatial difference:TN's rainfall driving factor varied from 1.15 to 1.24,with an average of 1.20 and TP's rainfall driving factor varied from 1.22 to 1.33,with an average of 1.28;the terrain driving factor varied from 0 to 2.22while the average was 0.77;the TN surface runoff value calculated by the SCS-CN model was between 1207?1597mm with an average of 1464mm;the annual TP erosion calculated by the USLE was 0?1433t·hm-2·a-1with an average of 140t·hm-2·a-1;the variation range of underground storage factor was 1.00?1.04 with the average value was 1.01;the mean values of TN and TP retention factors were 3.66 and 3.37,respectively.Although there were strong collinearities between different environmental impact factors,considering the direct relationship between there environmental impact factors and pollutant transport,it was believed that surface runoff and plant interception were the main environmental impacts of the development of non-point source pollution in the Changle River Basion factor.?4?Using the selected environmental factors as the correction coefficients,the coupling equation of the one-dimensional water quality equation-export coefficient of the river was improved,and the amount of nitrogen and phosphorus export load of Changle River basin was estimated.The results showed that TN export coefficients of paddy field,dry land,human residential,forest land and wasteland were 26.34±0.41kg·ha-1·yr-1?64.79±0.40 kg·ha-1·yr-1?42.97±0.38 kg·ha-1·yr-1?9.00±0.78 kg·ha-1·yr-1 and 6.38±3.47kg·ha-1·yr-1,and the TP export coefficients were 2.29±0.44kg·ha-1·yr-1?2.28±0.44kg·ha-1·yr-1?4.57±0.29 kg·ha-1·yr-1?1.38±0.88 kg·ha-1·yr-1 and 0.57±0.89kg·ha-1·yr-1.The inflows of TN and TP in Changle River basin calculated by the inversion of the improved one-dimensional water quality equation-coupling model of the export coefficient were 1745t·yr-1 and 128 t·yr-1,respectively.Source analysis of TN and TP inflows of different lan-use types,in which the contribution rates of TN inflows from large to small were dry land?51%?,paddy field?20%?,forest land?16%?,human residential?11%?and wasteland?1%?,while the contribution rate of TP inflow from large to small were forest?34%?,dry land?25%?,paddy field?24%?,human residential?16%?and wasteland?1%?. |
PDF Full Text Request