The objectives of this study were to characterize heterogeneities in agricultural non-point source (NPS) pollution loads, and to identify the uncertainty of time series of water flow and NPS pollution loadings at different scales. The Daily flow rates, concentrations of ammonium nitrogen (NH3), total nitrogen (TN), total phosphorus (TP), and the permanganate index (IMn) and the degradation coefficients of pollutants were measured in a river basin during the period from 2013 to 2015. The dynamic time warping distance (DTW) was used to characterize the differences of runoff flow rates and NPS pollution (i.e., NH3, TN, TP, and IMn) loadings under different underlying surfaces at the sub-basin and basin scales. Information entropy and complexity were used to measure the uncertainty and predictability of different variables at the 2 scales. At both sub-basin and basin scales, NPS pollution loadings increased nonlinearly with rainfall until the rainfall reached 40 mm, and then the NPS pollution loadings maintained stable. The coefficients of variation for NH3, TN, TP, and IMn at the basin scale were 69.1%, 47.0%, 14.2%, and 85.8% higher than those at the sub-basin scale, respectively, with the rainfall higher than the threshold amount. During the dry seasons, the differences in NPS pollution loads between the sub-basins were higher than those between the sub-basins and basin, which were mainly affected by the different pollution sources in the regions. The differences in NPS pollution loadings were significantly higher during the wet seasons than during the dry seasons at both the sub-basin and basin scales. Compared with the NPS pollution loads during the dry seasons, the differences in the NPS pollution loads between the 2 sub-basins and between the sub-basins and the basin increased by 3.18 times and 2.44 times, respectively, during the wet seasons. The differences in fluxes of NH3, TN, and TP between the sub-basins and between the sub-basins and basin were mainly attributed to the underlying surface conditions and the pollutions sources. Compared with the results at the sub-basin scale, the information entropy values for the time series of the water flux per unit area, TN, TP and IMn loads at the basin scale were decreased by 4.8%, 9.3%, 31.9% and 10.7%, respectively, but NH3 were increased by 15.3%. The efficient measure complexity increased with the spatial scale. Compared with the sub-basin scale, the efficient measure complexity values at the basin scale for the water flux per unit area, NH3, TN, TP and IMn loads increased 4.6%, 15.4%, 17.4%, 49.5% and 19.8%, respectively. The result indicated that more parameters were required at the basin scale than at the sub-basin scale for the efficient prediction. The NPS pollutions load and flow processes were not synchronous at different spatial scales. For the flow rates and the NPS pollution loads, the information entropy decreased and effective measure complexity increased with the basin scales, indicating that the uncertainty decreased and the predictability decreased with the scales. The investigation on the sensitivity of NPS loadings to the rainfall and underlying surface at different scale, and physical basis of the NPS loadings at different scales will provide an insight into the theories of distributed hydrology and NPS simulation model.%针对流域面源污染负荷差异性及其不确定性的尺度特性问题,于2013-2015年在釜溪河流域测定了不同尺度汇流区的面源污染负荷和污染物转化动力学参数.分别采用动态时间弯曲距离DTW(dynamic time warping distance)和信息测度度量了不同尺度汇流区面源污染的负荷差异性和不确定性.结果表明:不同的汇流区尺度上,降雨量小于临界值(40 mm)的情况下,氨氮(NH3)、总氮(TN)、总磷(TP),和高锰酸盐指数(IMn)负荷均随降雨量的增加而非线性增大,降雨量超过临界值后,流域面源污染出现最大负荷.降雨量超过临界值后,由于尺度增加后下垫面对径流过程调蓄能力的增大,相比子流域尺度,流域尺度上NH3、TN、TP和IMn负荷的变异系数分别增加了69.1%、47.0%、14.2%和85.8%.枯水期和汛期面源污染负荷主要受到污染源流域分布特性和下垫面径流条件的影响,不同尺度汇流区的NH3、TN、TP和IMn负荷在枯水期的差异性均显著小于汛期的差异性,子流域之间、以及子流域与流域之间4种污染负荷的差异性平均增大了3.18倍和2.44倍.相比子流域尺度,在流域尺度上单位面积流量、TN、TP和IMn负荷基质熵分别减小了4.8%、9.3%、31.9%和10.7%,而NH3增加了15.3%;有效测定复杂度分别增加了4.6%、15.4%、17.4%、49.5%和19.8%.不同尺度汇流区的面源污染负荷过程与流量过程不具有完全同步性.随着汇流区尺度的增大,面源污染负荷不确定性减小;有效测量复杂度随尺度增大表明在更大的尺度上对于面源污染负荷有效预测的参数数量显著增加;涨落复杂度和平均信息增量关系表明随着尺度的增加,面源污染负荷对降雨量的敏感性降低,而对下垫面条件的敏感性增加.不同尺度条件下,面源污染对降雨和下垫面的敏感性变化规律、以及面源污染负荷变异性机理等方面的研究将有助于提升分布式水文及面源污染模型理论.
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