澜沧江流域氮磷流失垂向分布特征及梯级水库累积滞留效应研究

The watershed in the Southeastern China is characteristic with the unique vertical pattern with the dramatically decrease of topography. The topography also cause the vertical distribution pattern of territorial conditions and non-point source nitrogen and phosphorus loss, which is also affected by the retention impacts by the cascade reservoirs in the middle and downstream of the basin. The Lancang river Basin was selected as the case study area to explore the vertical loss dynamics of typical non-point source pollutants between upper higher evaluation areas with the middle- down stream of the basin. The cascade reservoirs in the middle and downstream of the basin also can highlight the accumulated retention impacts. Based on the previous field eco-hydrology monitoring in cold condition, the field measurements about surface runoff, soil water and non-point sources of nitrogen and phosphorus pollution will be carried supplementary in the upper stream cold plateaus watershed. The soil-plant-meteorological-hydrological monitoring networks will be set to explore the non-point source nitrogen and phosphorus loss mechanism under the impact of the temperature in thawing process and rainfall in summer. Two subbasins were selected to compare the loading differences under the combined impacts temperature and rainfall in cold plateaus. The watershed territorial vegetation distributions patterns were expressed by the series MODIS images, which was positive for the formation understanding of the NPS pollution. Based on the operation parameters of the cascade reservoirs, the SWAT modeling system was calibrated with the historical monitoring data. With the watershed land use from 1975 to 2016, long-term spatial patterns of non-point source pollution in the whole watershed was quantified. The transmission process of non-point source pollutants in the river basin of cascade dam can be expressed. The study covered the innovative points of non-point source pollution formation in Southwest watersheds and the accumulated detention of cascade dams, which will provide scientific guidelines for integrated basin water resources and environmental management.

西南地区特有的高落差地形和气候环境使得陆面氮磷流失呈现独特的海拔垂向分异，尤其是不同海拔地区温度和降雨对非点源污染输出和迁移存在显著的空间异化特征。选择澜沧江流域为案例区开展研究，可以识别西南地区非点源氮磷污染陆面流失的垂向特征及其在梯级水库建设流域中的传输特征，具有良好的示范性和科学创新性。开展澜沧江流域不同海拔的小流域生态水文和非点源氮磷污染的流失监测，采用土壤-作物-气象-生态水文监测网络甄别不同海拔区域非点源氮磷流失机制，以上游子曲流域和下游漾濞江流域开展对照分析，识别不同海拔区温度和降雨双因子驱动下流域非点源污染输出特征。运用MODIS遥感数据开展流域植被时空变化特征甄别，进一步分析流域非点源污染形成与迁移的陆面特征。结合梯级水库运行参数分析澜沧江流域非点源污染河道传输过程，为西南地区梯级水坝流域水资源水环境综合管理提供科学指导。

1、澜沧江流域多源气象数据评估及温度、降水空间变化.针对气象资料的缺乏及海拔差异，首先开展多源气象数据的可靠性分析。气温空间化数据时序评估性能较降水更优。TRMM在降雨时序模拟上略有不足，体现在对低强度降雨的空报和对高强度降雨探测数值偏高，GRID_pre则具备插值数据的稳定优势。MODIS的探测结果与GRID_pre探测效果总体差异不大。在海拔较高地区对降水数据进行融合，得到优化降水空间化数据。澜沧江流域多年降水总体呈微弱上升趋势，低海拔区降雨变化平缓波动下降；而高海拔地区的增温趋势更强，最低气温的增温现象最为明显，降水的总体变化趋势受海拔影响不明显。.2、澜沧江流域SWAT模型率定和验证.运用昌都与允景洪两个水文监测站的数据，通过SWAT-CUP程序运行率定，确定了参数相对最优值，昌都水文站率定的结果R2=0.74，Ens=0.58，验证时R2=0.70，Ens=0.64；允景洪水文站率定结果R2=0.81，Ens=0.77，验证R2=0.70，Ens=0.51，模拟结果均位于合理的区间。取2016年1月1日~12月31日土壤水的日数据进行拟合，SWAT模拟的土壤水与SMAP观测值较为接近，R2=0.837，p<0.01，说明SWAT陆面参数模拟的效果较好、数据可靠性高。.3、澜沧江流域农业非点源污染流失时空特征.澜沧江流域每年8月流量达到年内最大值，3月份为流域出口处径流量最小的月份。泥沙2月到4月份有上升的趋势，5月份形成一个小波谷，在6月份达到较高的数值。澜沧江流域非点源总氮负荷之中，有机氮所占的比重相较于硝态氮更大，总磷负荷的分布主要与有机磷及矿物质磷类似。近40年上游及中上游地区的总磷负荷有降低的趋势，下游总磷负荷的变化不大，低海拔区的总磷负荷量仍旧较为明显地高于高海拔区。.4、流域非点源污染对海拔的响应规律.澜沧江流域土壤侵蚀呈现海拔差异，中海拔地区的泥沙负荷量最少，其次是高海拔地区，而低海拔地区的泥沙负荷量最高。总氮、总磷的负荷具有较为明显的一致性，负荷量均是低海拔>中海拔>高海拔，主要因低海拔地区的土壤侵蚀量、降雨量均高，且低海拔地区全部种植双季稻，施肥量高于单季稻。降雨量、泥沙负荷、氮、磷负荷量具有较为相似的年内变化趋势，高、中、低海拔区域降雨量及泥沙负荷均在7、8月份达到年内最高值。