近20a三峡库区泥沙输移比估算与吸附态氮磷污染负荷模拟

该文把泥沙输移比细化到栅格空间,以反映流域水文过程的地形指数作为泥沙受汇流的动力系数、植被截留阻力作为泥沙输移的阻力系数,构建泥沙输移比模型,最后运用已有的土壤侵蚀模型、泥沙负荷模型和吸附态氮磷污染负荷模型估算近20 a三峡库区吸附态氮磷污染负荷,结果表明:1影响库区泥沙输移的动力系数主要集中于中等以上区间(0.4,0.8),空间异质性不显著,而阻力系数表现较为复杂,坡度低的平行岭谷区和河流冲积缓坡以及台地区较高,坡度陡的秦巴山地北部区和武陵山区的高山峡谷地带偏低;2库区泥沙输移比呈"单峰"结构,近似正态分布,均值为0.48。空间上具有显著的异质性,中、西部平行岭谷区泥沙输移比较小,武陵山区和秦巴山区较高,以河流河道为中心向两侧呈梯度增大趋势;3泥沙负荷均值与负荷总量的年际变化趋势相同,泥沙负荷总量的模拟值(0.9亿t)与公报监测值(0.92亿t)最为接近的是1995年。空间格局上因近10 a库区泥沙负荷量的均值变化不大,泥沙负荷的低值区与高值区的空间分布比较稳定,低值区的分布范围广泛,集中度高,而高值区的分布较为离散和破碎;4吸附态氮磷负荷量与土壤侵蚀模数、泥沙负荷量在数值上同比增长,在2010年负荷总量达到最大值,分别为1.2和0.6亿t。空间上总体分布相似,具有不平衡特征,从东向西呈逐渐减小趋势。与监测数据的相关分析,吸附态氮负荷的模拟效果比吸附态磷更好,且吸附态氮磷负荷在库区流域内存在空间相关性。

Estimation of sediment delivery ratio and modelling of absorbed nitrogen and phosphorus load in Three Gorges Reservoir Area nearly 20 years

Abstract: In this paper, sediment delivery ratio was spatially rasterized, and the model of sediment delivery ratio was constructed by the motivation cofficient and the resistance cofficient. Among them, the motivation cofficient was expressed by topographic index which reflected hydrological process, and the resistance cofficient was expressed by the vegetation interception resistance. Finally, the exsting soil erosion model, sediment load model and absorbed nitrogen and phosphorus load model were used to estimated the pollution load of absorbed nitrogen and phosphorus in the Three Gorges Reservoir area from 1990 to 2010. The results showed that the motivation coefficient affacting sediment delivery was primarily on median range from 0.4 to 0.8 in the Three Gorges Reservoir area. Moreover, its spatial heterogeneity was not significant (p > 0.05?). However, the performance of resistance coefficient was more complicated. The parallel ridge and valley zone, river alluvial gentle slope zone and mesa zone had high resistance coefficient, due to low gradience of slopes, while the northern zone of Qinba Mountain area, and the Alpine and Valley zone of Wuling Mountain area possessed low resistance coefficient due to steeper slopes. The results also showed that the sediment delivery ratio was in approximately normal distribution in the Three Gorges Reservoir area with a single peak. Its mean value was 0.48. It exhibited significant spatial heterogeneity. The ratio of sediment delivery in the middle and western parallel ridge and valley zone was much smaller than the Qinba Mountain and Wuling Mountain areas. At the same time, it had the tendancy of the gradient increase from the center of the river to the sides. Moreover, the change trend of mean sediment load was the same as the interannual variation of total sediment load in the Three Gorges Reservoir area. Simulation of the total sediment load (0.9 t) and the value of monitoring from bulletin (0.92 t) was the most close in 1995. At the spatial patterns, the spatial distribution of the low value zone and high value zone of sediment load were relatively stable due to little change in mean sediment load during 1990-2010. The distribution ranges of the low value zone was very wide with a high concentration degree. The distribution of high value area was very discrete and broken. In addition, absorbed nitrogen and phosphorus load possessed on value year-on-year growth with soil erosion modulus and sediment load in the Three Gorges Reservoir area. The maximum values of the total load in 2010 reached 1.2 tons and 0.6 tons respectively for nitrogen and phosphorus. Overall, they had similar spatial distribution with an unbalanced characteristics. Absorbed nitrogen and phosphorus load presented gradually decreasing tendency from east to west. The simulation result of adsorbed of nitrogen load was better than adsorbed phosphorus load when their correlation analysis was made with monitoring data. Absorbed nitrogen and phosphorus load had spatial correlation within in the Three Gorges Reservoir area.