^137Cs示踪法研究太湖流域土壤侵蚀分布与总量

USING ^(137)Cs TRACER TECHNIQUE TO INVESTIGATE SOIL EROSION DISTRIBUTION AND TOTAL EROSION AMOUNT IN TAIHU LAKE CATCHMENT

利用137Cs示踪法研究了太湖流域不同地貌和土地利用类型的土壤侵蚀速率分布,初步估算了太湖流域的土壤侵蚀总量。结果表明,土地利用类型相同时,丘陵山坡中点的土壤侵蚀速率与整个坡面的平均值相近;太湖流域山坡中上部以自然坡地为主,土壤侵蚀速率仅为186.6t/km2.a;山坡下部以茶园种植为主,土壤侵蚀速率为3898.5t/km2.a。平原区水田的侵蚀速率与其到山脚的距离正相关,随距离的增大由堆积转变为侵蚀并逐渐增大,山脚水田堆积量和湖岸水田侵蚀量分别为2585.9和6325.7t/km2.a,平均侵蚀速率约为1869.9t/km2.a。太湖流域土壤侵蚀总量约为3446.7×104t,流域土壤侵蚀导致的输入太湖的泥沙量年均约为34.5×104t,与实际监测结果基本一致,说明土壤侵蚀是太湖泥沙输入的主要来源。本研究结果初步证明了利用137Cs示踪法研究太湖流域土壤侵蚀与湖泊沉积通量定量关系的可行性。

The soil erosion distribution of different landforms and land use types in Taihu Lake catchment was investigated by using ^137Cs tracer technique, and the total annual erosion amount was primarily estimated by the distribution of soil erosion and area of each land use type. The results show that the erosion rate of middle mountain side is equal to the average of the total slope at the same land use type. In Taihu Lake basin, the upper and middle mountain side is main natural forest lands with a low erosion rate of 186.6 t/km^2 · a, while the lower mountain side is main tea plantations with a high erosion rate of 3 898.5 t/km^2 · a. The erosion rates of paddy fields in plain are positively related to their distance to the hill. The accumulation rate of paddy fields at the mountain food and the erosion rate of paddy fields near the lake are 2 585.9 t/km^2 · a and 6 325.7 t/km^2 · a respectively, and the average erosion rate of paddy fields in Taihu Lake basin is 1 869. 9 t/km^2 · a. The total annual erosion amount is about 3 446.7 104 t/a, which induced about 34. 5 104 t/a transport into the Taihu Lake. The result is consistent with monitoring data suggesting that soil erosion is the main source of the sediment in the Taihu Lake basin. Our study primarily proved the feasibility of quantifying the relationship between soil erosion and lake sediment flux by using ^137Cs tracer technique.