近50年沂蒙山区两个不同岩性小流域塘库的拦沙效应

在沂蒙山区选取代表性花岗岩与石灰岩小流域各一处,即分别为姜庄和泉安子小流域,对比分析了两个不同岩性小流域塘库近50年的拦沙效应。沿主沟道方向于两个塘库中央位置各取3孔沉积物样芯,参照流域人类活动和环境演变历史,探明了各孔137 Cs、210 Pbex、黏粒和容重深度分布变化特征。以137 Cs和210Pbex示踪法进行沉积物断代,参照塘库原始库容曲线,计算建坝以来塘库不同时段的年均淤沙量,以表征拦沙效应。姜庄和泉安子塘库各孔、各时段拦沙效应的计算结果分别为(394±142)~(121±43)t/a和(22±7)~(59±21)t/a,平均值分别为(208±75),(41±15)t/a,建库以来的总拦沙量分别为10 475,2 097t。姜庄塘库拦沙效应明显大于泉安子塘库,这是此两座塘库分别控制的花岗岩与石灰岩小流域在人类扰动作用下产沙强度的差异所致。近50年两个塘库拦沙效应的变化趋势反映了不同岩性小流域人类活动及其产沙强度响应的近期特征和规律。

Sediment Interception Effects of Two Reservoirs Controlling Contrasting Lithological Catchments in the Yimeng Mountain Region

In this study, the reservoir deposits were used to compare the effect of dam construction on sediment interception from two representative small catchments underlain by granite and limestone, namely the Jiangzhuang and Quananzi catchments, respectively, over the past 50 years in the Yimeng Mountain Region. Three cores were collected from reservoirs in the both catchments. The activities of ¹³⁷Cs and ²¹⁰Pb_ex at different depths, clay contents, and dry sediment bulk densities in cores from the two reservoirs were analysed with reference to human activity and environmental change in the catchment over the past 50 years. The chronologies of the cores were established by ¹³⁷Cs and ²¹⁰Pb_ex dating methods. The mean annual sediment interception for different time periods since dam construction were estimated from each core by referring to the original reservoir capacity curve, which could be generally used to represent the sediment interception effect of the reservoir. The sediment interception effects estimated from the three cores in the Jiangzhuang and Quananzi reservoirs ranged between (394±142)~(121±43) t/year, and (22±7)~(59±21) t/year, with mean values of (208±75) and (41±15) t/year respectively. The total sediment interceptions since the dam construction were about 10 475 and 2 097 t for Jiangzhuang and Quananzi reservoirs, respectively. Overall, the temporal trends of sediment interception associated with the two reservoirs reflect the different patterns of sediment yield response to the environmental change influenced by human activity in the two contrasting lithological small catchments over the past 50 years.