Effects of Hydraulic Engineering Applications on Recent Sedimentation Rates in Nansi Lake

Fallout radionuclides137 Cs and210Pb tracer techniques were used to measure recent sedimentation rates in Nansi Lake,Shandong Province.The effects of hydraulic engineering applications on the lake sedimentation patterns were analyzed to provide more information to guide sustainable development of Nansi Lake.The137 Cs and210Pb dating of two sedimentation cores(DS2 and WS2),picked respectively from the Higher Lake and the Lower Lake of Nansi Lake,indicated that the ratio of accumulation of137 Cs between DS2 and WS2 was about 9.7.Affected by Grade Ⅱ dam application,137 Cs inventory and erosion losses of DS2 were much greater than that those of WS2.Vertical profiles of137 Cs in the lake sediment were different,with patterned distribution based on atmospheric deposition sequences.Besides137 Cs natural decay,post-depositional redistribution and water turbulence,the main possible reason was the catchment derived137 Cs input.The peak of137 Cs accumulation had no significance on time mark.The times based on sample mass-depth of the two cores calculated by210 Pb constant rate of supply(CRS) model indicated that the sedimentation rates of the Higher Lake and the Lower Lake were not stable over the past 150 years.Using the completion of the Grade Ⅱ dam(1960) as a time marker,it was estimated that the mean sedimentation rates for the Higher Lake and the Lower Lake were 0.069 and 0.160 g/(cm2·a) before1960,and 0.218 and 0.072 g/(cm2·a) from 1960 to 2010,respectively.The results showed that the application of the GradeⅡ dam significantly affected the sedimentation rates in Nansi Lake.The dates derived from210 Pb CRS model were reliable.Further study should focus on the pollutant and nutrient transformation processes using210 Pb CRS technique.