Sedimentary Flux Variation and Environment of Dongping Lake During the Last Century

Key words: 
• 210Pb

Abstract: Dongping lake is located in the southwest of Shandong Province, it is the second lake in size in Shandong Province and is also an important flood control reservoir at the lower reaches of the Yellow River. Based on the modern sedimentary age sequence of the Dongping Lake which was established according to 210Pb and 137Cs methods, the sedimentary flux changes since 1889 were estimated and the reasons were analyzed and discussed. By using 137Cs method, three obvious peaks were observed in the core and the sedimentary flux was 0.145
g·cm2·a1 by 137Cs time marker(1963). The CRS model of 210Pb dating was used to caculate the sedimentary flux at different time intervals since 1989, the results showed that the sedimentary flux changed greatly, indicating that the sedimentary environment of Dongping Lake was unstable more than a century: from 1989 to 1938, the average sedimentary flux was high and stable, which was about 0.292 g·cm2·a1; decreased year by year during 1938 to 1965, with an average of 0.213 g·cm2·a1; was low and stable and showed a good agreement with the 137Cs method from 1965 to 2000; and started increasing year by year since 2000, with an average of 0.167 g·cm2·a1. The early high depostion flux maybe relevant to the fact that Dongping Lake has acted as a natural flood storage basin of the Yellow River, and the latter as a result of human activities (lake governance, water conservancy construction of the Yellow River, and so on) which controled the natural flooding of the Yellow River and led to a decline in sedimentary flux and tend to be stable, while the recent rise is a reflect of the increased economic activity. In this paper, the spatial distribution regularity of sedimentary flux and the relationship between the sedimentary flux and nature and human activities were explored so as to reveal the evolutionary history of the sedimentory environment of Dongping Lake more than a century and offer valuable basic information for protection and sustainable exploration of the Dongping Lake.