A Dam Construction Event Recorded by High-Resolution Sedimentary Grain Size in an Outflow-Controlled Lake (Hulun Lake, China)

Abstract

The distribution of sediment grain size can record past environmental conditions and human activity. In this study, radioisotope of 210Pb and 137Cs and a grain size of a 41 cm core in Hulun Lake were applied to reconstruct the high-resolution sedimentation history. The profiles of the grain size of the lake sediments show that silt (4–63 µm) was the largest contribution with an average content of 84.05%, and the second largest contribution was sand (>63 µm) with an average content of 15.68%. The median grain size and the mean grain size in the whole sediment core was 22.39 μm and 36.85 μm, respectively. Correlations of the sedimentological variables with instrumental measurements were also analyzed. The peak–trough value of the mean grain size of the sediments in Hulun Lake can reflect the magnitude of rainfall intensity and river discharge. The clay and silt contents at a depth of approximately 32–38 cm was different from other depths throughout the core, which showed continuous maxima with an average content of 0.35% and 94.08%. These changes in grain size correspond to the period of dam construction in 1963–1970. Therefore, the sediment grain size of Hulun Lake effectively recorded the dam-building activity.