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

The distribution of sediment grain size can record past environmental conditions and human activity. In this study, radioisotope of Pb-210 and Cs-137 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 mu m) was the largest contribution with an average content of 84.05%, and the second largest contribution was sand (>63 mu m) with an average content of 15.68%. The median grain size and the mean grain size in the whole sediment core was 22.39 mu m and 36.85 mu m, 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.