Lake sediments record the environment during the lake sedimentation whose characteristics can infer environmental changes and human activities. In this study, the Pb-210 chronologies and sedimentation rate of the sediment core in Honghu Lake were calculated by the Constant Rate of Supply model. The characteristics of the sedimentary environment were analysed by using physical and chemical indicators. Four stages were divided as follows: Stage A (before 1900): The relatively low sedimentation rate and nutrient content indicated an extremely stable sedimentary environment. Stage B (1900-1949): With the growth of population, the intensity of land use began to increase, with an averaged sedimentation rate of 0.252 gcm(-2)a(-1). Stage C (1949-1980): The sedimentation rate and nutrient content increased markedly. The intense human activity has damaged the surrounding vegetation leading to soil erosion and accelerated sedimentation rate. With the deterioration of the lake water environment, the organic matter source was mainly the internal source represented by algae and bacteria. Stage D (1980-2011): Influenced by the difference in land use types along the coast, the sedimentation rate of HH-A (0.570 gcm(-2)a(-1)) is higher than that of HH-B (0.445 gcm(-2)a(-1)). The results are of significance to the management of rural lakes and reservoirs.

The net change in the carbon inventory of arctic tundra remains uncertain as global warming leads to shifts in arctic water and carbon cycles. To better understand the response of arctic tundra carbon to changes in winter precipitation amount, we investigated soil depth profiles of carbon concentration and radionuclide activities (Be-7,Cs-137,Pb-210, and(241)Am) in the active layer of a twenty-two-year winter snow depth manipulation experiment in moist acidic tussock tundra at Toolik Lake, Alaska. Depth correlations of cumulative carbon dry mass (g cm(-2)) vs. unsupported(210)Pb activity (mBq g(-1)) were examined using a modified constant rate of supply (CRS) model. Results were best fit by two-slope CRS models indicating an apparent step temporal increase in the accumulation rate of soil organic carbon. Most of the best-fit model chronologies indicated that the increase in carbon accumulation rate apparently began and persisted after snow fence construction in 1994. The inhomogeneous nature of permafrost soils and their relatively low net carbon accumulation rates make it challenging to establish robust chronologic records. Nonetheless, the data obtained in this study support a decadal-scale increase in net soil organic carbon accumulation rate in the active layer of arctic moist acidic tussock tundra under conditions of increased winter precipitation.