• 标题：Anthropogenic control of coupled changes in organic and inorganic carbon burial in karst landscape: Sediment evidence from two lakes of subtropical China
• 关键词：Karst landscape;Carbon burial;Hydrological regulation;Agricultural development;Subtropical lake
• 作者：Qiaohua Han;Lu Wang;Linpei Huang;Rui Li;Ping Li;Tao Zhang;Qi Zhou;Guangjie Chen

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Hydrological regulation and land uses are known to alter lake organic carbon stock, while inorganic carbon cycling in karst landscapes may as well be shifted due to its rapid kinetic rate. To date, the synchronous pattern in the variations of sediment organic carbon (TOC) and inorganic carbon (TIC) burial in karst lakes largely remains to be quantified along the gradient of catchment development. Two karst lakes with contrasting nutrient level and water depth from Southwest China, both of which were converted to medium-sized reservoirs in ∼1985, were selected for sediment multi-proxy analyses on the temporal and spatial variation of carbon burial in the last ∼80 years. While hydrological fluctuations were well recorded by the sediment variation of particle size, the gradual decrease in median grain size showed a trend of increasing water depth that is consistent with the damming events for both lakes. Meanwhile, the nutrient variables revealed an acceleration of eutrophication since ∼2000 when a rapid expansion of catchment croplands was documented for both lakes. While diatom assemblage showed a significant response to hydro-climatic fluctuation and nutrients at both lakes, algal production (i.e. chlorophyll and cyanobacterial pigments) significantly increased with eutrophication at both lakes. The TIC content in the mesotrophic Taiping Lake and the TOC content in the eutrophic lake of Sanjiaohai both showed a significant increase with agricultural expansion, however, the contents of TOC in Taiping and of TIC in Sanjiaohai remained relatively stable over time. While a significant increase in the sediment flux with decreasing bulk sediment C:N ratios suggests elevated autochthonous input, the temporal change of TIC and TOC flux showed a significant synchrony at both lakes. Meanwhile, the sediment content and flux of TIC is significantly higher than those of TOC in Taiping Lake with a higher rate of carbon turnover, but lower than those of TOC in Sanjiaohai. Thus, the accumulation of TIC was disproportionally promoted in deep lakes while the burial of TOC is more favorable in eutrophic and shallow lakes. Overall, our sediment evidence highlights that agricultural expansion and hydrological regulation could interact in altering the sediment stock of TIC and TOC, and their synchronous variation in Karst landscapes.