Water table drawdown reshapes soil physicochemical characteristics in Zoige peatlands

Warming and human activities have caused peatland degradation and water table drawdown, which greatly influence the physicochemical characteristics of soil at different depths. How water table drawdown affects soil physicochemical characteristics is not well understood for the Tibetan Plateau, especially the Zoige peatlands. This study measured variations in C/N ratio, ash content, δ13C, and humification index (HI) as a function of water table drawdown and depth by sampling 100-cm soil columns from three sites with different water tables in the Zoige peatlands. C/N ratio decreased while ash content and HI increased with water table drawdown, suggesting greater decomposition of soil organic matter at sites with a lower water table. The response of soil physicochemical characteristics to water table drawdown varied with depth: in the layer above the water table, C/N ratio did not vary, ash content decreased and HI increased; in the layer below the water table, C/N ratio and HI decreased, while ash content increased. The physicochemical characteristics above the water table were influenced mainly by new carbon input, while the characteristics below the water table were influenced mainly by decomposition. The depth profile of C/N ratio, ash content and HI aligned well with peat formation and decomposition and may be indicators of peat degradation. δ13C did not vary with water table drawdown, depth, or decomposition process. These insights into the variation of soil physicochemical characteristics with depths and water table may help elucidate the processes behind peatland degradation.