Assessing Carbon Pool Dynamics in Sedimentary Systems of Tibetan Plateau Urban Wetlands, China

Highland urban wetlands are primarily located in high-altitude, low-temperature regions, possessing unique ecological and regulatory functions. Following ecological restoration and supplemented by artificial interventions, wetlands in Xining City play a significant role in carbon sequestration, oxygen release, and water purification. Against the backdrop of China’s “carbon peak and carbon neutrality” goals, investigating carbon cycling processes in high-altitude urban wetlands has emerged as a current research focus. However, systematic exploration integrating the three elements-“high-altitude,” “urban ecosystems,” and “sediment carbon pools”-remains largely unexplored. This study examines the sediment carbon pools in Xining’s wetlands—specifically Haihu (semi-artificial wetland), Ninghu (artificial wetland), and Beichuanhe (riverine wetland)—within the Hangsui River Wetland Park. Key findings include: (1) The short-term sedimentation rate was determined to be 0.50–0.75 cm·a−1 based on the “inflection point” of biogenic elements in wetland sediments. (2) Significant differences (p < 0.05) in average TOC content were observed across different wetland sediments during distinct periods. Sediment TOC content is higher under plant cover than without plant cover. (3) The mean sediment carbon density ranged from 6.58 ± 1.38–13.02 ± 3.91 g·cm−2, with sediment organic carbon burial rates between 0.67–1.65 g·cm−2·a−1. (4) The sediment carbon stock in the wetland was 20,856.09 Mg·C.