Spatial heterogeneity and seasonal dynamics of vegetation-soil carbon storage in shallow lake wetlands of eastern China.

Shallow lake wetlands have important vegetation and soil carbon pools; yet, habitat-level differences in carbon storage among lake types have been insufficiently quantified. In this study, we compared three representative shallow lake wetlands in eastern China, Qin Lake, Changdang Lake, and Hongze Lake, during low- and high-water periods. We combined Sentinel-2-based land-cover classification with field measurements to distinguish aquatic vegetation functional types and to estimate vegetation carbon density, surface soil organic carbon density, and combined vegetation-surface soil organic carbon storage. The three lakes showed distinct habitat composition and carbon-storage structures. Qin Lake had the highest proportion of emergent vegetation, Changdang Lake had the highest proportion of floating-leaved vegetation, and Hongze Lake was dominated by open water with relatively strong aquaculture disturbance. Under the biomass-accounting scheme adopted in this study, emergent vegetation showed the highest estimated vegetation carbon density and generally made a relatively high contribution to the estimated vegetation carbon pool, whereas surface soil carbon dominated the combined carbon pool, accounting for 69.82%-93.93% of total estimated storage. Period-averaged combined carbon storage was 8.75, 85.70, and 1023 kt C in Qin Lake, Changdang Lake, and Hongze Lake, respectively. Between the low- and high-water periods, the combined carbon storage was estimated to be lower in Qin Lake and Hongze Lake but higher in Changdang Lake, reflecting differences in habitat composition and habitat-specific carbon density. These results illustrate the value of habitat-level and functional-type-based carbon accounting for interpreting carbon-storage heterogeneity in shallow lake wetlands.