Spatiotemporal dynamics and future projections of carbon sink in the Dongting Lake wetland (2000–2060): a multi-scenario simulation incorporating hydrological variability based on the PLUS–CASA–GSMSR model

Wetlands are important global carbon sinks that help mitigate atmospheric CO₂ concentrations. However, climate change and human activities introduce uncertainty into wetland carbon evaluation and future management. Despite the significant influence of hydrological fluctuations on lake wetlands carbon dynamics, few studies have assessed carbon sequestration capacity while explicitly accounting for dynamic water area changes. This study employed a coupled PLUS–CASA–GSMSR framework to simulate land use/cover (LULC) patterns, and explore the spatiotemporal dynamics and driving mechanisms of net ecosystem productivity (NEP) in the Dongting Lake wetland in three SSP-RCP scenarios (SSP1-2.6, SSP2-4.5, and SSP5-8.5), with a focus on dynamic water area transitions. From 2000 to 2020, water area shrank, reed area expanded, cropland area decreased, sedge area recovered, and forest area increased first and then decreased. Mean spatial annual NEP was 45.93 g C/m 2 /a, with an overall declining trend. Spring and autumn were the main carbon sink seasons, while NEP declined in summer due to vegetation inundation. From 2020 to 2060, water area was first projected to increase and then decline. Sedge and forestland areas expanded in SSP1-2.6, cropland and reed areas expanded in SSP2-4.5, whereas cropland expansion dominated in SSP5-8.5. NEP increased in all three scenarios, with the largest increase in SSP1-2.6 (0.79 g C/m 2 /a) and the smallest increase of 0.29 g C/m 2 /a in SSP2-4.5. The spatial distributions and transitions of LULC types, especially forestland, sedge, and cropland, dominated NEP spatial heterogeneity (Q = 0.20). However, natural factors (Q = 0.56), including climate and terrain, exhibited greater explanatory power for overall NEP variations than anthropogenic drivers such as LULC and socio-economic factors (Q = 0.51), except in SSP5-8.5. Water level (WL) was also negatively correlated with NEP during the growing season (r = −0.54, p = 0.078), underscoring the regulatory role of hydrological dynamics. Future management should integrate location-specific optimization, hydrological coordination, and scenario-adaptive strategies. The findings provide a transferable framework for scenario-adaptive lake wetland management in support of national carbon neutrality targets.