Spatiotemporal Dynamics and Climatic Associations of a Reed-Dominated Wetland in the Yongding River Basin: A Two-Stage Framework Combining Field Surveys and Remote Sensing

Wetlands sustain biodiversity and regulate hydrology, yet their internal functional heterogeneity is still poorly understood. Using a two-stage approach, we surveyed ten plots along the upper, middle, and lower reaches for plant communities, aboveground biomass, and environmental variables, and then monitored a selected site monthly with GF-1 and Sentinel-2 imagery (June 2023–June 2025). Ward clustering grouped the plots into three clusters; Dongzhangwu Wetland (LF10) was separated as a provisional singleton in the six-variable clustering and had the highest cluster-mean aboveground biomass (816.5 ± 426.2 g/m2; reed-dominated quadrats exceeded 900 g/m2) and a distinct soil–water profile. At LF10, NDVI peaked at 0.55 in summer and fell below 0.2 in winter, while NDWI-derived exposed water surfaces varied by more than 1 km2, peaking in winter and reaching their lowest point in spring and summer; these extrema may partly reflect masking by emergent vegetation and, in winter, reduced evapotranspiration and possible water supplementation. Air temperature was most strongly correlated with NDVI and negatively correlated with water extent; both relationships persisted after deseasonalization (r = 0.45 for NDVI and −0.42 for water extent), while precipitation was unrelated to water extent. Given the short record, these associations should not be read as causal. The relatively high productivity of LF10 appears associated with its dominant reed community, seasonal hydrological regime, and favorable downstream hydrothermal conditions. The two-stage approach could provide a practical framework for basin-scale wetland monitoring, pending validation at additional sites.