Experimental manipulation of freshwater wetland hydroperiod alters litter decomposition and macroinvertebrate assemblage structure.

Climate-driven shifts in hydrological cycling are altering freshwater wetlands globally and may disrupt carbon processing, yet the impacts on litter decomposition and the underlying drivers are still poorly understood. We experimentally manipulated hydroperiod in twelve wetlands in Georgia, U.S. to include permanent, temporary, and dry ponds from 2018 to 2021. Litterbags were deployed and collected at early (30-day), mid (60-day), and late (90-day) sampling intervals to quantify detrital processing including decomposition rate (n = 343) and macroinvertebrate assemblages (n = 148). Decomposition rates (k × 10-3day-1) followed an overall hydroperiod gradient, with the fastest rates in permanent ponds (7.9), which was 25% faster than temporary ponds (6.3) and 42% faster than dry ponds (5.6), although the magnitude of hydroperiod differences varied across intervals. Across all ponds, decomposition was fastest during the early sampling interval and declined over time. Permanent ponds supported higher macroinvertebrate richness, diversity, Ephemeroptera-Plecoptera-Trichoptera (EPT), density, and biomass than temporary ponds. Community composition diverged as drying progressed and the late sampling interval showed increased stochasticity in temporary ponds. Temperature was positively associated with litter decomposition rates, whereas community composition was negatively associated. Macroinvertebrate density showed interval dependent effects on decomposition, with positive relationships emerging during the mid and late stages. Shifts toward shorter or more variable hydroperiods are likely to slow decomposition, shift community assemblages, and reduce carbon turnover. These results highlight hydroperiod as a key control on wetland ecosystem function and suggest that approaches aimed at restoring inundation regimes will be critical for sustaining wetland function.