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Dissolved organic matter (DOM) drives biogeochemical processes in aquatic ecosystems. Yet, how hydrologic restoration in nutrient‐enriched ecosystems changes DOM and the consequences of those changes for the carbon cycle remain unclear. To predict the consequences of hydrologic restoration on carbon cycling in restored wetlands, we need to understand how local environmental factors influence production, processing, and transport of DOM. We collected surface water samples along transects in restored peat (organic‐rich, macrophyte‐dominated) and marl (carbonate, periphyton‐dominated) freshwater marshes in the Everglades (Florida, U.S.A.) that varied in environmental factors (water depth, phosphorus [P] concentrations [water, macrophytes, periphyton, and soil], and primary producer biomass) to understand drivers of dissolved organic carbon (DOC) concentrations and DOM composition. Higher water depths led to a “greening” of DOM, due to increasing algal contributions, with decreasing concentrations of DOC in peat wetlands, and a “browning” of DOM, due to increasing humic contributions, with increasing DOC concentrations in marl wetlands. Soil total P was positively correlated with DOC concentrations and microbial contributions to DOM in peat wetlands, and periphyton total P was positively correlated with algal contributions to DOM in marl wetlands. Despite large variations in both vegetation biomass and periphyton biovolume across transects and sites, neither were predictors of DOC concentrations or DOM composition. Hydrologic restoration differentially alters DOM in peat and marl marshes and interacts with nutrient enrichment to shift proportions of green and brown contributions to surface water chemistry, which has the potential to modify wetland food webs, as well as the processing of carbon by micro‐organisms. 

Abstract Degradation of wetland ecosystems results from loss of hydrologic connectivity, nutrient enrichment, and altered fire regimes, among other factors. It is uncertain how drivers of wetland ecosystem processes and wetland vegetation communities interact in reversing the ecological trajectory from degraded to restored conditions. We analyzed biogeochemical and vegetation data collected in wetlands of the Florida Everglades at the start of (2015) and during (2018 and 2021) the initial stages of rehydration. Our objectives were to analyze the allocation of carbon and nutrients among ecosystem compartments and correlated trajectories of vegetation community change following rehydration, to identify the drivers of change, including fire, and analyze macrophyte species‐specific responses to drivers. We expected to see changes in vegetation toward more hydric communities that would differ based on wetland baseline conditions and the magnitude of the hydrologic change. During the study period, both length of inundation and surface water depth increased throughout wetlands in the region, and four fires occurred, which affected 51% of the sampling locations. We observed biogeochemical shifts in the wetland landscape, driven by both hydrology and fire. Total phosphorus concentrations in soil and flocculent detrital material decreased, while soil carbon:phosphorus and nitrogen:phosphorus mass ratios increased at sites further away from water management infrastructure. Transitions in vegetation communities were driven by an increase in hydroperiods and by the distinct changes in nutrient concentrations or soil stoichiometric ratios in each subregion. The abundance of macrophyte species typical of short‐hydroperiod prairies strongly decreased, while dominant long‐hydroperiod species, such asEleocharis cellulosa, expanded. Fire facilitated the expansion of thickly vegetated plumes of invasiveTyphaat sites close to the water inflow sources. Overall, restored hydrology shifted vegetation community composition toward higher abundance of long‐hydroperiod species within six years. In contrast, removal of invasive vegetation controlled by soil phosphorus concentrations will likely require long‐term and interactive restoration strategies.