Mucking About: Hydrologic Regime and Soil Carbon Storage in Restored Subtropical Wetlands

Wetlands are extremely important ecosystems that have declined drastically worldwide, continue to be lost, and are threatened globally. They perform a number of important ecosystem services such as flood control, provide habitat for many species, and have aesthetic and recreational value. Wetlands are also important to the global carbon (C) cycle. Wetland soils are especially effective C sinks because they have high primary productivity and low decomposition rates due to flooded, anoxic conditions. Increased recognition of wetlands\u27 value has led to more ecological and hydrological restoration of degraded wetlands to mitigate the effects of wetland destruction. Hydrological restoration, which attempts to recreate natural hydroperiod and water levels in wetlands, is expected to increase soil C storage. Many studies have estimated the C stock in different wetland ecosystems across biomes, but few have examined hydrological drivers of soil C variation across wetland types. This study investigated the relationship between hydrologic variables (hydroperiod and average water depth) and soil C storage in three types of hydrologically restored wetlands (marsh, bay swamp, and cypress swamp) at the Disney Wilderness Preserve (DWP) in central Florida, USA. I collected 150 50-cm soil cores along existing monitoring transects in sampled wetlands where water elevation data had been collected since 1995 to examine the relationship between hydrologic variable and soil C storage. I analyzed a combination of generalized linear mixed models (glmm), evaluated using AICc. Mean water depth was a better predictor than hydroperiod of soil C concentration and stock. Mean water depth had a significant positive relationship with soil C concentration in bay swamps and marshes and soil C stock in marshes. However, this effect was small and often outweighed by other factors such as differences in vegetative community, soil depth, or local site conditions. Water depth had no significant relationship with soil C concentration in cypress swamps or upland communities or on soil C stock in bay swamps, cypress swamps, or uplands. Wetland community type had a strong influence on soil C variation, with bay swamp soils having the highest mean soil C concentration followed by cypress swamp, marsh, and upland soils, respectively. Soil C concentration generally decreased with soil depth. Bay swamps also had the highest soil C stock, followed by cypress swamp, marsh, and upland soils, respectively. Together, the sampled wetland communities cover approximately 22% of the sampled communities at DWP, yet store an estimated 47% of the total soil C to a 90 cm depth. The results of this study affirm the importance of inundation for soil C storage in wetlands, but also highlight that there are a number of other complex variables affecting soil C in different types of wetlands such as differences in litter quality and decomposition rates