Wetlands

Wetlands are an essential part of the water management system in South Florida, providing many ecosystem services. However, the hydrologic connections of many wetlands, including Loxahatchee Slough in Florida, are poorly understood. Loxahatchee Slough is Palm Beach County’s most diverse natural area and a site of ongoing restoration. The primary objective of this research was to characterize the spatial and temporal variability of surface-groundwater exchange at Loxahatchee Slough. The Magnitude of groundwater seepage to the canal varied spatially. Little seasonal variability in exchange was identified in this study. Canal stage had a strong relationship with groundwater levels and slough stage indicating its important influence. This study provides more insight into the heterogeneous nature of wetland-canal exchange and the need for site-specific evaluation at wetlands for successful management.

Storing almost a third of the global soil carbon pool, wetlands are an essential component of the carbon cycle, and carbon-rich peat soil accumulates when carbon input through primary productivity exceeds output through decomposition. However, woody shrub encroachment in herbaceous wetlands can alter soil carbon processes, potentially diminishing stored carbon. To examine the effects of shrub encroachment on soil carbon, I compared soil carbon input through litterfall and fine root production, output through decomposition, and below-canopy microclimate conditions between Carolina willow shrub (Salix caroliniana) and herbaceous sawgrass (Cladium jamaicense) in the Blue Cypress Marsh Conservation Area (BCMCA), FL. To assess the level of production and its response to water level, I compared aboveground green biomass by measuring normalized difference vegetation index (NDVI) and photosynthetic stress by measuring photochemical reflectance index (PRI) between sawgrass and willow. I collected willow litterfall using litter traps and measured sawgrass and willow fine root production with fine root ingrowth bags. Litter decomposition was measured with decomposition bags deployed using a reciprocal litter placement design at BCMCA and incubated in a greenhouse to examine the effects of char and water level on decomposition. Above and belowground microclimate conditions were measured using sensors installed within sawgrass and willow canopies. Despite experiencing more photosynthetic stress, willow produced more green biomass than sawgrass. However, willow produced fewer fine roots than sawgrass and these roots were deeper within the soil. Willow litter decomposed faster even though sawgrass decomposition increased under drier conditions. Compared to the sawgrass canopy, the willow canopy had greater light availability, lower evaporative demand plus warmer and drier soils; however, litter decomposition did not differ between the canopies. These results suggest that willow encroachment can reduce the amount and alter the distribution of carbon within an herbaceous wetland, likely resulting in a net loss of soil carbon. Although willow encroachment may increase aboveground biomass carbon stocks, these stocks will likely be offset by a loss of soil carbon due to reduced fine root production and increased decomposition. Therefore, the transition from herbaceous wetland to shrub wetland will likely result in a loss of stored soil carbon.