Saturated for most of the year, wetlands accumulate large amounts of biomass in thick organic soil horizons with slow rates of decomposition due to anaerobic conditions. Wetland soils thereby sequester large amounts of organic carbon in relative long-term storage. Municipal water demands in west-central Florida are largely met through extensive groundwater pumping. These withdrawals can impact ecosystems dependent on surface water levels that are ultimately linked to confined aquifers. Soils in a subset of cypress swamps that are monitored by the Southwest Florida Water Management District (SWFWMD) were sampled and analyzed to ascertain the health of the wetlands impacted by groundwater pumping. Soil water content, bulk density, and carbon and nitrogen content were systematically measured on replicate samples from three elevations in transects through the wetlands. "Healthy" wetlands were found to have higher soil water retention and consequently higher soil organic carbon (SOC) content in the top 30 cm of soil than "harmed" and "significantly harmed" cypress domes. However this trend was only significant at the lowest, central elevation of the wetland, at an elevation of the normal pool level minus 12 inches. These results provide quantitative evidence to support the notion that saturation of soils during most of the year is required to maintain the conditions that are conducive to the accumulation of soil organic matter. Conversely, unsaturated soils appear to be mineralizing large quantities of their stores of organic carbon. Since soil moisture and organic carbon contents are well correlated in the wetlands that were sampled, monitoring of soil water content may prove a convenient proxy for determining the organic carbon stores and thus the relative health of the wetland.

Soil organic matter (SOM) provides many ecosystem services that are necessary for continued ecosystem function. The accumulation of SOM in an ecosystem is a function of its persistence time which can range from days to thousands of years. Ecosystem properties including dominant vegetation type, soil texture, and soil moisture in various habitats can regulate the persistence time of SOM. Wetlands, because of their associated ecosystem properties, promote SOM accumulation, but little has been done to determine the ecosystem properties that regulate its persistence over time. In west-central Florida, urbanization and increased water demands have suppressed water tables in isolated wetland ecosystems via hydrological connectivity between ground and surficial waters. In this study, variability in wetland ecosystem properties, in particular dominant vegetation type and hydrological parameters, were tested as mechanisms driving SOM accumulation and stability. Cypress wetlands had significantly more organic matter, carbon (C), and nitrogen (N) than herbaceous marshes. In addition, increased wetland inundation promoted stable SOM accumulation in forested wetlands. By increasing the percent time a forested wetland spent aerobic, decreases occurred in both labile and stable C and N pools. As large storage units of SOM, the decreases in both labile and stable C and N pools in wetland soils have large implications for global C and N cycling. Increased manipulation of wetland water levels, especially in short time scales, can mineralize both short-term and long-term storage units of C and N. Globally, the increase mineralization of large SOC and SON stocks would exacerbate the release of air and water quality pollutants. The sensitivity of both labile and stable SOM pools draws concern when anticipating continued water demands and land use changes of the Tampa Bay region.