Print PageLabile fractions of soil organic carbon and nitrogen represent easily lost nutrients from ecosystems and can be determined by the ability of microorganisms to mineralize soil organic matter (SOM). Wetland soils typically experience long periods of anaerobic moisture conditions inhibiting mineralization by decreasing the efficiency of microbial respiration and allowing organic C and N pools to accumulate. In Florida, a low-relief landscape and the hydrological connectivity between ground and surface water provides a tight link between the shallow water table and soil moisture conditions in the freshwater wetlands around Tampa Bay. Over the last few decades, water table drawdown in many wetlands may have reduced soil moisture and promoted aerobic soil respiration. We conducted soil physical and biogeochemical analyses in 29 wetlands to investigate two questions. (1) Has water table drawdown reduced the labile fraction of SOM, leaving smaller, more recalcitrant pools of organic C and N? (2) Comparing cypress forest and herbaceous marsh wetland types, how does the complexity of the organic matter affect total and labile organic C and N pools?
Results/Conclusions
Water table drawdown appears to have increased aerobic soil respiration by microorganisms. Wetlands experiencing years to decades of lowered water tables have decreased amounts of total organic C and N, and smaller fractions of labile material than those wetlands exhibiting higher water tables. Relative to soils from herbaceous marshes, soils from cypress forest wetlands contain more SOM. Variability in labile carbon and nitrogen is also exhibited when comparing cypress and marsh soil organic matter.
