Graduation Year

2008

Document Type

Thesis

Degree

M.S.

Degree Granting Department

Geology

Major Professor

Jonathan G. Wynn, Ph.D.

Keywords

Hydrology, Cypress domes, Hydric soils, Isotopes, Nitrogen

Abstract

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.

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