Pore Water Circulation in Isolated Wetlands: Implications to Internal Nutrient Loading.
Abstract
The potential of wetland soils to accumulate and release pollutants including nutrients has been the motivation for numerous studies related to measuring the concentration, fate, and transport mechanisms of these substances in soils. While external nutrient loading from anthropogenic sources such as agricultural and cattle areas can be addressed through the implementation of Best Management Practices (BMPs), and interception strategies such as construction of storm-water treatment areas (STAs) in Florida, internal loading through shallow sediments has prevented the rapid improvement of water quality in numerous watersheds in South Florida, including the Lake Okeechobee drainage basin. The internal release of nutrients can occur via two different yet equally important mechanisms: advection and diffusion. These processes may mix the pore water not only within the sediment but also with the overlying water column over short periods of time (e.g., days or weeks). This provides sufficient time for diagenesis to alter the reactive chemical components of nutrients that may ultimately increase the nutrient fluxes to the overlying water column. The objectives of this research are to present a plausible and testable technique to collect pore water samples from saturated wetland soils, and to evaluate the importance of pore water circulation as a mechanism for mobilizing nutrients into the water column from within shallow sediments in isolated wetlands. Pore water sampling can be a difficult task to perform in low permeable wetland soils using standard sampling devices such as pore water equilibrators (peepers) and mechanical vises (Rheeburg squeezers). However, our attempt at using Multisamplers, which is in fact a multi-level piezometer capable of collecting up to ten pore water samples to a depth of 110 cm below the soil-water interface in a single deployment, proved to be a success. The ability to collect samples from multiple depths from a single location is an important feature because large vertical changes in chemical composition of the pore water could be useful in calculating potential diffusive fluxes associated with pore water circulation. While the concentration of macro-nutrients such as total phosphorus (TP), total dissolved phosphorus (TDP), soluble reactive phosphorus (SRP) and total organic carbon (TOC) showed a general depleting trend from the sediment-water interface downward, the dissolved oxygen (DO) concentration fluctuated between 6.55 to 1.69 mg/L. The nonzero concentrations of oxygen could indicate the lack of complete microbial reduction of the oxygen in the pore water, more likely the result of advective mixing of the pore water due to bioturbation.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2005
- Bibcode:
- 2005AGUFM.H21B1331B
- Keywords:
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- 1830 Groundwater/surface water interaction