Type of Document Dissertation Author El-Rifai, Hasan Moustafa URN etd-07052007-210258 Title Assessment of the Utility of Chemical Pretreatments for Estimating Carbon and Phosphorus Sequestration in Soils by 13C and 31P NMR Spectrscopy Degree Doctor of Philosophy Department Chemistry and Biochemistry, Department of Advisory Committee
Advisor Name Title William T. Cooper Committee Chair John G. Dorsey Committee Member Joseph B. Schlenoff Committee Member Sanford A. Safron Committee Member William M. Landing Committee Member Keywords
- Acid Hydrolysis
- 31P NMR
- 13C NMR
Date of Defense 2007-07-02 Availability unrestricted AbstractABSTRACT
Sandy soils are a major forest resource in the southeastern U.S and intensive forest management is escalating; yet the effect of forest management on soil organic carbon (SOC) is not well documented. It is unclear to what degree root and aboveground litter inputs add to SOC; and if the relative importance of an input source changes with forest management. All these questions add to the ongoing discussion on the role of the soil in SOC storage and sequestration, as well as the impact of forest management. Investigating the questions described above will allow us to better understand SOC sequestration and protection.
In the first part of this work we have characterized labile and recalcitrant SOC pools from upland and wetland forests by acid hydrolysis (6 M HCl, 1 M HCl) and hot-water extraction. 13C nuclear magnetic resonance (NMR) spectroscopy was used to quantify the effect of acid hydrolysis and hot-water extraction on recalcitrant and labile carbon pools.
Burial of phosphorus associated with organic matter has been reported as a major mechanistic sink for phosphorus in wetlands. Wetland soils tend to accumulate organic matter due to the production of detrital (plant) material from wetland biota and the suppressed rates of decomposition. Soil accretion rates for constructed wetlands are on the order of millimeters per year, although accretion rates in productive natural systems such as the Everglades have been reported as high as one centimeter per year or more. Current design of constructed wetlands for phosphorus removal is based upon this soil accretion. The rate of phosphorus accretion through this process is used to calculate the area needed to meet designed effluent criteria. However, although much of the phosphorus added to wetlands is retained within the system, this can serve as a phosphorus source to the water column for long periods of time, even after external loads are reduced.
Wetlands are often used as `buffer zones' between agricultural areas and adjacent water bodies. The long-term effectiveness of these wetlands to retain and store phosphorus in stable forms depends upon interacting biogeochemical processes in water, detrital layers, and soil. Recognizing that detrital tissue and soil organic matter are the dominant components of wetlands, the breakdown of these materials and the release of nutrients have direct bearing on water quality and productivity of the ecosystem. Relationships developed between processes and physical and chemical properties of detrital plant tissue and soil organic matter can be incorporated into predictive models for extrapolation of results to other sites.
The second phase of the research summarized in this dissertation addresses this important issue, and has several unique themes. First, the organic phosphorus forms in a range of wetland ecosystems and their relationships with soil physical and chemical properties have never been studied. We have addressed these issues here by employing state-of-the-art NMR techniques to provide insight into the forms of inorganic and organic phosphorus and organic carbon in recently accreted and native Everglades soils.
Second, rarely have linkages been developed between organic carbon and organic phosphorus forms as they relate to their stability under a range of environmental perturbations, but this is of key importance for understanding the biogeochemistry of organic phosphorus in the environment. This research therefore provided information on the composition and stability of soil organic phosphorus and carbon in wetlands, again using primarily NMR techniques. Liquid chromatography and high resolution time-of-flight mass spectrometry were also used to validate the NMR studies.
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