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SEDIMENT GEOCHEMICAL MODEL
Eldridge, P M. AND J. Morse. SEDIMENT GEOCHEMICAL MODEL. Chapter III, Dunton (ed.), Effects of Dredge Deposits on Seagrasses: An Integrative Model for Laguna Madre. U.S. Army Corps of Engineers, Galveston, TX, I:III-1-32, (2003).
Until recently, sediment geochemical models (diagenetic models) have been only able to explain sedimentary flux and concentration profiles for a few simplified geochemical cycles (e.g., nitrogen, carbon and sulfur). However with advances in numerical methods, increased accuracy and precision of chemical analyses, and a greater understanding of sedimentary processes, a new generation of models have been developed that incorporates most of the important sedimentary geochemical cycles simultaneously. In Chapter III we borrowed heavily from these models to develop a geochemical model that describes sedimentary processes in seagrass beds. The seagrass geochemical model is unique in that it includes a simulation of the seagrass rhizosphere (sediment geochemical zone influenced by seagrass roots and rhizomes). The rhizosphere simulation is important since seagrass pump O2 from their root system into the sediments to reduce the concentration of toxic sulfides. The O2 is routed through a transport structure (lacunae) from the shoots, where it is produced by photosynthesis, to the roots and rhizomes where it diffuses into the sediments. The model is optimized to operate in the rapidly fluctuating environments found in lagoons and bays of Texas. Chapter III describes the model structure, its parameterization and calibration. The calibration data set was developed for sediments of Syringodium filiforme, Thalassia testudinum, and Halodule wrightii seagrass beds (see Chapter VII). The model was validated with a separate data set collected during a dredge event in lower Laguna Madre (Chapter V). The results of that simulation verified the accuracy of the model under condition found over an annual cycle.
The goal of the diagenetic model development was to provide an accurate geochemical model that could be coupled to the seagrass production model (Chapter I). However the results of the calibration phase of this study showed an interesting interaction between the seagras
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