Biogeochemical cycling of carbon, nitrogen, and phosphorus in saltwater marshes of Lavaca Bay, Texas

Armstong, NE
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Center for Research in Water Resources, Environmental Health Engineering Research Laboratory, Civil Engineering Department, University of Texas at Austin

It was the purpose of this project to perform studies leading to descriptions of the biogeochemical cycles of carbon (C), nitrogen (N), and phosphorus (P) in the saltwater marshes of Lavaca Bay and to state these descriptions in a quantitative form suitable for inclustion in the Board's mathematical model. Both laboratory and field tests were conducted. Special sediment slurry uptake studies were performed for the purpose of developing Freundlich-like isotherms relating sediment concentrations of C, N, P to the equilibrium concentrations in water and to show the effects of sediment composition, salinity, and temperature on uptake. The flux of N and P into and out of sediment were studied in fixed-bed systems by continuously adding various amounts of N and P to these systems and following uptake in the sediments until equilibrium conditions were established, then stopping the additions and following the release of nutrients from the sediments. Also, portions of the marsh were isolated in several cylindrical plexiglass chambers in the laboratory and nutrient exchange studies performed. Mass balances were made for C, N, and P added in spiked and non-spiked Bay water, and productivity measurements were taken to determine the stimulatory effects of these nutrient additions. The field studies involved the collection of hydraulic and nutrient data at several stations in a bayou off Swan Lake in Lavaca Bay to determine net nutrient transport and exchange from and in the saltwater marshes. Three field trips were made covering flooded, dry, and moderately wet conditions in the marsh. From these studies, mathematical models describing the sediment uptake of C, N, and P as a fraction of the mass transfer coefficient and the difference between equilibrium (as related to the sediments) and ambient nutrient concentrations were to be developed. These models were to be of such form as to be used directly in the Board's larger water quality model. The organization of this report is as follows. Chapters are numbered by Roman numerals, and pages, tables, and figures are numbered within individual chapters using the chapter Roman numeral followed by an Arabic numeral (e.g. II-1, IV-2, etc.). Figures are placed at the end of each chapter. The results of the literature review are presented in Chapter II followd by the methods used in this study in Chapter III. Results of the field and laboratory investigations are contained in Chapter IV, and the results are discussed in Chapter V. Finally, the conclusions of this study and recommendations for future work are given in Chapter VI.

85 pages
carbon, chemical cycles, marshes, nitrogen, phosphorus, saltwater marshes