Effects of Anthropogenic Nutrient Enrichment on Exotic and Restored Native Aquatic Vegetation

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water quality, wastewater, detention basin, Alternanthera philoxeroides, Eichhornia crassipes, Pistia stratiotes, Schoenoplectus californicus
thesis / dissertation description
Understanding how nutrient input into coastal wetlands influences aquatic vegetation and the fate of anthropogenic nutrient inputs can help improve water quality management plans. The goals of this study were to (1) compare nutrient concentrations in various storage compartments downstream from two point nutrient sources (a sewage treatment plant outfall and a residential detention basin) in Armand Bayou, a coastal brackish wetland in the Galveston Bay (Texas, USA) watershed, and (2) determine if nutrient storage in those compartments helped improve water quality downstream. Water column nutrients can be assimilated by aquatic vegetation, adsorbed to sediment, or diluted within the system as distance from source input increases. To determine the fate of nutrients to Armand Bayou, I measured nutrient concentrations in the sediment, water column, pore water, and tissue of exotic and restored native plants downstream from a sewage treatment plant and a residential detention basin. To assess nutrient removal potential of a common exotic species, I determined relative growth and nutrient uptake rates of Eichhornia crassipes. Water column total nitrogen, NH₄⁺ and NO₃ˉ concentrations decreased by 95, 96 and 99 percent downstream from the sewage outfall (~2200 m distance). Water column NH₄⁺ and NO₂ˉ concentrations decreased by 93 and 75 percent downstream from the detention basin (~2500 m distance). Exotic species Alternanthera philoxeroides, Pistia stratiotes and E. crassipes showed higher aboveground/emergent tissue nutrient content than restored, native Schoenoplectus californicus for both tributaries. Schoenoplectus californicus had the largest biomass although appeared to be limited in its ability to remove nitrogen from the water column. Nutrient uptake rates by E. crassipes were low and did not change with increasing distance from nutrient source, but high relative growth rates in both tributaries suggest the nuisance potential of this exotic species. Low sediment and pore water nutrient concentrations for both tributaries suggest these compartments are not sinks. All plant species did not respond to changes in water column nutrient concentrations with increasing distance from source input suggesting dilution to be the main factor in water column nutrient decline for both tributaries. This study will provide water quality resource managers guidance on the development of total maximum daily loads (TMDLs) for water bodies impaired by high nutrient loading and the implementation of wetland plants efficient in nutrient removal for water quality improvement.

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