Master of Science (MS)
Oceanography and Coastal Sciences
Atmospheric carbon dioxide (CO2) levels and global eutrophication are anthropogenic stressors impacting the environment of specific interest in wetland systems. Wetlands occupy a critical interface between terrestrial and aquatic environments. Fertilizer use for agriculture and treated wastewater disposal has increased nutrient loading to wetlands. Conflicting results on impacts of nitrogen loading to coastal wetland soils have been reported, though most studies have investigated short-term impacts of nutrient loading, not long-term integrated impacts. I investigated an 11-year period of nutrient loading on soils in an oligohaline coastal wetland. Nitrogen treatments of 0, 50, 200, and 1200 kg ha-1 yr-1 were paired with phosphorus treatments of 0, 131 kg ha-1 yr-1. I measured soil physiochemical characteristics, microbial biomass N (MBN), potentially mineralizable N rates (PMN), and denitrification rates. Total P increased with P additions. There were no significant differences in measures of soil microbial biomass or activity with N or P loading. Results suggest that after bioavailable nutrients are incorporated into the soil matrix, there are no lasting effects on measured microbial activities of these coastal marsh soils. I also investigated the impacts of increased CO2 levels on biogeochemical cycling and associated microbial activity. I conducted a 2-year experiment with CO2 treatment applications of 710 and 410 ppm applied to vegetated and non-vegetated wetland soils. I measured soil physiochemical properties, extracellular enzyme activity, MBN, PMN, and extractable NH4+. Phosphatase activity decreased (p = 0.09) with increased CO2 in the non-vegetated soils. PMN and extractable NH4+ varied significantly with the interaction between vegetation presence and CO2 (p=0.07, p=0.0001). Total P and organic matter content were significantly higher in the vegetated soils (p = 0.05, p=0.06). Higher bioavailable nutrient concentrations in non-vegetated soils under elevated CO2 indicate there is a mechanism to increase microbial activity under elevated CO2 conditions, with implications for carbon sequestration.
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Steinmuller, Havalend Ellen, "Anthropogenic Impacts on Soil Microbial Processes in Coastal Wetlands: Nutrient Loading and Rising CO2 Levels" (2015). LSU Master's Theses. 3401.