Master of Science (MS)
Oceanography and Coastal Sciences
Coastal Louisiana is at risk from increases in salinity from storm surge and nutrient loading from the Mississippi River. Increased salinity causes plant death, decreases in microbial productivity, and shifts in biogeochemical processes. Eutrophication is linked to shifts in plant communities and changes in wetland biogeochemical properties. We hypothesized that 1) storm surge would increase soil porewater salinity and decrease extractable ammonium (NH4), and 2) long-term nutrient loading would decrease soil extracellular enzyme activity and increase total nutrients. Intact soil cores from two sites in the Wax Lake Delta were continually flooded with 35 g L-1 salt water for 1, 2, and 4 weeks. Salinity averaged 1.46 in the mudflat and 1.03 in the marsh soils. Salinity levels increased significantly in the top 8 cm of the marsh and top 6 cm of the mudflat cores after the first week of flooding. Approximately 53% and 80% of the salt that diffused into the mudflat and marsh, did so during the first week of flooding. Extractable NH4 did not change significantly after the first week of flooding, but increased significantly from 4-12 cm in the mudflat soil and in the top 14 cm in the marsh cores at four weeks. This study found that even a short flood can significantly increase soil porewater salinity in a majority of the plant rhizosphere. Intact soil cores from an ongoing fertilization experiment in Madisonville, LA were analyzed for extracellular enzyme activity. Mean activities in the control were 18058 nmol MUF g-1 hr-1, 2850 nmol MUF g-1 hr-1, and 330 nmol MUF g-1 hr-1 for phosphatase, â-glucosidase, and sulfatase, respectively. Enzyme activity was not significantly affected long term nutrient loading. Total N and C were not significantly affected by nutrient loading, but total P significantly increased with P loading. No differences in extracellular enzyme activities suggest that soil microorganisms have not been functionally affected by a decade of nutrient loading. Our results indicated how salinity and nutrient loading impacted coastal wetland soil, and these results can be used to augment management techniques to help stem further coastal degradation.
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McKee, Morgan, "Effects of Storm Surge and Nutrient Loading on Coastal Wetland Soil Processes: Implications for Ecosystem Function" (2014). LSU Master's Theses. 1648.