From the River to the Gulf: An Investigation of Biogeochemical Cycling in Wetland Soils and Coastal Shelf Sediments
Semester of Graduation
Master of Science (MS)
Oceanography and Coastal Sciences
Louisiana is home to 40% of the coastal wetlands in the lower 48 states, yet accounts for 80% of the coastal wetland loss in this region. This loss is attributed to decreased sediment supply, levee alteration, sea level rise, channelization, and subsidence. The levee system in Louisiana disconnected coastal wetlands from the main stem of the Mississippi River (MSR), reducing the amount of land-building sediment that reaches coastal wetlands. This disconnection also allows a greater percentage of river discharge, including agricultural contaminants and runoff, to flow into the northern Gulf of Mexico (NGOM).
The 2012 Coastal Master Plan proposed eight sediment diversions to combat coastal land loss within Barataria and Breton Basins. The Mid-Barataria Sediment Diversion (MBSD) is projected to divert up to 2,100 m3 s-1 of sediment-laden water into degraded areas of Barataria Basin. In Chapter 1, we aim to quantify the effects of incoming river water temperature from the MBSD on nitrate removal in marsh and bay sediments within Barataria Basin. Results show that influx of colder river water limited nitrate removal processes from 5-14°C, before increasing 2-fold in 20°C treatments. Findings from this study can inform restoration modelers of the net impact of the MBSD on Barataria Basin.
Nitrate removal properties of coastal wetlands are becoming increasingly important as hypoxia remains an issue for the NGOM. Excess N and P from the MSR has led to a seasonally presenthypoxic area with /L O2 in bottom waters, approximating 26,000 km2 in 2017. Under low oxygen conditions, sedimentary P can become an internal source to marine systems through iron reduction. Benthic P flux can potentially combine with excess N in the water column to support primary production and possibly prolong hypoxia. In Chapter 2, we aim to quantify the significance of P mobilization in the NGOM. Despite variations in seasons of sediment collection, bottom water oxygen concentrations, and differences in P pool concentrations, there was no benthic P flux into the water column. This is the first study to report P speciation in NGOM sediments coupled with benthic P flux rates on a spatial and temporal scale.
Bowes, Katie, "From the River to the Gulf: An Investigation of Biogeochemical Cycling in Wetland Soils and Coastal Shelf Sediments" (2018). LSU Master's Theses. 4809.
White, John R.