acase@tulane.edu

Degradation processes change the chemical composition of oil and can be affected by the mixing of oil into the environment. Here, a ramped pyrolysis (RP) isotope technique is implemented to investigate thermochemical and isotopic changes in coastal environments impacted by the 2010 BP Deepwater Horizon oil spill (DwH). Marsh sediment determined to contain oil by PAH analysis display relatively low thermochemical stability and depleted stable carbon (13C) and radiocarbon (14C) isotopic signatures. The ability of RP to separate oil from background organic material (OM) is established by high oil composition for pyrolysates evolved at low temperatures, as determined by radiocarbon measurement. Applying the RP isotopic technique to beach sediment, tar, and marsh samples collected over a span of 881 days reveals a predominance of oil in the organic material for up to 881 days and varying rates of degradation. Pyrolysis profiles show that the oil degraded faster where rates of mixing were higher. Observing how oil changes thermochemically over time provides a new perspective on oil degradation and its relationship with mixing. / acase@tulane.edu

The Wax Lake Delta (WLD) is one of the few areas of land gain in coastal Louisiana and provides an analog for a naturally developing subdelta created by a river diversion. This study examined the spatial and temporal variability of benthic respiration to broaden our current understanding of the biogeochemical functioning of diversion-created estuarine systems. Spatial and seasonal benthic respiration rates were quantified during distinct periods of discharge and water temperature conditions, which included a spring period of peak river discharge (May 2012, 2013), a summer period of low discharge and maximum seasonal water temperatures (August/Sept, 2012), and an autumn period of low discharge and intermediate water temperatures (October 2013). Benthic respiration rates for the Wax Lake Delta ranged from 4.4 – 46.8 and averaged 16.7 (± 1.5) mmol O2 m-2 d-1 . Atchafalaya Bay sites ranged from 10.3 - 26.5 and averaged 17.1 (± 1.5) mmol O2 m-2 d-1 across all sites and seasons. Benthic respiration generally increased along two spatial gradients: 1) with distance offshore from the delta into Atchafalaya Bay, and 2) toward the interior of a mouth bar island. These patterns were related to similar increases in sediment OC and N content, which were derived from a mix of terrigenous and marine sources and varied with season. Sediment organic (OC and N) content and water temperature were identified as main drivers influencing benthic respiration in the Wax Lake Delta estuary. Seasonal changes in riverine discharge and wind-driven sediment resuspension events were likely to influence the seasonal variability of benthic respiration by governing water temperature and organic matter supply to the sediments. Benthic oxygen consumption rates in the Wax Lake Delta were most sensitive to increases in water temperature during low discharge conditions (< 2,000 m3 /s) of the MI-AR system. In context of coastal restoration, results from this study suggest that opening a sediment diversion during spring peak discharge conditions will have less of an effect on benthic oxygen consumption rates than during warmer low flow conditions. / acase@tulane.edu

acase@tulane.edu

This dissertation combines laboratory experiments and analysis of field samples to examine tungsten (W) geochemistry. Data from low ionic strength experimental solutions at room temperature containing between 0.01 M to 0.0002 M total sulfide and 0.0027 M - 0.0001 M tungstate were analyzed using UV/VIS spectrophotometry. Stability constants have been determined for the formation of mono-thiotungstate log K01= 3.43 ± 0.61, di-thiotungstate log K12 = 3.02 ± 0.61, tri-thiotungstate log K23 = 2.82 ± 0.02, and we estimated the tetra-thiotungstate log K34 ~ 2.34. Analysis of W, Mo, Mn, and Fe concentrations in estuarine surface and pore waters and sediments captured environmental samples from oxic and sulfidic conditions. Both surface waters and sediments demonstrated a positive correlation between W and Fe. Unlike Mo, which was depleted in sulfidic salt marsh pore waters, W was enriched in all pore waters in comparison to overlying waters. Thermodynamic modeling of W and Mo thioanion species in sulfidic pore water samples predicts ≤ 50% of tungstate (WO42-) forms thiotungstate species and complete conversion of molybdate (MoO42-) to tetrathiomolybdate (MoS42-). Unlike tetrathiomolydate that is known to be more particle reactive than molybdate, increases in dissolved W coincide with increases in dissolved sulfide in pore waters, suggesting thiotungstates are less particle reactive than thiomolybdates at circum-neutral pH. Finally, sediment analysis suggests sequestration of W is dependent on surface water salinity in the intermediate marsh sediments, and long-term W entrapment occurs in sulfidic salt marsh sediments. / acase@tulane.edu

It is well recognized that rivers are the primary pathway that delivers sediment to the ocean. However, the fate of these sediments is poorly understood, and is complicated by relative sea level rise and meteorological forcings. One coastal system to examine these issues is the Atchafalaya River-Chenier Plain (ARCP) of southwest Louisiana, which relies on Mississippi River sediment supply and is vulnerable to coastal erosion and land loss. Despite regional coastal degradation, some land gain and marsh growth have been observed here. Land gain in south Louisiana is generally observed at the mouths of the rivers – the Bird’s Foot, and the Atchafalaya and Wax Lake deltas. However, satellite imagery and sedimentological analyses indicate that coastal lakes in southwest Louisiana have also filled in and converted into salt marshes in the last 40 years. To understand sediment delivery in these marshes, multiple short cores were collected in a central Chenier Plain tidal creek system, and analyzed for 210Pb, 137Cs, 7Be, δ13C, and grain size distribution. We propose that Chenier Plain reactivation processes are triggered by the increase in Atchafalaya River flow that began in the early 1900s. Fluvial sediments delivered through westward longshore transport and resuspended during energetic events become available to the sediment-starved Chenier coast, leading to deposition, infilling, mudflat progradation, and marsh growth. / acase@tulane.edu

Adam Wei is employing homegrown UBC technology to help manage the sustainability of China’s fir trees.

The dissertation is comprised of three manuscripts presenting rare earth element (REE) and neodymium (Nd) isotopic analyses for the groundwaters, surface waters, sediments, and bedrocks of two estuaries along the eastern coast of the United States: Indian River Lagoon, Florida, and Pettaquamscutt Estuary, Rhode Island. This research was performed to understand the behavior of REEs in subterranean estuaries, the REE SGD fluxes, and the Nd isotopic composition of SGD. The selection of these sites offers contrasting geology (carbonate/sand matrix aquifer versus glacial till aquifer sourced from granitoids) and contrasting subterranean estuary structure. In the first site, the flux of REEs to the Indian River Lagoon, FL is comprised of a nearshore source of terrestrial SGD displaying a HREE-enriched fractionation pattern, and LREE- and MREE-enriched sources that originate from the reductive dissolution of Fe (III) oxide/hydroxides in the subterranean estuary and transported by bioirrigation to the overlying lagoon. The εNd(0) value the Indian River Lagoon groundwater is much more radiogenic than those of the surface water and sediments which could be due to the use of fertilizers in adjacent communities. The surface waters Nd isotopic composition appears to be a mixture of weathering of the Anastasia Formation and dissolution of eolian-transported Saharan Dust. In contrast at the second site, phosphate minerals control the surface and groundwaters of the Pettaquamscutt estuary, RI. The weathering of apatite and precipitation of secondary REE phosphate minerals most likely produce the MREE-enriched fractionation patterns of the Pettaquamscutt groundwaters. The further precipitation of the secondary REE phosphates in the surface waters of the Pettaquamscutt yields HREE-enriched fractionation patterns. The radiogenic Nd isotopic ratios of the Pettaquamscutt waters relative to the bedrock further suggest that apatite is the source of REEs. The Nd flux of SGD for both sites is roughly equal to the respective river fluxes; however, the Nd flux of SGD to the Pettaquamscutt is approximately 3 times greater than the SGD flux to the Indian River Lagoon. More research is needed in both environments to evaluate the impact of SGD on the Nd isotopic budget of the oceans. / acase@tulane.edu