The Environmental Chemical Sciences (ECS) program of the Division of Chemistry will support the collaborative RAPID research project of Prof. Thomas Bianchi of Texas A & M University, Prof. Robert Cook of Louisiana State University and Prof. Michael Perdue of Georgia Institute of Technology. The collaborative team will investigate the impact of oil contamination from the Deep Horizon Disaster in the Gulf of Mexico on the composition of dissolved organic matter (DOM) in the Louisiana coastal marshes. The study aims to prove that changes in the component signature of DOM collected from the Louisiana coastal marshes will be indicative of the impact of the Deep Horizon oil spill on geochemical processes in the Louisiana marshes. The team of investigators will utilize boats from the Louisiana Marine Universities Consortium (LUMCON), located in Terrebonne, LA to collect water samples from marshes along Terrebonne Bay. The samples will be filtered to collect the DOM from the water samples. Advanced analytical methods will be used to analyze the DOM content.
The study is crucial to elucidate the impact of the Deep Horizon oil spill on the ecosystems along the Louisiana coast. Better understanding of this impact is imperative to development of strategies to restore the marshes to their condition prior to the Deep Horizon oil spill disaster.
Intellectual Merit Our describes first results of an initial assessment of the impact of a water diversion event on the concentration and chemical composition of dissolved organic matter (DOM) and on bacterioplankton community composition and structure in Barataria Bay, Louisiana U.S.A, an important estuary within the Mississippi River Delta complex. Concentrations and spectral properties of DOM, as reflected by UV/visible absorbance and fluorescence, were strikingly similar at 26 sites that were sampled along transects near two western and two eastern sites in Barataria Bay in July 2010. In September 2010, dissolved organic carbon (DOC) was significantly higher (568.1 - 1043 uM C, x = 755.6 +/- 117.7 uM C, n = 14) compared with July 2010 (249.1 - 577.1 uM C, x = 383.7 +/- 98.31 uM C, n = 14); conversely, Abs254 was consistently higher at every site in July (0.105 to 0.314) than in September (0.080-0.221), averaging 0.24 ± 0.06 in July and 0.15 ± 0.04 in September. Fluorescence data via the fluorescence index (FI450/500) revealed that only 30% (8 out of 26) of the July samples had a fluorescence index (FI450/500) value above 1.36, compared to 96% (25 out of 26) for the September samples, which is indicative of the July DOM being of more terrestrial origin. In July, bacterioplankton in samples from eastern Barataria Bay differed in composition from bacterioplankon in samples from western Barataria Bay. These differences appeared to result from reduced salinities caused by the freshwater diversion. Thus, the observed trends in bacterioplankton and DOM were likely due to changes in water masses (e.g., Mississippi River water in July to estuarine waters in September). Discharge of water from the Davis Pond Freshwater Diversion (DPFD) through Barataria Bay may have in part, mitigated some adverse effects of the oil spill, inasmuch as DOM is concerned. Broader Impacts This study was undertaken to detect transient signals from the diversion of water through the DPFD that might be encoded in the chemical composition of DOM and accessible through a careful examination of spatial and temporal variations in the spectral properties of DOM and the microbial community responsible for its mineralization. Although not major focus on this study, we also observed no convincing evidence for the presence of oil or its degradation products was obtained through the analysis of DOM. Asphaltenes, a major component of this particular crude oil, have relatively featureless UV/visible absorbance spectra that vaguely resemble the spectra of DOM samples. Fluorescence EEM’s of crude oil in seawater and in seawater containing chemical dispersants share some of the characteristic features of DOM. More detailed work on the hydrocarbons is needed to better understand possible oil effects. Finally, the coastal marshes in the northern Gulf of Mexico typically contains some of the highest concentrations of DOC in the U.S., even higher than DOC concentrations in the lower Mississippi River. The lower DOC concentrations in Barataria Bay in July, when the diversion of water via the DPFD was at a maximum, are a consequence of relatively low concentration of DOC in the lower Mississippi River, and the higher DOC concentrations of DOC in Barataria Bay in September, when flow from the DPFD had largely ceased, are typical of Barataria Bay. This study has the incidental benefit of providing background data that are relevant for the restoration of North America’s largest delta. Plans to restore the Mississippi River Delta rely heavily on partial diversion of the flow of the Mississippi River to provide the sediments and freshwater that is necessary for accretion of wetlands. Although there have been several key studies on the impacts of river diversions on nutrient geochemistry, little evidence exists on the impacts of such diversions on the DOC pool or on the broader-scale distribution of salinity. The opening of the DPFD during the summer of 2010 introduced massive quantities of Mississippi River water into Barataria Bay over the course of just a few months, causing a transient perturbation of the distribution and characteristics of DOC in Barataria Bay. In essence, these results have broader applications to management of coastal system in Louisiana, one of the most environmentally disrupted coastal regions in country. This work resulted in the publication of paper that is now "in press" entitled: Impacts of Diverted Freshwater on Dissolved Organic Matter and Microbial Communities in Barataria Bay, Louisiana, U.S.A. by: Thomas S. Bianchi, Robert L. Cook, E. Michael Perdue, Paulina E. Kolic, Nelson Green, Yaoling Zhang, Richard W. Smith, Alexander S. Kolker, Alex Ameen, Gary King, Loice Ojwang, Caroline Schneider, Anna Normand, and Robert Hetland 5 of the co-authors on this paperare graduate students and 2 are undergraduates.
