TRACE ELEMENT, PAH AND NUTRIENT DISTRIBUTIONS IN WATERS AFFECTED BY THE DEEPWATER HORIZON OIL SPILL

In order to understand the impact of the Deepwater Horizon oil spill on trace element, nutrient and polycyclic aromatic hydrocarbon (PAH) distributions, samples were collected from both oil contaminated and uncontaminated areas around oil rig explosion site during three cruises in early and late May and October 2010. The results of PAH analyses revealed significant concentrations near the wellhead, decreasing with distance away from it. The vertical PAH distribution showed relatively high concentrations in a subsurface oil plume, at a depth around 1100-1300 m. The proportion of methyl naphthalenes was high in the subsurface oil plume and low at the surface, indicating fractionation of PAH’s during transport as well as probably volatilization effects. Nitrate, phosphate and dissolved oxygen (DO) showed similar distributions, being slightly depleted in the subsurface plume. However, no effect on dissolved silica was noted. This indicates bacterial consumption of the nutrients and DO during break down of the oil. Trace element distribution could be affected both indirect and direct ways. Directly, some trace elements enriched in crude oil such as Ni, V, Cr and Zn can be released to the water column. Indirectly, the speciation, solubility, and chemical fluxes could be altered by a) distribution of oxygen (e.g., oxygen depletion), b) the addition of complexers (e.g., sulfur compounds and organic matters in the crude oil), and c) effects of oil on the surface of particles and sediments. Ongoing analyses show minor impacts on trace element distributions. For instance, dissolved V was unaffected whereas slight increases in Ba and Cr in the subsurface plume were noted.