Changes in the concentration and relative abundance of alkanes and PAHs from the Deepwater Horizon oiling of coastal marshes.

We determined changes of 28 alkanes and 43 different PAHs in 418 wetland soil samples collected on ten sampling trips to three Louisiana estuaries before and after they were oiled from the 2010 Deepwater Horizon disaster. There was a significant decline in 22 of the 28 alkane analytes (0.42% day(-1)), no change in 6, over 2.5 years. The concentration of five aromatic petroleum hydrocarbons (PAHs) increased (range 0.25-0.70% day(-1)), whereas the total PAH pool did not change. Of these five, naphthalene and C-1-naphthalenes are suggested to be of higher toxicity than the other three because of their relatively higher volatility or solubility. The relative proportions of alkane analytes, but not PAHs, does not yet resemble that in the pre-oiled marshes after 3 years, The trajectories of nine indicators for degradation/weathering were either inconclusive or misleading (alkanes) or confirmed the relatively meager degradation of PAHs.

Sediment-preserved diatom assemblages can distinguish a petroleum activity signal separately from the nutrient signal of the Mississippi River in coastal Louisiana.

We analyzed the preserved diatom assemblages in dated sediment cores collected from five locations in the Louisiana Bight to test if there was a signature of petroleum extraction activities (hopanes and barium) distinct from the well-documented effects of nutrient loading. The results of a multi-dimensional scaling analysis indicate that the diatom assemblage changes documented throughout the 40 year record could be explained by three variables: barium and hopanes concentrations, and Mississippi River nitrogen loading. The results of a canonical correspondence analysis demonstrated that these signals could be distinguished through correlations with specific diatom species. The abundance of Actinoptychus senarius, for example, was negatively correlated with barium and the Pseudo-nitzschia delicatissima complex was positively correlated with nitrogen loading. These results provide a "proof-of-concept" demonstration that diatom assemblages preserved in the sediments can be used to study the effects of petroleum extraction activities, and that these 'petroleum signals' may be distinguished from other significant influences such as nutrient loading.

Historical polycyclic aromatic and petrogenic hydrocarbon loading in Northern Central Gulf of Mexico shelf sediments.

The distribution of selected hydrocarbons within ten dated sediment cores taken from the Mississippi River Bight off coastal Louisiana suggests a chronic contaminant loading from several sources including the river itself, oil and gas exploration in the central Gulf of Mexico (GOM) shelf area, and natural geologic hydrocarbon seeps. Data were grouped as either total polycyclic aromatic hydrocarbons (PAH's), which were indicative of pyrogenic PAH's; or estimated total hopanes (indicative of petrogenic hydrocarbons). The total PAH concentrations and estimated total hopanes begin increasing above background levels (approximately 200 ng g(-1)) after the 1950s. The distribution of these hydrocarbons and hopanes within the dated sediment cores suggests that the Mississippi River is a regional source of pyrogenic PAH's, and that the hopanes are from natural geologic hydrocarbon seeps, oil and gas exploration in the GOM, or both.

Application of glass capillary columns to monitor petroleum-type hydrocarbons in marine sediments.

High resolution glass capillary columns coated with SE 52 liquid phase were used to resolve the indigenous hydrocarbons extracted from sediment samples collected from three outer continental shelf areas. The extracts were than spiked with small amounts of aliphatic or aromatic components isolated from a Louisiana crude oil and rechromatographed. The resolution was sufficient to separate almost all the isoprenoid, branched and cyclic alkanes associated with petroleum. Additionally, many of the key petroleum aromatics could also be resolved from naturally occurring organics. Such chromatographic procedures will aid in distinguishing between indigenous hydrocarbons of contemporary origin and those known to be associated with fossil hydrocarbon pollution of marine sediments.