The role of Mississippi River discharge in offshore phytoplankton blooming in the northeastern Gulf of Mexico during August 2010

How Did the Deepwater Horizon Oil Spill Affect Coastal and Continental Shelf Ecosystems of the Gulf of Mexico?

“…In contrast to the results on the Louisiana coast, Hu et al, (2011) andO'Connor et al (2016) reported an anomalous phytoplankton bloom north of the DWH spill location during August 2010, based on satellite-derived ocean color observations (Figure 4). Based on historical satellite data, the intensity and location of this anomaly were unusual, as normalized fluorescence line height (nFLH, a relative measure of surface biomass) derived from the measurements of the Moderate Resolution Imaging Spectroradiometer (MODIS) reached a maximum as compared with any August before or after 2010.…”

“…It is possible that pyrogenic hydrocarbons originated from the incomplete combustion of large surface oil slicks in summer 2010 (~222,000-313,000 barrels were burned) and/or from intense weathering of surface oil slicks exposed to high summer temperatures (25°C-30°C) that enhanced the evaporation of low molecular weight compounds (Ryerson et al, 2012;Romero et al, 2015). Also, these results support the hypothesis that high Mississippi River discharge during the summer of 2010 affected the chemistry of the water column with large inputs of terrestrial-derived dissolved organic matter, sediments, and nutrients that mixed with the spilled oil (Bianchi et al, 2011;O'Connor et al, 2016). In addition, water samples containing hydrocarbon concentrations higher than baseline levels and of petrogenic origin were still found in the water column in 2011-2012 for both coastal and continental shelf areas (total hydrocarbons: 8.6 ± 1.1 ppb; PAHs: 1.1 ± 0.5 ppb; BTEX: 2.3 ± 0.01 ppb).…”

“…Based on the hydrocarbon source ratios, oilderived hydrocarbons account for ~23% (or 36,465 MT) of the total amount of hydrocarbons in the water column (~160,895 MT). The remaining ~77% (or 124,430 MT) is predominantly of terrestrial and mixed sources, indicating a larger impact of the Mississippi River system on water-column processes during the DWH oil spill than previously described in more spatially restricted studies (Bianchi et al, 2011;O'Connor et al, 2016). Relative to the DWH spill, oil-derived hydrocarbons accounted for 15 ± 2% (or 5,930 ± 959 MT) in the coastal area and 75 ± 45% (or 30,535 ± 18,392 MT) on the continental shelf of the total oil discharge from DWH (~40,857 MT of saturated, aromatic, and BTEX fractions for one month of the spill; Reddy et al, 2011).…”

Structural Classification of Marshes with Polarimetric SAR Highlighting the Temporal Mapping of Marshes Exposed to Oil

“…In order to help prevent oil from reaching coastal wetlands during the DWH spill event, freshwater releases from the Mississippi River were increased or initiated from locations ranging from just upriver of New Orleans to downriver in the delta north of Barataria Bay [77][78][79][80]. The largest of these releases began on 30 April 2010, ten days after the DWH spill began, with the specific intent of lessening oil entry into Barataria Bay.…”

Functioning of Coastal River-Dominated Ecosystems and Implications for Oil Spill Response: From Observations to Mechanisms and Models

“…Wind-driven circulation interacting with complex freshwater flows derived from numerous river inputs influenced the trajectory of oil on the shelf (Kourafalou and Androulidakis, 2013;Özgökmen et al, 2016) and made predictions of oil transport and impacts difficult (Joye et al, 2016;Özgökmen et al, 2016). The ability to forecast the movement of the oil was further complicated by river diversions that augmented river discharge in an attempt to keep oil from coming ashore in certain areas (O'Connor et al, 2016). The challenges of predicting DWH spill effects were exacerbated by the three-dimensional (3-D) movement of the oil from depth.…”