Effects of Oil from the 2010 Macondo Well Blowout on Marsh

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Effects of Oil from the 2010 Macondo Well Blowout on Marsh Foraminifera of Mississippi and Louisiana, USA Charlotte A. Brunner,*,† Kevin M. Yeager,‡ Rachel Hatch,‡ Sondra Simpson,† Joseph Keim,† Kevin B. Briggs,§ and Patrick Louchouarn∥ †

Department of Marine Science, University of Southern Mississippi, Stennis Space Center, Mississippi 39529, United States Department of Earth and Environmental Sciences, University of Kentucky, Lexington, Kentucky 40506, United States § Marine Geosciences Division, Naval Research Laboratory, Stennis Space Center, Mississippi 39529, United States ∥ Department of Marine Sciences, Texas A&M University, Galveston, Texas 77554, United States ‡

S Supporting Information *

ABSTRACT: Foraminifera responded to both heavy and light oiling of marshes relative to unoiled control sites by changes to both standing stock and depth of habitation (DOH) in sediment following the 2010 Macondo well blowout. Push cores were taken from the middle marsh at sites classified as unoiled, lightly oiled, and heavily oiled based on concentrations of total polycyclic aromatic hydrocarbons ([TPAH]). Cores were sliced and stained with rose Bengal to detect live specimens of foraminifera. Short-term, sediment-mixing depths were determined using the penetration depths of excess 234Th, and sedimentary organic carbon and carbonate were measured to distinguish depositional environments. Marsh foraminifera reacted to the highest oil concentration (5,000− 18,000 ng/g of TPAH) by reducing standing stock and shortening the DOH compared with the control sites. At a second, less heavily oiled site, foraminifera responded with a shallower DOH, but with a boom in standing stock. Deformed, dead foraminifera occurred in all heavily oiled coresbut not elsewhere. Live foraminifera responded with a population boom at lightly oiled sites with [TPAH] near 1,100 ng/g. Changes in standing stock and DOH with [TPAH] suggest disturbance to the marsh food web, apparently due to oil pollution, and support the use of foraminifera as sentinel species.

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INTRODUCTION The Macondo well blew out on April 20, 2010, spewing crude oil, gas, and formational water into the Gulf of Mexico for three months until BP capped it in mid July and sealed it in early August. During the blowout, surface oil and tar balls coated marshes from the Florida Panhandle to western Louisiana, and tar ballsperhaps remobilized from submerged oil mats offshorecontinued to soil the coastline. Coastal marshes of the Mississippi Sound received trace to light amounts of oil, the Biloxi marshes on the west shore of the Chandeleur Sound received patches of light to heavy amounts of oil, whereas parts of Barataria Bay received moderate to heavy amounts of oil from the Macondo well (the National Oceanographic and Atmospheric Administration’s Environmental Response Management Application [ERMA] Gulf Response;1,2 Figure 1). Marshes are among the most vulnerable of coastal environments to oil spills,3 and concerns continue for the health of these marshes, including their flora and fauna. In this study, we examine how infaunal foraminifera can act as sentinel species for deleterious effects from oil pollution. The study focuses on marshes from the Mississippi Sound, Chandeleur Sound, and Barataria Bay. Tides in the region are © XXXX American Chemical Society

diurnal and microtidal, with a range of less than half a meter. Prevailing winds are southeasterly in spring and summer, the season of the spill, but reverse in the winter. Storm setupas from tropical stormscan elevate sea level significantly compared with tides. Salinities can vary widely in these estuaries, and most are monitored by the USGS,4,5 which reports 5-year medians as well as daily averages (Table S1). The three western Mississippi Sound sites have the lowest salinity,