Heavily Oiled Salt Marsh following the Deepwater Horizon Oil Spill, Ecological Comparisons of Shoreline Cleanup Treatments and Recovery

RESEARCH ARTICLE Heavily Oiled Salt Marsh following the Deepwater Horizon Oil Spill, Ecological Comparisons of Shoreline Cleanup Treatments and Recovery Scott Zengel1,2*, Brittany M. Bernik3, Nicolle Rutherford1, Zachary Nixon1,4, Jacqueline Michel1,4 1 Emergency Response Division, Office of Response and Restoration, National Ocean Service, National Oceanic and Atmospheric Administration (NOAA), Seattle, Washington, United States of America, 2 Research Planning, Inc. (RPI), Tallahassee, Florida, United States of America, 3 Department of Ecology and Evolutionary Biology, Tulane University, New Orleans, Louisiana, United States of America, 4 Research Planning, Inc. (RPI), Columbia, South Carolina, United States of America * OPEN ACCESS Citation: Zengel S, Bernik BM, Rutherford N, Nixon Z, Michel J (2015) Heavily Oiled Salt Marsh following the Deepwater Horizon Oil Spill, Ecological Comparisons of Shoreline Cleanup Treatments and Recovery. PLoS ONE 10(7): e0132324. doi:10.1371/ journal.pone.0132324 Editor: Wei-Chun Chin, University of California, Merced, UNITED STATES Received: November 13, 2014 Accepted: June 14, 2015 Published: July 22, 2015 Copyright: This is an open access article, free of all copyright, and may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose. The work is made available under the Creative Commons CC0 public domain dedication. Data Availability Statement: Our data are publically available on NOAA’s Deepwater Horizon Environmental Response Management Application (ERMA), http://gomex.erma.noaa.gov/erma.html (see the “NOAA Treatment Testing and Set-Asides Study” files under the “Response Sampling and Monitoring” folder). Funding: This work was conducted in part under The Deepwater Horizon Unified Command (U.S. Coast Guard, State of Louisiana, and BP). Funding was provided by BP in part, as the Responsible Party. However, SZ, NR, ZN and JM were funded through Abstract The Deepwater Horizon oil spill affected hundreds of kilometers of coastal wetland shorelines, including salt marshes with persistent heavy oiling that required intensive shoreline “cleanup” treatment. Oiled marsh treatment involves a delicate balance among: removing oil, speeding the degradation of remaining oil, protecting wildlife, fostering habitat recovery, and not causing further ecological damage with treatment. To examine the effectiveness and ecological effects of treatment during the emergency response, oiling characteristics and ecological parameters were compared over two years among heavily oiled test plots subject to: manual treatment, mechanical treatment, natural recovery (no treatment, oiled control), as well as adjacent reference conditions. An additional experiment compared areas with and without vegetation planting following treatment. Negative effects of persistent heavy oiling on marsh vegetation, intertidal invertebrates, and shoreline erosion were observed. In areas without treatment, oiling conditions and negative effects for most marsh parameters did not considerably improve over two years. Both manual and mechanical treatment were effective at improving oiling conditions and vegetation characteristics, beginning the recovery process, though recovery was not complete by two years. Mechanical treatment had additional negative effects of mixing oil into the marsh soils and further accelerating erosion. Manual treatment appeared to strike the right balance between improving oiling and habitat conditions while not causing additional detrimental effects. However, even with these improvements, marsh periwinkle snails showed minimal signs of recovery through two years, suggesting that some ecosystem components may lag vegetation recovery. Planting following treatment quickened vegetation recovery and reduced shoreline erosion. Faced with comparable marsh oiling in the future, we would recommend manual treatment followed by planting. We caution against the use of intensive treatment methods with lesser marsh oiling. Oiled controls (no treatment “set-asides”) are essential PLOS ONE | DOI:10.1371/journal.pone.0132324 July 22, 2015 1 / 27 Oiled Salt Marsh Treatment and Recovery NOAA, serving as members of the NOAA Scientific Support Team to the U.S. Coast Guard. Additional funding was provided by the NOAA Emergency Response Division, Office of Response and Restoration. BMB was supported by an EPA STAR Fellowship. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. BP is a commercial funding source; authors SZ, ZN, and JM are employed by RPI, a commercial company; this does not alter the authors' adherence to PLOS ONE policies on sharing data and materials. Competing Interests: The authors of this manuscript have the following competing interests: SZ, NR, ZN and JM served under the Deepwater Horizon Unified Command in Shoreline Cleanup Assessment Technique (SCAT) Program and NOAA Scientific Support Team roles to the U.S. Coast Guard during the emergency response. SZ, ZN and JM also provide scientific support to NOAA for natural resource damage assessment and restoration. SZ, ZN and JM are employed by RPI, a commercial company. There are no patents, products in development or marketed products to declare. This does not alter the authors' adherence to PLOS ONE policies on sharing data and materials. for judging marsh treatment effectiveness and ecological effects; we recommend their use when applying intensive treatment methods. Introduction The Deepwater Horizon oil spill resulted in the oiling of 796 kilometers (km) of coastal marsh shorelines according to Shoreline Cleanup Assessment Technique (SCAT) surveys during the emergency response [1]. Of this total, 135 km of shoreline were described as heavy marsh oiling, based on a combination of oiling width across the shore, oiling percent cover, and oil thickness [1]. Persistent heavy oiling was most widespread in salt marshes in northern Barataria Bay, Louisiana, in marshes dominated primarily by Spartina alterniflora, and to a lesser extent by Juncus roemerianus [1–4]. Due to the degree and nature of oiling in this area, typical low-intensity “cleanup” treatments, including use of sorbents and low-pressure water flushing, were not effective for the most heavily oiled marshes [2], presenting continuing oil remobilization and exposure risks for adjacent habitats and wildlife (see [5] for an overview of oiled marsh treatment methods). In addition, due to the degree of heavy oiling, and experience from prior spills with similar oiling, there was concern that the long-term recovery of these marshes could be at risk without treatment, due primarily to the presence of thick emulsified oil layers, which can be very slow to degrade in coastal wetland environments [5–8]. At the same time, there was the competing concern that aggressive oil removal, such as manual or mechanical cutting (...truncated)