Post-spill state of the marsh: Remote estimation of the ecological impact of the Gulf of Mexico oil spill on Louisiana Salt Marshes Deepak R. Mishra a, b, ⁎, Hyun J. Cho c , Shuvankar Ghosh a, b , Amelia Fox a , Christopher Downs a, b , Paul B.T. Merani d , Philemon Kirui e , Nick Jackson e , Sachidananda Mishra a a Department of Geosciences and Geosystems Research Institute, Mississippi State University, United States b Northern Gulf Institute, Mississippi State University, United States c Department of Integrated Environmental Science, Bethune-Cookman University, United States d School of Natural Resources, University of Nebraska, Lincoln, United States e Department of Biology, Jackson State University, United States abstract article info Article history: Received 26 May 2011 Received in revised form 11 November 2011 Accepted 18 November 2011 Available online 22 December 2011 Keywords: Gulf of Mexico LA Deepwater horizon oil spill Ecological impact Salt marsh Canopy chlorophyll Above ground biomass Field spectroscopy Landsat TM One and a half years after the worst oil spill in U.S. history, we present the first quantitative assessment on the ecological impact of the spill on the salt marsh habitats along the southeastern Louisiana (LA) coast. This re- search combined satellite and ground data to quantify the impact of the oil and dispersant on the salt marshes in terms of their photosynthetic capacity and physiological status over a large spatial scale. Two of the most important marsh biophysical characteristics, including distribution of canopy chlorophyll content and above ground green biomass, were monitored across the southeastern LA coast during the salt marsh growing season (May–October) of 2009 (pre-spill) and 2010 (post-spill) in order to compare and isolate the spill impacted areas. The initial assessment showed that there was a significant post-spill increase in areas with reduced biomass and canopy chlorophyll (> 400 km 2 ) during the 2010 growing season compared to 50–65 km 2 during the 2009 growing season. Phenological analysis of the post oil-spill data revealed a sig- nificant decrease in the magnitude of biomass and canopy chlorophyll during the peak of the 2010 growing season. June was consistently found to be the worst month in terms of salt marsh health across LA over the 2010 phenological cycle followed by the initial signs of recovery along the fringing marsh areas proximal to the shoreline that were first impacted by oil. Interior marsh patches exhibited persistent signs of stress to- wards the end of the growing season. Extensive reduction in photosynthetic activity was observed during the peak of the growing season, particularly in Plaquemines Parish and St. Bernard Parish. The products gen- erated through this study successfully delineate the critical hotspots of marsh stress so that prioritization of areas needing immediate restoration can be performed. © 2011 Elsevier Inc. All rights reserved. 1. Introduction Salt marshes are considered to be the most vulnerable coastal environment (vulnerability index of 10 from a 1–10 scale) that can be adversely affected by an oil spill, with the predicted residence times of over 10 years (Gundlach & Hayes, 1978; Pezeshki et al., 2000). Salt marshes generally have more oil-sensitive vegetation than freshwater marshes and the oil impact on vegetation is most significant in highly organic soils of salt marshes (Lin & Mendelssohn, 1996; Pezeshki et al., 2000). The direct and immediate physical impact of an oil spill on wetland vegetation includes the coating of the plant and soil surfaces causing temperature stress, and reduced photosynthesis due to block- age of stomata and transpiration pathways. Petroleum hydrocarbons also adversely affect the ability of salt marsh vegetation to tolerate salin- ity, which increases the potential of dieback and hampers recovery (Gilfillan et al., 1989). Additional damage can be caused by the resulting cleanup activities such as skimming, oil collection, burning, flushing, use of dispersants, and plant cutting (Allen & Ferek, 1993; Kiesling et al., 1988; Mendelssohn et al., 1990; Owens et al., 1993a, 1993b). To complicate matters further, the effects of oil spills vary with vegetation types and season. For example, previous research shows that, of the more common Gulf Coast vegetation species, Spartina alterniflora is more sensitive to oiling than Juncus roemerianus (Pezeshki & DeLaune, 1993). Furthermore, flora are more sensitive to oiling during the grow- ing season than during the pre-dormancy or dormant season (Pezeshki et al., 2000). It is advised that summer burns of contaminated marsh patches be avoided if possible (Lindau et al., 1999), because flooding fol- lowing burning also adversely affects plant growth in many species (Pezeshki et al., 2000). The Deep Water Horizon Macondo MC252 oil spill beginning on April 20, 2010 poured more than 200 million gallons of crude oil in the Gulf waters off southeastern Louisiana (LA), and an Remote Sensing of Environment 118 (2012) 176–185 ⁎ Corresponding author at: Department of Geosciences, Mississippi State University, P.O. Box 5448, Mississippi State, MS 39762-5448, United States. Tel.: + 1 662 268 1032x233; fax: +1 662 325 9423. E-mail address: dmishra@gri.msstate.edu (D.R. Mishra). 0034-4257/$ – see front matter © 2011 Elsevier Inc. All rights reserved. doi:10.1016/j.rse.2011.11.007 Contents lists available at SciVerse ScienceDirect Remote Sensing of Environment journal homepage: www.elsevier.com/locate/rse