Assessment of marsh health is essential to the evaluation of the short-term impact of the BP Deepwater Horizon spill and for the prioritization of future restoration actions. This study will allow the identification of hotspots of marsh degradation by evaluating marsh biophysical characteristics including distribution of chlorophyll content, green leaf area, and green marsh canopy cover. These characteristics are the primary indicators of photosynthetic capacity and physiological status of marsh vegetation. NASA's Moderate Resolution Imaging Spectroradiometer (MODIS) satellite images will be used to retrieve and map these characteristics across the coastal Louisiana salt marshes before and after the spill. Pre and post spill weekly composite maps of salt marsh biophysical characteristics for the entire Louisiana coast will be generated showing the extent of damage and recovery. By examining the satellite images, the overall health and productivity of coastal salt marsh can be inferred and the ecological impact of the oil and oil/dispersant on health and productivity of these sensitive ecosystem can be effectively analyzed.
The maps and tools produced by this study will be helpful to coastal managers across Louisiana as they evaluate and prioritize the massive marsh restoration effort that is going to take place because of the spill. For the first time, tangible map products will be generated that can quantitatively assess the effect of the restoration activities and speed of marsh ecosystem recovery. The proposal also directly addresses the Gulf of Mexico Alliance's (GOMA) long term goal to enhance monitoring for the conservation and restoration of coastal wetlands throughout the Gulf of Mexico.
The overall objective of this study was to quantify the short-term (3 year) impact of the BP DeepWater Horizon oil spill on the photosynthetic activity and physiological status of the Louisiana coastal salt marshes by combining satellite data with ground experiments. This objective was achieved by analyzing two biophysical or health characteristics of marsh vegetation including canopy chlorophyll content (CHL) and green biomass (GBM) generated through a remote sensing mapping protocol. The specific objectives included, (1) application of a suite of algorithms combining Landsat satellite 30-m (2009-2011) and MODIS satellite 250m (only for 2012) datasets with field data to map CHL and GBM across southeastern LA salt marshes; and (2) compare and quantify the changes observed in CHL and GBM distribution during the salt marsh growing season between 2009 (pre-spill), 2010 (during-spill), and 2011-2012 (post spill) to isolate the spill impact and monitor the marsh growth. The products generated through this research will provide restoration decision makers across LA with a practical tool to inform the prioritization of marsh restoration effort to the areas, most affected by the spill. Funding from NSF was primarily used for field data collection (remote sensing and biophysical) in the salt marsh habitats. Intensive monthly field campaigns (May-Oct 2010 and 2011) were conducted in LA recording precise in situ remote sensing reflectance and other biophysical parameters from salt marsh areas with different degrees of contamination. A comprehensive time series remote sensing and biophysical parameters database was developed as part of the study from 137 sites in LA coast. Products developed through the past three years of this project were used in combination with the biogeochemical and climatological data for assessing the productivity of marshes that are impacted by the oil spill and dispersants, thus providing state regulators important information for restoration and managements. In summary, our chlorophyll and biomass centered study framework is conceptually well grounded in basic plant physiology. After Hurricane Gustav made landfall on September 1, 2008, Landsat data provided strong evidence that the wetlands and barrier islands off the LA coast were lost from hurricane-related flooding (NASA News Report on 1/12/09). Fortunately, 2009 and 2010 were relatively quiet storm seasons, and LA wetland habitats were on a recovery stage after the Gustav related damage. Theoretically, therefore, 2010, with no hurricanes reported, should have been a better year in term of marsh physiological growth. However, the Deep Water Horizon (DWH) oil spill dramatically reversed the recovery trend by exerting a massive negative short-term impact to the salt marsh habitats during the middle of the growing season. However, we found that the fringing marshes showed significant recovery in 2011 and attained almost full recovery in 2012 to a pre-spill status. We believe that the short-term damage due to oil spill was less in magnitude than that of a major hurricane, but the lingering residual oil will have a sustained long-term impact on the overall health and productivity of the Gulf Coast salt marsh. The estimated time-series CHL and GBM maps produced from Landsat imagery showed great potential to quantify the ecological impacts of the oil spill on salt marsh structure and function. These products can be used in conjunction with biogeochemical data to analyze the changes in one of the most important wetland functions i.e., carbon sequestration reduction related to the oil spill effects. For the first time, managers can have access to the large-scale maps of southeastern LA coastal wetland productivity generated through this research allowing identification of problem areas (areas impacted by the spill), which should be a high priority for restoration and the relative success of prior restoration efforts.
