Hazard Moderation

Changing Distributions of Salt Marshes and Mangroves

The value of ecosystem services that accrue from the intertidal wetlands of the Mississippi River delta and adjacent Gulf Coast are directly related to the total area of wetland and plant community composition. Current literature suggests that ecosystem services like wave attenuation by intertidal wetlands are non-linearly related to area with diminishing returns to scale (Barbier et al., 2008), while others suggest a nearly linear relationship (Costanza et al., 2008). Regardless, change in total wetland area is still the most direct and practical measurement of change in ecosystem services in Gulf Coast wetlands.

The wetlands in the Gulf Coast region are changing on several time scales. There is a long-term loss of wetlands due to subsidence, sea-level rise, and a variety of other issues (Boesch et al., 1994; Morton et al., 2002; Bernier et al., 2006). There are also episodic changes due to storms (Turner et al., 2007; Steyer et al., 2010) and now possibly those associated with the DWH oil spill. Distinguishing the background trends and variability associated with storms, droughts, and other factors from oil-spill-related effects will be challenging. The effort will require sampling large areas with sufficient temporal frequency and spatial detail to resolve episodic changes using a combination of ground surveys and remote sensing. Fortunately, the tools exist and the groundwork is in place for detecting changes in GoM coastal wetlands.

Advances in technology and decreasing cost are making remote sensing (RS) and geographic information systems the tools of choice for classifying and quantifying coastal landscapes. RS, or the capture and analysis of spectral information from a remote target, is a highly effective method for analyzing estuarine and coastal landscapes (Phinn et al., 2000; Klemas, 2001; Kelly and Tuxen, 2009) used to efficiently map, monitor, and detect change in wetlands (Zhang et al., 1997). Satellites carrying sensors with spatial resolutions of 1-5 m and spectral resolutions of 200 nm are being launched to more accurately detect these changes (Klemas, 2001). The classification of wetland area and plant communities is also improving as data from satellites are combined with those collected from fixed-wing aircraft. LIDAR (Light Detection and Ranging), an optical system that can measure the distance to a target and other properties using pulses from a laser, is one of the sensors now commonly included on fixed-wing aircraft. This tool is

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