possible. In some instances, the assessment of injuries has been straightforward because the service products are well characterized in the economic marketplace (e.g., the income loss from the closure of a particular fishery). However, the connections between many service products and ecosystem condition have not been well characterized. In other cases, baseline data may not exist (e.g., hydrocarbon levels in marsh sediments) or baseline ecological data may be available but without an assessment of services (e.g., acreage of wetlands may be known, but not the value to fisheries).

Ecosystem services describe the benefits people receive from a multitude of resources and processes that are provided by ecosystems. They are produced as a consequence of the functioning of the ecosystem—the interactions of plants, animals, and microbes with the environment—and are ubiquitous and immensely valuable to society. They include

•    provisioning services or the material goods provided by ecosystems (often simplified to food, feed, fuel, and fiber);

•    regulating services (e.g., climate regulation, flood control, water purification);

•    cultural services (e.g., recreational, spiritual, aesthetic); and

•    supporting services (e.g., nutrient cycling, primary production, soil formation).

The magnitude and depth of the DWH event, in concert with the complexity of the GoM ecosystem and the difficulties in establishing baseline values, pose serious challenges to the trustees charged with carrying out the NRDA process, which has historically been applied to shallow-water events of much more limited extent and scale. Recent studies suggest that an “ecosystem services approach” may expand the potential to capture, value, and restore the full breadth of impacts to the ecosystem and the public.

Recognition of the unprecedented nature of the DWH spill and concerns about both short- and long-term impacts on the GoM and its citizens were immediate and international in scope. Among the many concerned with the fate of the GoM and its communities were members of the U.S. Congress, who requested a study by the National Academy of Sciences to assess the impacts of the DWH spill on the natural resources of the Gulf. A committee made up of 16 members representing a broad range of disciplines was formed in January 2011 and met twice in early 2011. To provide advice to the federal agencies during their preparation of the NRDA, the committee was asked to produce an interim report that covers questions 1 through 3 of the Statement of Task (Box S.1). A final report, encompassing the interim report and including questions 4 through 8, will be delivered in the spring of 2013.

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