Mapping watershed integrity for the United States

What is it about?

Watersheds provide a variety of ecosystem services valued by society. Production of these services is sensitive to watershed alteration by human activities. Flotemersch and others (2015), defined watershed integrity (WI) as the “capacity of a watershed to support and maintain the full range of ecological processes and functions essential to the sustainability of biodiversity and of the watershed resources and services provided to society.” They argue that six key functions must be present for a watershed to have integrity: hydrologic regulation, regulation of water chemistry, sediment regulation, hydrologic connectivity, temperature regulation, and habitat provision. We developed and mapped an index of WI for the conterminous USA based on these six key functions by incorporating human landscape stressors from the EPA’s StreamCat dataset, that have been shown to degrade key functions in watersheds. The index is mapped at 1:100,000 scale at the stream catchment resolution, and provides a consistent way to compare WI across the Nation. Specific factors that highly influence WI scores signal effective management approaches for restoration, protection and restoration of watersheds.

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Why is it important?

The development of a watershed integrity (WI) index and a national map of WI for the conterminous United States (CONUS) provides a powerful tool for the USEPA Office of Water and state environmental and natural resource agencies to consistently compare WI for the nation. The WI index can be decomposed into specific factors that influence index scores that can be targeted for adaptive management by informing protection, rehabilitation, and restoration efforts within watersheds. The WI index provides a watershed integrity value for all 2.65 million stream catchments associated with the National Hydrography Dataset Plus Version 2 (NHDPlusV2). The national map of watershed integrity is of interest to the Healthy Watersheds and Biocriteria groups within the Office of Water, and will also be used to investigate national patterns in health and economic benefits. This map also contributes to an FY16 deliverable under SSWR 3.01B.

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