POLLUTION LOCATOR|WATERSHED VULNERABILITY INDICATORS

Aquatic/Wetland Species at Risk:
This indicator provides information about the presence of species at risk in a given watershed. The Natural Heritage Network and The Nature Conservancy (TNC) assess the conservation status of plants and animals, and map out the population occurrences of those species at greatest risk of extinction. This indicator represents the number of aquatic or wetland-dependent species documented in a watershed that are classified by the Heritage Network as critically imperiled (identified by TNC as G1), imperiled (G2), or vulnerable (G3), or that are listed under the federal Endangered Species Act (ESA) as threatened or endangered. The presence of rare or endangered species in a watershed is not necessarily an indication of poor watershed conditions. Indeed, it more likely indicates the opposite: in many instances these species persist only in areas of exceptionally high quality habitat. The presence of species at risk in a watershed indicates, however, that these watersheds are especially vulnerable to future water quality or habitat degradation, which could jeopardize the maintenance or recovery of these organisms.

Pollutant Loads Discharged Above Permitted Limits: Toxics:
The Clean Water Act requires that EPA or states set permit limits on the amount of pollutants that facilities such as sewage treatment or industrial plants may discharge into a waterbody. Effluent limits established under the National Pollutant Discharge Elimination System (NPDES) are set according to national technology-based standards. This indicator adds up the total amount of toxic pollutants allowed to be discharged through NPDES permits into each watershed, and compares this to the total amount of pollutants actually discharged. Watersheds with pollutant loads greater than the total permit limits of all facilities are considered vulnerable to future declines in aquatic health. Such toxic pollutants include cadmium, copper, lead, and mercury.

Pollutant Loads Discharged Above Permitted Limits: Conventional:
This indicator adds up the total amount of conventional pollutants allowed to be discharged through NPDES permits into each watershed, and compares this to the total amount of pollutants actually discharged. Watersheds with pollutant loads greater than the total permit limits of all facilities are considered vulnerable to future declines in aquatic health. Conventional pollutants include biochemical oxygen demand, total suspended solids, and nutrients.

Urban Runoff Potential:
This indicator estimates the potential magnitude of runoff from urban areas. Regional rainfall characteristics are combined with measures of urbananization and imperviousness. Imperviousness is a useful indicator for predicting the impacts of land development on aquatic ecosystems. Studies have linked the amount of imperviousness to changes in the hydrology, habitat structure, water quality and biodiversity of aquatic ecosystems. Increased imperviousness can change the hydrology of a receiving stream, increasing runoff volume and rate and decreasing the receiving streams capacity to handle floods.

Agricultural Runoff Potential:
A composite index was constructed to show which watersheds had the greatest potential for possible water quality problems from combinations of pesticides, nitrogen, and sediment. Watersheds with the highest composite score have a greater risk of water quality impairment from agricultural sources. Watersheds could be ranked high because of a very high ranking of a single component, or moderately high rankings from two or more components.

Population Change:
The growth of human populations can result in increased pollution of our waters as land cover and land uses change. These changes include construction impacts, increased impervious surfaces, loss of wetlands, and increased sewage flows.

Hydrologic Modification:
The health of the aquatic system in a watershed can be compromised by extensive impoundment or hydrologic modification of water resources. This index shows the relative dam storage capacities in watersheds, which provides a picture of the relative degree of modification of hydrologic conditions in a watershed. The index is constructed from a Federal Emergency Management Agency database which inventories U.S. dams in excess of six feet in height and a maximum water impounding capacity of at least fifty acre feet; or dams at least twenty-five feet in height and a maximum water impoundment capacity in excess of fifteen acre-feet. It contains information on 75,187 dams throughout the U.S. and its territories.

Estuarine Pollution Susceptibility:
This measures an estuary's susceptibility to pollution based on its physical characteristics and its propensity to concentrate pollutants. Susceptibility is defined as the relative vulnerability of an estuary to concentrations of dissolved and particulate substances. The National Oceanic and Atmospheric Administration (NOAA) developed the Coastal Assessment Framework (CAF), which identifies all watersheds associated with the coast. NOAA quantified susceptibility to pollution by combining information about dissolved concentration potential and particle retention efficiency with estimated loadings and predicted concentrations of nitrogen and phosphorus.

Atmospheric Deposition:
This measures the atmospheric loading of nitrogen compounds onto a watershed, which can result in acidification or nutrient imbalances. The information is derived from the National Atmospheric Deposition Program.