Editor's note: The goal of The EBM Toolbox is to promote awareness of software tools for facilitating EBM processes, and to provide advice on using those tools effectively. It is brought to you by the EBM Tools Network (www.ebmtools.org), a voluntary alliance of leading tool users, developers, and training providers.
By Sarah Carr
Many pollutants to the marine environment, particularly excess nutrients and sediments, come from terrestrial sources. Effective watershed management is therefore critical to marine EBM, and watershed models are an essential part of the EBM toolkit. Watershed models use factors such as rainfall, land cover, soil type, impervious surface coverage, and slope to predict runoff from watersheds into bodies of water. When coupled with marine ecosystem models, watershed models can help predict how changes in land use (such as urban growth and conversion of agricultural lands) and pollution management (such as improved sewage treatment and fertilizer application) will affect marine ecosystems.
Tools that help predict these types of impacts range from relatively simple to quite complex. A few examples of available watershed models include:
Impervious Surface Analysis Tool (ISAT) – Estimates the percentage of impervious surface and, from this, water quality in a user-defined area (www.csc.noaa.gov/crs/cwq/isat.html).
Nonpoint Source Pollution and Erosion Comparison Tool (N-SPECT) – Estimates runoff, pollutant, and sediment loads from a user-defined area and can compare pollutant concentrations in receiving waters to water quality standards (www.csc.noaa.gov/crs/cwq/nspect.html).
Chesapeake Bay Watershed Model (a customized regional model based on the general Hydrologic Simulation Program Fortran [HSPF] watershed model) – Estimates runoff, pollutant, and sediment loads to the Bay through comprehensive simulations of relevant hydrologic and nutrient cycles (www.chesapeakebay.net/modeling.aspx). It is linked to an estuary model for the Bay. Together, these models have been used to set limits on nutrient input into the Bay, track nutrient loads, and determine how further reductions in nutrient and sediment loads would affect Bay water quality.
Resources for learning about other useful watershed models are:
"Using GIS Tools to Link Land Use Decisions to Water Resource Protection" – a brief by the National Association of Counties at www.naco.org.
EPA's Watershed and Water Quality Modeling Technical Support Center, at www.epa.gov/athens/wwqtsc/html/watershed_models.html.
(Sarah Carr is coordinator for the EBM Tools Network. Learn more about EBM tools and the EBM Tools Network at www.ebmtools.org. Sign up for Network updates and contact Sarah at www.ebmtools.org/contact.html.)