The USGS has released an online, interactive decision support system that provides easy access to six newly-developed regional models describing how rivers receive and transport nutrients from natural and human sources to sensitive waters, such as the Gulf of Mexico.
Excessive nutrients in the nation's rivers, streams and coastal areas are a major issue for water managers, because they cause algal blooms that increase costs to treat drinking water, limit recreational activities, threaten valuable fisheries, and can be toxic to humans and wildlife.
“Protecting ecosystems like the Great Lakes and Gulf of Mexico is critical to ensuring that those areas continue to be important economic engines for our nation. These new models and the decision support system are excellent tools that will help states, water managers, and federal agencies target sources and areas in order to design effective nutrient reduction strategies to improve water quality,” said Lori Caramanian, Deputy Assistant Secretary, Water and Science, Department of Interior and a member of the Mississippi River Gulf of Mexico Watershed Nutrient Task Force.
"A majority of the nation's estuaries are moderately to highly impacted by nutrient pollution which threatens living resource habitats, causes oxygen-depleted 'dead zones' and can fuel harmful algae blooms," said Dr. Robert Magnien, Director of NOAA's Center for Sponsored Coastal Ocean Research. "This USGS decision support system represents a major advance in the availability of sound scientific information to enable the effective management of this growing threat to our valued coastal resources and economies."
Each region and locality has a unique set of nutrient sources and characteristics that determine how those nutrients are transported to streams.
"Using the decision support system, users can evaluate combinations of source reduction scenarios that target one or multiple sources of nutrients and see the change in the amount of nutrients transported to downstream waters – a capability that has not been widely available in the past," said Stephen Preston, USGS hydrologist and coordinator for these regional models.
For example, the decision support system indicates that reducing wastewater discharges throughout the Neuse River Basin in North Carolina by 25 percent will reduce the amount of nitrogen transported to the Pamlico Sound from the Neuse River Basin by three percent; whereas a 25 percent reduction in agricultural sources, such as fertilizer and manure, will reduce the amount of nitrogen by 12 percent.
The new USGS regional models were developed using the SPARROW (SPAtially Referenced Regressions On Watershed attributes) modeling framework. Results detailing nutrient conditions in each region are published in the Journal of American Water Resources Association, and can be accessed with the decision support system online.
Based on the six regional model results, waste-water effluent and urban runoff are significant sources of nutrients in the Northeast and mid-Atlantic, while agricultural sources like farm fertilizers and animal manure contribute heavily to nutrient concentrations in the Midwest and central regions of the nation. Atmospheric deposition is the largest contributor of nitrogen in many streams in the eastern United States, and naturally occurring geologic sources are a major source of phosphorus in many areas.
Additionally, the six models used in the decision support system show that the amounts of nutrients transported varies greatly among the regions, because nutrients can be removed in reservoirs or used by plants before they reach downstream waters. Temperature and precipitation variation across the country also affect the rates of nutrient movement and loss on the land and in streams and reservoirs.
The USGS developed the SPARROW water-quality model to assist with the interpretation of available water-resource data and provide predictions of water quality in unmonitored streams. These regional SPARROW models incorporate geospatial data on geology, soils, land use, fertilizer, manure, wastewater treatment facilities, temperature, precipitation and other watershed characteristics, from USGS, NOAA, USDA, and USEPA. These data are then linked to measurements of stream flow from USGS streamgages and water-quality monitoring data from approximately 2,700 sites operated by 73 monitoring agencies. Information on SPARROW modeling applications, data, and documentation can be accessed online.
The model was developed by the USGS National Water Quality Assessment Program, which provides information about water-quality conditions and how natural features and human activities affect those conditions. Federal, regional, and state agencies, including USEPA, USDA, Bureau of Reclamation and others have used the SPARROW model results to inform water-quality management decisions.