Estimation of Nutrient and Sediment Loading in the Mississippi River and Great Lakes Basins with Regional SPARROW Models
Principal Investigators: Dale M. Robertson and
Cooperators: U.S. Environmental Protection Agency
Period of Project: October 2005 – Continuing
Throughout the country, declining water quality in rivers and streams has been linked to excessive inputs of nutrients, particularly nitrogen and phosphorus. Nutrient over-enrichment in streams and rivers can lead to eutrophication in downstream waterbodies, causing hypoxia and threatening fish and other aquatic animals. These problems can arise both locally and regionally; for example, one of the principal causes for the increasing size of the Gulf of Mexico hypoxic zone is believed to be the increasing supply of nitrogen delivered to the Gulf from the Mississippi River Basin.
The NAWQA Program has adopted SPARROW modeling to assess nutrient conditions in large regions of the conterminous United States. These nutrient modeling studies are part of NAWQA's Major River Basin (MRB) status and trends assessments of stream chemistry, with emphasis on nutrients, pesticides, and ecosystem health. Wisconsin Water Science Center researchers have been focusing their efforts on both the Mississippi model and the model for Major River Basin 3 (MRB3), which includes the Great Lakes and the Ohio, Upper Mississippi, and Souris-Red-Rainy River basins (upper Midwest).
SPARROW (SPAtially Referenced Regressions On Watershed attributes) is a mass-balance watershed modeling technique for relating water-quality measurements made at a network of monitoring stations to nutrient inputs and other attributes of the watersheds containing the stations. SPARROW tracks the transport of nutrients from local, inland watersheds to regional, coastal waters by explaining spatial patterns in stream water-quality conditions in relation to human activities and natural processes. The system uses calibrated models to predict long-term average loads, concentrations, yields, and source contributions (and associated error estimates) for all stream reaches within the modeled watersheds. SPARROW models have been developed for a variety of water-quality constituents and time periods.
|This project will develop calibrated SPARROW models to estimate nutrient loading from streams.
The SPARROW project has three phases:
- Compile existing water-quality information from federal, state, and local agencies and universities; use these data to estimate nutrient loads from streams in large regions of the country.
- Develop SPARROW models to estimate loads and sources of nutrients in streams and rivers. Models are developed at a range of scales, including national and major river basin models. Wisconsin Water Science Center researchers are responsible for the Mississippi/Atchafalaya River Basin (MARB) and MRB3 (upper Midwest) models.
- Build web-based tools to illustrate results of the SPARROW models and evaluate effects of specific management decisions.
Mississippi/Atchafalaya River Basin
Mississippi/Atchafalaya River Basin (MARB) SPARROW model, primarily based on 1992 data and published in Environmental Science and Technology in 2008, evaluated the watersheds that deliver nitrogen and phosphorus to the Gulf of Mexico. The model showed that while Illinois, Iowa, Indiana, Missouri, Arkansas, Kentucky, Tennessee, Ohio and Mississippi make up only one-third of the 31-state Mississippi River drainage area, they contribute more than 75 percent of nitrogen and phosphorus to the Gulf. Agricultural nonpoint sources contribute more than 70 % of the nitrogen and phosphorus delivered to the Gulf, versus only about 9 to 12 % from urban sources.
Corn and soybean cultivation was the largest contributor of nitrogen to the Gulf. The study reported that 66% of nitrogen originated primarily from cultivated crops, mostly corn and soybean, with animal grazing and manure contributing only about 5 percent. Atmospheric contributions also were important, accounting for 16% of nitrogen.
Animal manure on pasture and range lands contribute nearly as much phosphorus as cultivated crops, 37 versus 43 percent, suggesting that the wastes of unconfined animals is a much larger source of phosphorus in the Mississippi River Basin than previously recognized.
Read the full press release here.
Uncertainties in the nutrient yield estimates from the MARB SPARROW model published in the Journal of the American Water Resources Association in 2009, were incorporated into a statistical ranking procedure to determine the probability that a watershed is within the top 150 delivering the highest nutrient yields to the Gulf.
Model findings show that 11 watersheds are reliably placed in the top 150 category for total nitrogen (3 for total phosphorus) delivered to the Gulf of Mexico with 90 percent certainty. Although only a few watersheds could be placed into the top 150 category, numerous watersheds could be removed from consideration of being in the top 150 category. A total of 513 watersheds for total nitrogen and 505 watersheds for total phosphorus are reliably placed outside of the top 150 category with 90 percent uncertainty.
Probabilistic ranking of watershed nutrient yields can assist water managers, policy makers, and scientists in identifying watersheds that may be primarily responsible for nutrient delivery to the Gulf of Mexico.
Read the full press release here.
An updated model with 2002 data is being developed and planned to be released in Fiscal Year 2012.
Results for the MRB3 (Upper Midwest) SPARROW models, based on 2002 data, were published in the Journal of the American Water Resources Association in 2011. Results indicated that recent (2002) U.S. loadings to Lakes Michigan and Ontario are similar to those in the 1980s, whereas loadings to Lakes Superior, Huron, and Erie decreased. Highest loads were from tributaries with the largest watersheds, whereas highest yields were from areas with intense agriculture and large point sources of nutrients.
Input from agricultural areas was a significant source of nutrients, contributing 33-44% of the phosphorus and 33-58% of the nitrogen to each of the Great Lakes, except for areas around Superior with little agriculture. Point sources were also significant in some areas, contributing 14-44% of the phosphorus and 13-34% of the nitrogen to each of the Great Lakes.
Watersheds around Lake Erie contributed nutrients at the highest rate (similar to intensively farmed areas in the Midwest) because they have the largest nutrient inputs and highest delivery ratio, while those aroundLake Superior contributed the least nutrients. Nutrient deposition in lakes and reservoirs on tributaries to the Great Lakes was important in reducing nutrient delivery to the lakes.
Read the full press release here.
SPARROW Mapper: MRB3 2002 Nutrient Models
This mapper displays SPARROW nutrients load and yield data and the importance of various nutrient sources for the MRB3 basin using maps, graphs and tables. Rankings available by major watershed, state, HUC8, tributary, and catchment. Modeling data can be exported as an Excel spreadsheet.
SPARROW Decision Support Tool
The Decision Support System displays model predictions of water-quality conditions and sources by stream reach and catchment, tracking transport to downstream receiving waters, and evaluating management source-reduction scenarios. Complementary map overlays include land use, shaded relief, street-level data, and hydrologic unit boundaries. Models currently available include national nitrogen, phosphorus, and suspended sediment models as well as regional nutrient models.
USDA's Mississippi RIver Basin Healthy Watersheds Initiative (MRBI)
Minnesota Pollution Control Agency's Nitrate Standards
An updated model with a refined stream network (NHD) is planned to be released in Fiscal Year 2013.
Publications and Reports
Robertson, D.M. and D.A. Saad, 2011. Nutrient Inputs to the Laurentian Great Lakes by Source and Watershed Estimated Using SPARROW Watershed Models. Journal of the American Water Resources Association
Booth, N.L., E.J. Everman, I.-L. Kuo, L. Sprague, and L. Murphy, 2011. A Web-Based Decision Support System for Assessing Regional Water-Quality Conditions and Management Actions. Journal of the American Water Resources Association
Saad, D.A., G.E. Schwarz, D.M. Robertson, and N.L. Booth, 2011. A Multi-Agency Nutrient Dataset Used to Estimate Loads, Improve Monitoring Design, and Calibrate Regional Nutrient SPARROW Models. Journal of the American Water Resources Association
Robertson, D.M., Schwarz, G.E., Saad, D.A., and Alexander, R.B., 2009, Incorporating uncertainty into the ranking of SPARROW model nutrient yields from Mississippi/Atchafalaya River basin watersheds. Journal of the American Water Resources Association, v. 45, n. 2, p. 534-549.
Alexander, R.B., Smith, R.A., Schwarz, G.E., Boyer, E.W., Nolan, J.V., and Brakebill, J.W., 2008, Differences in phosphorus and nitrogen delivery to the Gulf of Mexico from the Mississippi River Basin. Environmental Science and Techology, v. 42, n. 3, p. 822-830
Smith, R.A., Alexander, R.B., and Schwarz, G.E., 2003, Estimating the natural background concentrations of nutrients in streams and rivers of the conterminous United States, Environ. Sci. Tech., 37, 3039-3047.
Smith, R.A., Schwarz, G.E., and Alexander, R.B., 1997, Regional interpretation of water-quality monitoring data, Water Resources Research, 33, 12, 2781-2798.
Robertson, Dale and Richard Alexander. 29 June 2007. SPARROW modeling in the Mississippi and Atchafalaya River Basins (MARB) (SPARROW_MARB_Ranking_1992.pps)
Robertson, Dale M., Saad, D.A., Alexander, R.A., and Schwarz, G.E. 24 July 2008. SPARROW Modeling – with special emphasis on modeling in the Mississippi River Basin and Upper Midwest. Upper Midwest Partnership Meeting. (MWPartnership_SPARROW_July2008.ppt)
Robertson, Dale M., and Saad, D.A., 2011. New Science and Online Management Tools to Help Guide Action on Nutrients in Rivers of the Upper Midwest Region of the U.S., Especially in the Great Lakes Region (MRB3_Online_Tools_Webinar.pptx)