SPARROW modeling: Estimating nutrient, sediment, and dissolved solids transport

NEW RELEASE: Point Source Load Estimation Tool

NEW RELEASE: Point Source Load Estimation Tool

Access software for annual wastewater nutrient data preparation and load estimation using the Point Source Load Estimation Tool (PSLoadEsT) and the accompanying report.

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Science Center Objects

SPARROW (SPAtially Referenced Regressions On Watershed attributes) models estimate the amount of a contaminant transported from inland watersheds to larger water bodies by linking monitoring data with information on watershed characteristics and contaminant sources. Explore relations between human activities, natural processes, and contaminant transport using interactive Mappers.

Integration of monitoring and modeling is critical to our future understanding and management of the Nation’s water quality. Monitoring is the direct observation, often over time, of water-quality properties and characteristics, and models are tools for interpreting these observations.

Documentation for SPARROW can be found here.

Nitrogen Sources within the continental United States

A map of the continental United States showing the largest sources of Nitrogen around the country and their type.


SPARROW models are used to estimate long-term average values of water characteristics, such as the amount of a contaminant that is delivered downstream, on the basis of existing monitoring data, location and strength of contaminant sources, and characteristics of the landscape.

Modeling results can help managers determine how to reduce loads of contaminants and design protection strategies; design strategies to meet regulatory requirements; predict changes in water quality that might result from management actions; and identify gaps and priorities in monitoring.


Access SPARROW Mappers, interactive tools that allow the user to explore river nutrient loads and yields and the importance of different sources of contaminants in a particular river basin. Data can be visualized using maps and interactive graphs and tables, and rankings can be shown by country, state/province, HUC, and catchment. Modeling results can be exported as an Excel spreadsheet or a geospatial dataset. Mappers currently are available for the Mississippi Basin and large sub-basins within or adjoining it. The Mappers replace the SPARROW Decision Support System (Booth and others, 2011).


Nutrients and the Nation’s Estuaries

Access maps of watershed nutrients flowing to the Nation’s estuaries and download data tables of nutrient sources and loads. Compare nutrient sources and watersheds that contribute elevated nutrient loads to downstream receiving waters, such as the Southeast Atlantic and Gulf of Mexico, inland and coastal waters of the Northeast, the Upper Mississippi and Great Lakes, Puget Sound and the Northwest coast, and the California coast.

Estuary and bird

The San Francisco Bay Estuary.


National Models

SPARROW models are unique in that they retain the spatial detail of underlying data sets while extending over areas as large as the conterminous United States. This allows the simultaneous assessment of water-quality conditions in many water bodies. National SPARROW models have been developed for a number of water-quality constituents including nutrients and total dissolved solids.


Regional Models

SPARROW models are flexible—they can be applied to any region where there are specific needs for water-quality information and where data to support modeling are abundant. For example, several models have been developed for the Chesapeake Bay, contributing to restoration efforts.

SPARROW models can provide:

  1. Guidance for monitoring network design
  2. A basis for prioritizing areas for agricultural management implementation
  3. Information for watershed-scale nutrient reduction policy


International Models

SPARROW models can be applied in any part of the world where sufficient data are available to support model development. Examples include models developed for New Zealand to identify the primary sources of nutrients to streams (Alexander and others, 2002), and a joint U.S.-Canadian effort to build nutrient models for the Red – Assiniboine watershed to better understand and manage nutrient loads to Lake Winnipeg (Benoy and others, 2016).


Applications of SPARROW models

Once built and calibrated, SPARROW models can be applied in a variety of ways to better understand the environmental factors affecting water-quality conditions in streams. SPARROW models were applied at the national scale to estimate natural background levels of nutrients to help guide the potential development of nutrient criteria in streams. A model developed for the upper Midwest was used to identify the benefits of management practices designed to limit the amount of agricultural nutrients reaching streams (Garcia and others, 2016). And a Chesapeake Bay SPARROW model was used to identify those areas that export nitrogen to streams with the greatest efficiency (Ator and Garcia, 2016).


Research using SPARROW models

SPARROW models can be used as tools in research to better understand the environmental processes that affect water-quality conditions. A SPARROW model for the Mississippi drainage was used to evaluate the role of stream size on denitrification and attenuation of nitrogen levels with transport downstream. Previous studies based on a limited number of sites had hypothesized that the rate of denitrification was significantly greater in smaller streams due to greater sediment contact. This was confirmed by the SPARROW model for which the results were consistent with the other studies, but based on a much larger area and many more measurement locations (Alexander and others, 2000).


The national data bases used in the SPARROW models have value in themselves and can be used for other scientific evaluations. Attributes, such as point sources discharges, agricultural fertilizer / manure nutrients, atmospheric deposition, climate, geology / soils, land cover, hydrologic characteristics and physical characteristics, are available for all catchments in the RF1 and NHDPlus digital stream networks.

Stream network datasets and watershed attribute data

The EPA RF1 data set (with attributes) is defined at the 1:500K scale and has stream catchments that are on average 130 km2 in area.

The NHDPlus data set (with attributes) is defined at the 1:100K scale and has stream catchments that are on average 3 km2 in area.

Descriptions of these data sets and how they are used in SPARROW models can be found in Brakebill and others. (2011).

Questions about SPARROW?

Find commonly asked questions and their answers here.

What’s New …

  • Although SPARROW models are typically based on a single time period, dynamic versions of SPARROW models are being developed to take advantage of new data sets. Dynamic SPARROW models will account for temporary storage of contaminants and to simulate seasonal variations. It also will allow simulation of contaminant loads through time to estimate the time needed for management actions on the land to affect loads in streams.
  • SPARROW models are being made more flexible by using Bayesian statistical methods to refine the calibration. This will allow parameter values to shift on a regional basis to better account for spatial variations in factors affecting contaminant loads, and will provide more accurate estimates of overall model uncertainty by better accounting for measurement error in load estimates. The Bayesian techniques will be part of a new version of the SPARROW software built using the R coding language. The R-SPARROW package is being published and will be released in 2019. Stay Tuned!