SPARROW Modeling for North Carolina Watersheds

Science Center Objects

In North Carolina, excessive nutrient and sediment loadings have contributed to the degradation of surface-water quality across the state as a result of agricultural activities and population growth increases. To further understand the influences of human activities and natural processes on surface-water quality, the U.S. Geological Survey (USGS) developed the SPARROW (SPAtially Referenced Regressions On Watershed attributes) modeling framework to relate water-quality monitoring data to upstream sources and watershed characteristics. The model can be used to predict pollutant concentrations, loads, and yields in streams and has been used to evaluate alternative hypotheses about the relative importance and contributions of various pollutant sources.

 

Stream bank erosion, Swift Creek, Cary, NC

Stream bank erosion, Swift Creek, Cary, NC

(Public domain.)

North Carolina geomorphological features

North Carolina geomorphological features

(Public domain.)

The North Carolina Department of Environmental Quality (NCDEQ) has implemented several strategies for basin-wide nutrient management, yet gaps remain in understanding the complexities of nutrient and sediment transport. In particular, improved assessment of the status of nutrient loadings to lakes and estuaries is needed, including characterizing nutrient and sediment sources, relative contributions, and identifying additional monitoring needs. As DMS works to improve its RBRP methodology and products, new tools are needed to help efficiently and scientifically target mitigation efforts in areas where allocated resources will most likely have the greatest benefit to local watershed functions.

Research Objectives

The North Carolina SPARROW model will be developed to address the following:

  1. Quantify what is attainable in terms of water quality by accounting for background or natural sources of nutrients and sediment.
  2. Identify catchments within the basins where best management practices would most likely lead to significant reductions in nutrient and sediment loads and benefit to local watershed functions.
  3. Characterize predominant sources and transport factors of nutrient loss and delivery in NC basins.
  4. Development of a SPARROW model that supports North Carolina conservation efforts by assisting North Carolina Division of Mitigation Services identify and prioritize watersheds with a maximum functional return on water quality.

Study Area

Map of North Carolina River Basins

Figure 1. Location of major river basins in North Carolina at the hydrologic unit code (Huc) six scale. Major river basins are labeled using the Watershed Boundary dataset (WBD) convention.

(Public domain.)

We are using information from the fourteen major river basins to inform the SPARROW model (Fig. 1). Data collected at 235 water quality monitoring stations throughout the state across several different agencies are used to inform the model. Other datasets are gathered from remote sensing techniques and is post-processed to extract necessary information for the model.

Nutrient and Sediment Models

Nitrogen and phosphorus are accounted for in two separate models. Preliminary results indicate point sources, atmospheric deposition, poultry count, and road length to be the major sources of nitrogen throughout the state. For the phosphorus model, major sources include point sources, background phosphorus, poultry count, road length, and fertilizer. Predicted total yield is calculated for both models to understand the distribution of nutrients throughout the state and determine problem areas. Preliminary results from the sediment model runs indicate road length as a major source of sediment throughout the state. Residuals of model results are mapped to determine locations with major sediment supply.