Priority Watersheds for Nutrient Reduction

The nutrient priority watersheds in Tennessee were identified using the Tennessee-specific SPARROW (SPAtially Referenced Regression On Watershed attributes) models for nitrogen and phosphorus. These models provided data aggregated at the HUC 10 level, offering a detailed analysis of nutrient contributions across watersheds. While the SPARROW model can also analyze data at a broader HUC 8 level, which includes areas beyond state borders, this analysis focused on HUC 10 watersheds primarily within Tennessee. An exception was made for the Memphis area due to its significant contribution of nutrients to the Mississippi River.

For each watershed, the SPARROW model estimated the nutrient yield delivered to the HUC 10 outlet, measured in pounds per year per acre (lb/yr/acre). Nitrogen data was provided by the model, indicating the relative yield from various sources, including atmospheric deposition, manure, fertilizer, urban land, and wastewater. The percentage contribution from each sector was calculated for each watershed, and watersheds were ranked by overall nitrogen yield. The top 10 watersheds for each sector (wastewater, urban land, and agriculture - manure and fertilizer combined) were then identified.

Nitrogen Prioritization

• One watershed ranked in the top 10 for both agriculture and overall nitrogen yield.
• Three watersheds ranked in the top 10 for urban land and overall nitrogen yield.
• Six watersheds ranked in the top 10 for wastewater and overall nitrogen yield.
  

Similarly, phosphorus data was analyzed to determine the relative yield from sources such as soil-parent rock, mined land, manure, agricultural land, urban land, and wastewater. The prioritization followed the same method as for nitrogen, focusing on the top 10 watersheds for wastewater, urban land, and agriculture.

Phosphorus Prioritization

• One watershed ranked in the top 10 for both agriculture and overall phosphorus yield.
• No watersheds ranked in the top 10 for both urban land and overall phosphorus yield.
• Three watersheds ranked in the top 10 for wastewater and overall phosphorus yield.

This prioritization helps to identify key areas where nutrient management efforts can be targeted to improve water quality in Tennessee's watersheds.