Recovery Potential Screening
Scenario Fact Sheet Series I Nutrients

oEPA

July 2022

Background & Purpose

The Recovery Potential Screening (RPS) Tool provides a systematic method to compare a
group of watersheds and evaluate priorities for watershed management. Key steps in the RPS
process include selecting watersheds to screen and choosing indicators that serve as the basis
for comparison and prioritization (Figure 1). Recognizing that these steps can be challenging
for beginner RPS Tool users, the US Environmental Protection Agency (EPA) developed the
RPS Scenario Fact Sheet Series to support users who have a basic understanding of RPS
concepts but are uncertain about how to begin their own screening. Readers that are new to
the RPS Scenario Fact Sheet Series can first review the RPS Scenario Fact Sheet Introduction to
understand how to apply the concepts presented in this Fact Sheet.

This Fact Sheet describes concepts for watershed and indicator selection for a screening that
focuses on addressing excess levels of nutrients (nitrogen and phosphorus) in surface waters.

While the approaches described in this Fact Sheet offer a starting point for conducting a
screening with the RPS Tool, users can refine and customize their watershed and indicator
selections based on their own specific objectives and initial results (Figure 1).

Select Watersheds

Although a screening can include ail HUC12 subwatersheds1 in a state or river basin,2 RPS Tool
users often target a subset of relevant HUC12s to compare within a screening. The HUC
Subsets tab of the RPS Tool contains an interactive menu to define a HUC12 subset. Table 1
lists example indicators that could be used to create a HUC12 subset for a nutrients-focused screening. The indicators
measure characteristics that are relevant to nutrient loading and can help to identify HUC12s with nutrient issues.

Table 1. Example indicators in the RPS Tool for identifying HUC12s with known or potential nutrient issues.

Indicator Subcategory

Example Indicators

Pollutant Loading Severity

Nitrogen Yield in HUC12; Phosphorus Yield in HUC12

Impaired Waters

Nutrient Impaired Waters Count in HUC12

Urban/Developed Cover

% Urban in HUC12

Impervious Cover

% Impervious Cover in HUC12

Agricultural Cover

% Cultivated Crops in HUC12

Nutrient Application and Deposition

Manure Nitrogen Application in HUC12; Manure Phosphorus Application in HUC12

Hazardous Waste & Wastewater

National Pollutant Discharge Elimination System (NPDES) Permit Count in HUC12

RPS Tool files for contiguous US states are pre-loaded with the indicators listed in Table 1, which include;

•	Average annual nitrogen and phosphorus yields from a HUC12 (i.e., the amount of nitrogen and phosphorus exported to
surface waters from sources within the HUC12),

•	The number and extent of nutrient-impaired waters in a HUC12 (i.e., waters included on a state impaired waters list due
to nutrient-related causes of impairment),

•	The extent of developed and agricultural land cover, agricultural nutrient applications, and wastewater dischargers in a
HUC12. Several studies have highlighted relationships between nutrient levels in waterbodies and these characteristics.3 4

1	HUC12s are subwatershed delineations in the National Watershed Boundary Dataset. HUC12s are referenced by their 12-digit
Hydrologic Unit Code.

2	The RPS Tool files available on the RPS website are configured for single states, however, RPS Tool files can be customized for river
basins or other regions of interest. Email us at HWP-Team(S>epa.gov for more information on developing a custom RPS Tool.

3	Preston, SD, et. al. 2011. Factors Affecting Stream Nutrient Loads: A Synthesis of Regional SPARROW Model Results for the

Continental United States. Journal of the American Water Resources Association (JAWRA) 47(5):891-915.

4	EPA. 2014. Wisconsin Integrated Assessment of Watershed Health. EPA 841-R-14-001.

Figure 1. The RPS process. This
Fact Sheet focuses on the
Select Watersheds and
Indicators step.

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RPS Scenario Fact Sheet Series I Nutrients

As a starting point for HUC12 subsetting, users could enter one or more of the following criteria in the RPS Tool to select
HUC12s with known or potential nutrient issues:

•	Phosphorus Yield greater than the state median yield in kilograms per square kilometer

•	Nitrogen Yield in Watershed greater than the state median yield in kilograms per square kilometer

•	Nutrient Impaired Waters Count greater than zero

Selection criteria for subsetting HUC12s can be refined to better match a user's specific geographic setting and screening
objective by including additional indicators or adjusting thresholds for HUC12 selection. Examples include refining thresholds
for nitrogen and phosphorus yields or adding minimum levels of urban or agricultural cover as subsetting criteria.

Select Indicators

The indicators selected for a screening serve as the basis for users to compare watersheds and evaluate priorities for
restoration and protection. For a nutrients-focused screening, the Ecological indicator selections can reflect attributes that are
associated with healthy aquatic ecosystems and functional watershed processes; the Stressor indicator selections can reflect
the presence of key nutrient sources in a user's geographic area; and the Social indicator selections can reflect social or
programmatic factors that are favorable for successful nutrient reduction. A complete list of indicators available in the RPS
Tool and indicator descriptions are provided on the Indicator Info tab of the RPS Tool for users to review when selecting
indicators

As a starting point for indicator selection, Table 2 highlights example indicators for a nutrients-focused screening. The example
indicators in Table 2 are intended to assist users in setting up an initial screening in the RPS Tool to understand how the RPS
Tool functions and the results that are generated.

Table 2. Example indicators for an initial screening to identify priority HUC12sfor nutrient management

Category

Subcategory

Indicator Name

Description

Ecological

Integrated Watershed
Health Index &
Sub-Indices

PHWA Watershed Health Index,
State

The statewide Watershed Health Index score for the
HUC12 from the EPA Preliminary Healthy
Watersheds Assessment (PHWA).

Stressor

Agricultural Cover

% Cultivated Crops in HUC12

Percent of the HUC12 that is classified as cropland
cover.



Livestock

Livestock Density in HUC12

Livestock population density in the HUC12,
measured in animal equivalent units (1,000 pounds
of animal weight per acre).



Nutrient Application
and Deposition

Manure Phosphorus
Application in HUC12

Average annual rate of phosphorus applied to
agricultural lands as animal manure in 2012
(kilograms of phosphorus per hectare per year).





Synthetic Fertilizer Phosphorus
Application in HUC12

Average annual rate of phosphorus applied to
agricultural lands as inorganic fertilizer in 2012
(kilograms of phosphorus per hectare per year).



Impervious Cover

% Impervious Cover in HUC12

Percent of the HUC12 with impervious cover.



Urban/Developed
Cover

% Urban in HUC12

Percent of the HUC12 classified as urban cover.

Social

Participation in

Conservation

Programs

USDA Conservation Reserve
Program Area in HUC12

Area of land enrolled in the US Department of
Agriculture (USDA) Conservation Reserve Program
(CRP) in the HUC12.





Nutrient Nonpoint Source (NPS)
Project Presence in HUC12

Presence or absence of nutrient-related nonpoint
source pollution control projects funded by Clean
Water Act Section 319 grants in the HUC12,

s>EPA

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RPS Scenario Fact Sheet Series I Nutrients

Below is additional discussion of the example indicators for an initial screening listed in Table 2 and their relevance to a
nutrients-focused screening:

•	The Ecological indicator listed in Table 2 is the Watershed Health Index from the EPA Preliminary Healthy Watersheds
Assessment (PHWA). The Watershed Health Index is an integrated measure of watershed condition that combines several
indicators which reflect six key attributes of watershed health: Landscape Condition, Geomorphology, Habitat, Water
Quality, Hydrology, and Biological Condition. Higher Watershed Health Index scores correspond to greater potential for a
HUC12 to support healthy aquatic ecosystems and provide important ecosystem services to surrounding communities. An
Overview of the Preliminary Healthy Watersheds Assessments Project provides additional background and methodology
on the PHWA.

By including the Watershed Health Index in a screening, users can factor overall watershed condition into the
identification of priority HUC12s for nutrient management. Depending on the interests and perspectives of a reader, both
high and low scoring HUC12s could be considered priorities. Higher scoring HUC12s may contain aquatic ecosystems that
are healthy but threatened by increased nutrient loading while lower scoring HUC12s may be good candidates for efforts
to restore degraded ecosystems.

•	The Stressor indicators listed in Table 2 describe the extent of developed, impervious, and cultivated crop land cover
types in the HUC12, the magnitude of agricultural nutrient applications, and the density of livestock populations. Each of
these reflect typical sources of nutrients in a HUC12 that could be the focus of management practices to reduce nutrient
loading.

•	The Social indicators listed in Table 2 describe the extent of lands protected through conservation easements and the
presence of nutrient reduction projects that are funded by Clean Water Act Section 319 grants. These highlight past
stakeholder engagement in the HUC12 and the potential for partnerships to implement additional nutrient management
strategies.

Users may choose an alternative set of ecological, stressor, and social indicators depending on a user's specific geographic
setting and screening objective. For example, stressor indicator selections could be refined to target nutrient sources that are
most relevant to a user's area while social indicators could be refined to align with a user's organization's preferences and
approach to priority-setting.

After running a screening and reviewing results, users may refine their initial watershed and indicator selections. For example,
a user could be interested in evaluating how the screening results change when an indicator is removed or a new indicator is
added. Iterative adjustments to watershed or indicator selections are an important part of the RPS process (Figure 1) and the
RPS Tool is designed to allow users to easily adjust watershed and indicator selections.

Links to RPS Tools and Additional Information

RPS Tool files are available for download from the EPA RPS website.

The training and user support page of the EPA RPS website includes several reports that provide detailed descriptions of
projects that applied the RPS Tool to identify potential priority watersheds for addressing excess nutrients in Kentucky,
Tennessee, Louisiana, New Mexico, Iowa, North Dakota, Kansas, and Massachusetts.

oEPA

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