Data and Tools

Water Body Types

Identifying water body types is an important initial step in the planning phase because they define the resources for which you will be setting management goals and developing numerical nutrient criteria (NNC).

Reference Condition: Computation

In step 3, you will typically (1) estimate a distribution of each set of screened variable values and (2) select a percentile cutoff point within that distribution that defines the value that will serve as the NNC.

Conceptual Models

A conceptual model visually and descriptively outlines relationships between stressors and ecological conditions. It aids in deriving numeric nutrient criteria by detailing biological, physical, and chemical interactions of a water body.

Reference Condition: Classification

This page covers developing a classification scheme and your reference water body classification database.

Reference Condition

This page describes the reference condition approach to develop numeric nutrient criteria.

Data Considerations

High-quality data sets are critical to deriving successful numeric nutrient criteria. This section provides basic info about selecting variables as well as acquiring, organizing, and reviewing variable data for possible use in developing criteria.

Assessment Endpoints

Assessment endpoints are measurable water body traits that link nutrient pollution to management goals, helping support designated uses like fisheries and recreation by identifying necessary nutrient concentrations.

Stressor-Response: Data Preparation

The availability of data often determines whether stressor-response analysis can be applied.

Select Approach

A range of factors—including regulatory priorities, spatial scales, conceptual models, data quantity and quality, and resource constraints—should be considered in selecting the analytical approach, or combination of approaches, to use for developing NNC.

Mechanistic Modeling: Data Preparation

Data are required to define the parameters for mechanistic models, setup model spatial boundaries, describe boundary conditions, and calibrate model predictions to observed conditions.

Stressor-Response: Calculation

Simple linear regression is the recommended approach for estimating relationships between stressor and response within groups of water bodies.

Stressor-Response: Classification

To classify water bodies for stressor-response analysis, you identify groups of water bodies that have similar stressor-response relationships.

Data Overview

Data are the foundation for developing effective nutrient criteria that result in healthy water environments that meet their designated uses.

Mechanistic Modeling: Classification

The nutrient criteria development process uses a classification system to clarify variability of water bodies that exist across the country.

Mechanistic Modeling

This page provides an overview, with four successive pages that provide more detail on mechanistic modeling and how states can use mechanistic models to derive numeric nutrient criteria.

Stressor-Response

Stressor-response modeling is used when data are available to estimate a relationship between nutrient concentrations and a response measure.

Mechanistic Modeling: Configuration & Calibration

In addition to gathering and entering appropriate data into the model, you also must establish the model’s spatial extent and specify the size of its computational cells, or reaches.

Mechanistic Modeling: Simulation

After you set up the model, you can run scenarios at different nutrient concentrations.

N-STEPS Online Resource Library

References, resources, and data sources to aid in planning and developing numeric nutrient criteria.

Communicating Final Criteria

Once candidate criteria have been derived, and final criteria selected, it is important to be able to clearly communicate how the final criteria are protective of designated uses.