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About N-Sink

Download the complete EPA N-Sink Technical Report

Project Development

The development of the N-Sink tool dates back to 2007.  The prototype was originally planned and designed as an extension to be used with ESRI ArcMap desktop GIS software. The prototype for N-Sink created by the University of Rhode Island, in partnership with Arizona State University and the University of Connecticut, was supported by both USDA NIFA and EPA ORD; this phase took about 4 years.  The current project, supported by U.S. EPA’s Nitrogen Management Group as part of the Sustainable and Healthy Communities program, focuses on transforming N-Sink into a web-based tool using ArcGIS Viewer for Flex

This current beta version of N-Sink has the Nitrogen Removal Tool, which tracks N sinks from any chose point in the watershed, giving a percent relative removal.  It does not yet have the Nitrogen Loading Estimation Tool, which will allow the user to draw a polygon and estimate loadings from that area, either using existing or an assigned land cover.  N-Sink’s geographic coverage currently includes 19 HUC-12 watersheds in the coastal area of Southeastern CT/Southwestern RI.

Go to 2010 paper on N-Sink prototype

How N-Sink estimates N sources and sinks

Go to complete explanation of sources and sinks

Landscape N Sources

N-Sink currently recognizes two types of N sources: unsewered developed land and agriculture as row crops. Future versions of N-Sink will distinguish between different types of developed land, such as different densities of residential development, and different types of agricultural land.

N-Sink lumps all developed land (e.g., residential development, institutional, commercial) and assumes that it leaches N at a rate similar to unsewered medium density residential development. N-Sink currently assumes that agricultural land is cultivated as row crops, with N loading similar to silage corn. This is a crop that is common to southern New England and can contribute N loads comparable to unsewered residential development. N-Sink assumes crops are fertilized with manure and that no cover crop is planted. By assuming no cover crop, we are presenting a “worst case” scenario.

Landscape N sinks

N-Sink identifies three types of landscape N sinks: riparian wetlands, lentic water bodies (ponds, lakes, or reservoirs), and lotic water bodies (stream reaches). All landscape N sinks are characterized as having Low, Medium, or High potential for N removal, based on estimates calculated for each sink. Because each type of sink has a different range of N removal potential, we have currently chosen to create break points for Low/Medium/High that differ for the three types (Table 1). For example, 30% removal would be considered High for stream reaches, but Low for riparian wetlands. This approach recognizes the inherent characteristics of the different types of sink that affect critical N removal factors, such as retention time. The breakpoints can be changed in future versions.

Table 1. N-Sink High/Medium/Low N removal designations for landscape N sinks

N Sink Type % N removal
High Medium Low
Riparian Wetlands > 60% 40 to 60% < 40%
Pond/Lakes/Reservoirs > 50% 25 to 50% < 25%
Stream Reaches > 30% 15 to 30% < 15%