United States Environmental Protection Agency	Office of Research and Development

National Exposure Research Laboratory
Research Abstract

Government Performance Results Act (GPRA) Goal 4
Annual Performance Measure 266

Significant Research Findings:

Evaluation of Significant Uncertainties in Modeling Nitrogen
Cycling to Support Multimedia Management Strategies

Nitrogen, one of the most critical elements necessary to life, is also a
multimedia pollutant that contributes to significant deleterious effects on
human health and ecosystems. Various forms of reactive nitrogen (Nr)
contribute to tropospheric ozone formation, stratospheric ozone depletion,
air toxics, acid rain, global climate change, cold sensitivity of trees, toxicity
to fish and humans, and nuisance algal blooms. Because nitrogen can enter
the environment via combustion, fertilizers, and human and animal wastes
via air, water, and soil pathways, effective nitrogen management strategies
depend on integrated models that deal with the important nitrogen forms,
sources, and pathways. These models also operate efficiently and
effectively within the regulatory frameworks available to air and water
quality managers. The objective of this project was to identify and evaluate
the uncertainties in nitrogen modeling that present the greatest barriers to
effective multimedia management strategies, in order to help prioritize EPA
research efforts,

Research	The original project plan was to convene a workshop bringing together

Approach	experts in nitrogen cycling and program office staff in order to prioritize a

lengthy list of research recommendations that had emerged from an
international nitrogen workshop convened by ORD in 2001. As plans for
this workshop were being made, EPA's Science Advisory Board (SAB)
announced their intention to form a panel to study the nitrogen as a
multimedia pollutant. Rather than developing a priority list that would be
overtaken by the recommendations of the SAB panel, it was decided that
this project could more effectively contribute it's objectives by
systematically interviewing air and water quality managers in EPA's
Program and Regional Offices in order to determine the sources of
uncertainty in multimedia nitrogen modeling that created the most
significant barriers to management actions by EPA and the States and
Tribes, and to provide the results to the SAB panel for their consideration.

Scientific
Problem and
Policy Issues

Project staff then identified the most significant regulatory opportunities


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(development of Total Maximum Daily Loads (TMDLs) and best
management practices (BMPs) for nitrogen in streams and estuaries,
development of water quality standards and nutrient criteria, and benefits
assessments to support various nitrogen emissions reductions programs
proposed by EPA's Office of Air and Radiation. Project staff and their
contractor attended the Office of Water Joint Coordinators meeting in
November, 2003, and subsequently conducted structured interviews with
the TMDL Coordinators from each of the EPA Regions and the staff at the
Office of Air Quality Planning and Standards involved with benefits
assessment. The draft results were tabulated and summarized and
submitted to OW and OAR management for comment, and a final report
prepared for delivery to the SAB Nitrogen panel, ORD, and the Programs
and Regions.

Results and	An unexpected result of the project was discovery of the wide range of

Impact	differing opinions as to the needs and priorities among the Regions with

respect to nitrogen as a water pollutant. The most common regulatory
endpoint was eutrophication of streams and estuaries, but nitrate and
ammonia toxicity were the most significant in other regions. The most
significant uncertainties were modeling of atmospheric deposition and non-
point source runoff, depending on whether the regions considered
atmospheric deposition as a component of TMDLs. Priorities and
approaches for developing nitrogen criteria and standards varied
significantly among regions, and there was significant differences of
opinion as to the timeliness of new research tools (ranging from now or
never to whenever). Most coordinators noted that because nutrient criteria
for nitrogen would not be implemented until 2006-08, with many TMDLs
to follow, research projects of 3-5 years duration could have a positive
impact. Opinions as to important emerging issues with respect to nitrogen
also varied significantly among regions, but the most common theme was
the contribution of non-point and atmospheric sources of nitrogen to coastal
waters.

Among the most useful research outcomes would be:

-	Effects-based approaches for nutrient criteria development
(determining appropriate aquatic effects endpoints, threshold nutrient
concentrations for adverse effects, and linkages of effects endpoints
with appropriate nutrient species)

-	Better understanding of the impacts of nitrogen-to-phosphorous (N:P)
ratios and non-baseflow conditions

-D Criteria effective for threatened and endangered species
-D Tools for interpolating nitrogen deposition data

-	Source identification for non-point source N loads

-	High-flow criteria

-	Developing better mathematical forms for criteria

-	Developing truly multimedia N models with appropriately interlinked


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time and space scales
-D Better targeting approaches and methods for determining the

effectiveness of BMPs
-D Better modeling of the effects of denitrification in removing N from
streams

-D The beneficial effects of alternative wastewater technologies for
removing N

-D Better modeling of N loads from concentrated animal feeding

operations (CAFOs).

In the area of multimedia benefits estimation, the most useful research
outcomes appear to be:

-D Updating benefits related to reducing N emissions to air (the

Chesapeake Bay data are 20 years old!)

-D Better understanding of air N emissions from CAFOs
-D Being able to model costs and benefits of the "nitrogen cascade" (the
idea that a molecule of NOx released to the air can have multiple,
different environmental costs and benefits as it is transported and
transformed to reactive N entering the world ocean.

These research suggestions are based on the priorities identified during the
interviews.

This project was conducted by a team of NERL staff scientists and an
outside contractor consultant with many years of experience in water
management (FTN Associates). EPA's Office of Water and Office of Air
Quality Planning and Standards and TMDL Coordinators in each of EPA's
Regions cooperated and provided technical input. The results are
summarized in an internal EPA report: Assessment Science Improvements
to Enhance Regulatory Programs Related to Nitrogen as a Multimedia
Pollutant. The report has been internally reviewed and cleared, but is
available for distribution only within EPA. It will be provided to the SAB
Panel on Nitrogen through the ORD liaison with that panel.

Future Research The information resulting from this project should be useful to inform

ORD research planners and useful to the SAB integrated nitrogen planning
team deliberations.

Questions and inquiries can be directed to:

Robin Dennis, Ph.D.

US EPA, Mail Drop E243-01
National Exposure Research Laboratory
Research Triangle Park, NC 27711
Phone: 919/541-2870
E-mail: dennis.robin@epa.gov

Research
Collaboration and
Research
Products

Contacts for

Additional

Information

Federal funding for this research was administered under EPA
DOC/COMMITS Contract # 50-CMAA-9-00065.


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