Development of Protocols and Decision-Support Tools for Assessing Watershed System Assimilative Capacity (SAC) in Support of Risk-Based Ecosystem Management/Restoration Practices

Development of Protocols and Decision-Support
Tools for Assessing Watershed System Assimilative
Capacity (SAC) in Support of Risk-Based Ecosystem
Management/Restoration Practices

Introduction to the Problem

System assimilative capacity (SAC) is an important
ecosystem characteristic for evaluating sustainability
and assessing risk in a managed ecosystem. SAC also
represents an important ecosystem restoration option.

An appropriate evaluation of a system's capacity to
assimilate stressors is needed before sound ecosystem
management decisions can be made, particularly if
active (intrusive) restoration practices are being
considered.

Background

Lake Texoma, a Corps of Engineers lake on the
Oklahoma/Texas border, serves as a major recreational
and drinking water resource for southern Oklahoma
and northern Texas. EPA is currently conducting
research on Lake Texoma to develop decision-support
tools and gather information that will help evaluate the
transport and attenuation of contaminants and stressors in a lake ecosystem and link them to observable ecological
effects. EPA is leading this research effort and is collaborating with the U.S. Geological Survey, U.S. Army Corps
of Engineers, University of North Texas, and Oklahoma University in collecting and analyzing data to target
stressor inputs into Lake Texoma.

Objectives

The initial goal of the project will be to develop tools and gather information needed to evaluate the transport and
attenuation of contaminants and stressors into the lake ecosystem and to link them to observable ecological effects.
The final goal of the project will be to develop a model decision-support system. The system will provide the
information needed to:

• Evaluate the transport and attenuation of stressors in the lake ecosystem and link them to observable
ecological effects

• Determine whether the SAC is being exceeded

• Assist in the risk-based ecosystem/watershed management decision process

The National Risk Management Research Laboratory's mission is to advance scientific and engineering
solutions that enable EPA and others to effectively manage current and future environmental risks.
NRMRL possesses unique strengths and capabilities and is dedicated to providing credible
technological information and scientific solutions that support national priorities
and protect human health and the environment.

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Approach

A number of representative site and chemical sources will be
characterized in detail. The potential release scenarios include
leaking underground storage tanks, landfills, and nonpoint sources
(such as agricultural sites for pesticides and fertilizers and near-
shore residential development areas). A detailed assessment of the
transport and attenuation processes for different stressor scenarios
will be developed. These assessments will be used to produce
exposure indices based on location (transport path to lake), size
(mass loading) and geological setting (attenuation values).

Historical data, surveys, and geographical information system (GIS)
data will be used to evaluate the relative numbers and placement of
potential stressor sources in the Lake Texoma watershed.

Concurrent and coordinated ecological effects monitoring will be conducted to identify links, if present, between
stressor input locations or events and alterations in ecosystem functions. A GIS/stressor, input/eco-effects database
will be developed for watershed-level assessment of the potential risks to the Lake Texoma system and for
development of SAC determination of various stressor types in the watershed/ecosystem.

Accomplishments to Date {February 2003)

Participating collaborators have collected numerous physical, chemical, and biological datasets from study sites in
around and the lake ecosystem. Data have been collected from both surface water and ground water locations. Over
108 spatial datasets residing in five spatial databases have been collected and can be accessed and queried for GIS
and modeling purposes. Historical water-quality biological and physical data were retrieved from EPA's STORET
database. This historical data will be used with current data to identify possible links between past and present
stessor inputs. A database management system is under development; it will include all the data collected during
the project.

Near-Future Tasks

A study is being conducted on the stream inflows from the watershed into the lake. This study not only focuses on
the potential stressors, but also the flow volume into the lake after high and low rainfall events. This information
will help support the development of the hydrologic model of the lake; the model will eventually be included in the
Lake Texoma Decision-Support System.

Investigators

David S. Burden
Timothy J. Canfield
U.S. EPA

Ground Water and Ecosystem Restoration Division
Ada, Oklahoma 74821

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