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Like most states, Texas has embarked on the process of developing quantitative or numerical nutrient criteria in response to EPA's 1998 national initiative. Texas is dealing with many complex issues in developing appropriate criteria, and one is simply determining what is to be the technical basis for the criteria. EPA's proposed methodology for lakes and reservoirs was based on a percentile of data from reference systems, with no consideration of the designated uses. In contrast, the language in the Clean Water Act is fairly specific as to the relationship between designated uses and criteria. Furthermore, recent significant documents including the National Research Council's 2001 review of the TMDL program, and the General Accounting Office's 2003 review of EPA's efforts, suggest there is interest and support for developing appropriate and attainable designated uses and having criteria that are tied to those uses.

In response to the need for developing a better understanding of uses and supporting criteria, the Trinity River Authority undertook a project with the support of the Clean Rivers Program of the Texas Commission on Environmental Quality (TCEQ). The goal of the project was to explore the relations between a comprehensive list of actual uses that exist for a variety of reservoirs and attempt to develop a process for setting criteria that might be supportive or based on those uses. This paper describes the methods and results of this project performed in parallel with efforts by the TCEQ to develop numerical criteria for some reservoirs. The major findings were that for the nine study reservoirs, the major uses appeared to be supported. Of the major nutrients (nitrogen and phosphorus) and response variables (chlorophyll a and water clarity), the parameter most directly related to uses and thus criteria development was chlorophyll a. There is a measure of conflict in the level of use support and the concentration of chlorophyll a and a method to achieve an optimal balance is needed.

Document Type: Research Article


Publication date: January 1, 2003

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