DEVELOPING NUTRIENT CRITERIA/TMDLs TO MANAGE EXCESSIVE FERTILIZATION OF WATERBODIES
Abstract:Excessive fertilization is one of the most common and significant causes of the impairment of the beneficial uses of waterbodies. As a result of the widespread occurrence of excessive fertilization of waterbodies, the US EPA has initiated development of chemical-specific (nitrogen and phosphorus compounds) numeric water quality criteria designed to be the basis of control of the excessive fertilization of waterbodies. These criteria will be used to establish state water quality standards, where exceedance of the standard will be used to designate Clean Water Act 303(d) “impaired” waterbodies that will lead to the need to implement a TMDL to achieve the nutrient water quality standard. The Agency has established 2004 as a date by which state regulatory agencies must have made significant progress toward adopting chemical-specific nutrient criteria/standards. This means that, by the mid 2000s, there could be a large number of additional waterbodies, beyond those already classified as nutrient-impaired, that need to have TMDLs developed and implemented in order to satisfy nutrient control requirements.
The US EPA has adopted two approaches for developing nutrient water quality criteria/standards. One of these is the Agency's “default” approach, where emphasis is on assessing the pre-cultural nutrient concentrations in a waterbody as a basis for establishing the allowable nutrient concentrations. If no non-culturally impacted (no urban or agriculture activities occur in the watershed) representative reference waterbodies are available in the area, the Agency proposes to use the 25th percentile of the existing nutrient concentrations for current total P and total N including organic nitrogen as the criterion/standard value. Adopting this default approach means that 75 percent of the waterbodies in a region would violate the nutrient criterion/standard and therefore be subject to nutrient TMDL development. The US EPA's proposed approach for developing default nutrient criterion is recognized by many who are familiar with how nutrients impact water quality as technically invalid. It ignores the large amounts of high quality information that was developed in the 1960s and ‘70s on how nutrients impact water quality and how fertility of a waterbody impacts its beneficial uses. The Agency's approach could result in massive expenditures for nutrient control from point and non-point sources beyond that needed to achieve the desired nutrient-related beneficial uses of a waterbody. Further, this approach could be significantly detrimental to the aquatic life (fisheries)-related beneficial uses of a waterbody as a result of adversely impacting the trophic structure of waterbodies.
The Agency's other proposed approach for developing nutrient criteria/standards potentially involves the regulatory Agencies and the regulated community, as well as others interested, working together to develop site-specific nutrient criteria/standards for a waterbody or group of similar waterbodies. According to the US EPA, the site-specific criterion development approach must be “scientifically defensible.” The Agency; however, does not define what that means. This paper discusses recommended approaches for developing site-specific nutrient criteria that will protect the nutrient impact-related beneficial uses of a waterbody, without significant unnecessary expenditures for nutrient control. Particular attention is given to developing a sitespecific stakeholder assessment of the desired nutrient-related water quality in a waterbody(s), and site-specific nutrient load eutrophication response relationships for the waterbody that can be used to determine the degree of nutrient control needed to achieve the desired nutrient-related water quality in the waterbody. In addition to being applicable to developing site-specific nutrient criteria, the issues discussed in this paper are also applicable to developing appropriate nutrient-related TMDL goals. This paper is based on 42 years of the author's experience in investigating and managing excessive fertilization of waterbodies in the US and many other countries. Background information on these issues is provided on the author's website, www.gfredlee.com.
Document Type: Research Article
Publication date: January 1, 2002
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