History of the EPT taxa richness metric

Bulletin of the North American Benthological Society
Summer, 1996; Vol. 13(2)

David R. Lenat and David L. Penrose, North Carolina Division of Environmental Management, Water Quality Section, 4401 Reedy Creek Road, Raleigh, NC 27607

Introduction

Monitoring groups throughout the United States have adopted EPT (Ephemeroptera + Plecoptera + Trichoptera) taxa richness as a useful measure of stream water quality. This metric also is being used in other countries, showing up as far away as New Zealand (Quinn and Hickey 1990). Widespread use of this metric may be due to its inclusion in EPA' s rapid bioassessment protocols (Plafkin et al. 1989). Wallace et al. (1996) recently endorsed use of the EPT metric because it was easy to use, it was stable at reference sites and it effectively tracked changes in water quality.

The recognition of Ephemeroptera, Plecoptera, and Trichoptera as intolerant groups was essentially synchronous with the use of benthic macroinvertebrates to evaluate water quality in the United States, dating back to Richardson's (1928) studies of the Illinois River. The use of macroinvertebrates to monitor water quality became more widespread in the 1950's, and publications of this period also cited Ephemeroptera, Plecoptera and Trichoptera as intolerant taxa (Gaufin and Tarzwell 1952). During this period, investigators started to classify organisms as tolerant, facultative or intolerant (Surber 1953, Beck 1953, Weber 197 3), eventually culminating in the development of biotic indices (Chutter 1972, Hilsenhof f 1977)

Use of EPT taxa richness in North Carolina

The EPT metric had its origin in "208" (nonpoint) studies conducted in North Carolina in the late 1970's under the supervision of David Penrose. Much of the original data analysis is buried in memos and other unpublished government reports. As we accumulated large amounts of data from control sites in the North Carolina mountains, it became apparent that summer taxa richness values (listed for 10 major taxonomic groups) was fairly predictable for unstressed rivers. We developed "Mountain River Control" and "Mountain Stream Control" data sets, using information from composite kick-net samples (Penrose et al. 1980).

Our Biological Assessment Group started to conduct annual monitoring in 1981 at fixed sites, and developed standardized qualitative collection methods. While these methods were not formally published until much later (Lenat 1988, Eaton and Lenat 1991), the collection methods had been standardized by 1982. Classification criteria were developed for both total taxa richness and EPT taxa richness in three ecoregions (NC DEM 1983), although the total taxa richness criteria were dropped in 1986. Trend analysis at unimpacted sites had s hown that EPT taxa richness was more stable (and hence more predictable) than total taxa richness. To our knowledge, the first published use of "EPT taxa richness" was in Lenat (1983).

Biologists with the NC Division of Environmental Management continue to work on EPT taxa richness criteria. In-house studies have been conducted looking at the effects of both stream size (width) and season on EPT taxa richness.

Acknowledgments

Development of biocriteria by the NC Division of Environmental Ma nagement reflects the inputs of many other individuals, including Trish MacPherson, Larry Eaton , Neil Medlin, Nancy Guthrie, and Kathy Herring.

Literature Cited

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