Development of Idaho Macroinvertebrate Temperature Occurrence Models
David C. Richards, Ph.D.
Aquatic Ecologist, Cramer Fish Sciences
Michael Bilger
Senior Aquatic Ecologist, EcoAnalysts, Inc.
Gary Lester
Senior Aquatic Ecologist, EcoAnalysts, Inc.
Introduction
Federal regulations implementing the Clean Water Act (CWA) require states to specify appropriate uses to be achieved and protected for their waters (40 CFR 131.10). The CWA requires that, wherever attainable, all waters of the nation be protected for “propagation of fish and shellfish, and wildlife and provides for recreation in and on the water.” This is often shortened to the statement that waters must be “fishable and swimmable.” These are the minimum set of uses, unless unattainable. The federal regulations also say that states must consider the value of water for public water supply, agricultural and industrial uses, navigation, and aquatic life in specifying uses of their waters. States may also adopt sub-categories of a use with appropriate criteria to reflect the varying needs of such uses. Collectively these are known as beneficial uses.
Aquatic Life Existing Uses
The State of Idaho uses three major categories of aquatic life use: cold, seasonal cold and warm. These are mostly temperature driven distinctions, for example the cold-water aquatic life use has temperature criteria that require the water to have an instantaneous temperature < 22º C or a daily average of < 19º C. Benthic macroinvertebrates are the preferred indicator fauna because they have either limited migration patterns or a sessile form of life. This makes them well suited for managers to evaluate local environmental conditions. Some macroinvertebrate species only reside in streams with cold temperatures. If these species are present, then one can conclude that the stream likely has consistently cold temperatures. Lists of macroinvertebrate cold-water indicator species are being developed from two sources: 1) this analysis and 2) review of published literature reports.
In addition, the State of Idaho needs a list of indicator species that would help them identify those streams that support seasonal cold-water aquatic life criteria. These criteria are slightly less stringent than the cold-water: instantaneous temperatures below 26º C with daily average no greater than 23º C. The temperature criteria for seasonal cold only apply from June 20 to Sept 20. Outside of that time period those waters would have the same temperature criteria as the cold-water streams. The idea behind these two categories is to acknowledge that in some cases streams in Idaho are naturally warmer in the summer.
Goal
The purpose of this analysis was to identify and develop a list of cold-water obligate macroinvertebrate taxa that the State of Idaho can use to determine if cold-water aquatic life is a currently existing use in streams being assessed in Idaho. An additional goal was to evaluate and potentially identify macroinvertebrate taxa that may be indicators of seasonal cold-waters.