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Types of Reference Condition

The term reference condition can have multiple meanings. Therefore, consistent and specified definitions of reference condition can greatly enhance collaboration among states and the transfer of best practice technology and expertise. In all cases, reference condition is the benchmark against which changes in current biological conditions are evaluated. The following definitions distinguish among four specified types of reference condition:

Reference Condition for Biological Integrity, RC(BI): the natural biological condition of a water body, undisturbed by human activity. As a conceptual aid, it is useful to think of an absolute “natural” or pristine condition that could exist in the absence of all historical and current human disturbances. This definition recognizes the need for a reference condition term reserved for “naturalness” or “biological integrity” even though we might only approximate it in most parts of the world.

Minimally Disturbed Condition, MDC: the biological condition found in water bodies in landscapes with minimum human disturbance. Places that meet the criteria for RC(BI) are rare or impossible to find. Human activity is present throughout the global ecosystem, affecting remote systems through long-range atmospheric transport and deposition of pollutants onto pristine landscapes. Biological integrity in places with a low amount of human activity might not be significantly affected. The phrase “minimally disturbed condition” describes the biological condition in places with a minimal amount of human disturbance.

Least Disturbed Condition, LDC: in altered landscapes, the biological condition found in water bodies with the least amount of human disturbance compared to similar water bodies in the region of interest. There is a clear need to describe the best condition of water bodies in landscapes that have been moderately to heavily disturbed by human activities. Definitions like “minimally disturbed condition” are of little practical use in these situations. Therefore, the phrase “least disturbed condition” has been applied to describe the condition in water bodies that are the least disturbed in a landscape altered by significant human activity. LDC should not be used as a benchmark for biological integrity. Further, in certain severely altered landscapes, LDC may not even be useful as a benchmark for meeting CWA aquatic life use protection and propagation goals.

Best Potential Condition, BPC: the highest possible biological condition deemed achievable through the implementation of best management practices and other rehabilitation activities that can be undertaken in a given landscape given social and economic considerations. In some circumstances, a condition could be achieved that is better than the least disturbed condition (i.e., better than the condition at the best sites) with implementation of the best available practices to remove or minimize stressors. Even though the biological potential might approach biological integrity if the stressors are removed, societal/economic constraints typically mean that a condition is achieved that differs from biological integrity. The term “best potential condition” describes this condition, where the biological expectations are set somewhere between the least disturbed condition and biological integrity.

Material above taken from Best Practices for Identifying Reference Condition in Mid-Atlantic Streams.

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Biological Indicators | Aquatic Biodiversity | Statistical Primer

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