Setting Expectations for the Ecological Condition of Streams: The Concept of Reference Condition

Abstract

An important component of the biological assessment of stream condition is an evaluation of the direct or indirect effects of human activities or disturbances. The concept of a "reference condition" is increasingly used to describe the standard or benchmark against which current condition is compared. Many individual nations, and the European Union as a whole, have codified the concept of reference condition in legislation aimed at protecting and improving the ecological condition of streams. However, the phrase "reference condition" has many meanings in a variety of contexts. One of the primary purposes of this paper is to bring some consistency to the use of the term. We argue the need for a "reference condition" term that is reserved for referring to the "naturalness" of the biota (structure and function) and that naturalness implies the absence of significant human disturbance or alteration. To avoid the confusion that arises when alternative definitions of reference condition are used, we propose that the original concept of reference condition be preserved in this modified form of the term: "reference condition for biological integrity," or RC(BI). We further urge that these specific terms be used to refer to the concepts and methods used in individual bioassessments to characterize the expected condition to which current conditions are compared: "minimally disturbed condition" (MDC); "historical condition" (HC); "least disturbed condition" (LDC); and "best attainable condition" (BAC). We argue that each of these concepts can be narrowly defined, and each implies specific methods for estimating expectations. We also describe current methods by which these expectations are estimated including: the reference-site approach (condition at minimally or least-disturbed sites); best professional judgment; interpretation of historical condition; extrapolation of empirical models; and evaluation of ambient distributions. Because different assumptions about what constitutes reference condition will have important effects on the final classification of streams into condition classes, we urge that bioassessments be consistent in describing the definitions and methods used to set expectations.

Developing a Benthic Index of Biological Integrity and Some Relationships to Environmental Factors in the Subtropical Xiangxi River, China

“…Part of the decline in water resources stems from insufficient consideration of their biological structure and function (KARR, 1999;STODDARD et al, 2006). Some factors have been reported which are linked to river degradation.…”

Theoretical predictions of observed to expected ratios in RIVPACS-type predictive model assessments of stream biological condition

“…Of the remaining 16 papers, 10 built on Wright et al (1984) and described aspects or refinements of the modeling approach, 3 explored aspects of the regionalization or typology approaches to setting reference expectations (Hughes et al 1986, Hawkins et al 2000a 1 ; Fig. 1), 1 treated the overall challenges in identifying reference conditions and applying them in a uniform manner (Stoddard et al 2006), 1 paper described how paleolimnological data could be used in lakes to identify historical conditions for individual sites (Dixit et al 1999), and 1 compared the performance of different types of biotic indices (Reynoldson et al 1997; Fig. 1).…”

“…Policy makers and resource managers generally agree that in the context of ecological assessments benchmarks should represent ecological properties associated with naturalness (e.g., Landres et al 1999, Hering et al 2003, Stoddard et al 2006 [ Fig. 1]), but no general consensus exists regarding how pristine a condition a benchmark should characterize.…”

Development and preliminary application of a method to assess river ecological status in the Hai River Basin, north China

“…Reference condition refers to a reach with favorable ecological status, which acts as a baseline for the evaluation of different ecological levels. There are several interpretations of reference condition, including minimally disturbed condition, historical condition, least disturbed condition, and best attainable condition (Stoddard et al, 2006). The least disturbed condition was chosen as the reference condition in the HRB, because disturbances exist throughout the HRB, no natural rivers could be found, and there is a lack of historical data.…”