The following description of the Index of Biological Integrity (IBI) is excerpted with the author's permission from Diagnosis of stream environments with index of biological integrity for Japanese streams, E.M. Rossano. (Tokyo, Japan: Sankaido, 1996).

Biological integrity has been defined as "The ability to support and maintain a balanced, integrated adaptive assemblage of organisms having species composition, diversity, and functional organization comparable to that of natural habitat of the region" (Karr and Dudley 1981, Karr et al. 1986). As a result of evolution, each organism is adapted to the environmental conditions in its native biogeographic region. An environment that supports an assemblage of organisms similar to that produced by long-term evolutionary processes has high biological integrity. Changes of the environmental condition resulting from human activities cause a decline in biological integrity and can make the environment uninhabitable for appropriate organisms.

A biological integrity approach consists of four steps: 1) defining biological condition in a minimally disturbed area - what the natural condition in the area should be, 2) defining biological attributes that change along the gradient of human influence, 3) associating those changes with specific human impacts, and 4) identifying management practices for improving biological integrity. The IBI can convey broad biological information expressed both numerically and narratively.

An index of biological integrity (IBI) is a synthesis of diverse biological information which numerically depicts associations between human influence and biological attributes. It is composed of several biological attributes or 'metrics' that are sensitive to changes in biological integrity cased by human activities. Metrics are based on either taxa richness (the number of taxa found at a study site) or the percentage of individual organisms which share common biological characteristics that increase or decrease along the gradient of human influence (e.g., percentage of individuals classified as oligochaete worms).

The B-IBI for the Puget Sound for the Puget Sounds lowlands is based on ten (10) metrics (denoted by a ·) including:

Taxa richness and composition Pollution Tolerance

• Total number of taxa (10, 20)

• Number of intolerant taxa (0.5, 2)

• Number of Mayfly (Ephemeroptera) taxa (3, 5.5)

• % of individuals in tolerant taxa (50, 20)

• Number of Stonefly (Plecoptera) taxa (3, 5.5)

• Number of Caddisfly (Trichoptera) taxa (2, 4.5)

• Number of long-lived taxa (0.5, 2)

Feeding Ecology Population Attributes

• % of predator individuals (5, 10)

• % dominance (2 or 3) taxa (75, 50)

• Number of clinger taxa (8, 15)

To analyze data collected using the B-IBI sampling protocol, one must first know the maximum taxa abundance for the geographical area sampled. This number is obtained from sampling the least impacted streams in a geographic area and determining the maximum number for each of the categories listed above. This number is then applied to all streams in the geographical area as the maximum taxa abundance expected in area streams (e.g., the Puget Sound Lowlands). For example, a maximum taxa abundance is derived for mayflies, stoneflies, caddisflies, long-lived taxa, etc. These maximum numbers are then divided into 3 partitions. The lower third partition is given the value of 1, the middle third is given a value of 3, and the highest third is given a value of 5.

For example, according to the maximum number of stoneflies expected in the Puget Sound lowlands, a stream with 0-3 stonefly taxa is given a 1 for the stonefly taxa metric, a 3 if the sample contains 4-5.5 stonefly taxa, or a value of 5 if it has more than 5.5 taxa stonefly taxa. This exercise is completed for each of the ten Puget Sound Lowland metrics listed above. (Note that a 1 is given for larger results for the % of individuals in tolerant taxa and % dominance taxa metrics). When all the data is partitioned in this way, the values from each of the ten metrics are added up. The final B-IBI score will total between 10 and 50. Streams with low B-IBI scores will indicate high human impact while streams with high scores indicate lower impact.

The individual metric scores and the final B-IBI score allow monitors to understand the processes occurring within a stream system from the point of view of the taxa living in the stream. A high taxa richness score (total taxa richness) may indicate that there are a lot of different insects present, but if they are mostly composed of pollution tolerant species, the final B-IBI score may be low. Thus, the B-IBI does not focus on a single human impact such as water chemistry or toxicity, but focuses on a stream's biological integrity as a whole (Rossano 1996).

Tuesday, 16-Jul-2002 11:15:26 PDT