The Cold Water BMIBI was developed by staff of the State Hygienic Laboratory in partnership with the Iowa DNR (http://publications.iowa.gov/21843/). The cold water BMIBI is used in the northeast portion of the state, where cold water streams are common and a separate BMIBI was needed to more accurately measure the biotic integrity of these streams.

Metric Descriptions

Taxa Richness Metrics

MH CW Taxa Richnessis the number of CW designated taxa (Appendix B) handpicked from all the different types of benthic habitat in the sampling reach. Several CW taxa are not likely to be encountered in SH samples but should be collected in MH samples if present in the reach. This metric is strongly correlated with the MH Trichoptera taxa richness metric, and many of the CW taxa collected during the “standard” July –October field season are caddisflies. This metric may prove to be quite sensitive if applied to a springtime sampling (March-June).

MH Trichoptera taxa richness (no Hydropsychinae & Hydroptilidae) is the number of caddisfly taxa handpicked from all the different types of benthic habitat in the sampling reach, excluding the groups named in the metric. Observations during sampling suggested that several caddisfly taxa are commonly associated with quality coldwater streams (e.g. Brachycentrus spp and Glossosoma spp) and several others are less often encountered. We feel this metric (though redundant) may also be an indicator of coldwater stream habitat quality/diversity and could assist in discriminating between streams that are thermally altered (or misclassifiedas coldwater) and streams with water quality or physical habitat deficiencies. Hydropsychinae, a sub family of Hydropsychidae that includes the genera Ceratopsyche and Hydropsyche, tend to occur in nearly all streams are excluded from the metric. Hydroptilidae larvae, which cannot be identified below the generic level, are also excluded because they seem ubiquitous and are found in most Paleozoic Plateau streams.

MH sensitive taxa richness is the number of sensitive taxa handpicked from all the different types of benthic habitat in the sampling reach. Sensitive taxa are defined as those which have a BTI value of 3 or less (scale of 0-10 with increasing values reflecting increasing organic enrichment; see SH BTI metric description below). Most of the CW taxa are also sensitive, but this metric should assist in discriminating between streams that are thermally altered (or misclassified as coldwater) and streams with water quality or physical habitat deficiencies.

MH % tolerant taxa is the proportion of all taxa handpicked from all the different types of benthic habitat in the sampling reach that are tolerant taxa. Tolerant taxa are defined as those which have a BTI value of 7 or more (scale of 0-10 with increasing values reflecting increasing organic enrichment; see SH BTI metric description below). This metric showed a broader response to environmental gradients than was expected.

Proportional abundance metrics (calculated from SH samples only)

SH Benthic Tolerance Index (BTI) is adapted from the Hilsenhoff Biotic Index which was developed as an indicator of stream organic enrichment (Hilsenhoff, 1987). The scale ranges from 0-10 with increasing values reflecting increasing organic enrichment. This metric’s effectiveness in both warmwater and coldwater streams is not surprising, as its development was driven by Hilsenhoff’s dissatisfaction with how the diversity indices of his day underrated cold, pristine northern Wisconsin streams. The tolerance values are a combination of several regional resources (Hilsenhoff 1987, Hilsenhoff 1988, Huggins and Moffett 1988, Bode et al. 1991, Lenat 1993, Barbour et al. 1999, Bode et al. 2002) that were used to more accurately characterize the tolerance values of benthic macroinvertebrate communities within Iowa versus Hilsenhoff’s Wisconsin focus.

SH % CW individuals is the proportion of the total number of organisms that belong to the CW designated taxa. This metric is strongly correlated with the SH CW taxa richness, which was eliminated due to redundancy. The decision of which metric to retain was partially based on our observation that in quality coldwater streams one CW taxa can often dominate the community. Mass emergences can quickly change benthic macroinvertebrate community composition and retaining this metric insures that coldwater dominated communities will be reflected temporally.

SH % Hydropsyche individuals is the proportion of the total number of organisms that belong to the Trichoptera genus Hydropsyche. Hydropsyche betteni is found in most small to medium sized streams in Iowa but its abundance seems to be notably limited in high quality coldwater streams. It is likely an indicator of both extremes in the coldwater stream condition spectrum.

SH % Hydropsychinae individuals is the proportion of the total number of organisms that belong to the Hydropsychidae sub-family Hydropsychinae, which includes the genera Hydropsyche (mentioned above) and Ceratopsyche, but not coldwater obligates, Diplectrona modesta and Parapsyche apicalis (both family Hydropsychidae). Ceratopsyche and Hydropsyche spp. have been collected in nearly all Paleozoic Plateau streams, but their abundances seem to be depressed in the Iowa reference coldwater streams. This metric displayed a broader response across the environmental gradients than the SH % Hydropsyche individuals metric alone.