Koontz, J., D.G. Huggins, C.C. Freeman, D.S. Baker - Central Plains ...

Macroinvertebrate MMI
Metrics
Of the 44 metrics evaluated in the development of various versions of the MMI; only 18 were
statistically significant and of discriminatory value when evaluating a priori reference and nonreference
groups using the t-test method described by Stoddard et al. (2008). Many of the
metrics originally proposed for rivers and streams were inappropriate because the specific
macroinvertebrate taxa used in the metrics are not a common part of the wetland fauna and were
not found in our samples. Substitutions were made and 44 metrics were selected for evaluation
using the macroinvertebrate samples collected during both studies (Table 11). The use of
Hydrophilidae was adopted since Helophoridae were not present in any of the samples. Both
families belong to the superfamily Hydrophiloidea and thus may provide the similar structural
and functional information about the macroinvertebrate community. Other notable additions
were the measures of intolerant species proposed by Huggins and Moffitt (1988). The count of
intolerant taxa was derived by taking only those records with tolerance values < 3 (scale of 0-5).
Huggins and Moffitt (1988) developed tolerance values for taxa relative to five major pollutant
categories: agricultural pesticides (AP), heavy metals (HM), nutrient and oxygen demanding
compounds (NOD), persistent organic carbons (POC), and suspended solids and sediments
(SSS). A Percent Less Than Mean Regional Tolerance Value (RTV) metric was calculated from
records with known regional tolerance values as the percentage of records having less than the
calculated mean value for that specific site. Chironomidae diversity metrics and overall
Margalef‟s Index were also evaluated as potentially robust measures of diversity among the
samples. Count Collembola Taxa and Percent Parasitic Taxa were the only metrics that failed
the range tests, with representation occurring in less than 25% of sample population (n = 52).
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