NAMC Report Contents

Site and sample info

NAMC reports sample information provided by the customer and number of
individuals identified by NAMC. 

Index results

Bioassessment index scores and condition classes are the most common use of macroinvertebrate data, and NAMC provides this information to states and regions as requested. For more information see the index report page.

Metrics

We provide values for metrics used to characterize different components of macroinvertebrate assemblages. These metrics include diversity indices, and density and richness metrics for different taxonomic groups or groups of traits such as functional feeding group. For a complete list of metrics calculated see the example report below. Note that values for richness-based metrics are calculated based on unique taxa within a sample after computer resampling all samples to a maximum of 300 individuals, but density metrics are based on the original lab subsample counts and raw taxa lists.

Taxa matrix

We provide a standardized taxa by sample matrix for ease of comparing taxa across samples, and this matrix can easily be imported into statistical software packages for additional analyses. Columns in this worksheet are samples coded by NAMC Sample ID and the rows are taxa. Values are counts of individuals for each taxa after standardizing (computer resampling) to a maximum of 300 individuals for each sample to account for differences in sampling effort among samples. The taxa list is standardized to Operational Taxonomic Units (OTU) that are common across samples. OTUs are primarily at the genus taxonomic level, but if index scores are reported the OTU is specific to the index used.

Raw taxa list

We provide a raw list of taxa identified for ease of importing data into databases and searching for specific taxa of interest, which may not have been present in the resampled, standardized taxa list.

Considerations for interpreting data

Number of Individuals identified

Samples containing < 150 individuals may be indicative of either poor biological conditions or poor field sampling, and additional samples are likely needed to determine biological conditions.

Accounting for natural gradients

The metrics we report in the metrics worksheet are not adjusted for the effect of the natural environmental differences among sites. If you are seeking to compare metrics among sites rather than through time at a single site, we recommend first accounting for these natural environmental gradients. Bioassessment index scores, on the other hand, are adjusted for variability among sites in naturally occurring environmental conditions. However, it is important to consider the "Model Applicability" column that we provide to determine if the natural environmental settings at your site are similar to those used for sites that were used to develop indices. For more information see the "Model Applicability" column metadata.

Non-perennial streams

Taxa richness and index scores in nonperennial streams may be inherently low and assemblage composition may be variable through time and unpredictable because of the effects of frequent natural disturbance. Please contact us if you think your sites may be prone to frequent drying events so we can discuss available scoring tools to help interpret your data.

Changes in trait info or taxonomic hierarchy

NAMC periodically updates our taxonomic assignments and traits associated with taxa. Please reach out to us for historical data exports if you have any concerns regarding these changes over time.