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COMPARISON OF LABORATORY SUBSAMPLING METHODS OF BENTHIC SAMPLES FROM BOATABLE RIVERS USING ACTUAL AND SIMULATED COUNT DATA
Citation:
Flotemersch, J E. AND K A. Blocksom. COMPARISON OF LABORATORY SUBSAMPLING METHODS OF BENTHIC SAMPLES FROM BOATABLE RIVERS USING ACTUAL AND SIMULATED COUNT DATA. Presented at North American Benthological Society, Pittsburgh, PA, May 28-June 1, 2002.
Impact/Purpose:
The goal of this research is to develop methods and indicators that are useful for evaluating the condition of aquatic communities, for assessing the restoration of aquatic communities in response to mitigation and best management practices, and for determining the exposure of aquatic communities to different classes of stressors (i.e., pesticides, sedimentation, habitat alteration).
Description:
We examined the effects of using a fixed-count subsample of 300 organisms on metric values using macroinvertebrate samples collected with 3 field sampling methods at 12 boatable river sites. For each sample, we used metrics to compare an initial fixed-count subsample of approximately 300 organisms and a "full" count of up to 2000 organisms. Metrics based on proportions were very similar between the initial 300 count and the "full' count, but taxa richness differed between the two counts. The proportion of "full" count taxa represented in the initial 300 count (68% on average) was significantly positively correlated (r-0.965, p<0.001) with the proprotion of total individuals sorted. Computer simulations of subsampling using the "full" count data indicated that at fixed counts of 100, 200, 300 and 500 organisms, an average of 49, 57, 64, and 69% of taxa in the "full" count, respectively, were represented. The proportion of taxa represented was negatively correlated with the number of taxa and the percent individuals in the dominant taxon in the "full" count, regardless of fixed-count size. Finally, although taxa richness metric values were shifted from one subsample size to another, the separation of impaired and relatively unimpaired sites was usually unaffected.