Sample size determination for soft‐bottom sampling in large rivers and comparison with the chironomid pupal exuvial technique (CPET)

Abstract

AbstractOur objective in this study was to determine the adequate sample size for the use of grab sampling in the biomonitoring of large soft‐bottom rivers. We also compared two sampling methods, grab sampling and the Chironomid Pupal Exuvial Technique (CPET), in detecting anthropogenic impacts in a large boreal river and assessed the degree of concordance between the two data sets. Sample size determination showed that, at the lowest possible taxonomic level, a minimum of eight benthic samples was required to obtain a reliable picture of benthic communities. When using the CPET, the number of chironomid species was nearly twice that of all benthic macroinvertebrates in the grab samples. In addition, a majority of the chironomid species found in the grab samples was also detected using the CPET. Although both data sets indicated significant differences in benthic communities between the sampling sites in the river Kymi, a Mantel test showed that patterns in community composition were not concordant. This was mainly because benthic samples from the deep depositional areas of the river indicated poorer ecological status than did the CPET data, which integrate species from various depths and habitats. Thus, samples from a single macrohabitat may not adequately represent environmental conditions of large rivers. Overall, our results suggest that the CPET provides a reliable and cost‐effective alternative, or a supplementary assessment tool, to more traditional sampling methods when assessing anthropogenic stresses in large boreal rivers. Copyright © 2008 John Wiley & Sons, Ltd.