Influence of macroinvertebrate sample size on bioassessment of streams

Abstract

In order to standardise biological assessment of surface waters in Europe, a standardised method for sampling, sorting and identification of benthic macroinvertebrates in running waters was developed during the AQEM project. The AQEM method has proved to be relatively time-consuming. Hence, this study explored the consequences of a reduction in sample size on costs and bioassessment results. Macroinvertebrate samples were collected from six different streams: four streams located in the Netherlands and two in Slovakia. In each stream 20 sampling units were collected with a pond net (25Â25 cm), over a length of approximately 25 cm per sampling unit, from one or two habitats dominantly present. With the collected data, the effect of increasing sample size on variability and accuracy was examined for six metrics and a multimetric index developed for the assessment of Dutch slow running streams. By collecting samples from separate habitats it was possible to examine whether the coefficient of variation (CV; measure of variability) and the mean relative deviation from the ''reference'' sample (MRD; measure of accuracy) for different metrics depended only on sample size, or also on the type of habitat sampled. Time spent on sample processing (sorting and identification) was recorded for samples from the Dutch streams to assess the implications of changes in sample size on the costs of sample processing. Accuracy of metric results increased and variability decreased with increasing sample size. Accuracy and variability varied depending on the habitat and the metric, hence sample size should be based on the specific habitats present in a stream and the metric(s) used for bioassessment. The AQEM sampling method prescribes a multihabitat sample of 5 m. Our results suggest that a sample size of less than 5 m is adequate to attain a CV and MRD of £ 10% for the metrics ASPT (Average Score per Taxon), Saprobic Index and type Aka+Lit+Psa (%) (the percentage of individuals with a preference for the akal, littoral and psammal). The metrics number of taxa, number of individuals and EPT-taxa (%) required a multihabitat sample size of more than 5 m to attain a CV and MRD of £ 10%. For the metrics number of individuals and number of taxa a multihabitat sample size of 5 m is not even adequate to attain a CV and MRD of £ 20%. Accuracy of the multimetric index for Dutch slow running streams can be increased from £ 20 to £ 10% with an increase in labour time of 2 h. Considering this low increase in costs and the possible implications of incorrect assessment results it is recommended to strive for this £ 10% accuracy. To achieve an accuracy of £ 10% a multihabitat sample of the four habitats studied in the Netherlands would require a sample size of 2.5 m and a labour time of 26 h (excluding identification of Oligochaeta and Diptera) or 38 h (including identification of Oligochaeta and Diptera).

The STAR project: context, objectives and approaches

“…Experimental field studies were devised to consider a spectrum of relevant issues (Sˇporka et al, 2006;Vlek et al, 2006) whilst Verdonschot (2006b) examined the significance of varying levels taxonomic precision on the biological typology of European streams and rivers.…”

Analysis on the Relationship between Biological Indices and Survey Area of Benthic Macroinvertebrates Using Mathematical Model

“…일정수준 이하의 면적 에서 저서성 대형무척추동물의 군집지수 값은 조사면적에 따라 민감하게 반응할 수 있다고 알려져 있다 (Duggan and Collier, 2002;Kim et al, 2013;Vlek et al, 2006). 생태학 적 분석에서 나타날 수 있는 오류의 요인 중 표본크기는 가장 중요한 요인으로 작용할 수 있으며(Morin, 1997), 이 에 따라 종 다양성 및 풍부도와 유사성은 물론 먹이망 구 조에 대한 해석이 달라질 수 있다( (Bagon et al, 1986;Cao et al, 2002).…”

“…생태학 적 분석에서 나타날 수 있는 오류의 요인 중 표본크기는 가장 중요한 요인으로 작용할 수 있으며(Morin, 1997), 이 에 따라 종 다양성 및 풍부도와 유사성은 물론 먹이망 구 조에 대한 해석이 달라질 수 있다( (Bagon et al, 1986;Cao et al, 2002). 국외에서는 군집에 대한 대표성과 비용효율을 고려한 표 본크기의 연구 (Bartsch et al, 1993;Resh and Price, 1984) 를 비롯하여 개체수 (Duggan and Coller, 2002;Lorenz et al, 2004)와 채집면적 (Vlek et al, 2006) 기준의 표본크기 에 대한 연구가 이루어져 왔다. 그러나 이들 연구의 대부 † To whom correspondence should be addressed.…”

Comparison of bioassessment results and costs between preserved and unpreserved macroinvertebrate samples from streams

“…Apart from accuracy and variability, costs play an important role in decision-making related to the standardization of methods. The costs for collection and processing of macroinvertebrate samples are high and (can) depend strongly on the sampling technique used (e.g., Barbour and Gerritsen 1996;Metzeling et al 2003;Vlek et al 2006).…”

“…Many studies have focused on variability, accuracy, and/or costs in terms of sampled area (e.g., Metzeling and Miller 2001;Vlek et al 2006), number of samples (e.g., Canton and Chadwick 1988), sampling device (e.g., Drake and Elliott 1982;Mackey et al 1984;Barton and MetcalfeSmith 1992;Cheal et al 1993), sampled habitats (e.g., Kerans et al 1992), intensity of sorting (e.g., Barbour and Gerritsen 1996;Courtemanch 1996;Growns et al 1997), and taxonomic resolution of identification (e.g., Nijboer and Verdonschot 2000;Bailey et al 2001;Lenat and Resh 2001). An important aspect of sample processing, which has only been the subject of a few studies, is the preservation (or not) of samples immediately after collection.…”