Detecting Invertebrate Species Change in Running Waters: An Approach Based on the Sufficient Sample Size Principle

摘要

The EU Water Framework Directive (WFD) is in need of a practical method and index suitable for comparingthe ecological status of invertebrate fauna in rivers throughout Europe. The uncertainties that characterize lotic samplingmethods can be omitted by increasing sampling effort up to a species detection probability threshold. We describe astatistical model which provides the background for applying a sampling protocol aiming to record the total number ofcommon and abundant species. Methods, sample standards and sorting time become less significant to the result as longas the total sample is sufficiently large to detect common species. An index called the Intercalibrated Benthic InvertebrateBiodiversity Index – IBIBI – is proposed based on Observed / Expected species ratios for EPT groups. The EcologicalQuality Ratio thus obtained may then be adjusted to WFD’s ecological status scale within each region or river type acrossEurope, which then can be compared and intercalibrated. Although offering a possible solution to the problem ofintercalibration, further studies are needed.