Uncertainty of methodologies assessing ecological status in transitional water systems

Assessments of ecological status according to the principles devised by the Water Framework Directive (WFD) are always associated with some degree of uncertainty. This uncertainty stems from the inevitable imperfection of the assessment criteria (ie development of indicators of ecological status, refinement of reference conditions and class boundaries, and routines for integrated assessment) and from the uncertainty of measurements. Here, we address the ecological status classification issue in transitional water ecosystems, using benthic macroinvertebrates and four proposed multimetric indices (BAT, BITS, M-AMBI and ISS), likely to respond differently to different sources of stress and natural variability adding uncertainty to resulting classifications. In order to investigate the possible contrasting behavior of the four multimetric indices, we propose two multivariate Bayesan hierarchical models in which the ...