Data rich, information poor? Phytobenthos assessment and the Water Framework Directive

Abstract

The Water Framework Directive (WFD) provides the legal basis for water management in the European Union (EU). Twelve years after it was passed, all but five EU Member States had phytobenthos assessment methods for rivers, whilst nine had methods for lakes. Most are based on diatoms, although a few are supplemented by evaluations of non-diatoms and some include macroalgae as part of parallel macrophyte assessments. Norway is the exception, with assessment based on non-diatom algae alone. Over half of all states have methods based wholly or partly on weighted average metrics developed before the onset of the WFD, with nine choosing the Indice de Polluosensibilité Specifique. Such metrics generally have high correlations with the predominant nutrient or organic pollution gradient and, as such, represent pragmatic solutions to ecological status assessment. However, their widespread use raises questions about what, exactly, 'ecological status' means. Strong relationships with chemical pressure gradients may be a mixed blessing as pressure gradients are often composed of several intercorrelated variables, making it difficult to disentangle correlation and causation in the absence of ecophysiological studies of individual species. Moreover, the focus on strong relationships with chemical gradients means that most phytobenthos metrics describe the scale of hazard at a site rather than the risk posed to other trophic levels and to ecosystem services. This first generation of phytobenthos assessment tools may be inadequate when catchment managers need guidance on remediation strategies for particular water bodies. A second generation of assessment tools, focused on the fitness of the phytobenthos as part of aquatic ecosystems, rather than just as indicators of chemical conditions, is needed if the goal of good ecological status around Europe is to be achieved.

Establishment of equilibrium states and effect of disturbances on benthic diatom assemblages of the Torna-stream, Hungary

“…As case and comparative studies accumulated, doubts started to emerge about the overall applied methods and their appropriateness in assessing real ecological status. In his seminal paper, Kelly (2013) concluded that more Gomphonema parvulum (6.8%) Sp 5 Navicula gregaria (3.3%) , Na …”

“…One of the most robust arguments for using diatoms in ecological status assessment is their high species number. Although methods of status assessment from sampling to data analyses, including the applied indices, improved markedly, the underlying ecological knowledge has remained incomplete (Kelly, 2013). Until now, process-based research on relationships between environmental factors, population dynamics, and community attributes has been largely missing.…”

Benthic soft-bodied algae as bioindicators of stream water quality

“…The US national bioassessments are largely based on diatom community composition, supplemented by total algal biomass data and proportional abundance of all algal taxonomic groups. Ecological integrity and ecological status are holistic concepts not confined to any single taxonomic group and require understanding of both the state of a particular indicator group and its interaction with other organisms and the catchment (Kelly, 2013). In theory, information gained from the entire benthic algal community can provide a more comprehensive indication of environmental conditions (Kelly, 2006).…”

“…The current state-of-art in algae-based river and stream bioassessment in the EU shows that the diatoms are developed and intercalibrated as proxies for phytobenthos, gradually narrowed to an application of a few diatom indices (Poikane, 2015). The softbodied algae supplement either phytobentos or macrophyte stream assessment systems in several states, and the abundance of the phytobentos is not evaluated (Kelly, 2013;Poikane, 2015). The only exception is Norway, whose stream bioassessment is based completely on soft-bodied algae (Schneider andLindstrøm, 2009, 2011).…”

Assessment of ecological status in UK lakes using benthic diatoms

“…Most of these indices are mathematically identical to the transfer functions widely used in palaeolimnology to reconstruct variables such as total P (TP) (e.g., Bennion et al 1996, Hall andSmol 2010). However, the objective of contemporary assessment is not to provide a proxy for a variable that can be measured relatively easily, but to distill biological information into a value that can be related to biological condition (Kelly 2011(Kelly , 2013.…”