A Water Framework Directive-compatible metric for assessing acidification in UK and Irish rivers using diatoms

Abstract

Freshwater acidification continues to be a major problem affecting large areas of Europe, and while there is evidence for chemical recovery, similar evidence for biological recovery of freshwaters is sparse. The need for a methodology to identify waterbodies impacted acidification and to assess the extent of biological recovery is relevant to the EU Water Framework Directive, which requires methods to quantify differences in biology between impacted and unimpacted or reference sites. This study presents a new WFD-compliant metric based on diatoms (Diatom Acidification Metric: DAM) for assessing the acidification status of rivers. A database of 558 benthic diatom samples and associated water chemistry data was assembled. Diatom taxa were assigned to one of 5 indicator classes on the basis of their pH optimum, assessed using Gaussian logistic regression, and these indicator values used to calculate a DAM score for each site using weighted averaging. Reference sites were selected on the basis of their acid neutralising capacity (ANC) and calcium concentration, and a regression model developed to predict expected DAM for each site using pH and total organic carbon (TOC) concentration. Site-specific DAM scores were used to calculate ecological quality ratios ranging from ≥1, where the diatom assemblage showed no impact, to (theoretically) 0, when the diatom assemblage was indicative of major anthropogenic activities. The boundary between 'high' and 'good' status was defined as the 25th percentile of Ecological Quality Ratios (EQRs) of all reference sites. The boundary between 'good' and 'moderate' status was set at the point at which nutrient-sensitive and nutrient-tolerant taxa were present in equal relative abundance. The methodology was evaluated using 2 long-term data from 11 sites from the UK Uplands Waters Monitoring Network and is shown to perform well in discriminating naturally acid from acidified sites.

Small Water Bodies in Great Britain and Ireland: Ecosystem function, human-generated degradation, and options for restorative action

“…Similar responses have been documented for phytobenthos ( Kelly et al, 2008 ). Acidification usually results in reduced macrophyte richness and dominance of liverwort taxa ( Ormerod et al, 1987 ), and changes in the diatom assemblage composition ( Juggins et al, 2016 ).…”

European aquatic ecological assessment methods: A critical review of their sensitivity to key pressures

“…However, many other methods have been published and many of them could fill in gaps identified in this study, e.g. acidification in rivers ( Juggins et al, 2016 ), hydromorphological pressures in lakes ( Miler et al, 2013 ; Mjelde and Hellsten, 2013 ), toxic pollution in rivers ( Archaimbault et al, 2010 ). We also suspect (and in some cases know) that such “off-piste” approaches are used to inform local decision-making.…”

“…For instance, pressure-specific methods have been developed in Europe for acidification (lakes: McFarland et al, 2010 ; rivers: Juggins et al, 2016 ), hydromorphological degradation (lakes: Urbanič, 2014 ; rivers: Lorenz et al, 2004 ), eutrophication (lakes: Carvalho et al, 2013 ; rivers: Kelly et al, 2008 ; coastal waters: Vollenweider et al, 1998 ), organic pollution (rivers: Brabec et al, 2004 ; coastal waters: Word, 1980 ) and toxic pollution (rivers: Archaimbault et al, 2010 ).…”

The “Forgotten” Ecology Behind Ecological Status Evaluation: Re-Assessing the Roles of Aquatic Plants and Benthic Algae in Ecosystem Functioning

“…If each component that constitutes the multi-metric index is related to a specific stressor, information about both type and magnitude of the stressor that causes the overall degradation can easily be extracted by tracing each individual metric. The benthic flora has mainly been used to assess nutrient enrichment , but is sensitive to a number of additional stressors, among them acidification (Arts et al 1990;Schneider and Lindstrøm 2009;Juggins et al 2016), salinization (Smith et al 2009), hydromorphological alterations , siltation (Wagenhoff et al 2013), increased dissolved organic carbon concentrations (Brothers et al 2014), exotic herbivores (Krupska et al 2012), and contaminants (Ricart et al 2010). It should therefore be possible to develop a multi-metric index that can do both overall status assessment (by combining the individual metrics, for example, by following the "worst case" principle), and diagnose different causes of degradation (by tracing each individual metric; Fig.…”