Bernadette Ní Chatháin

Bio: Bernadette Ní Chatháin is an academic researcher from University of Limerick. The author has contributed to research in topics: Water Framework Directive & Cobble. The author has an hindex of 3, co-authored 3 publications receiving 117 citations.

THE conceptual basis of ecological-status assessments using diatoms

Abstract: Most member states of the EU have chosen to use existing diatom-based metrics for assessment of ecological status, as required by the Water Framework Directive (WFD), rather than develop new methods. In this paper we assess the suitability of such methods in light of the requirements of the normative definitions of ecological status. In particular, we focus on the rationale for the placement of ecological-status boundaries. As the WFD defines ecological status in terms of the 'structure and functioning' of aquatic ecosystems, we interpret changes in the diatom assemblage in light of changes in entire phytobenthos. Whilst we believe that analysis of diatom assemblages is a sensible approach to developing a first generation of WFD-compatible tools, bearing in mind tight deadlines and limited budgets, the potential of non-diatoms should not be ignored when developing future methods.

Benthic diatoms of the river deel: diversity and community structure

Abstract: This paper compares the diversity and structure of the benthic diatom assemblages on boulder and cobble substrata and examines the influence of site and seasonal factors on diatom diversity in the River Deel, Co. Limerick. One hundred and ten diatom species were identified from the River Deel, with 85 species found on boulders over a two-year period and 102 species found on cobbles over a one-year period. There was little difference in the composition of the diatom community on boulders between sites. Some differences were noted between sites for cobbles, with a small number of species being more associated with certain sites than others. The absence of marked differences between the sites was attributed to the lack of longitudinal variation in the main channel of the River Deel. On both substrates, indicator species analysis showed that the abundance of most diatom species was not related to sampling date. On boulders, only fourteen species in 1999 and twenty-one species in 2000 had a significant association with any sampling date. Twelve cobble species had a significant association with a sampling date (principally May). There was little correspondence between significant indicator species on cobbles and boulders. The patterns of dominance of diatom species differed between the boulder and cobble substrates over the sampling period, and Detrended Correspondence Analysis (DCA) showed that diatom samples formed two distinct groupings based on substrate.

The reference condition: predicting benchmarks for ecological and water-quality assessments

Abstract: Benchmarks provide context and are a critical element of all ecological assessments. Over the last 25 y, hundreds of papers have been published on various aspects of ecological assessments, and most of the analyses described in these papers depend on specifying an ecological benchmark for context. Freshwater scientists and managers usually use reference sites (typically sites in natural or least-disturbed condition) to assess the ecological conditions at other sites. Accurate and precise assessments require that assessed sites be matched with appropriate reference conditions. Two general types of approaches have been proposed to predict reference conditions: classifications based on natural environmental settings and models that use continuously variable environmental attributes as inputs. Two types of classifications have been examined: geographic-dependent regionalizations based on general landscape features and geographic-independent typologies that are typically based on combinations of region...

Recent views on river pollution and diatoms

Abstract: The first studies of diatoms and river pollution were carried out 60 years ago, and the suitability of these micro-algae as bioassessment indicators for monitoring river quality was quickly demonstrated. The objective of this review is to describe the state of the art of the study of diatoms and river pollution between 1999 and 2009. The objective was to group the publications homogeneously according to subject and to indicate which subjects never overlap. To this end a lexical analysis was conducted on the abstract structure of these publications and seven K-means clusters were defined. Most of the items in this area were found to have been published in Hydrobiologia. One group (group 6) comprises publications about a discipline (ecotoxicology); several others group publications on the basis of the same approaches, for example species (group 3), basin (group 7), or spatial approaches (group 2). Other publications are brought together because the studies used a common method of using data, namely predictive models (group 1) or biotic indices (group 4). One group of publications was of studies performed in the same area—South Africa (group 5). Several remarks can be made. First, ecotoxicological studies are mostly experimental and restricted to small study areas. To answer society’s demand for new assessment tools for micropollutant assessment, the next step would be to have more in-situ tests on larger spatial scales. Second, diatom biomonitoring uses the word “species” extensively, because this is the basis for establishing the lists of flora which are used extensively in such subject areas. Species is closely related to taxonomy; nevertheless this discipline is very rarely addressed in the papers. Third, phylogeny is never addressed in the publications. This is significant because phylogenetic studies for freshwater macroinvertebrates enable appropriate definition of taxonomic aggregations that can be used as accurate indicators of particular environmental stressors.

Setting Expectations for the Ecological Condition of Streams: The Concept of Reference Condition

Abstract: An important component of the biological assessment of stream condition is an evaluation of the direct or indirect effects of human activities or disturbances. The concept of a ''reference condition'' is increasingly used to describe the standard or benchmark against which current condition is compared. Many individual nations, and the European Union as a whole, have codified the concept of reference condition in legislation aimed at protecting and improving the ecological condition of streams. However, the phrase ''reference condition'' has many meanings in a variety of contexts. One of the primary purposes of this paper is to bring some consistency to the use of the term. We argue the need for a ''reference condition'' term that is reserved for referring to the ''naturalness'' of the biota (structure and function) and that naturalness implies the absence of significant human disturbance or alteration. To avoid the confusion that arises when alternative definitions of reference condition are used, we propose that the original concept of reference condition be preserved in this modified form of the term: ''reference condition for biological integrity,'' or RC(BI). We further urge that these specific terms be used to refer to the concepts and methods used in individual bioassessments to characterize the expected condition to which current conditions are compared: ''minimally disturbed condition'' (MDC); ''historical condition'' (HC); ''least disturbed condition'' (LDC); and ''best attainable condition'' (BAC). We argue that each of these concepts can be narrowly defined, and each implies specific methods for estimating expectations. We also describe current methods by which these expectations are estimated including: the reference-site approach (condition at minimally or least-disturbed sites); best professional judgment; interpretation of historical condition; extrapolation of empirical models; and evaluation of ambient distributions. Because different assumptions about what constitutes reference condition will have important effects on the final classification of streams into condition classes, we urge that bioassessments be consistent in describing the definitions and methods used to set expectations.

Interactions between diatoms and fine sediment

Abstract: Excessive mobilisation and delivery of fine sediments to water bodies has detrimental impacts on those biotic elements used for waterbody status classification, including macroinvertebrates, fish and macrophytes. The relationship between fine sediment and diatoms is a reciprocal one, with diatoms influencing the production and retention of fine sediments, as well as being impacted by fine sediment derived from the catchment. Diatoms can increase the retention of fine sediments in benthic environments as a result of various mechanisms, including shear stress modification, surface adhesion, and bed clogging. Enhanced retention of fines can have important implications for the transfer and fate of sediment-associated nutrients and contaminants. Excessive fine sediment loadings impact diatom assemblages via shading, burial and scouring. Indirect impacts of increased fine sediment stress can result from changes in habitat availability, herbivory or predator changes which cascade down the food chain. Indices based on the relative abundance of motile species have been proposed for using diatoms to assess waterbody status. However, disentangling the potential confounding impacts of alternative environmental stressors on these simplistic indices remains a significant challenge. Coupling sediment pressure models, capable of predicting the potential impact of mitigation, with meaningful diatom based indices, remains a challenge for catchment planning for sediment abatement and the attainment of improved, or protection of, ecological status. Existing targets for sediment management in river catchments are largely based on relationships between sediment stress and impacts on fish, but these thresholds have been widely criticised. There remains a need to develop generic modelling toolkits coupling sediment stress and impacts on a range of biological quality elements to support a weight of evidence approach.