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- PublicationThe impact of a catastrophic storm event on benthic macroinvertebrate communities in upland headwater streams and potential implications for ecological diversity and assessment of ecological statusUpland headwater streams are dynamic systems, responding rapidly to changes in climatic conditions. This study examined the effects of a catastrophic rainfall event, that occured on 24 October 2011 on the east coast of Ireland, on the macroinvertebrate community composition and structure of four headwater streams in the river Liffey catchment located in the Wicklow Mountains. The ecological status before and after the storm were also evaluated. The water level and pH of each stream were recorded using continuous monitoring equipment, while rainfall data for the study period were sourced from a local weather station. Benthic macroinvertebrates were investigated before and after the storm event using Surber sampling. Results showed rapid and large increases in water level and significant declines in stream pH in response to intensive rainfall during the storm. The high water levels also caused major physical damage and abrasion in all four streams, that significantly altered instream habitats. The storm event induced significant losses to the richness and/or density of most taxonomic groups, with the exception of the Plecoptera. Furthermore, the overall community composition and structure changed significantly, most likely as a result of physical disturbance, given the relative persistence of acid-sensitive taxa and the relatively short period of harsh acidic conditions (<5 pH). Interestingly however, the ecological status of each of the four study sites, tested using Stream Risk Score (SSRS), Biological Monitoring Working Party (BMWP) and the Average Score Per Taxon (ASPT) indices, was unaltered by the loss in richness and densities. This was likely a result of the maintenance of plecopteran richness and the absence of organic pollution, thus highlighting the need to develop appropriate indices to assess the ecological status of streams and rivers affected by physical disturbance caused by large storm events. Ultimately, catastrophic storm events in upland headwater streams have potentially major implications for the maintenance of regional macroinvertebrate diversity within affected regions.
- PublicationProgressing understanding of episodic stream acidification in upland plantation conifer forested subcatchments in IrelandEpisodic stream acidification associated with managed conifer forests in upland acid-sensitive subcatchments, sometimes referred to simply as ‘the forest effect’, is among the most scientifically complex water quality challenges facing Irish foresters and water quality managers today. The lack of adequate understanding of this evolving phenomenon has arguably stifled the emergence of a universally accepted set of mitigating management measures. This study addresses four general areas of the topic in which a further progression of understanding may advance efforts to reach a consensus on how and where to introduce or implement policy modifications. First, data from two previous studies are combined and supplemented with new data from this study and all are reanalysed to verify the existence of the forest effect in nearly all types of Ireland’s acid-sensitive subcatchments with substantial managed conifer forest cover. Second, the various mechanisms, or drivers, by which the streams are acidified, are explored in further detail. In contrast with the findings of studies two decades ago, no evidence of significant acidification effects from pollutant deposition from the atmosphere in the East of Ireland was found in more recent data. Third, the factors external to the forest potentially contributing to acidification are tested for associations with increasing stream acidity. In some cases, associations between stream acidity and subcatchment and meteorological variables were found to be the opposite of those found in studies of other northern European subcatchments. Finally, the question is answered in the affirmative as to whether such potentially causal variables, including per cent of subcatchment forested, could be used in regression analysis to allow geology and soil-specific forest cover thresholds critical to proper management of water quality to be predicted. Conclusions, some unprecedented in Ireland, are made about the extent of evidence for the forest effect and its associated drivers and the explanatory powers of potentially acidifying variables. Recommendations are offered consistent with continuing efforts to develop models to predict forest effect acidification at the subcatchment level.