Summary Floods and droughts are predicted to increase in intensity, duration and frequency in many future climate scenarios, yet long‐term data that track before‐and‐after responses of natural communities remain scarce. We explored the impacts of a series of extreme events, including a particularly catastrophic flood, over 13 years in the Glenfinish River in Ireland. Overall, seasonal cycles of absolute and relative abundance were the strongest temporal signal in the data, and the community as a whole was relatively persistent. At interannual scales, a core of c. 15 taxa were present throughout most of the time series, which spanned >10 generations for most taxa, whereas extreme events had negligible or weak effects, with two notable exceptions. The catastrophic 1986 summer flood triggered a 10‐fold decline in abundance: although most populations returned to their pre‐disturbance state in <3 years, some took up to a decade to recover. In 1988–1989, two contrasting extreme low‐rainfall and storm events occurred within a year and were associated with far more marked compositional and functional shifts than were seen in the 1986 flood, although abundance was not so strongly affected. Contrasting extreme events that occur close to one another in time and/or at atypical times of year (e.g. floods in summer, when base flow is low) can have particularly strong effects, whereas at other times even the most extreme events may leave little longer‐term footprint. Therefore, both the temporal context and the magnitude of events determine the biota's response. Effects of the events also varied across taxa and organisational levels: the more r‐selected taxa (e.g. Chironomidae) were relatively unaffected compared with the larger, more K‐selected taxa. Community‐level responses were mostly driven by shifts in relative abundances, rather than species loss or turnover, and the functional diversity of species traits was more resilient still. The apparent stability in relative abundances of functional groups in the face of significant variation at the species level is suggestive of high functional redundancy, but without exhaustive further analyses using null‐model approaches, this remains unproved. In turn, relatively high levels of redundancy and the reshuffling of species with similar traits could confer resilience in the face of all but the most extreme events.

No abstract

Plantation conifer forest can increase the risk of acidification in acid-sensitive catchments with consequences for macroinvertebrates and ecosystem functioning. This study compared headwater streams in forested and non-forested catchments to appraise the distance required for the acid effect on macroinvertebrates to diminish downstream. Strict criteria were followed in the selection of paired streams, including similarities in elevation, aspect, stream order, geographical proximity, geology and soil type, with no inflowing tributaries in the first 2.5 km and no major land-use other than plantation forest and moorland. Consequently two headwater streams (one forested, one non-forested) drained Ordovician sedimentary geology and two headwater streams (one forested, one non-forested) drained Old Red Sandstone (ORS) were selected. All streams drained peaty soils. Up to six sites at 500 m intervals were sampled in triplicate by multihabitat kick sampling. Ecological impact and recovery from acid effects involved the entire macroinvertebrate community, but varied between seasons.Acid-sensitive Ephemeroptera revealed marked effects of episodic acidification, with Baetis rhodani and Rhithrogena semicolorata found to be transient between seasons. The increase in acid-sensitive ephemeropteran species with increasing distance downstream indicates the finite effects of forest mediated acidification on soft water streams in Ireland. Ecological impact appears, therefore, to be localised within the catchment, with ecological recovery occurring a short distance downstream. This is the first study to have reported such results.

ABSTRACT

Integrated Constructed Wetlands (ICWs) constitute an alternative option for the treatment of agricultural wastewater in Ireland. These surface flow systems are formed by interconnected ponds and have the capacity to fit into the landscape and provide habitat for a wide range of biota, including macroinvertebrates that have enormous potential for biodiversity enhancement. For these reasons, five ICW systems were studied. In addition, five natural ponds were investigated to account for the potential of ICW ponds to mimic natural conditions. Nine river sites were also investigated to allow for an evaluation of the catchment biodiversity contribution of the ICW systems. The present study revealed that the last ponds in the chain of these ICW systems are capable of supporting a similar number of taxa as natural ponds. Furthermore, the contribution of the last ponds to the macroinvertebrate diversity at the catchment level was high. ICWs seem to integrate their effluent management and purifying properties with that of biodiversity enhancement and landscape fit. This is the first study to investigate the potential of constructed interconnected ponds, used for wastewater treatment, to enhance biodiversity in agricultural landscapes.