Re-examining the effects of episodic acidity on macroinvertebrates in small conifer-forested streams in Ireland and empirical evidence for biological recovery

Abstract

:ABSTRACTResearch throughout Europe has indicated the continuing reductions in acidic aerial deposition and associated improvements in freshwater pH. However, information on macroinvertebrate responses to these on-going changes is rare. During 2009, 2010 and 2011, 34 peat-dominated catchments in three geologically distinct acid-sensitive regions of Ireland were sampled for macroinvertebrates (6 occasions) and chemistry (3 seasons) to assess the effects of reduced sulphate and nitrate deposition in an ecoregion with historically low acidic deposition. Streams drained moorland catchments without forest, catchments with 20%–50 % (low) and catchments with forest cover and >50% (high) forest cover. Results indicate ecological improvements have occurred in many forested catchments when compared with findings in the early 1990s, especially on metamorphic and igneous geologies. However, episodically low pH (<5.7) and high inorganic aluminium concentrations (>150μg l−1), associated with storm-flow events, resulted in periods of ecological degradation. Nevertheless, the reductions in ecological health appeared seasonal, associated with antecedent hydrochemistry and climate. Interestingly, acid-sensitive Baetidae were present in the majority of forested streams in Ireland, owing to the recent improvements in water quality. However, caution must be advised as there are still many hydrochemical and ecological uncertainties in peat-soil forested catchments, owing to the high concentrations of dissolved organic carbon, climate change and changes to catchment management.