Variations in levels of deposition of atmosphere-borne industrial pollutants at three oligotrophic lakes in Ireland over the last 50–150 years: sediment-based archives of sources, levels and ecological sensitivity

Abstract

Atmosphere-borne acidic pollutants constitute an important, potentially critical, risk to aquatic ecosystems. Long-time series datasets are a requirement in the assessment of the biological impacts of both increased and decreased loadings of acidic pollutants and allow for the anticipation of future pollution loadings and their effects that can be acted upon with some confidence. Little is known concerning levels of deposition of atmospheric pollutants and their effects on acid-sensitive aquatic ecosystems in Ireland. Moreover, unequivocal evidence of acidification by atmospheric deposition is limited. The objective of this study was to provide a preliminary assessment of pH response in three lake sites that are situated in acid-sensitive areas of Ireland, and to determine whether pH response tends to be uniform or differs due to variations in atmospheric loading and catchment properties. Levels of spheroidal carbonaceous particle (SCP) deposition have been used as a general indicator of the timing and extent of atmospheric pollutant loading and ecosystem response has been assessed by estimating diatom-inferred pH with a weighted-averaging calibration model (72 lakes) developed specifically for the Irish ecoregion. Levels of diatom-inferred pH (DI-pH) appear to respond to increased and decreased levels of atmospheric pollution loads—as represented by SCPs—at two of the three sites examined in the east and west of Ireland. In contrast, the site situated in the southwest of Ireland showed a varying and less directional DI-pH response, possibly due to lower deposition pressures, large lake size, and more buffered edaphic geology.