Abstract of PhD Thesis

Lake sediment-based reconstructions of variations in levels of deposition of atmospheric pollutants from the industrial-scale combustion of fossil fuels and ecosystem response at three remote Irish lake sites

Barry O'Dwyer, Trinity College Dublin (2009)

Levels of atmospheric-borne pollutants are of concern due to their detrimental impacts on ecosystem health: relationships between the direct (e.g. by altering ecological structure) and indirect (e.g. by pre-disposing ecosystems to further damages by other stressors such as climate change) effects of increased levels of deposition of atmospheric pollutants on freshwater ecosystems have long been recognised. However, little is known about long-term variations in levels of deposition of atmospheric pollutants, and as a result, it is difficult to determine the relationship between the relative sensitivities of differing ecosystems to variations in levels of atmospheric contamination. This thesis, utilising a palaeolimnological approach, examines long-term variations in levels of deposition of atmospheric pollutants from the industrial-scale combustion of fossil fuels and associated ecosystem response at three lake sites in Ireland (Kelly’s Lough, Lough Maumwee, and Upper Killarney Lough), each of which is situated in a distinct region of atmospheric pollutant deposition. All three sites are oligotrophic and situated in acid sensitive catchments, relatively remote from industrial or urban sources of pollution.

Short cores of sediment were obtained from the three study sites and, according to 210Pb, 137Cs, and SCP dating methods, account for time periods that are considerably longer than existing instrumental and documentary records of atmospheric pollution and their effects in Ireland, with the base of the temporally-longest sediment record dating to the late 19th century. Utilising sediment-based records of industrial combustion by-products (SCPs, trace elements and PAHs), both inter- and intra-site variations in levels of deposition of atmospheric pollutant from the industrial-scale combustion of fossil fuels were reconstructed for the three study sites, while sediment-based remains of diatoms and consensus-based SQG ratios were used to assess ecosystem response, particularly levels of acidification and toxicity. SCP records indicate that atmospheric contamination by industrial-scale fossil fuel combustion sources has varied both temporally and spatially, showing the highest levels in the east of Ireland. Differences between the three study sites in the temporal occurrence of SCP peak abundances can be explained predominately by inputs of SCPs originating from national sources and prevailing wind direction, and would appear to call into question the use of a single, country-wide SCP dating technique in Ireland. Temporal variations in levels of trace element and PAH contamination at the three study sites were quantified, with the most likely origin of some trace element deposition in the west of Ireland being north-American sources, as evidenced at Lough Maumwee and Upper Killarney Lough, while the highest contemporary levels of PAH contamination were measured at Lough Maumwee. Diatoms were used to determine the sensitivity of each lake ecosystem to acidification pressures while consensus-based SQG ratios were calculated to determine levels of ecosystem toxicity. Variations over time in reconstructed diatom assemblages and DI-pH highlight differing sensitivities to acidification pressures and, in particular, differing ecosystem response to changes over time in the severity of acidification pressures, which appear to result from differences in pollution load, biotic factors, hydromorphology, catchment characteristics, precipitation levels and location. Calculated SQG ratios indicate that levels of ecosystem toxicity as a result of depositions of atmospheric-borne contaminants are relatively low and are not expected to have a detrimental impact on aquatic biota.