Daltomn, Catherine Phillipa; (2000) A palaeolimnological investigation of acidity in humic lake waters in Connemara, Western Ireland. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

This thesis describes a palaeolimnological investigation of lakewater acidity in peat catchments in Connemara, Ireland. The overall aim is to provide an explanation of why these surface waters are acidic and highly humic, with high measured dissolved organic carbon (DOC). This 'clean' area constitutes the largest concentration of acid sensitive waters in the country, in a region of low acid deposition. The largest forestry plantation in h-eland was established here in 1953. Palaeolimnology techniques using diatoms enable the reconstruction of historical lake water chemistry and are used here to evaluate the impacts of peat development and recent catchment afforestation on surface water acidity. Twenty-two lakes were sampled seasonally and analysed for a range of chemical determinands to establish contemporary chemistry. The results demonstrate that afforested sites tend to be more acidic with elevated levels of organic acids, distinguishing the data-set from many other training-sets. DOC was identified as a significant influence on surface sediment diatom assemblage variation. A diatom model or transfer function was derived for DOC with moderate predictive powers (r2 = 0.44, RMSEP = 1.5 mg 1-1 DOC). The model was then applied to fossil diatom data from a lake sediment core and the acidity history of the site reconstructed. A dynamically changing catchment responding to paludification of the soils and the development of blanket peat, promoted initially by climatic factors but exacerbated by anthropogenic influences was inferred from the palaeo- reconstruction. Past lake diatom inferred DOC indicates a history of dystrophication, however correlations between peat expansion and recent catchment afforestation were not established. Overall, the results highlight important implications for the use of diatom-DOC models and palaeolimnological reconstructions including complex relationship between diatoms and DOC, the importance of species habitat, and the necessity for more critical use of DOC transfer functions in future research.

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