Peat erosion and atmospheric deposition impacts on an oligotrophic lake in eastern Ireland |
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| Authors: | M Leira E E Cole and F J G Mitchell |
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| Institution: | (1) Department of Botany, School of Natural Sciences, Trinity College Dublin, Dublin 2, Ireland;(2) Present address: Faculty of Science, Campus da Zapateira, University of A Coru?a, 15071 A Coruna, Spain;(3) Present address: 4 Railway Place, High Street, Cork, Ireland |
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| Abstract: | The Holocene diatom and pollen records from Kelly’s Lough have been analysed to determine the timing and extent of the acidification
in this upland lake. The pollen data during the early Holocene reflect the typical vegetation changes that occur in sediments
throughout Ireland during this period. The diatom record begins by being dominated by circumneutral and acidophilous benthic
forms. Later tychoplanktonic Aulacoseira species begin to expand and dominate indicating increased water transparency following the stabilization of catchment soils.
Peatland development in the catchment is evident from approximately 6,450 cal year BP. The main change in the diatom assemblages
at this time is the decline of Aulacoseira species and expansion of periphytic species. At around 1,450 cal year BP, loss-on-ignition (LOI) values, Calluna pollen and microscopic charcoal all increase suggesting the initiation of a major phase of peat erosion and an increased
inwash of organic matter to the lake. Lake acidity changed significantly although the initial acidification is very subtle
as indicated by the diatom-inferred pH record. Changes in the diatom assemblages might be largely the result of increasing
erosion and inwash of organic matter from the catchment to the lake leading to reduced water transparency and more acidic
conditions. The diatom flora remains relatively stable until the mid-twentieth century when more acidibiontic species increase.
These diatom changes result in the reconstructed pH curve showing a moderate recent acidification from pH 5.7 to 5.1. About
half of the total change in pH took place by around the late 1960s. The lowest diatom-inferred pH value occurs in the late
1970s, and parallels the peak in SO2 emissions in Ireland. Acidic conditions seem to have prevailed in Kelly’s Lough throughout its entire history and alkalinity
has been low or absent for much of the time. However, soil acidification and inwash of organic acids from peatlands are not
a sufficiently effective mechanism to explain the low pH levels found today in Kelly’s Lough. The effect of acid deposition
on the waters of Kelly’s Lough is clear and it has probably caused these already naturally acid waters to acidify further. |
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| Keywords: | Acid-sensitive lakes Acidification Peatlands Diatoms Pollen Ireland |
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