Chemical analyses of cations and anions from five Irish midland raised bogs, from blanket bogs in Galway and Mayo and from groundwater-influenced sites in Mayo, Connemara and the Burren are presented. Principal components analysis clearly separated ombrotrophic from groundwater-influenced sites and showed a clear relation between geography and water chemistry among the ombrotrophic bogs. Nitrification was evident in many stored samples taken from fen sites and in some samples taken from raised-bog peat under birch at a pH of approximately 4.0, The occurrence of Schoenus nigritans in western lowland blanket bogs cannot be explained by raised pH or nutrient status due to sea spray, by freedom from aluminium toxicity near the west coast or by historical differences in grazing between Scotland and Ireland, The data show beyond doubt that S nigricans occurs extensively in truly ombrotrophic sites in western Ireland, The cation-anion balance shows a substantial anion deficit in the midland raised bogs (with no Schoenus), but little or none in the western lowland blanket bogs, Irish blanket-bog occurrences of Schoenus may form part of a wide north-west European pattern: obligate 'fen' plants under continental conditions moving successively into ombrotrophic sites with increasing oceanicity-involving in turn, inter alia, Etiophorum angustifolium, Nartheaum ossifragum and S, nigricans.
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