Evidence from water chemistry as a criterion of ombrotrophy in the mire complexes of Abernethy Forest,Scotland

Question: Can cation analyses of water samples within a peatland site be used to infer solute sources to the samples, and so provide an objective criterion of ombrotrophy? Location: Mire complexes within native Pinus sylvestris forest, in Abernethy Forest, north of the Cairngorm Mountains, Scotland, UK. Methods: Chemical analyses of major cations in 200 water samples, and χ² analysis of contingency tables relating species occurrence in the corresponding quadrat samples to the ombrotrophic‐telluric division. Results and conclusions: The chemical data (especially the ratios Ca²⁺/Mg²⁺ and Na⁺/Mg²⁺) indicated a separation of about 140 essentially ombrotrophic samples from about 60 showing clear telluric influence; these conclusions are consistent with published rainwater analyses. For hydrological and meteorological reasons, a sharp separation cannot be expected, so the limit adopted here (Ca/Mg=1.0) is to some extent arbitrary, but the methods described provide a more objective criterion of ombrotrophy than any other. Contingency tables showed highly significant associations between species occurrence and the ombrotrophic‐telluric division. The strongest associations included: (ombrotrophic) Eriophorum vaginatum, Odontoschisma sphagni and Sphagnum cuspidatum; (telluric) Carex panicea, Potentilla erecta, Carex echinata, Narthecium ossifragum, Sphagnum auriculatum s.l., Agrostis canina, Molinia caerulea, Eriophorum angustifolium, and Sphagnum recurvum s.l. The Abernethy mires are arguably more comparable with mire complexes on base‐poor rocks in southern Scandinavia than with most ombrotrophic sites further south and west in Britain. As in Sweden, Narthecium ossifragum and Eriophorum angustifolium, generally ubiquitous on British and Irish ombrotrophic bogs, are “fen” plants at Abernethy.