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Summary0 Analyses are presented of major ion concentrations in surface water samples\ and exchangeable cations in peats\ collected in NovemberÐDecember 0881 from 05 ombro! trophic bogs in England and Wales and one in Scotland\ spanning most of the range from the lowest "Dartmoor\ west Wales\ west Highlands# to the highest "south Pennines\ north Yorkshire# of the mean 0875Ð77 rainwater concentrations of hydro! gen ions and non!marine sulphate "NMS#[ 1 There was a strong positive correlation "r ¦9[78# between surface water pH and mean rainwater pH\ and a less close correlation "r ¦9[60# between surface water pH and total hydrogen ion deposition[ 2 The correlation between surface water pH and mean concentration of rainwater NMS "which may be taken as a surrogate measure of acid deposition# was r Ð9[74\ and that between surface water pH and total deposition of NMS was r Ð9[54[ 3 The intercept of the regression of surface water pH on NMS is at pH 3[39 "84) con_dence limits 3[11Ð3[47#\ suggesting this as the winter pH of an ombrotrophic bog surface in the absence of acid atmospheric pollution[ 4 Total sulphur content of intact surface peats from 00 sites correlated well "r ¦9[89# with mean rainwater total sulphate concentration[ 5 The H ¦ ion concentration in wet deposition\ plus the net H ¦ input resulting from metabolism of deposited NO 2 Ð and NH 3 ¦ \ is insu.cient to account for the di}erence between the inferred pH of an unpolluted bog surface and pH values "up to 9[7 pH units lower# measured in the _eld in polluted sites[ Analogy with deposition of NMS suggests that this discrepancy is accounted for quantitatively by seederÐfeeder enhancement\ cloudwater deposition\ and dry deposition of acidity[ 6 Ombrotrophic bog surface waters are bu}ered by the cation!exchange properties of the peat[ They are likely to be less sensitive to moderate acid deposition than weakly bicarbonate!bu}ered near!neutral peats\ soils and fresh waters[ Keywords] acid rain\ air pollution\ dry deposition\ non!marine sulphate\ sulphur content of peat\ water chemistry\ wet deposition Journal of Ecology "0887# 75\ 218Ð239

Measurements of gas fluxes at the soil surface are useful for determining exchanges of gases between the soil and the atmosphere, but they may not be representative of total gas production below the surface. Here we present an improved technique that enables sampling of soil atmosphere gas from any depth in the soil profile, regardless of soil moisture status. The method utilises the equilibration of gas from the soil pore space with that in a small headspace probe by means of diffusion through a silicone rubber membrane. The method demonstrated is capable of 98Ϯ1% recovery of soil-entrapped CH 4 and N 2 O and has potential for use in a wide range of circumstances. 369