The effect of acidifying pollutants deposition on organic upland soils in the UK
This Thesis presents the results of various studies on peat soils and organic surface horizons of peaty podzols derived from acidification-sensitive parent materials. It aims primarily at finding out which peat and organic surface horizon chemical properties correlate most significantly with acidifying deposition parameters, the effect that acidifying pollutant deposition has on growth of vegetation (Calluna vulgaris) and litter decomposition, and the fate of ammonia in peat soils. Two regional surveys were carried out throughout Scotland. Significant correlations were found particularly between the chemical properties of peat and the effective concentrations of the acidifying deposition components. The more significant correlations found with peat pH(water), rather than with pH(CaCl2), point to the fact that the mobile anion effect is important. A method was established for estimating the pH of soil solution at field conditions, i.e. at a dilution factor of unity, and a close similarity was subsequently found between this estimated pH and the effective pH of deposition. It is suggested that this provides an excellent basis for pH prediction for ombrotrophic peats. Significant seasonal variations in peat chemistry were found, with peat pH(water), for example, varying by up to 0.4 pH units throughout the year. A 7-month pot experiment demonstrated significantly lower growth rates of Calluna vulgaris, and slower litter decomposition rates, at higher acidifying deposition inputs. Studies on the retention of NH4+ in peats clearly show that there is only a limited capacity for biological immobilisation of NH4+ at high input concentrations. More information is needed on the fate of NH4+ inputs in the soil, and on the extent to which retention is via cation exchange and biological uptake, and this needs to be taken into consideration when setting critical loads for N.