The effects of acid nitrogen and acid sulphur deposition on CH4 oxidation in a forest soil: A laboratory study

Abstract

Sieved soil and soil core experiments were performed to determine the potential sensitivity of forest soil CH4 oxidation to oxidised N, reduced N and oxidised S atmospheric deposition. Ammonium sulphate was used to simulate reduced N deposition, HNO3 oxidised N deposition and H2SO4 oxidised S deposition. The effects of NH4+, NO3-, SO42- and H+ on soil CH4 flux were shown to be governed by the associated counter-anion or cation of the investigated ions. Ammonium sulphate, at concentrations greater than those that would be experienced in polluted throughfall, showed a low potential to cause inhibition of CH4 oxidation. In contrast, HNO3 strongly inhibited net CH4 oxidation in sieved soils and also in soil cores. In addition, soil CO2 production was inhibited and the organic and mineral soil horizons acidified in HNO3 treated soil cores. This suggested that the HNO3 effect on CH4 flux might be indirectly mediated through aluminium toxicity. Sulphuric acid only inhibited CH4 oxidation when added at pH 1. At concentrations more representative of heavily polluted throughfall, H2SO4 had no effect on soil CH4 flux or CO2 production from soil cores, even after 210 days of repeated addition. In contrast to HNO3 additions, acidification of the soil was not marked and was only significant for the mineral soil. The findings suggest that the response of forest soil CH4 oxidation to atmospheric acid deposition is strongly dependent on the form of acid deposition.