Acid rain links to CH4 emissions from wetlands

Gauci, Vincent (2001). Acid rain links to CH4 emissions from wetlands. PhD thesis The Open University.

Abstract

A variety of approaches, spanning a range of spatial and temporal scales, were applied to the investigation of the effects of low dose SO42- deposition, at rates comparable to those experienced in acid rain impacted areas, on methane (CH4) emissions from natural wetlands.

Over two years of experimental manipulation of SO42- deposition to a peatland in northeast Scotland, CH4 emissions were suppressed by around 40%. There was no significant difference in suppression of CH4 flux within the sol- deposition range of 25-100 kg-S ha-1yr-1. In a similar short-term controlled environment SO42- manipulation experiment, the suppressive effect of SO42- was found to be independent of the simulated SO42- deposition rate within a range of 15-100 kg-S ha-1yr-1. The possibility that suppression of CH4 fluxes may have been the result of a 'salt effect' was ruled out. Both temperature and water table controlled the extent of CH4 flux suppression in acid rain impacted wetlands.

Sulfate reduction potential in SO42- treatments were found to be 10 times larger than in control plots, suggesting that long-term suppression of CH4 fluxes is the result of the formation of an enlarged population of competitively superior sulfate reducing bacteria.

SO42- concentrations were smaller in peat pore water from SO42- treatments than from controls. This is possibly the result of a stimulated SO42- reducing community scavenging available SO42-, thereby decreasing concentrations to below ambient levels. In northern peatlands (>50°) the effect of SO42- deposition at 1990 rates may have been sufficient to reduce emissions from these systems by around 15% annually. Globally, the effect of acid rain SO42- deposition may be sufficient to reduce CH4 emissions by as much as 22-28 Tg by 2030, which places this interaction within the same size category as many other components of the global CH4 budget that have received far greater attention.

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