Acid rain links to CH₄ emissions from wetlands

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

DOI: https://doi.org/10.21954/ou.ro.0000e2c3

Abstract

A variety of approaches, spanning a range of spatial and temporal scales, were applied to the investigation of the effects of low dose SO₄^2- 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 SO₄^2- 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 SO₄^2- manipulation experiment, the suppressive effect of SO₄^2- was found to be independent of the simulated SO₄^2- 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 SO₄^2- 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.

SO₄^2- concentrations were smaller in peat pore water from SO₄^2- treatments than from controls. This is possibly the result of a stimulated SO₄^2- reducing community scavenging available SO₄^2-, thereby decreasing concentrations to below ambient levels. In northern peatlands (>50°) the effect of SO₄^2- deposition at 1990 rates may have been sufficient to reduce emissions from these systems by around 15% annually. Globally, the effect of acid rain SO₄^2- 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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