METHANE PRODUCTION AND EMISSION FROM PEAT - THE INFLUENCE OF ANIONS (SULFATE, NITRATE) FROM ACID-RAIN

The influence of sulphate concentrations on the production and emissio n of methane in two contrasting peal sites was determined. Seasonal ch anges in sulphate concentrations appeared to influence the amount of o rganic carbon oxidised to carbon dioxide by sulphate reduction at both peat sites. For the majority of the year at both sites the amount of carbon mineralised through sulphate reduction exceeded that being tran sformed to methane by methanogenic bacteria, except when sulphate redu ction became sulphate limited. In order to sustain the high sulphate r eduction rates measured in the peat sulphide formed from dissimilatory sulphate reduction must be reoxidised rapidly to sulphate within;the peat. Laboratory experiments showed that addition of 500 mu M sulphate and 100 mu M nitrate to peat samples significantly inhibited methanog enesis. Sulphate appeared to be the more important inhibitor of methan ogenesis since inhibition of methane formation occurred with additions of sulphate reflecting in situ concentrations. Supplements of either acetate and/or hydrogen in combination with molybdate to pear samples revealed that methanogenesis was hydrogen limited and that the majorit y of active methanogens were hydrogen-utilising methanogens. Methanoge nesis in peat samples appeared to be dependant on sulphate reducing ba cteria for provision of substrates. Great Dun Fell, receiving the larg est sulphate loading, had the lower rates of microbial activity (metha ne formation and sulphate reduction rates) than Ellergower, which rece ived less than half the annual sulphate deposition of Great Dun Fell. This implied that some other factor-possibly organic matter lability, was limiting microbial rates of methane formation and sulphate reducti on at Great Dun Fell. (C) 1998 Elsevier Science Ltd. All rights reserv ed.