Recovery of in-situ methanotrophic activity following acetylene inhibition

Abstract Methane (CH 4 ) is the second most important greenhouse gas after carbon dioxide (CO 2 ). To understand CH 4 cycling, quantitative information about microbial CH 4 oxidation in soils is essential. Field methods such as the gas push-pull test (GPPT) to quantify CH 4 oxidation are often used in combination with specific inhibitors, such as acetylene (C 2 H 2 ). Acetylene irreversibly binds to the enzyme methane monooxygenase, but little is known about recovery of CH 4 oxidation activity after C 2 H 2 inhibition in situ, which is important when performing several experiments at the same location. To assess recovery of CH 4 oxidation activity following C 2 H 2 inhibition, we performed a series of GPPTs over 8 weeks at two different locations in the vadose zone above a petroleum hydrocarbon-contaminated aquifer in Studen, Switzerland. After 4 weeks a maximum recovery of 30% and 50% of the respective initial activity was reached, with a subsequent slight drop in activity at both locations. Likely, CH 4 oxidation activity and CH 4 concentrations were too low to allow for rapid recovery following C 2 H 2 inhibition at the studied locations. Therefore, alternative competitive inhibitors have to be evaluated for application in conjunction with GPPTs, especially for sites with low activity