Sensitivity of soil methane fluxes to reduced precipitation in boreal forest soils

In order to better predict soil sinks of methane, we need to examine soil methane flux patterns and responses to altered soil moisture regimes. Estimates of the global atmospheric CH4 budget must also account for fluxes in the vast boreal region. We measured methane fluxes into the soil surface, methane concentrations, water content, and temperature in the soil profile in two interior Alaskan forests, over two growing seasons. At each site, a 0.10 ha rain-shelter limited summer precipitation from entering the soil. Limiting summer precipitation at the upland site generally increased that site's soil uptake of methane. Average rates of soil methane uptake among upland plots ranged from 0.10 to 0.95 mg m(-2) day(-1). At the floodplain site, limiting precipitation decreased the soil methane uptake of that site, and the rates here ranged from -0.02 to 0.57 mg m(-2) day(-1). Using soil profile methane concentrations, we calculated CH4 fluxes using Fick's Law. Our inability to precisely measure the concentration gradient across the soil surface resulted in calculated flux estimates that more likely represent fluxes within the soil profile. Methane sources and sinks in the soil profile also confounded the comparison of measured and calculated fluxes. (C) 2000 Elsevier Science Ltd. All rights reserved.