Soil–atmosphere CO 2, CH 4 and N 2O fluxes in boreal forestry-drained peatlands

Abstract

Greenhouse gas emissions from managed peatlands are annually reported to the UNFCCC. For the estimation of greenhouse gas (GHG) balances on a country-wide basis, it is necessary to know how soil–atmosphere fluxes are associated with variables that are available for spatial upscaling. We measured momentary soil–atmosphere CO 2 (heterotrophic and total soil respiration), CH 4 and N 2O fluxes at 68 forestry-drained peatland sites in Finland over two growing seasons. We estimated annual CO 2 effluxes for the sites using site-specific temperature regressions and simulations in half-hourly time steps. Annual CH 4 and N 2O fluxes were interpolated from the measurements. We then tested how well climate and site variables derived from forest inventory results and weather statistics could be used to explain between-site variation in the annual fluxes. The estimated annual CO 2 effluxes ranged from 1165 to 4437 g m −2 year −1 (total soil respiration) and from 534 to 2455 g m −2 year −1 (heterotrophic soil respiration). Means of 95% confidence intervals were ±12% of total and ±22% of heterotrophic soil respiration. Estimated annual CO 2 efflux was strongly correlated with soil respiration at the reference temperature (10 °C) and with summer mean air temperature. Temperature sensitivity had little effect on the estimated annual fluxes. Models with tree stand stem volume, site type and summer mean air temperature as independent variables explained 56% of total and 57% of heterotrophic annual CO 2 effluxes. Adding summer mean water table depth to the models raised the explanatory power to 66% and 64% respectively. Most of the sites were small CH 4 sinks and N 2O sources. The interpolated annual CH 4 flux (range: −0.97 to 12.50 g m −2 year −1) was best explained by summer mean water table depth ( r 2 = 64%) and rather weakly by tree stand stem volume ( r 2 = 22%) and mire vegetation cover ( r 2 = 15%). N 2O flux (range: −0.03 to 0.92 g m −2 year −1) was best explained by peat CN ratio ( r 2 = 35%). Site type explained 13% of annual N 2O flux. We suggest that water table depth should be measured in national land-use inventories for improving the estimation of country-level GHG fluxes for peatlands.