Werner et al. 2007. Soil-atmosphere exchange of N2O, CH4, and CO2 and controlling environmental factors for tropical rain forest sites in western Kenya

Werner, C., R. Kiese, and K. Butterbach-Bahl (2007), Soil-atmosphere exchange of N₂O, CH₄, and CO₂ and controlling environmental factors for tropical rain forest sites in western Kenya, J. Geophys. Res., 112, D03308, doi:10.1029/2006JD007388.


Abstract

N₂O, CH₄ and CO₂ soil-atmosphere exchange and controlling environmental factors were studied for a 3-month period (dry-wet season transition) at the Kakamega Rain forest, Kenya, Africa, using an automated measurement system. The mean N₂O emission was 42.9 ± 0.7 μg N m⁻² h⁻¹ (range: 1.1–324.8 μg N m⁻² h⁻¹). Considering the duration of dry and wet season the annual N₂O emission was estimated at 2.6 ± 1.2 kg N ha⁻¹ yr⁻¹. Large pulse emissions of N₂O were observed after the first rainfall events of the wet season, and the magnitude of N₂O emissions steadily declined thereafter. A comparable trend in soil CO₂ emissions (mean: 71.8 ± 0.3 mg C m⁻² h⁻¹) indicates that the rapid mineralization of litter accumulated during the dry period produced the high N₂O emissions at the start of the wet season. Manual N₂O emission measurements at four additional rain forest sites were comparable to those measured at the main site, whereas N₂O emissions measured at a regrowth site were significantly lower. Spatial differences in N₂O emissions could be explained by differences in soil texture and topsoil C:N-ratio (CO₂: subsoil C and N concentrations), whereas the temporal variability of N₂O and CO₂ emissions was primarily driven by soil moisture. Soils predominantly acted as sinks for CH₄ (−56.4 ± 0.8 μg C m⁻² h⁻¹). For some chamber positions, episodes of net CH₄ release were observed, which could be due to high WFPS and/or termite activity. CH₄ fluxes were weakly correlated with soil moisture levels but showed no relation to temperature, texture, pH, carbon or nitrogen contents.