Greenhouse gas dynamics in boreal, littoral sediments under raised CO2 and nitrogen supply

Abstract

SUMMARY 1. The effects of increasing CO2 and nitrogen loading and of a change in water table and temperature on littoral CH4, N2O and CO2 fluxes were studied in a glasshouse experiment with intact sediment cores including vegetation (mainly sedges), taken from a boreal eutrophic lake in Finland. Sediments with the water table held at a level of 0 or at −15 cm were incubated in an atmosphere of 360 or 720 p.p.m. CO2 for 18 weeks. The experiment included fertilisation with NO3– and NH4+ (to a total 3 g N m−2).2. Changes in the water table and temperature strongly regulated sediment CH4 and cCO2 fluxes (community CO2 release), but did not affect N2O emissions. Increase in the water table increased CH4 emissions but reduced cCO2 release, while increase in temperature increased emissions of both CO2 and CH4.3. The raised CO2 increased carbon turnover in the sediments, such that cCO2 release was increased by 16–26%. However, CH4 fluxes were not significantly affected by raised CO2, although CH4 production potential (at 22 °C) of the sediments incubated at high CO2 was increased. In the boreal region, littoral CH4 production is more likely to be limited by temperature than by the availability of carbon. Raised CO2 did not affect N2O production by denitrification, indicating that this process was not carbon limited.4. A low availability of NO3– did severely limit N2O production. The NO3– addition caused up to a 100‐fold increase in the fluxes of N2O. The NH4+ addition did not increase N2O fluxes, indicating low nitrification capacity in the sediments.