Long-term effects of boreal reservoirs on the landscape-atmosphere N_2O exchange

摘要

Freshwater reservoirs have been estimated to be globally significant sources of the two most important atmospheric greenhouse gases, carbon dioxide (CO_2) and methane (CH_4), thus their construction may contribute to global warming (St. Louis et al. 2000). However, fluxes of the third most important greenhouse gas, nitrous oxide (N_2O; IPCC 2001), are poorly known in artificial lake ecosystems (Huttunen et al. 2002b). Large CO_2 and CH_4 emissions in reservoirs result from decomposition of flooded organic matter and autochthonous and allochthonous organic matter (Kelly et al. 1997, St. Louis et al. 2000, Huttunen et al. 2003a). Thus, some N_2O might be produced during this organic matter turnover while simultaneously increasing nitrogen availability. In aquatic ecosystems, N_2O is produced in microbial nitrification and/or denitrification processes in water columns and sediments (Wetzel 2001). In nitrification, N_2O is a by-product when ammonium (NH_4~+) is oxidized to nitrite (NO_2). In denitrification, N_2O is an intermediate when nitrate is reduced to dinitrogen gas: NO_3~- → NO_2~- → NO → N_2O → N_2.