Carbon dioxide and methane production in small reservoirs flooding upland boreal forest

The FLooded Uplands Dynamics EXperiment (FLUDEX) was designed to assess the impact of reservoir creation on carbon cycling in boreal forests by (a) determining whether production of the greenhouse gases (GHG) carbon dioxide$({\rm CO}_{2})$and methane$({\rm CH}_{4})$in reservoirs is related to the amount of organic carbon (OC) stored in the flooded landscape, (b) examining temporal trends in GHG production during initial stages of flooding, and (c) considering the net difference between GHG fluxes before and after flooding to estimate the true effect of reservoir creation on atmospheric GHG levels. Three forested sites that varied in the amount of OC stored in soils and vegetation (30,870-45,860 kg C${\rm ha}^{-1}$) were experimentally flooded from June to September in 1999-2001. Throughout the study, net${\rm CO}_{2}$and${\rm CH}_{4}$production in all three reservoirs was not related to overall site OC storage. During the 1st flooding season, net${\rm CO}_{2}$production in the three reservoirs was 703-797 kg C${\rm ha}^{-1}$, but it decreased during the 2nd and 3rd flooding seasons to between 408 and 479 kg C${\rm ha}^{-1}$. However,${\rm CH}_{4}$production increased in all reservoirs with each flooding season, from about 3.2-4.6 kg C${\rm ha}^{-1}$in 1999 to 12.8-24.9 kg C${\rm ha}^{-1}$in 2000 and 29.7-35.2 kg C${\rm ha}^{-1}$in 2001. Over the long term, effects of boreal reservoir creation on atmospheric GHG levels may be largely due to net changes in${\rm CH}_{4}$cycling between the undisturbed and flooded ecosystems.