Land degradation in northeastern Iceland: present and past carbon fluxes

Abstract The objectives of this paper are to define the present and past terrestrial fluxes of carbon in three river catchments in northeast Iceland and assess the effect of land degradation and future climate change on the fluxes. The carbon fluxes are: (1) present gross primary production (GPP); (2) net primary production (NPP); (3) net ecosystem exchange (NEE) of terrestrial vegetation in the catchments; (4) river transport out of the catchments of dissolved inorganic carbon (DIC) in 1998; (5) dissolved organic carbon (DOC); (6) river particulate organic carbon (POC); and (7) the average present ( pr NBE) and (8) past 10 000 years net biome exchange (NBE 10 000 ). The GPP is the largest of the carbon fluxes and increases from west to east as vegetation cover and bedrock age increase. The NPP and NEE, however, were highest in the Jökulsá á Dal catchment where wetlands are extensive. The DIC flux is the largest of the river export fluxes, being highest when the GPP is lowest, dictated by the rapid chemical weathering rate of the young basaltic rocks, rather than vegetation. Thus, a greater portion of the autotrophic and heterotrophic respiration escapes to the atmosphere where the GPP is largest. The NBE 10 000 rate increases from west to east. The pr NBE is negative and larger than the small positive NBE 10 000 flux in the Jökulsá á Fjöllum and it is also negative in the Fellsá catchments, indicating land degradation. Conversely, the pr NBE is positive and higher than NBE 10 000 in the Jökulsá á Dal catchment, where soil organic carbon stock is increasing. In the future, NBE of two of the three catchments will probably increase because of climate warming and consequently increased vegetation cover and ecosystem stability. Copyright © 2006 John Wiley & Sons, Ltd.