land degradation & development Land Degrad. Develop. 17: 401–417 (2006) Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/ldr.746 LAND DEGRADATION IN NORTHEASTERN ICELAND: PRESENT AND PAST CARBON FLUXES M. I. KARDJILOV 1 , G. GISLADOTTIR 1 * AND S. R. GISLASON 2 1 Department of Geology and Geography, Faculty of Science, University of Iceland, Askja, Sturlugata 7, 101 Reykjavik, Iceland 2 Institute of Earth Sciences, University of Iceland, Askja, Sturlugata 7, 101 Reykjavik, Iceland Received 26 April 2005; Revised 19 October 2005; Accepted 16 December 2005 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 Jo ¨kulsa ´a ´ 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 Jo ¨kulsa ´a ´ Fjo ¨llum and it is also negative in the Fellsa ´ catchments, indicating land degradation. Conversely, the pr NBE is positive and higher than NBE 10 000 in the Jo ¨kulsa ´a ´ 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. key words: river catchment fluxes; GIS; NPP (net primary production); NEE (net ecosystem exchange); NBE (net biome exchange); DOC (dissolved organic carbon); POC (particulate organic carbon); Iceland INTRODUCTION The objectives of this paper are to define the present and past terrestrial fluxes of carbon in three basaltic river catchments in northeast Iceland and to assess the effect of land degradation and climate change on the fluxes. Basaltic rocks are highly susceptible to weathering (Gislason, 2005) and consequently have a much greater effect on atmospheric CO 2 consumption than might be expected from their area extent on Earth. Estimates for present-day CO 2 consumption due to silicate weathering on land suggest that between 30 and 35 per cent may be attributable to basaltic rocks although basalts constitute less than 5 percent of the continental area (Dessert et al., 2003). Soils at higher latitudes store globally significant organic carbon because of their relatively low temperatures and low carbon turnover. Thus they are sensitive to climate changes. Turunen et al. (1999) reported that 5 per cent of the previously ‘unaccounted’ C in the global C budget was stored in mineral subsoil under boreal mires. Icelandic volcanic soils are higher latitude soils with high potential for carbon storage and they are sensitive to land Copyright # 2006 John Wiley & Sons, Ltd.  Correspondence to: G. Gisladottir, Department of Geology and Geography, Faculty of Science, University of Iceland, Askja, Sturlugata 7, 101 Reykjavik, Iceland. E-mail: ggisla@hi.is Contract/grant sponsors: Icelandic Governmental Fund for Graduate Education; Institute of Earth Sciences, University of Iceland.