Introduction

Global riverine transport of organic carbon (OC) is estimated to be 0.4-0.9 Pg annually (Meybeck 1982; Hope et al. 1994; Aitkenhead-Peterson et al. 2005). Therefore, the riverine export of OC from drainage basins to the ocean represents a major component of the global carbon cycle (Spitzy and Leenheer 1991; Hedges et al. 1997). Recent evidence from Northern Europe about increased dissolved organic carbon (DOC) concentrations in surface waters draining upland areas and wetlands (Freeman et al. 2001; Frey and Smith 2005), highlights the importance of understanding the transfer of C between soil and freshwater systems. Although the magnitude of the fluxes involved in land-atmosphere C exchange is significantly larger than that associated with surface waters, rates of DOC transport in streams draining subarctic catchments rich in organic soils are comparable to rates of C sequestration in the soil-plant system of high latitudes (Hope et al. 1994; Billet et al. 2006).

The Arctic drainage basin (~24 x 106 km2) processes about 11% of both global runoff and DOC (Lobbes 2000; Lammers et al. 2001). Heavily influenced by permafrost, arctic river basins demonstrate the highest susceptibility to climate change. With 23-48% of the world's soil organic carbon (SOC) stored in the high-latitude region, the arctic/subarctic river basins have an enormous potential to mobilize and transport terrestrial OC to the Arctic Ocean (Guo and Macdonald 2006).

The response of permafrost soils to warming is crucial for understanding potential change in terrestrial C export to rivers. High hydraulic conductivity, low mineral content, and low DOC sorption capacity of the shallow soil active layer overlying impermeable permafrost together lead to quick DOC transport to streams and rivers, with limited microbial transformation, especially during snowmelt. As the depth, temperature and seasonal duration of the active layer increase with climate warming, new inputs of DOC may derive from thawed permafrost and/or vegetation changes (Sturm et al. 2001; Neff et al. 2006). However, significant differences in geomorphology, hydrology, permafrost distribution, soil types and

Anatoly S. Prokushkin

V.N. Sukachev Institute of Forest SB RAS, Akademgorodok, Russia email: [email protected]

R. Margesin (ed.) Permafrost Soils, Soil Biology 16,

DOI: 10.1007/978-3-540-69371-0, © Springer-Verlag Berlin Heidelberg 2009

vegetation among basins of Siberian rivers exert uncertainty in overall response of riverine DOC export to global warming. Moreover, climate change itself has both negative and positive feedbacks, and triggers complex interactions in atmosphere-vegetation-soil-river system (Serreze et al. 2000). This chapter summarizes available data on current DOC export from permafrost terrain, and attempts to assess its future projections.

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