Area (2008) 40.1, 117–127 Area Vol. 40 No. 1, pp. 117–127, 2008 ISSN 0004-0894 © The Authors. Journal compilation © Royal Geographical Society (with The Institute of British Geographers) 2007 Blackwell Publishing Ltd Dissolved and total organic and inorganic carbon in some British rivers Andy Baker, Sue Cumberland and Naomi Hudson School of Geography, Earth and Environmental Sciences, The University of Birmingham, Birmingham B15 2TT Email: a.baker.2@bham.ac.uk Revised manuscript received 1 August 2007 Rivers transport both organic and inorganic carbon from their sources to the sea. Results of ~800 organic and inorganic analyses from various British rivers of contrasting size and land use are presented here: (1) the headwater River Tern, a rural river of 852 km 2 catchment; (2) the Ouseburn, a small urban 55 km 2 catchment; (3) the River Tyne, a larger river system of ~3000 km 2 catchment; (4) a spatial survey from 205 sample sites on ~60 rivers from SW England. We found that, with the exception of peat-rich headwaters, DIC concentration is always greater than DOC. DIC is primarily in the form HCO 3 - , with DIC concentrations highest in highly urbanised catchments, typically greater than those observed in catchments with carbonate bedrock, demonstrating a significant and previously unrecognised anthropogenic inorganic carbon input to urban rivers. Key words: organic carbon, inorganic carbon, rivers, land use, British Isles Introduction The transfer of carbon, total and dissolved, organic and inorganic, from the land to the oceans via river systems is a key link in the global carbon cycle (Likens et al. 1981; Meybeck 1987; Ludwig et al. 1996; Amiotte-Suchet et al. 2003; Brunet et al. 2005; Richey 2005). It has been estimated that globally rivers transport on average 0.8 to 1.2 × 10 15 g of carbon annually (Ludwig et al. 1996). Dissolved and total organic carbon (DOC, TOC) is produced through the mobilisation of natural and anthropogenic organic matter, derived from the solution of allochthonous, soil-derived organic matter; from autochthonous, within-stream generation of organic material; or from anthropogenic sources such as effluents and industrial discharges. Total and dissolved inorganic carbon (TIC, DIC) is produced by weathering of carbonate and silicate rocks, although may also be present as CO 2 generated by the decomposition of dissolved organic matter (Das et al. 2005). These processes generate the alkalinity of the river water, and also influence the pH of water, which governs the subsequent partitioning of DIC between dissolved CO 2 , bicarbonate and carbonate ions. The fraction of DIC present as dissolved CO 2 is almost always at concentrations much greater than the atmosphere (Kempe 1982; Cole and Caraco 2001), which demonstrates that rivers are a source of CO 2 to the atmosphere. The only way that dissolved CO 2 can exist at supersaturated conditions in rivers is if allochthonous sources dominant, and/or the waters are net heterotrophic, fueled by carbon from land (Cole and Caraco 2001). Carbon fluxes in river systems are a function of hydrology and river flow, land use and geology, and climate, and fluxes of both organic and inorganic forms have been the increasing focus of recent research. Many studies have focused on either the spatial or seasonal patterns in carbon flux in large, global rivers (e.g. the Congo: Negrel et al. 1993; Probst et al. 1994; the Amazon: Gaillardet et al. 1997; Mortatti and Probst 2003; the Rhone: Aucour et al. 1999). Until recently, fewer studies have investigated long-term trends in riverine carbon flux. Dissolved organic carbon has been demonstrated to be increasing over recent decades in many mid-latitude river systems, with many studies focusing on UK rivers