title: Evasion of CO2 from streams - the dominant component of the carbon export through the aquatic conduit in a boreal landscape.
abstract: Evasion of gaseous carbon (C) from streams is often poorly quantified in landscape C budgets. Even though the potential importance of the capillary network of streams as C conduits across the land-water-atmosphere interfaces is sometimes mentioned, low-order streams are often left out of budget estimates due to being poorly characterized in terms of gas exchange and even areal surface coverage. We show that evasion of C is greater than all the total dissolved C (both organic and inorganic) exported downstream in the waters of a boreal landscape. In this study evasion of carbon dioxide (CO2 ) from running waters within a 67 km(2) boreal catchment was studied. During a 4 year period (2006-2009) 13 streams were sampled on 104 different occasions for dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC). From a locally determined model of gas exchange properties, we estimated the daily CO2 evasion with a high-resolution (5 × 5 m) grid-based stream evasion model comprising the entire ~100 km stream network. Despite the low areal coverage of stream surface, the evasion of CO2 from the stream network constituted 53% (5.0 (±1.8) g C m(-2)  yr(-1) ) of the entire stream C flux (9.6 (±2.4) g C m(-2)  yr(-1) ) (lateral as DIC, DOC, and vertical as CO2 ). In addition, 72% of the total CO2 loss took place already in the first- and second-order streams. This study demonstrates the importance of including CO2 evasion from low-order boreal streams into landscape C budgets as it more than doubled the magnitude of the aquatic conduit for C from this landscape. Neglecting this term will consequently result in an overestimation of the terrestrial C sink strength in the boreal landscape.
authors.affiliation: Department of Earth Sciences, Air Water and Landscape Sciences, Uppsala University, Villavägen 16, SE-752 36, Uppsala, Sweden. marcus.wallin@geo.uu.se
authors.forename: Marcus B
authors.initials: MB
authors.lastname: Wallin
authors.forename: Thomas
authors.initials: T
authors.lastname: Grabs
authors.forename: Ishi
authors.initials: I
authors.lastname: Buffam
authors.forename: Hjalmar
authors.initials: H
authors.lastname: Laudon
authors.forename: Ånneli
authors.initials: Å
authors.lastname: Agren
authors.forename: Mats G
authors.initials: MG
authors.lastname: Öquist
authors.forename: Kevin
authors.initials: K
authors.lastname: Bishop
mesh_terms: D002244:Carbon / Q000032:analysis*; D002245:Carbon Dioxide / Q000032:analysis*; D045483:Rivers / Q000737:chemistry*; D012987:Soil / Q000032:analysis
chemical_list: D012987:Soil; D002245:Carbon Dioxide; D002244:Carbon