title: Potential for long-term transfer of dissolved organic carbon from riparian zones to streams in boreal catchments.
abstract: Boreal regions store most of the global terrestrial carbon, which can be transferred as dissolved organic carbon (DOC) to inland waters with implications for both aquatic ecology and carbon budgets. Headwater riparian zones (RZ) are important sources of DOC, and often just a narrow 'dominant source layer' (DSL) within the riparian profile is responsible for most of the DOC export. Two important questions arise: how long boreal RZ could sustain lateral DOC fluxes as the sole source of exported carbon and how its hydromorphological variability influences this role. We estimate theoretical turnover times by comparing carbon pools and lateral exports in the DSL of 13 riparian profiles distributed over a 69 km(2) catchment in northern Sweden. The thickness of the DSL was 36 ± 18 (average ± SD) cm. Thus, only about one-third of the 1-m-deep riparian profile contributed 90% of the lateral DOC flux. The 13 RZ exported 8.7 ± 6.5 g C m(-2) year(-1) , covering the whole range of boreal stream DOC exports. The variation could be explained by local hydromorphological characteristics including RZ width (R(2) = 0.90). The estimated theoretical turnover times were hundreds to a few thousands of years, that is there is a potential long-lasting supply of DOC. Estimates of net ecosystem production in the RZ suggest that lateral fluxes, including both organic and inorganic C, could be maintained without drawing down the riparian pools. This was supported by measurements of stream DO(14) C that indicated modern carbon as the predominant fraction exported, including streams disturbed by ditching. The transfer of DOC into boreal inland waters from new and old carbon sources has a major influence on surface water quality and global carbon balances. This study highlights the importance of local variations in RZ hydromorphology and DSL extent for future DOC fluxes under a changing climate.
authors.affiliation: Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences (SLU), P.O. Box 7050, Lennart Hjelms väg 9, Uppsala, 750 07, Sweden.
authors.forename: José L J
authors.initials: JL
authors.lastname: Ledesma
authors.affiliation: Department of Earth Sciences, Uppsala University, Villavägen 16, Uppsala, 752 36, Sweden.
authors.forename: Thomas
authors.initials: T
authors.lastname: Grabs
authors.affiliation: Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences (SLU), P.O. Box 7050, Lennart Hjelms väg 9, Uppsala, 750 07, Sweden.|Department of Earth Sciences, Uppsala University, Villavägen 16, Uppsala, 752 36, Sweden.
authors.forename: Kevin H
authors.initials: KH
authors.lastname: Bishop
authors.affiliation: Department of Earth and Environmental Sciences, University of Waterloo, University Avenue West 200, Waterloo, N2L 3G1, ON, Canada.
authors.forename: Sherry L
authors.initials: SL
authors.lastname: Schiff
authors.affiliation: Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences (SLU), P.O. Box 7050, Lennart Hjelms väg 9, Uppsala, 750 07, Sweden.
authors.forename: Stephan J
authors.initials: SJ
authors.lastname: Köhler
mesh_terms: D002244:Carbon; D057486:Carbon Cycle; D057231:Climate Change; D008962:Models, Theoretical; D045483:Rivers; D012987:Soil; D013548:Sweden
chemical_list: D012987:Soil; D002244:Carbon
keywords: carbon 14; carbon cycling; climate change; ditching; hydromorphology; isotopic measurement; organic matter; primary production; total organic carbon; turnover time