Landscape controls on riverine export of dissolved organic carbon from Great Britain

Jennifer Williamson, Andrew Tye, Dan J. Lapworth, Don Monteith, Richard Sanders, Daniel J. Mayor, Chris Barry, Mike Bowes, Michael Bowes, Annette Burden, Nathan Callaghan, Gareth Farr, Stacey L. Felgate, Peter J. Gilbert, Geoff Hargreaves, Patrick Keenan, Vassilis Kitidis, Monica Jurgens, Adrian P. Martin, Ian MounteneyPhilip D. Nightingale, M Glória Pereira, Justyna Olszewska, Amy Pickard, Andrew Rees, Bryan Spears, Mark Stinchcombe, Debbie White, Peter Williams, Fred Worrall, Stuart Gibb, Chris Evans

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Abstract

The dissolved organic carbon (DOC) export from land to ocean via rivers is a significant term in the global C cycle, and has been modified in many areas by human activity. DOC exports from large global rivers are fairly well quantified, but those from smaller river systems, including those draining oceanic regions, are generally under-represented in global syntheses. Given that these regions typically have high runoff and high peat cover, they may exert a disproportionate influence on the global land–ocean DOC export. Here we describe a comprehensive new assessment of the annual riverine DOC export to estuaries across the island of Great Britain (GB), which spans the latitude range 50–60° N with strong spatial gradients of topography, soils, rainfall, land use and population density. DOC yields (export per unit area) were positively related to and best predicted by rainfall, peat extent and forest cover, but relatively insensitive to population density or agricultural development. Based on an empirical relationship with land use and rainfall we estimate that the DOC export from the GB land area to the freshwater-seawater interface was 1.15 Tg C year−1 in 2017. The average yield for GB rivers is 5.04 g C m−2 year−1, higher than most of the world’s major rivers, including those of the humid tropics and Arctic, supporting the conclusion that under-representation of smaller river systems draining peat-rich areas could lead to under-estimation of the global land–ocean DOC export. The main anthropogenic factor influencing the spatial distribution of GB DOC exports appears to be upland conifer plantation forestry, which is estimated to have raised the overall DOC export by 0.168 Tg C year−1. This is equivalent to 15% of the estimated current rate of net CO2 uptake by British forests. With the UK and many other countries seeking to expand plantation forest cover for climate change mitigation, this ‘leak in the ecosystem’ should be incorporated in future assessments of the CO2 sequestration potential of forest planting strategies.
Original languageEnglish
JournalBiogeochemistry
DOIs
Publication statusPublished - 16 Feb 2021

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