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Overview of competing theories for increases in freshwater DOC concentrations

This overview examines the competing theories for the increase in freshwater dissolved organic carbon (DOC) concentrations. It discusses long-term DOC data, seasonality, spatial differences, and various competing hypotheses, including increased temperatures, changing hydrology, land management changes, and more. The uncertainties and complexities in isolating specific mechanisms are also highlighted.

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Overview of competing theories for increases in freshwater DOC concentrations

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  1. Overview of competing theories for increases in freshwater DOC concentrations Julian Dawson Northern Rivers Institute School of Geosciences, University of Aberdeen 20th October 2009

  2. [DOC] = 0.15 mg L-1 yr-1 DOC Flux = 1.17 kg C ha-1 yr-1 Long-term DOC data • Allt a’Mharcaidh (Data from Marine Scotland)

  3. Seasonality • Increasing variability of seasonal DOC concentrations

  4. Spatial differences • across UK, N. Europe & N America • (Monteith et al., 2007) • Changes in [DOC] variable • 315 records, 216, 55 • (Worrall & Burt, 2007)

  5. Competing Hypothesis • Increased temperatures • Decreasing soil acidity/ionic strength • reduction in sulphate/marine salt deposition • Changing hydrology • precipitation/discharge/flow paths • Land management changes • Eutrophication • increasing N-deposition • CO2 fertilization • Increased mobilisation of soil carbon stores

  6. Uncertainties • Drivers not mutually exclusive, potential combination of factors. • No one individual contributory factor across spatially variable sites. Difficult to isolate mechanisms based on monitoring data alone. • Certain mechanisms may predominate in different study environments (soil-type, land-use) • Different drivers across temporal scales from daily to decadal and longer….

  7. Acknowledgements • Iain Malcolm (Marine Scotland) • Chris Soulsby, Doerthe Tetzlaff, Markus Hrachowitz (Northern Rivers Institute)

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