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Overview of competing theories for increases in freshwater DOC concentrations Julian Dawson Northern Rivers Institute School of Geosciences, University of Aberdeen 20th October 2009
Long-term DOC data Allt a’Mharcaidh (Data from Marine Scotland) [DOC] = 0.15 mg L-1 yr-1 DOC Flux = 1.17 kg C ha-1 yr-1
Seasonality Increasing variability of seasonal DOC concentrations
Spatial differences across UK, N. Europe & N America (Monteith et al., 2007) Changes in [DOC] variable 315 records, 216, 55 (Worrall & Burt, 2007)
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
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….
Acknowledgements Iain Malcolm (Marine Scotland) Chris Soulsby, Doerthe Tetzlaff, Markus Hrachowitz (Northern Rivers Institute)