Overview of competing theories for increases in

freshwater DOC concentrations

Julian DawsonNorthern 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)