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. 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

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)
UK, Nth America and Europe

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)