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)

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)