1. water@leeds
Mechanisms controlling DOC
transport; Surface flow vs pipes
vs groundwater
Pippa Chapman,
School of Geography
University of Leeds
2. water@leeds
• Sources of DOC in aquatic systems
– Allochthonous sources – are derived outside of
the stream from soil and vegetation within the
catchment (terrestrial organic matter)
– Autochthonous sources – are derived from in-
stream biological production (e.g. algae and
macrophytes)
3. water@leeds
• DOC is produced during the
decomposition of organic
matter in soil
• Peat soils contain most
organic matter
– Major source of DOC
• Production of DOC is a
biological process:
– Increases with temperature and
aeration
– So more produced in summer
From Hope et al., 1994
4. water@leeds
Transport of DOC in peatlands
Overland flow - typically saturation-excess driven.
Micropore throughflow - typically close to the surface (top 5
cm).
Macropore/tunnel/pipe ‘bypassing’ flow
5. water@leeds
Role of throughflow
There is a strong relationship
between soil water DOC at 10 cm
depth and stream water DOC (r2 =
0.47, P<0.001) at Cottage Hill
Sike, Moor House, N Pennines
(Clark et al., 2008).
This is consistent with hydrological
studies at this site that have
shown most runoff originates from
the top 5 cm (Holden and Burt,
2003).
From Clark et al., 2008
Note: despite large fluctuations in discharge little variation in DOC
6. water@leeds
Role of overland flow: based on Cottage Hill Sike from Clark et al., 2007
•DOC concentrations decreased
during autumn storms
•No relationship observed between
DOC and flow
•Flux calculation based on weekly
ECN sampling was 16% greater than
flux based on 4 hourly sampling.
•Excluding storm events resulted in
over-estimation of DOC flux
•50% of DOC export is associated
with the highest 10% of discharge
values. Hinton et al (1997) reported
similar findings for a catchment in
central Ontario, Canada.
7. water@leeds
North
Charr Flume
Brocky Burn
From Hinton et al., 1997. Biogeochem.
Soil Type
Hill Peat
Charr Peaty Podzol
Countesswells
Iron Podzol
Alluvial
Drumlasie Peaty Gley
Strathgyle Peaty Gley
Mundurno Peaty Gley
Ranker 0 2.50 km
1: 50000
Soil map of Glendye, NE Scotland (from Dawson)
8. Pipeflow runoff pathway
coupling
Saturation-excess overland flow
and near-surface through flow
Rapid near-surface macropore and matrix infiltration
Blanket peat
Very limited deep matrix seepage ?
Pipe network
Mineral substrate
Localised ephemeral interface flow
11. water@leeds
Importance of pipeflow in Cottage Hill Sike
Initial calculations suggest that:
• 20-30 % of stream flow originates from pipes
• 53 % of the DOC originates from the pipes (typically ranges
between 5-75 % depending on conditions)
• Pipe probably tap deep/old carbon as well as new carbon (to be
further tested with isotopic analysis)
• Very variable carbon response between pipes and between
storms
• Chemistry of at least one pipe suggests that ground water feeds
pipe at low flow
12. water@leeds
Summary
•DOC transported from peat to stream by a combination of overland flow, through
flow and pipe flow
•Response of stream water DOC to storm events dependent on number of source
waters and location within the catchment with respect to soil distribution
•Transport of DOC from peat and organo-mineral soils is not the same due to
differences in hydrology and soil profile properties
•Some streams fed by groundwater during low flow – low DOC, pH 6-7.
•Largest loss of DOC (~50%) from peat and organo-mineral soils occurs in only
10% of time during high flow events
13. water@leeds
• Acknowledgments
– Jo Clark, Joe Holden, Richard Smart, Andy Baird,
Mike Billett, Kerry Dinsmore
– NERC- funded Jo Clark’s PhD (2000-2004)
– NERC - funded Pipe project (2007-2010)
– ECN – use of data
– Natural England – use of Moor House NNR
