42
Effects of Landscape Drainage on Dissolved Carbon Export.
Brent Dalzell, Ph.D.Postdoctoral Research Associate
UNIVERSITY OF MINNESOTA
Department of Soil, Water, and Climate
MN-IA Drainage Research Forum: December 2nd, 2008
Effects of Landscape Drainage on Dissolved Carbon Export.
Acknowledgements:
Jennifer King, Jacques Finlay, Dave Mulla, Gary Sands, Katrina Hill, Tim Filley, Jon Harbor
Raymond 2005 (Nature)
Terrestrial Organic Matter
contributions to aquatic
ecosystems.
Raymond 2005 (Nature)
Terrestrial Organic Matter
contributions to aquatic
ecosystems – a broader
role in global
biogeochemical cycles.
Wabash
Riv
er
Big Pine Creek Watershed
•850 km2
•Over 80% row crops
0
5
10
15
20
25
0 50 100 150 200 250 300 350
Julian Day
Average Daily Flow
(1955-1987)
Str
eam
flow
(m
3se
c-1)
0
20
40
60
80
100
120
140
160
Big Pine Creek – Mean Daily
Discharge (period of study)
Str
eam
flow
(m
3se
c-1)
Influence of Stream Discharge on DOC
Dalzell et al., 2007 (GCA)
~80% of DOC flux occurs during less than 20% of the time!
Dalzell et al., 2007 (Geochimica et Cosmochimica Acta)
Annual DOC flux is dominated by short-term flow events
Short-term hydrologic variability plays a key role in carbon export from
small- to mid-sized agricultural watersheds.
This signal is not necessarily apparent in larger watersheds. (multiple sources and
timing? Rapid in-stream processing?)
Stable C isotope and molecular (lignin) proxies show that terrestrial organic matter is the
source of additional C during periods of increased flow.
Dalzell et al. (2005) J. of Geophysical Research; Dalzell et al. (2007) Geochimica et Cosmochimica Acta
Watershed scale dissolved organic carbon export
Dissolved organic carbon in drainage
University of
Minnesota
Southern Research
and Outreach Center
Agricultural Ecology Research Farm
Agricultural Ecology
Research Farm
Agricultural Ecology Research Farm –
Experimental Drainage Plots
Influence of Drainage Intensity on DOC concentration.
subtitle
0
50
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150
200
250
0
1
2
3
4
5
6
7
3/19/2007 5/8/2007 6/27/2007 8/16/2007 10/5/2007 11/24/2007
Flo
w (
m3
ha-
1 d
ay-1
)P
reci
p. (
mm
day
-1)
DO
C (
mg
L-1
)
Standard (13mm) drainage
intense (51 mm drainage)
plot 9 flow (m3 day-1)
precip (mm)
0
2
4
6
8
10
12
0 20 40 60 80 100 120
NP
OC
(m
g L-
1)
Mean Flow (m3 ha-1 day-1)
51 mm day-1
13 mm day-1
Narrow Spacing (51 mm day-1)
10/12 from Narrow Spacing (51 mm day-1)
Drainage intensity effects on DOC concentrations
Drainage Influences on Annual Water Yield
0
500
1000
1500
2000
2500
0 50 100 150 200 250 300 350
Cu
mu
lati
ve W
ate
r Y
ield
(m
3 h
a-1
)
Day of Year 2007
13 mm drainage
51 mm drainage
Water yield exerts greater
control on total DOC export.
Drainage intensity effects on annual DOC yield
DOC export at the field scale
0
2
4
6
8
10
12
0 20 40 60 80 100 120
daily flow (m3 ha
-1 day
-1)
DO
C (
mg
L-1
)
All field plots
Different processes influence DOC export at field vs.
watershed scale
Watershed
Scale
0
2
4
6
8
10
12
-2 -1 0 1 2 3 4 5 6daily flow (ln -transformed; m
3 ha
-1 day
-1)
DO
C (
mg
L-1
)
Field Plots
Amon and Benner (1996) Limnology and Oceanography
Molecular Weight Distribution
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
15 16 17 18 19 20 21 22 23 24 25
Elution Time (min)
Sign
al (
no
rmal
ize
d)
Field Drainage
Size-exclusion chromatography
Large Molecules
elute first Small molecules
elute later.
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
15 16 17 18 19 20 21 22 23 24 25
Elution Time (min)
Sign
al (n
orm
aliz
ed)
Field Drainage
High
Molecular
Weight
Low
Molecular
Weight
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
15 16 17 18 19 20 21 22 23 24 25
Elution Time (min)
Sign
al (n
orm
aliz
ed)
Field Drainage
Small Ditch
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
15 16 17 18 19 20 21 22 23 24 25
Elution Time (min)
Sign
al (n
orm
aliz
ed)
Field Drainage
Small Ditch
Large Ditch
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
15 16 17 18 19 20 21 22 23 24 25
Elution Time (min)
Sign
al (
no
rmal
ize
d)
Field Plot
Small Ditch
Large Ditch
LeSueur River
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
15 16 17 18 19 20 21 22 23 24 25
Elution Time (min)
Sign
al (
no
rmal
ize
d)
Site 9 4-10-08
ditch 1 4-23-08
Ditch 2 4-23-08
LeSueur River 4-23-08
As you go
downstream…
•Increases in high
molecular weight organic
matter.
•Decreases in low
molecular weight organic
matter.
Land Use Change Impacts on HCO3- export.
Mayorga; Raymond et al., 2008 Nature.
Raymond et al, 2008 Nature
Mississippi River at New Orleans
0
20
40
60
80
100
120
140
160
40
45
50
55
60
65
70
75
80
3/9/2007 4/28/2007 6/17/2007 8/6/2007 9/25/2007 11/14/2007 1/3/2008
Flo
w m
3 d
ay-1
ha-
1
DIC
mg
L-1
DIC 13mm Normal Drainage
DIC 51mm Intense Drainage
daily ave flow plot 9
precip mm
Drainage intensity effects on dissolved inorganic carbon concentrations
40
45
50
55
60
65
70
75
80
85
0 20 40 60 80 100 120
DIC
(m
g L-
1)
Mean Flow (m3 ha-1 day-1)
13 mm
51 mm
Ongoing work
Investigate scenarios of changes in rainfall timing (most of the projected increase in the
Midwestern US will occur during the non-growing season).
Compare DOM from subsurface drainage with leachates from surface soils and
determine the role of flow path on DOM quality (molecular weight distribution and
microbial availability).
Watershed scale: short-term flow events are key in delivering organic matter from
terrestrial to aquatic systems.
Conclusions:
Thank you!
Field scale: DOC concentration not strongly related to flow but annual loads are still
dictated by total water yield.
Field scale: Organic matter exported from subsurface drainage has greater relative
contributions from low molecular weight compounds. The relative abundance of these
compounds decreases with distance downstream
Field scale: Dissolved inorganic carbon export is greater from plots with more intense
drainage (due to increases in both concentration and water yield)
