Seasonal and elevational variation
of surface water d18O and d2H in
the Willamette River basin
J. Renée Brooks1, Parker J. Wigington1, Jr., Carol Kendall2,
Rob Coulombe3, and Randy Comeleo1
1Western
Ecology Division, U.S. Environmental Protection Agency
2U.S. Geological Survey, Menlo Park CA.
3Dynamac Corporation,
Project Goals

Part of a larger EPA project to determine
biological, physical and chemical linkages
between non-navigable headwater
streams and wetlands to the nation’s
navigable waters.

Isotopes could be a useful for tracing
these linkages.
Specific Objectives

Charactize spatial and temporal variation
of d18O and d2H in small watershed
streams within the Willamette Valley.

Determine the major drivers of variation.

Use the variation as a tool for
understanding navigable river dynamics
and linkages to small streams.
Water isotopes are partitioned by
hydrologic fluxes
Water isotopes change with phase changes:
Vapor ↔ Liquid (precipitation and evaporation)
Liquid ↔ solid (freezing and thawing)
Solid ↔ Vapor (snow and sublimation)
Variance in Precipitation
40
GMWL dD = 8 d18O +10
20
0
Precipitation
d2dD
H (‰)
-20
1
2
3
-40
in
Ra
ou
c
ffe
te
t
-60
Cloud
Vapor
-80
1
m
Te
2
p
e
ur
at
r
e
c
fe
ef
t
3
-100
-120
-16
-12
-8
-4
d18O (‰)
0
4
Evaporation
40
GMWL
20
RH=100%
0
Slope
depends
on RH
2H (‰)
ddD
-20
Evaporation line
(RH<100%)
-40
Remaining
liquid water
-60
Water
Vapor
-80
Precipitation input
(temperature & rainout
dependent)
-100
-120
-16
-12
-8
-4
d18O (‰)
0
4
Study Site


Willamette River
Basin, Oregon.
Bordered by
Coastal Range
(West)
 Cascade Range
(East)


Elevation gain
most on East
border.
1m
Annual
Precipitation
Patterns
4m

Mediterranean
Climate

Warm dry
summers

Cold wet winters

95% of rain falls
between Oct May
Study Design

Southern Willamette
Focus

Willamette River
Samples at each river
confluence

6 Major Tributary






Middle Fork Willamette
River
McKenzie River
Calapooia River
North Santiam River
Luckiamute River
Marys River

Samples are
collected quarterly




Summer low flow
(September)
Fall wet up
(November)
Winter rains
(February)
Spring snowmelt
(May)

Temporally
Intensive sampling


East-West Transect
3 Rivers:




Calapooia River
North Santiam River
Luckiamute River
Additional samples
are collected in
between the
quarterly samples
RESULTS
Characterizing variation of the
Small Elevational Watersheds
Isotopes in Corvallis Precipitation
0
-2
18
O (‰)
-4
-6
-8
-10
-12
-14
WY2003 WY2004 WY2005 WY2006 WY2007 WY2008 WY2009 WY2010
Small Watershed Elevation Gradient
0
-5
Small Elevation Watersheds
18
O (‰)
d18O
= -7.83 – 0.00304(Elevation)
-8
-10
-12
d2H = -54.7 – 0.0212(Elevation)
-60
-70
2
H (‰)
-40
-80
-90
0
200
400
600
800
1000
1200
1400
Mean Watershed Elevation (m)
1600
1800
Rainout vs Elevation
Coast Range Drainages
-6
Cascade Drainages
Luckiamute River
North Santiam River
Mary's River
McKenzie River
-8
18
O (‰)
-10
-12
-6
Storm Trajectory
Storm Trajectory
-8
-10
-12
0
200 400 600 800 1000 1200 1400 1600 1800 200 400 600 800 1000 1200 1400 1600 1800
Mean Watershed Elevation (m)
Evaporation Effects
-40
2
H (‰)
-50
-60
-70
-80
-90
-12
-10
-8
18
O (‰)
-6
-4
Small Watershed Seasonal Pattern
Luckiamute River
North Santiam River
-50
-60
High Elev
-70
H (‰)
-90
2
-80
-50
Low Elev
McKenzie River
Calapooia River
-60
-70
-80
Oct 10
Jun 10
Feb 10
Oct 09
Jun 09
Feb 09
Oct 08
Oct 10
Jun 10
Feb 10
Oct 09
Jun 09
Feb 09
Oct 08
-90
Small Watershed
Best Subset Regression Analysis
d2H
R2adj
79.0%
F
Variable
2108
81.3%
1218
WS
Elevation
+ Evap
+ Evap
84.1%
986
+WS Slope
85.5%
827
Variable
WS
Elevation
+ Long
d18O
R2adj
70.5%
F
1339
87.3%
1935
+ Long
89.5%
1595
+WS Slope
90.5%
1330
*Variables tried in model for small elevational watersheds:
WS Area, WS Elevation, WS Gradient, Flowpath Length, Topographic Index,
Mean WS Slope, Evap, Latitude, Longitude, Season and Water Temperature.
Isoscapes
based on small watershed elevation
d18O
2
dH
Small Watershed Elevation Gradient
-40
Small Watersheds
R2adj = 79%
2H
(‰)
-60
-70
-80
-90
0
200
400
600
800
1000
1200
1400
Mean Watershed Elevation (m)
1600
1800
-40
Small Watersheds
Major Tributaries
2H
(‰)
-60
-70
-80
-90
0
200
400
600
800
1000
1200
1400
Mean Watershed Elevation (m)
1600
1800
-40
Small Watersheds
Major Tributaries
Willamette River
2H
(‰)
-60
-70
-80
-90
0
200
400
600
800
1000
1200
1400
Mean Watershed Elevation (m)
1600
1800
Seasonal Patterns
-68
Willamette River
-70
-72
-76
2
H (‰)
-74
-78
-80
-82
-84
Sep 08 Dec 08 Mar 09
Jun 09
Sep 09 Dec 09 Mar 10
Jun 10
Sep 10 Dec 10
Seasonal Changes in Source
Water
Loc
Fall
Winter Spring Summer
Will-1
d2H (‰)
-73.0
-70.5
-73.1
-79.2
668
Will-6
876
Elev (m)
d2H (‰)
Elev (m)
857
-78.4
1,114
735
-76.6
1,026
858
-75.7
986
1,152
-82.0
1,286
d2H = -54.7 – 0.0212(Elevation)
Simple Willamette Mixing Model

Average Valley d2H = -62.0 (<800 m)
Average Mountain d2H = -79.3 (>800 m)

Winter

Summer

49% + 51%
99%
+
1%
Simple Willamette Mixing Model
Mean Monthly Flow (m3s-1)
1800
Willamette River
Valley Water
Mountain Water
1600
1400
1200
1000
800
600
400
200
0
Oct 08
Feb 09
Jun 09
Oct 09
Feb 10
Jun 10
Oct 10
Summary

Variation in small watershed streams:
Elevation effect caused by rainout of
precipitation
 No seasonal variation in small streams
 Minor evaporation effects


Willamette River and Large Tributaries
Water sources skewed to higher elevation
 Water sources shift seasonally



Increasing 400 m during the summer low flows
Willamette summer low flows are highly
dependent on mountain water
Useful tool for characterizing
linkages between water bodies.

Continue monitoring Willamette River
water isotopes.

How do Willamette water sources change with
climate?

What is the impact of changing snowpack?

Elevation pattern specific to West Coast

Characterization technique can be used in
many locations.