seasonal and elevational variation of surface water 18 o and 2 h in the willamette river basin j....
TRANSCRIPT
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 Agency2U.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
18O (‰)
-16 -12 -8 -4 0 4
D (‰)
-120
-100
-80
-60
-40
-20
0
20
40
GMWL D = 8 18O +10
1
3
2
1
2
3
Precipitation
Cloud Vapor Tempera
ture effe
ct
Rain out effect
d2H
Evaporation
18O (‰)
-16 -12 -8 -4 0 4
D (‰)
-120
-100
-80
-60
-40
-20
0
20
40
Slope depends
on RH
GMWL
Evaporation line (RH<100%)
Water Vapor
Remaining liquid water
Precipitation input (temperature & rainout dependent)
RH=100%
d2H
Study Site
Willamette River Basin, Oregon.
Bordered by Coastal Range
(West) Cascade Range
(East) Elevation gain
most on East border.
AnnualPrecipitation
Patterns
Storm Trajegory
Mediterranean Climate Warm dry
summers Cold wet winters 95% of rain falls
between Oct - May
1 m
4 m
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
RESULTSCharacterizing variation of the Small Elevational Watersheds
Isotopes in Corvallis Precipitation
WY2003 WY2004 WY2005 WY2006 WY2007 WY2008 WY2009 WY2010
18 O
(‰
)
-14
-12
-10
-8
-6
-4
-2
0
Mean Watershed Elevation (m)
0 200 400 600 800 1000 1200 1400 1600 1800
2H
(‰
)
-90
-80
-70
-60
-40
18O
(‰
)
-12
-10
-8
-50
Small Elevation Watersheds
Small Watershed Elevation Gradient
d2H = -54.7 – 0.0212(Elevation)
d18O = -7.83 – 0.00304(Elevation)
North Santiam River
Mary's River
Mean Watershed Elevation (m)
0 200 400 600 800 1000 1200 1400 1600 1800
-12
-10
-8
-6 McKenzie River
200 400 600 800 1000 1200 1400 1600 1800
Luckiamute River
18O
(‰
) -12
-10
-8
-6
Coast Range Drainages Cascade Drainages
Rainout vs Elevation
Storm TrajectoryStorm Trajectory
Evaporation Effects
18O (‰)
-12 -10 -8 -6 -4
2H
(‰
)
-90
-80
-70
-60
-50
-40
Small Watershed Seasonal Pattern
McKenzie River
Oct
08
Fe
b 0
9
Jun
09
Oct
09
Fe
b 1
0
Jun
10
Oct
10
North Santiam River
Calapooia River
Oct
08
Fe
b 0
9
Jun
09
Oct
09
Fe
b 1
0
Jun
10
Oct
10
2H
(‰
)
-90
-80
-70
-60
-50
Luckiamute River
-90
-80
-70
-60
-50
High Elev
Low Elev
d2H d18OVariable R2
adj F Variable R2adj F
WS Elevation
79.0% 2108 WS Elevation
70.5% 1339
+ Long 81.3% 1218 + Evap 87.3% 1935
+ Evap 84.1% 986 + Long 89.5% 1595
+WS Slope 85.5% 827 +WS Slope 90.5% 1330
Small WatershedBest Subset Regression Analysis
*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.
Isoscapesbased on small watershed elevation
d18O d2H
Small Watershed Elevation Gradient
Mean Watershed Elevation (m)
0 200 400 600 800 1000 1200 1400 1600 1800
2H
(‰
)
-90
-80
-70
-60
-40Small Watersheds
R2adj = 79%
Mean Watershed Elevation (m)
0 200 400 600 800 1000 1200 1400 1600 1800
2H
(‰
)
-90
-80
-70
-60
-40Small WatershedsMajor Tributaries
Mean Watershed Elevation (m)
0 200 400 600 800 1000 1200 1400 1600 1800
2H
(‰
)
-90
-80
-70
-60
-40Small WatershedsMajor TributariesWillamette River
Seasonal PatternsWillamette River
Sep 08 Dec 08 Mar 09 Jun 09 Sep 09 Dec 09 Mar 10 Jun 10 Sep 10 Dec 10
2H
(‰
)
-84
-82
-80
-78
-76
-74
-72
-70
-68
Seasonal Changes in Source Water
Loc Fall Winter Spring Summer
Will-1 d2H (‰) -73.0 -70.5 -73.1 -79.2
668 Elev (m) 857 735 858 1,152Will-6 d2H (‰) -78.4 -76.6 -75.7 -82.0876 Elev (m) 1,114 1,026 986 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
Willamette River
Oct 08 Feb 09 Jun 09 Oct 09 Feb 10 Jun 10 Oct 10
Mea
n M
on
thly
Flo
w (
m3 s-1
)
0
200
400
600
800
1000
1200
1400
1600
1800
Valley WaterMountain Water
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.