MONITORING CONDUCTIVITY IN HIGH ELEVATION STREAMS DRAINING THE CENTRAL SIERRA NEVADA
David Peterson, Madeline Solomon, Richard Smith, Stephen Hager, Fred Murphy, Iris Stewart, and King Huber
"doing less with less"
atmosphere
March 2005
Conductivity (µS cm-1)
120°
Sagehen Creek
West Walker near Bridgeport
Clark Fork
Happy Isles
20
Sagehen Creek
Happy Isles
0.20
0.15
Sagehen Creek
Merced River +35
Merced River
0.10
rain events
0.05
0
Jan
Feb
Mar
Apr
May
June
0
160
July Aug
2003
2003
Fig. 4 The inverse of river discharge is based
on a linear transform though the inverse relation
is nonlinear. Note the separation in red and green
conductivity near the start of the spring pulse
(Fig. 3). The same linear transform can be used
to closely describe the pre-spring pulse segment
of conductivity for SMD/conductivity
observations in years 2000 to 2004.
Fig. 2 Site map.
In general, conductivity is the inverse of
snowmelt discharge or as discharge increases,
conductivity increases.
2004
120
80
40
0
0
1
2
3
4
5
6
Sample Number (x 104)
Fig. 5 The Sagehen watershed above the creek gage
is seventeen times smaller than the Merced River
watershed above Happy Isles.
Happy Isles, Yosemite
National Park (2001)
Merced River Discharge (m3 s-1)
0
60
70
80
90 100 110 120 130 140
Conductivity (µS cm-1)
1.0
0.5
200
150
60
70
80
90 100 110 120 130 140
Conductivity (µS cm-1)
100
60
70
80
90 100 110 120 130 140
Conductivity (µS cm-1)

ha
rg
e
sc
di
g
in
in
450


ha
rg
e
sc
di
g
250
cl


ar
ge
rg
e
400
sc
h
ha
di
sc
de
di
500

g
rg
e
550
300

in
1.5
ha
350
g

2.0
sc
in

di
ris
in
rg
e
g
350
300
50
The watershed above the West
Walker near Bridgeport has a
high soil-to-bedrock ratio but
lower runoff (lower rate of
dilution), which further increases
the river conductivity (Fig. 6).
70

ha
in
in
Dissolved Si (µM L-1)
sc
cl
ris
ha
rg
e
di
rg
e
de
sc
g
ha
di
in
0.2


2.5
sc
g
in
di
ris
in
cl
g

0.4
de
in
in

3.0
ris
600
cl

0.6
400
de
3.5

0
0.8
Dissolved Ca (µM L-1)
5
The Stanislaus River above
Clark Fork, however, was not
glaciated at that time. Although
the runoff is the same in both
watersheds, the soil-to-bedrock
ratios differ. Because of the loss
of soil above Happy Isles, the
soil-to-bedrock ratio is low
compared to above Clark Fork.
The rock and mineral surface
area is greater in the Clark Fork
than Happy Isles watersheds.
The rate of supply of dissolved
salts is greater in Clark Fork, as
is the river conductivity, because
the rates of dilution are the same.
60
70
Data courtesy of Dave Clow,
USGS Hydrologic Benchmark Program.
80 90 100 110 120 130 140
Conductivity (µS cm-1)
Fig. 8 Sagehen Creek, 2002
Rising limb of the annual hydrograph are purple; the falling limb are green.
a) discharge vs.conductivity,
b) dissolved organic carbon (DOC) vs. conductivity.
The clockwise hysteresis here likely reflects a flushing response in which
solutes accumulated in the soil during the dry season are progressively
flushed out as discharge rises.
c) dissolved calcium versus conductivity,
d) dissolved silica vs. conductivity.
Note the strong linear correlation between conductivity and base cation
concentrations.
250
Hourly Sample, 2003
River Conductivity (µS cm-1)
spring pulse
40
discharge (SMD) correlate strongly
with the variations in air temperature,
and because the variations in air
temperature are large scale, the SMD
variations are large scale (Peterson, et.
al., 2001) and because the variations in
river conductivity correlate strongly
with the variations in SMD (Fig. 4), we
can extend the large-scale correlation in
SMD to river conductivity (Fig. 5).
variations in snowmelt discharge are a major source
of the variations in river and stream chemistry.
122°
60
Fig. 3 The variations in snowmelt
Fig. 1 The field monitoring is top-down because
Runoff (m3 s-1 km2)
Time
soil 
80
0.25
Conductivity (µS cm-1)
Vernal Fall in spring, 2001
Conductivity (µS cm-1)
t dis
c ha
rge
Discharge
Base Flow
s
 river chemistry 
Spring Pulse
now
mel
50
DOC (mg/L)
The interaction of climatic and geologic
controls causes both broad similarities and
specific differences in the seasonal and
diurnal stream salinity records. The
competing effects of salinity supply and
dilution rates are evident in a comparison of
high-flow and low-flow salinity variations
in different watersheds and in the hysteresis
evident in plots of salinity vs. river
discharge. Monitoring and analysis of the
salinity verses discharge behavior of high
elevation rivers can contribute to the
understanding of the individual
contributions of snowmelt, precipitation,
and groundwater to mountainous river and
stream discharge and its susceptibility to
climatic change.
Temporal variations in
conductivity are due to variations
in rates of dilution via snowmelt
discharge (climate). Spatial
variations in rates of supply of
dissolved salts are largely caused
by geology. The soil and talus
was cleaned from the Merced
River watershed above Happy
Isles during the last glacial
episode, which ended 10,000
years ago.
rain event
Merced River discharge
Observed Conductivity
Scaled Inverse
100
Discharge (m3 s-1)
In landscapes with low
soil-to-bedrock ratios, salinity is
relatively low during low and high
flow. In landscapes with high
soil-to-bedrock ratios, but with the
same runoff, salinity is relatively
high during high and low flow,
and conductivity increases further
in watersheds with decreases in
runoff (dilution).
0.30
120
Maximum Discharge
Merced River at Happy Isles
West Walker River near Bridgeport
Stanislaus River at Clark Fork
200
150
100
50
0
1500
2000
2500
3000
3500
4000
4500
Sample Number
140
River Discharge and Conductivity
snowpack
Here we present a preliminary analysis of
high resolution discharge and conductivity
measurements from several central Sierra
Nevada streams. Stream conductivity (total
dissolved solids, salinity) shows a strong
inverse relation with discharge. In the
central Sierra Nevada, climate is the major
control on river and stream salinity dilution
via runoff/discharge and geology is the
major control on river salt supply via the
soil-to-bedrock ratio of the watershed. As
snowmelt discharge increases, river
conductivity decreases because the salinity
of snowmelt is low compared to base flow
salinity.
Merced River at Happy Isles
River Discharge
Conductivity
Conductivity 2004 (min)
120
100
80
60
40
20
0
0
1
2
3
Hourly Sampling Number (x104), 2000-2004
4
Fig. 6, The variability in river conductivity is due to the supply and
dilution rates of dissolved salts. The watershed above Happy Isles has
a low rate of dissolved salt. Peak river discharge is sufficient to drive
the minimum conductivity to snow water values except in (dry) 2004,
when the peak discharge was not high enough (Fig. 7), less salt was
flushed from the watershed. The total salt flux was greater in 2004
than 2001 so the SMD magnitude and duration time scales are not yet
understood (i.e., how does river salinity respond to a high SMD or
long SMD?).
Fig. 7 Can a simple conceptual model explain the hysteresis
observed in conductivity versus discharge plots? An example from
the Merced River at Happy Isles is shown as background in the
poster. Note the change from a diurnal vertical to horizontal pattern,
this is probably when the diurnal peak in conductivity shifts from
after to before the diurnal peak in discharge (Peterson, et. al., 2004).
Perhaps the greatest gap in this effort is the absence of shallow
groundwater monitoring. The greatest help is the hydroclimate
monitoring work of others (cf. DiLeo, et. al., 2004).
For further information, please contact David Peterson, USGS 345 Middlefield Road, Mail Stop 496, Menlo Park, CA 94025
email: dhpete, phone: 650 329-4525