Geothermal solute flux monitoring using electrical conductivity in major of Yellowstone National Park By R. Blaine McCleskey, Dan Mahoney, Jacob B. Lowenstern, Henry Heasler Yellowstone National Park  Yellowstone National Park is well-known for its numerous , hot springs, mud pots, and vents  Yellowstone hosts close to 4 million visits each year  The Yellowstone Supervolcano is located in YNP Monitoring the Geothermal System: 1. Management tool 2. Hazard assessment 3. Long-term changes Monitoring Geothermal Systems

 YNP – difficult to continuously monitor  10,000 thermal features  YNP area = 9,000 km2  long cold winters

Thermal output from Yellowstone can be estimated by monitoring the chloride flux downstream of thermal sources in major rivers draining the park Chloride Flux  The chloride flux (chloride concentration multiplied by ) in the major rivers has been used as a surrogate for estimating the heat flow in geothermal systems (Ellis and Wilson, 1955; Fournier, 1989)  “Integrated flux”  Convective heat discharge: 5300 to 6100 MW  Monitoring changes over time

 Chloride concentrations in most YNP geothermal are elevated (100 - 900 mg/L Cl)  Most of the discharged from YNP geothermal features eventually enters a major river  Madison R., Yellowstone R., Snake R., Falls River  Firehole R., Gibbon R., Gardner R.

 Background Cl concentrations in rivers low < 1 mg/L Dilute Stream water -snowmelt -non-thermal -low EC (40 - 200 μS/cm) -Cl < 1 mg/L

Geothermal Water -high EC (>~1000 μS/cm) -high Cl, SiO2, Na, B, As,… -Most solutes behave conservatively Mixture of dilute water with geothermal water Historical Cl Flux Monitoring • The U.S. Geological Survey (USGS) and the National Park Service have collaborated on chloride flux monitoring since the 1970’s • Collected 28 water samples/year/site for Cl analyses • Difficult to sustain year-after-year 1. Weather 2. Funding 3. Staffing (long-term) 4. Distance between sample sites 5. Changing research interests Electrical Conductivity Monitoring  Beginning in 2010, we developed methods using electrical conductivity as a surrogate for chloride concentrations in major YNP rivers River Synoptic Sampling Identify thermal sources, solutes, fate and transport

• Madison R., Gibbon R., Firehole R. • Snake R. • Yellowstone R. and Gardner R. EC Monitoring Sites  Near USGS streamgage ( every 15 min)  Continuous electrical conductivity measurements concurrent with streamflow (every 15 min)  Low maintenance / checked EC with handheld meter

 Solute Concentrations– Electrical Conductivity Correlations  Collect water samples (filtered) and EC under wide range of flow conditions  Analyzed for major anions, cations, and trace metals  QAQC: Charge Balance and Electrical Conductivity Balance Cl Flux (g/year) =

Q (m3/s) Cl concentration (mg/L) (continuous 15 min - (28(>35,ooo samples/year) measurements/yr) >35,ooo measurements/yr)

USGS streamgage EC – Cl correlation Electrical Conductivity (continuous 15 min - >35,ooo measurements/yr) Snake River

400 300 d e t a )

m 250 i t m s c /

300 E S µ ) (

200 s / y 3 t i v m i ( t

c e u

200 150 g d r n a o h c C

s l i a

100 D c i r t

c 100 e l

E 50

0 0 9/1/2012 3/1/2013 9/1/2013 3/1/2014 9/1/2014 3/1/2015 9/1/2015 Chloride-Electrical Conductivity Correlations

90

80 Madison River Yellowstone River

) R² = 0.998 R² = 0.974

L 70 /

g 60 m

( 50

e 40 d i r 30 o l

h 20 C 10

0

80 Firehole River Gardner River

) R² = 0.997 R² = 0.983

L 70 /

g 60 m (

50 e

d 40 i r

o 30 l

h 20 C

10

0

80 Gibbon River Snake River

) R² = 0.999 R² = 0.987

L 70 /

g 60 m

( 50

e 40 d i r 30 o l

h 20 C 10

0 0 100 200 300 400 500 600 700 800 900 0 100 200 300 400 500 600 700 800 900 1000 Electrical Conductivity (µS/cm) Electrical Conductivity (µS/cm) Solute-Electrical Conductivity Correlations

200

HCO3 150 Na SiO 2 Firehole River Cl 100 In addition to Cl, 12 other 50 solutes correlate well (R2>0.95)

) with electrical conductivity

L 14 / SO

g 4 12 K m (

F 10 n Ca o i

t 8 a r

t 6 n

e 4 c

n 2 o C

1.0 B Li 0.8 As Br 0.6

0.4

0.2

0.0 150 200 250 300 350 400 450 500 550 600 Electrical Conductivity (µs/cm) Annual Cl Flux 30

Madison R. (46% of total Cl flux) 25 ) r y

/ 20 t k (

x u l

F 15

e

d Yellowstone R. (32%) i r o l 10 h C

5 Snake River (12%)

0 1980 1985 1990 1995 2000 2005 2010 2015 2020

USGS Professional Paper 1717 Hurwitz et al. (2007) and LoadESt Electrical Conductivity Method 640 Rain Event 11 Firehole River )

620 m c / S ) µ

s 600 (

/ 10

3 y t m i ( v

580 i t e c g 9 r u

a Eruptions 560 d h n c Electrical o s i C

8 Conductivity l D 540 a c i r t

520 c e

7 l E Discharge 500

10/22/10 10/24/10 10/26/10 10/28/10 10/30/10 11/01/10 Readily estimate water chemistry at popular swimming holes Advantages of Continuous Electrical Conductivity Monitoring  Primary goal – Cl flux (instantaneous and annual)  Cost- and labor-effective alternative to previous protocols  Eliminate data gaps  High resolution data  Depending on river insight into geyser eruptions and the effects of storms  EC correlates well with several solutes  Solute flux leaving the park  Estimate concentrations at popular swimming holes Continuously measure EC • USGS real-time EC-Geothermal Solute (Madison, Firehole, and Yellowstone) Madison, Firehole, and Yellowstone • Data logger Snake, Gibbon, Gardner (Snake, Gibbon, Gardner, Tantalus) Method not developed - Falls River • No monitoring (Falls River)

Chloride (or other solutes) Flux On my computer only (quarterly)! Goal – real time and available to NPS and other scientists Electrical Conductivity (Κ) where: λ (ionic molal cond.) is calculated from a series of equations m is speciated ion concentration  I ½  where: λ = λ (T) − A(T)  i 0  ½  1+ BI 

McCleskey, R.B., Nordstrom, D.K., Ryan, J.N., and Ball, J.W., 2012, A New Method of Calculating Electrical Conductivity With Applications to Natural Waters: Geochimica et Cosmochimica Acta, v. 77, p. 369-382. [http://www.sciencedirect.com/science/article/pii/S0016703711006181]

Non-linear α (ISO 7888): Circumneutral pH : pH<4 (Tantulus Cr.)

∗ ∗ McCleskey, R.B., 2013, New Method for Electrical Conductivity Temperature Compensation: Environmental Science & Technology, v. 47, p. 9874-9881. [http://dx.doi.org/10.1021/es402188r] Electrical Conductivity Transport Numbers  The relative contribution of an ion to the overall electrical conductivity λ λ m t = i = i i i Λ n ∑ (λ i m i ) i =1

 Transport numbers (ti) > 10%) – Na, Cl, HCO3, SO4, Ca

 Despite low ti, B, SiO2, As, and F correlate well with EC (Low concentration or uncharged species)  Fairly constant solute/Cl ratio in YNP thermal waters  Conservative in rivers 50

40

30 ) % ( 20 e c n

a 10 l a B 0 y t i v i t -10 c u d -20 n o

C -30

-40

-50 -50 -40 -30 -20 -10 0 10 20 30 40 50 Charge Imbalance (%)

21