Source and fate of inorganic solutes in the Gibbon River, Yellowstone National Park, Wyoming, USA. II. Trace element chemistry

Journal of Volcanology and Geothermal Research 196 (2010) 139–155

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Journal of Volcanology and Geothermal Research j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / j vo l g e o r e s

Source and fate of inorganic solutes in the Gibbon River, Yellowstone National Park, Wyoming, USA. II. Trace element chemistry R. Blaine McCleskey a,⁎, D. Kirk Nordstrom a, David D. Susong b, James W. Ball a, Howard E. Taylor a a b

U.S. Geological Survey, 3215 Marine St., Boulder, CO, 80303 USA U.S. Geological Survey, 2329 W. Orton Circle, Salt Lake City, UT, 84119 USA

a r t i c l e

i n f o

Article history: Received 13 October 2009 Accepted 3 May 2010 Available online 11 May 2010 Keywords: Yellowstone Gibbon River geothermal Norris Geyser Basin arsenic

a b s t r a c t The Gibbon River in Yellowstone National Park receives inflows from several geothermal areas, and consequently the concentrations of many trace elements are elevated compared to rivers in non-geothermal watersheds. Water samples and discharge measurements were obtained from the Gibbon River and its major tributaries near Norris Geyser Basin under the low-flow conditions of September 2006 allowing for the identification of solute sources and their downstream fate. Norris Geyser Basin, and in particular Tantalus Creek, is the largest source of many trace elements (Al, As, B, Ba, Br, Cs, Hg, Li, Sb, Tl, W, and REEs) to the Gibbon River. The Chocolate Pots area is a major source of Fe and Mn, and the lower Gibbon River near Terrace Spring is the major source of Be and Mo. Some of the elevated trace elements are aquatic health concerns (As, Sb, and Hg) and knowing their fate is important. Most solutes in the Gibbon River, including As and Sb, behave conservatively or are minimally attenuated over 29 km of fluvial transport. Some small attenuation of Al, Fe, Hg, and REEs occurs but primarily there is a transformation from the dissolved state to suspended particles, with most of these elements still being transported to the Madison River. Dissolved Hg and REEs loads decrease where the particulate Fe increases, suggesting sorption onto suspended particulate material. Attenuation from the water column is substantial for Mn, with little formation of Mn as suspended particulates. Published by Elsevier B.V.

1. Introduction The Gibbon River originates at Grebe Lake and flows nearly 40 km to the Firehole River where they combine to form the Madison River. The Madison River is one of four major rivers leaving Yellowstone National Park (YNP). The Gibbon River receives water and solutes from several geothermal sources including Norris Geyser Basin, Chocolate Pots, Gibbon Geyser Basin, Beryl Spring, and Terrace Spring. Knowing the source and fate of geothermal solutes is important because their concentrations are often elevated in rivers receiving geothermal inputs. In Part I of this series (McCleskey et al., 2010), the discharge, concentrations, loads, and geochemical behavior of major solutes in the Gibbon River were described and interpreted. Part I (McCleskey et al., 2010) also contains many details of the study including sampling locations and methods. This paper covers the trace element concentrations, loads, and geochemical interpretations. Numerous studies on the water and major ion loads in the Madison River exist (e.g., Norton and Friedman, 1985; Friedman and Norton, 1990; Hurwitz et al., 2007); however, there are no comprehensive DOI of original article: 10.1016/j.jvolgeores.2003.12.012. ⁎ Corresponding author. Tel.: + 1 303 541 3079. E-mail address: [email protected] (R.B. McCleskey). 0377-0273/$ – see front matter. Published by Elsevier B.V. doi:10.1016/j.jvolgeores.2010.05.004

chemical surveys that include discharge measurements allowing for the identification of sources, loads, and attenuation of trace elements in the Gibbon River. Several trace elements of ecologic importance have elevated concentrations in the Gibbon River, including As and Hg. Geothermal As from YNP causes high As concentrations in the Madison and Missouri Rivers in Montana and Wyoming (Nimick et al., 1998). This is of concern to water managers because some of this water is used for domestic and municipal water supply. Geothermal As in the Gibbon River has been studied previously (Thompson, 1979; Stauffer et al., 1980). Thompson (1979) studied As and F in the Upper Madison River System, including the Gibbon River, and found that Norris Geyser Basin is the primary source of As in the Gibbon River. Working with a small dataset and no discharge measurements, Stauffer et al. (1980) reported that most of the As flux in the Gibbon River drainage basin was precipitated or sorbed prior to the Gibbon River's confluence with the Firehole River at Madison Junction. The diel behavior of Hg has been studied in the Madison River (Nimick et al., 2007), but this study did not identify Hg sources or attenuation within the watershed. The source and fate of other trace metals, including Al, Fe, Mn, Hg, Zn, REEs, Ba, Be, Mo, Sb, Tl, and W, in the Gibbon River have not been previously studied. The purpose of this study was to quantify trace element loads, identify their sources, and identify processes of attenuation and transformation in the Gibbon River. This objective was accomplished

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Table 1 Location, discharge, pH, specific conductance, and trace element chemistry of synoptic samples. River Reach

Sample IDa

Upstream from NGB

Solfatara Creek (I1) Gibbon River at Museum of the National Park Ranger (G2) Realgar Creek (I2) Hazle Lake Drainage (I3) Gibbon River upstream from Tantalus Creek (G3) Tantalus Creek (I4) Gibbon River upstream from Flood Creek (G4) Flood Creek (I5) Southwest drainage from The Gap (I6) Gibbon River downstream from The Gap Inflow (G5) Gibbon River downstream from The Gap Inflow (G6) Unnamed Tributary (I7) Gibbon River at Elk Park (G7) Gibbon River downstream from Chocolate Pots (G8) Gibbon River downstream from Gibbon Geyser Basin (G9) Secret Valley Creek (I8) Gibbon River downstream from Secret Valley Creek (G10) Gibbon River downstream from Canyon Creek (G11) Gibbon River at gage (G12) Beryl Spring Terrace Spring drainage channel

NGB

CP GGB LGR

Downstream

Collection

Distance (km)

Date

Dischargeb (m3/s)

pH

SC (μS/cm)

Fraction

Al (mg/L)

As(T) (mg/L)

As(III) (mg/L)

B (mg/L)

Ba (mg/L)

0.1 0.7

9/12/2006 9/12/2006

0.73 ± 0.04 1.29 ± 0.06

6.96 6.88

84 118

Dissolved Dissolved

0.011 0.039

0.001 0.004

b0.001 b0.001

0.045 0.065

0.005 0.006

2.0 2.4 2.6

9/12/2006 9/12/2006 9/12/2006

0.0037±0.0007 0.016 ± 0.003 1.32±0.01

3.05 3.25 6.80

2330 1462 169

2.9 3.6

9/14/2006 9/13/2006

0.11±0.01 1.45 ± 0.12

3.02 6.68

2290 315

3.7 4.4 4.7

9/13/2006 9/13/2006 9/13/2006

0.067 ± 0.005 0.0045±0.0001 1.37 ± 0.21

7.11 3.18 —

615 1930 337

Dissolved Dissolved Dissolved Total Dissolved Dissolved Total Dissolved Dissolved Dissolved

3.65 3.55 0.183 0.264 2.59 0.338 0.443 0.350 2.18 —

1.52 0.475 0.031 0.033 1.79 0.151 0.165 0.098 1.37 —

0.035 0.041 0.009 — 0.029 0.009 — 0.003 0.088 —

8.06 3.17 0.278 0.294 7.63 0.860 0.847 1.03 6.69 —

0.111 0.047 0.009 0.010 0.083 0.016 0.016 0.010 0.134 —

5.1

9/13/2006

1.44 ± 0.15

6.83

347

5.5 6.1

9/13/2006 9/13/2006

0.0071±0.0004 1.41±0.07

8.41 6.99

1540 352

8.2

9/14/2006

1.66 ± 0.08

6.99

393

12.3

9/14/2006

1.99 ± 0.10

6.97

398

18.2 18.3

9/14/2006 9/14/2006

0.031±0.005 2.21±0.18

7.24 7.00

197 390

20.4

9/14/2006

2.36 ± 0.12

7.1a

380

28.7

9/14/2006

2.49 ± 0.15

7.20

429

13.5 27

9/14/2006 9/17/2008

6.67 8.86

2040 1396

Dissolved Total Dissolved Dissolved Total Dissolved Total Dissolved Total Dissolved Dissolved Total Dissolved Total Dissolved Total Dissolved Dissolved Total

0.297 0.397 0.051 0.227 0.362 0.308 0.375 0.222 0.277 0.223 0.240 0.299 0.232 0.292 0.241 0.282 0.190 0.038 0.016

0.155 0.177 0.793 0.149 0.180 0.163 0.177 0.157 0.172 0.0005 0.149 0.163 0.134 0.151 0.142 0.142 2.79 0.18 0.180

0.007 — 0.012 0.009 — 0.005 — 0.005 — b0.001 0.003 — 0.002 — 0.002 — — — —

0.979 1.09 4.96 0.975 1.10 1.06 1.19 0.885 1.07 b0.007 0.893 1.05 0.841 0.948 0.787 0.919 7.41 1.12 1.18

0.016 0.020 0.005 0.015 0.019 0.017 0.021 0.012 0.016 0.003 0.011 0.015 0.010 0.013 0.009 0.012 0.001 0.001 0.002

— —

a

Location on Fig. 1, Part 1 of this volume. Qualitative uncertainty indicated by ±. —, no data or not measured.

b

by collecting water samples and discharge measurements from the Gibbon River and its major tributaries around Norris Geyser Basin under low-flow conditions in September 2006. 2. Study area and sample locations A detailed map and a description of the sample locations and geology are found in Part I (McCleskey et al., 2010). Nineteen water samples were collected along a 28.7 km reach of the Gibbon River beginning upstream from Norris Geyser Basin and ending at the U.S. Geological Survey streamflow-gaging station (06037100) at Madison Junction. Eleven samples (G2–G12) were collected from the Gibbon River and eight samples (I1–I8) were collected from inflows. Seven of the inflow samples were collected from the Norris Geyser Basin reach and one sample was collected from Secret Valley Creek in the lower Gibbon River reach. 3. Methods A complete description of the discharge measurements, waterquality sampling, and quantification of loads can be found in Part I (McCleskey et al., 2010). Water temperature, pH, and specific conductance were measured at each sampling site. Water-quality samples were collected from the Gibbon River using a DH-81 depth-integrating sampler in approximately equal-width increments across the river. The water was composited on-site in a 4-L high-density polyethylene (HDPE) bottle, and dissolved splits were filtered by pumping the sample water through a 142-mm diameter plate filter with a 0.1-μm pore-size tortuous path filter membrane. Total recover-

able samples were unfiltered and were collected by decanting directly from the 4-L bottle. Because the inflows were smaller and thought to be well-mixed, water-quality samples were collected by pumping water directly from the source. Sample splits were preserved on-site using the methods described by Ball et al. (2006). Trace-metal concentrations were determined using a Perkin Elmer (Sciex Elan 6000) inductively coupled plasma-mass spectrometer (ICP-MS) using a method similar to that described in Garbarino and Taylor (1995) and Taylor (2001) and a Leeman Labs (DRE) inductively coupled plasma–atomic emission spectrometer (ICP-AES) (Garbarino and Taylor, 1979). Mercury concentrations were determined by the method described in Roth, et al. (2001) using a PS Analytical Merlin Cold Vapor–Atomic Fluorescence Spectrometer System. Iron redox species were determined using a modification of the FerroZine colorimetric method (Stookey, 1970; To et al., 1999) with a Hewlett Packard 8453 diode array UV/VIS spectrophotometer. Arsenic and Sb redox species were determined using a method similar to that of McCleskey et al. (2003) with a Perkin Elmer hydride generation atomic absorption spectrometer system (AAnalyst 300 and FIAS 100). Double-distilled de-ionized water and redistilled acids using a sub-boiling purification technique (Kuehner et al., 1972) were used in all standard preparations. For ICP-MS, external standards, blanks, sample dilutions, and spiking solutions were made with commercial trace analysis grade elemental standards. Mercury standards were prepared gravimetrically from semiconductor grade 99.9995% purity HgCl 2. Many of the quality assurance-quality control methods described by McCleskey et al. (2004) including use of USGS standard reference water samples (SRWS) as independent quality control standards and analyzing the

R.B. McCleskey et al. / Journal of Volcanology and Geothermal Research 196 (2010) 139–155

Sample IDa

(I1) (G2) (I2) (I3) (G3) (I4) (G4) (I5) (I6)

Br (mg/L)

Be (µg/L)

Cd (µg/L)

Ce (µg/L)

b0.05 b0.05

0.22 0.60

0.110 0.050

0.035 0.061

1.63 0.58 0.05 — 2.03 0.17 — 0.20 1.43 —

2.10 2.30 0.63 0.65 1.90 0.79 0.84 2.70 2.60 —

0.069 0.201 0.004 0.010 0.098 0.003 0.007 0.048 0.049 —

0.18 — 0.99 0.19 — 0.20 — 0.19 — b0.05 0.18 — 0.17 — 0.15 — 1.66 0.20 —

0.86 0.90 2.10 0.74 0.86 1.20 1.30 1.70 1.80 6.70 1.70 1.80 1.30 1.60 2.0 2.0 1.0 4.23 5.36

0.006 0.009 0.125 0.003 0.003 0.001 0.006 0.004 0.005 0.009 0.008 0.016 0.004 0.012 0.004 0.017 b1 b0.02 b0.02

Co (µg/L)

Cr (µg/L)

Cs (µg/L)

0.004 0.007

0.13 0.16

2.23 3.85

6.99 6.31 0.295 0.589 8.29 0.557 1.21 0.399 3.53 —

b 0.003 0.085 0.010 0.015 0.025 0.012 0.016 b 0.003 0.112 —

b0.05 b0.05 0.14 0.16 b0.05 0.20 b0.05 b0.05 b0.05 —

0.369 0.964 0.142 0.185 0.866 0.391 0.757 0.287 0.586 0.062 0.193 0.472 0.131 0.415 0.168 0.329 — 0.258 0.759

0.011 0.016 b 0.003 0.008 0.014 0.009 0.014 b 0.003 0.005 b 0.003 b 0.003 0.007 b 0.003 b 0.003 b 0.003 b 0.003 b7 0.034 0.044

0.11 0.14 b0.05 b0.05 b0.05 0.14 b0.05 0.09 b0.05 0.15 0.12 b0.05 0.09 b0.05 0.08 b0.05 b2 b0.3 b0.3

141

Cu (µg/L)

Dy (µg/L)

Er (µg/L)

Eu (µg/L)

Fe(T) (mg/L)

Fe(II) (mg/L)

Gd (µg/L)

Hg (ng/L)

b 0.1 0.2

0.015 0.021

0.011 0.016

0.0002 0.0002

0.027 0.054

0.015 0.029

0.012 0.017

1.6 2.0

370 145 11.5 11.5 378 41.1 42.3 17.9 250 —

0.4 1.1 0.1 0.5 0.8 b 0.1 0.2 b 0.1 0.2 —

0.976 0.757 0.040 0.082 1.23 0.091 0.173 0.087 0.939 —

0.538 0.458 0.028 0.050 0.749 0.056 0.100 0.060 0.540 —

0.113 0.060 0.0027 0.0044 0.084 0.0054 0.011 0.0031 0.103 —

1.10 1.06 0.097 0.190 1.27 0.122 0.263 0.186 3.09 —

0.296 0.491 0.054 — 0.203 0.048 — 0.131 1.80 —

0.930 0.649 0.037 0.071 1.25 0.082 0.157 0.080 0.932 —

22 38 6.7 — 17 12 — 47 18 13

44.6 44.1 205 43.6 43.6 46.7 46.2 42.8 42.6 1.64 41.3 41.1 38.7 37.9 36.9 36.7 — 28.9 29.6

0.1 5.2 0.3 b 0.1 0.2 b 0.1 0.3 b 0.1 1.2 0.1 b 0.1 0.2 0.2 0.7 0.2 0.3 b3 0.2 0.2

0.066 0.153 0.039 0.034 0.145 0.076 0.138 0.051 0.094 0.027 0.039 0.086 0.029 0.080 0.043 0.071 — 0.028 0.069

0.040 0.085 0.028 0.021 0.081 0.049 0.084 0.033 0.056 0.022 0.025 0.056 0.019 0.051 0.029 0.047 — 0.016 0.045

0.0039 0.0086 0.0015 0.0016 0.0075 0.0038 0.0073 0.0030 0.0064 0.0003 0.0025 0.0055 0.0014 0.0042 0.0019 0.0031 — 0.0013 0.0025

0.082 0.325 0.062 0.034 0.312 0.204 0.368 0.121 0.293 0.044 0.069 0.270 0.05 0.246 0.098 0.212 0.006 0.005 0.007

0.036 — 0.061 0.022 — 0.099 — 0.064 — 0.039 0.047 — 0.037 — 0.051 — 0.006 0.006 —

0.061 0.135 0.033 0.031 0.114 0.062 0.121 0.046 0.082 0.021 0.034 0.074 0.025 0.061 0.032 0.059 — 0.022 0.065

15 — 27 12 — 4.2 — 3.8 — 0.9 3.1 — 2.9 — 3.6 — 71 8.4 —

(G5) (G6) (I7) (G7) (G8) (G9) (I8) (G10) (G11) (G12)

(continued on next page)

samples by multiple methods (i.e., ICP-AES, ICP-MS, HGAAS) were utilized. For analyte concentrations greater than 10 times the method detection limit, all the measurements were within ± 8% of the most probable value (Woodworth and Connor, 2002, 2003). For analytes between the method detection limit and less than 10 times the method detection, the measurements were within ± 20% of the most probable value. The effect of geothermal discharge on solutes in the Gibbon River was studied by evaluation of 5 reaches: upstream from Norris Geyser Basin (NGB) (sites G1, G2, and I1), NGB (sites G3–G7 and I2–I7), Chocolate Pots (CP) (site G8), Gibbon Geyser Basin (GGB) (site G9); and lower Gibbon River (LGR) (sites G10–G12 and I8). A detailed description of the load calculations is in Part I (McCleskey et al., 2010). 4. Results and discussion Table 1 contains the discharge, pH, specific conductance, and trace element concentrations for the Gibbon River and inflows samples. For nearly all trace elements, the minimum concentrations are upstream from Norris Geyser Basin and the maximum concentrations are found just downstream from one of the geyser basin sources. Part I (McCleskey et al., 2010) contains collection date, discharge, pH, specific conductance, temperature, and results for the major ion water analyses for the same samples. 4.1. Trace element composition of a river affected by geothermal discharges To identify the effects of geothermal discharge, we compared trace element concentrations in the Gibbon River (Table 1) to global

concentrations typically found in major rivers (Fig. 1). The global ranges of trace element concentrations are based on some of the largest rivers in the world (Gaillardet et al., 2004). Although the global concentration ranges are based on rivers of different order, hydrology, and geology than the Gibbon River, they provide a framework for interpretation. Solutes from the Gibbon River can be grouped generally into categories of those below, within, overlapping and above, or greater than the global concentration range (Fig. 1). First, Ba, Co, Cr, Cu, Ni, and V are at or below global ranges. Because Co, Cr, Cu, Ni, and V concentrations are very low, it is reasonable to conclude that they are present at low concentrations in geothermal features within the Gibbon River watershed and further discussion on their sources and fate is not warranted. Analyses of geothermal waters from Norris and Gibbon Geyser Basin reveal that the concentrations of Co, Cr, Cu, Ni, and V are typically very low (b2 µg/L; Ball et al., 2001a,b, 2006; McCleskey et al., 2005). Barium concentrations are on the low end of the global range, most likely because of the elevated SO4 in some geothermal features and the low solubility of barite. The next group of solutes is present at concentrations within the global range (Cd, Ce, Fe, La, Lu, Nd, Pb, Re, Sm, Sr, Th, Tm, W, Zn, and Zr). A small group of solutes overlaps or exceeds the global range (Al, Dy, Er, Ho, Mn, Sb, U, Y, and Yb). It should be noted that all the rare earth elements (REEs) are at the high end of the range, if not higher than the range. Finally, there are solutes that are greater than the global range (As, B, Be, Cs, Li, Mo, Rb, and Tl). Many of the solutes in the last two groups derive their elevated concentrations from geothermal sources. Increases in Sb (47-fold), As (38-fold), W (19fold), B (12-fold), Cs (9.6-fold), and Li (6.8-fold) concentrations were

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Table 1 (continued)

Sample IDa (I1) (G2) (I2) (I3) (G3) (I4) (G4) (I5) (I6)

CH3-Hg (ng/L)

Ho (µg/L)

La (µg/L)

Li (mg/L)

Lu (µg/L)

Mn (mg/L)

Mo (µg/L)

Nd (µg/L)

0.04 0.05

0.003 0.005

0.020 0.035

0.039 0.062

0.002 0.002

0.05 0.23 0.10 — 0.04 0.12 — 0.22 0.06 0.12

0.189 0.156 0.009 0.016 0.242 0.019 0.037 0.019 0.169 —

3.29 3.15 0.144 0.298 2.94 0.238 0.520 0.260 1.20 —

2.72 1.16 0.133 0.146 3.93 0.383 0.403 0.385 2.66 —

0.12 — 0.36 0.06 — 0.13 — 0.15 — 0.04 0.10

0.014 0.029 0.009 0.007 0.028 0.016 0.027 0.011 0.020 0.007 0.008 0.017 0.006 0.017 0.010 0.015 — 0.006 0.014

0.162 0.431 0.079 0.086 0.393 0.171 0.345 0.145 0.294 0.044 0.107 0.243 0.077 0.217 0.095 0.176 — 0.116 0.371

0.408 0.425 1.93 0.405 0.422 0.453 0.488 0.461 0.488 0.047 0.455 0.489 0.428 0.479 0.421 0.472 5.52 0.881 0.834

Ni (µg/L)

0.052 0.045

2.3 2.0

0.029 0.049

0.010 0.169

0.056 0.050 0.003 0.007 0.078 0.007 0.012 0.008 0.055 —

0.043 0.133 0.057 0.060 0.088 0.063 0.064 0.096 0.075 —

b 0.5 2.8 2.0 2.0 49.6 6.3 6.5 13.7 25.6 —

4.07 3.10 0.162 0.301 5.03 0.339 0.693 0.274 3.31 —

0.005 0.012 0.003 0.003 0.011 0.006 0.011 0.004 0.007 0.004 0.004 0.007 0.003 0.006 0.004 0.006 — 0.002 0.004

0.062 0.063 0.015 0.055 0.056 0.094 0.095 0.040 0.041 0.020 0.031 0.033 0.024 0.027 0.020 0.023 0.02 0.008 0.017

7.0 7.0 94.6 7.8 7.9 8.3 8.4 8.0 8.0 0.2 8.5 8.5 8.1 8.1 13.1 13.1 13.6 41.0 41.6

0.235 0.571 0.098 0.121 0.529 0.251 0.476 0.196 0.368 0.056 0.140 0.296 0.096 0.276 0.124 0.218 — 0.109 0.337

Pb (µg/L)

Pr (µg/L)

Rb (µg/L)

Sb(T) (µg/L)

Sb(III) (µg/L)

0.016 0.013

0.006 0.011

12.2 22.4

0.038 0.104

b 0.5 b 0.5

0.150 0.272 0.083 0.286 0.630 0.035 0.120 0.062 0.449 —

0.384 0.833 0.026 0.106 0.878 0.062 0.231 0.055 0.252 —

0.990 0.815 0.040 0.080 1.16 0.080 0.161 0.068 0.659 —

415 241 33.6 33.3 486 67.7 67.4 65.1 252 —

37.4 14.3 0.605 0.652 53.4 6.31 6.65 3.29 49.2 —

0.7 b 0.5 b 0.5

0.120 0.874 0.277 0.047 0.160 0.151 0.238 b0.003 1.86 b0.003 b0.003 0.142 b0.003 0.252 b0.003 0.161 b2 0.127 0.237

0.059 0.181 0.110 0.036 0.148 0.049 0.147 0.023 0.137 0.033 0.015 0.090 0.012 0.106 0.025 0.105 b8 0.346 0.600

0.055 0.137 0.023 0.029 0.128 0.062 0.113 0.046 0.091 0.012 0.032 0.074 0.022 0.069 0.030 0.055 — 0.028 0.094

70.9 69.4 219 69.1 69.2 74.3 74.3 69.2 69.0 22.1 68.3 67.3 65.5 64.7 65.4 65.3 — 191 189

6.60 6.64 35.3 6.04 6.32 6.13 6.33 5.87 5.87 0.015 5.69 5.69 5.23 5.21 4.92 4.80 56.8 0.142 0.194

b 0.5

b 0.5 b 0.5 b 0.5 b 0.5

(G5) (G6) (I7) (G7) (G8) (G9) (I8) (G10) (G11) (G12)

0.15 — 0.09 — — — —

observed in the Gibbon River study reach (between sites G2 and G12). 4.2. Trace element sources, loads, and fate Many of the trace elements associated with geothermal waters also have substantial mass loads in the Gibbon River with B N Li N Al N Br N As (Table 2). Increases in solute loads between sample sites along the Gibbon River suggest that there are solute sources, either inflows or an instream geochemical process, in the reach. Decreases in dissolved solute loads may indicate attenuation through precipitation as suspended particles, sorption onto suspended particles, or outflows (to ground water) in the reach. Furthermore, diel variations in trace element concentrations (e.g., Gammons et al., 2005a,b; Nimick et al., 2005, 2007) may occur in the Gibbon River and its effects on our study are unknown. However, because most trace elements are not attenuated in the Gibbon River, the loading from the geothermal areas is thought to be larger than the diel effects. For each river reach, the net solute load gain or loss was quantified, but more closely spaced samples and diel studies would be required for more comprehensive interpretation. The percentage of the total trace element mass entering the Gibbon River was determined for each river reach (Fig. 2). Most of the Al, As, B, Ba, Br, Cs, Hg, Li, Rb, Sb, Tl, W, and REE loads enter the Gibbon River along the NGB reach. The greater part of the Sr load is present in the Gibbon River upstream from NGB, the bulk of the Fe and Mn loads comes from the CP reach, and the LGR reach is the primary source of Be and Mo. It was demonstrated in Part I (McCleskey et al., 2010) that the major solutes were not substantially attenuated or transformed to particulates

b 0.5 b 0.5 b 0.5 b 0.5 b 0.5 b 0.5 b 0.5 b 0.5 b 0.5 — —

in the Gibbon River. To identify the trace elements that are attenuated or transformed to particulates in the Gibbon River, the percentage of the dissolved load at the gage lost to instream processes (Fig. 3) was estimated using Eq. (1): ððloadCI −loadI Þ = loadCI Þ × 100

ð1Þ

where loadCI is the dissolved cumulative instream load and loadI is the dissolved instream load at the gage (Kimball et al., 2002, 2006, 2007). The load error (%) (McKinnon, 2002) was calculated using Eq. (2): 100 ×

qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi Qa2 ΔCa2 + Ca2 ΔQa2 = ðloadCI Þ

ð2Þ

where Qa is the discharge, Ca is the concentration, ΔQa is the discharge error, ΔCa is the concentration error, and loadCI is the dissolved cumulative instream load at the gage. Qualitative discharges errors were assigned (Table 1) based on characteristics of the measurement section and velocity distribution. The load error was determined for the entire river reach. The concentration error, ΔCa, is variable depending on the solute, its concentration, and the analytical method utilized. For solutes with concentrations greater than 10 times the method detection limit, ΔCa is about 3%, which is an estimate of our lab's analytical precision. Therefore, solutes with 5% or less of their dissolved load lost to instream processes (Fig. 3) in the Gibbon River (i.e., Mo, Li, B, Rb, Cs, Sr, and W) are not significantly attenuated or transformed to particulates because the amount of dissolved solute lost is less than the load error. However, ΔCa could be as large as 10% when considering both sampling variation and analytical precision and accuracy. Therefore, the error in the load estimate may be

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Sample IDa

(I1) (G2) (I2) (I3) (G3) (I4) (G4) (I5) (I6)

Se (µg/L)

Sm (µg/L)

Sr (mg/L)

Tb (µg/L)

Th (µg/L)

b 0.06 b 0.06

0.008 0.013

0.017 0.016

0.002 0.003

0.005 0.010

b 0.06 b 0.06 b 0.06 b 0.06 b 0.06 b 0.06 b 0.06 b 0.06 b 0.06 —

0.936 0.666 0.038 0.071 1.20 0.079 0.163 0.076 0.946 —

0.025 0.071 0.022 0.024 0.016 0.025 0.023 0.026 0.017 —

0.158 0.112 0.006 0.013 0.193 0.015 0.026 0.011 0.159 —

b 0.06 b 0.06 b 0.06 b 0.06 b 0.06 b 0.06 b 0.06 b 0.06 b 0.06 b 0.06 b 0.06 b 0.06 b 0.06 b 0.06 b 0.06 b 0.06 b 30 b 0.06 b 0.06

0.057 0.137 0.030 0.032 0.121 0.065 0.111 0.046 0.088 0.014 0.033 0.075 0.022 0.068 0.029 0.054 — 0.022 0.067

0.024 0.029 0.012 0.024 0.028 0.025 0.030 0.022 0.028 0.020 0.023 0.028 0.022 0.026 0.023 0.028 0.007 0.023 0.025

0.010 0.024 0.005 0.005 0.021 0.012 0.019 0.008 0.015 0.003 0.006 0.013 0.004 0.012 0.006 0.010 — 0.005 0.010

Tl (µg/L)

Tm (µg/L)

U (µg/L)

V (µg/L)

W (µg/L)

0.008 0.015

0.002 0.002

0.05 0.18

0.08 0.08

0.312 0.102 0.029 0.065 0.196 0.043 0.095 b0.03 0.219 —

0.363 0.089 0.033 0.037 0.942 0.126 0.113 b0.06 0.531 —

0.072 0.058 0.004 0.008 0.105 0.008 0.015 0.009 0.072 —

0.15 0.09 0.19 0.23 0.37 0.19 0.23 1.45 0.36 —

0.029 0.081 0.030 0.017 0.077 0.044 0.076 0.026 0.060 0.014 0.016 0.065 0.014 0.049 0.021 0.045 — 0.033 0.052

0.100 0.120 0.151 0.098 0.118 0.106 0.110 0.072 0.075 0.011 0.067 0.069 0.062 0.066 0.050 0.055 — 0.573 0.523

0.006 0.013 0.004 0.003 0.012 0.007 0.011 0.005 0.008 0.003 0.004 0.008 0.003 0.008 0.005 0.006 — 0.002 0.006

0.21 0.26 0.17 0.23 0.27 0.24 0.29 0.37 0.39 0.81 0.55 0.55 0.60 0.59 1.34 1.32 — 8.27 8.51

143

Y (µg/L)

Yb (µg/L)

Zn (µg/L)

Zr (µg/L)

0.03 0.28

0.12 0.18

0.010 0.015

0.96 1.76

0.049 0.125

1.56 1.01 0.10 0.19 1.65 0.18 0.05 0.41 0.80 —

25.5 18.2 0.89 0.97 43.5 3.88 4.70 6.23 25.4 —

5.01 4.34 0.28 0.55 7.51 0.56 1.04 0.60 5.27 —

0.414 0.368 0.025 0.045 0.542 0.049 0.085 0.049 0.445 —

9.82 8.07 2.02 9.78 20.8 2.23 6.36 2.47 18.1 —

0.354 0.241 0.072 0.894 0.558 0.212 0.308 0.349 0.342 —

b0.02 b0.02 0.96 b0.02 b0.02 b0.02 b0.02 b0.02 b0.02 0.07 b0.02 0.11 b0.02 b0.02 b0.02 0.16 b5 0.69 0.84

4.07 5.15 81.1 4.57 6.09 5.60 6.16 6.43 6.83 0.03 6.30 6.80 5.71 6.25 5.28 5.46 — b0.4 b0.4

0.40 0.90 0.30 0.23 0.83 0.49 0.84 0.35 0.60 0.26 0.28 0.57 0.22 0.55 0.35 0.55 — 0.20 0.46

0.035 0.074 0.023 0.020 0.076 0.045 0.075 0.031 0.053 0.024 0.023 0.047 0.017 0.047 0.028 0.048 — 0.014 0.037

2.52 6.43 1.54 1.78 5.09 2.54 6.70 1.75 8.68 1.74 1.92 4.94 1.24 4.89 1.80 9.87 b4 2.52 5.08

0.219 0.523 1.09 0.219 0.459 0.106 0.630 0.110 2.40 0.177 0.231 1.20 0.065 0.567 0.130 0.751 — 0.300 0.406

(G5) (G6) (I7)

(G8) (G9) (I8) (G10) (G11) (G12)

comparable to trace elements that have 5 to 10% of their dissolved load attenuated or transformed to particulates. Furthermore, small changes in load may be the result of loss of water to the hyporheic zone and not dissolved solute loss as is likely the case in the meadows near Elk Park (G7, 6.1 km). The calculated instream load for conservative constituents, such as Cl (Part I — McCleskey et al., 2010), decreased near Elk Park because of loss of water to the subsurface which was not measured. Solutes with more than 10% of their dissolved load attenuated or transformed to particulates are considered to be non-conservative because the amount of loss is greater than the load error. However, it should be noted that many of the “nonconservative” solutes undergo transformation and are transported downstream as suspended particles. For solutes that were minimally (b10%) attenuated in Fig. 3 (As, B, Br, Cs, Li, Mo, Rb, Sb, Sr, and W), element/Cl mass ratios were plotted against downstream distance (Fig. 4). Because Cl is elevated in many geothermal sources and is conservative (see Part I — McCleskey et al., 2010), plotting the Cl mass ratios against downstream distance can indicate the solute source and the effects of mixing of waters of different chemistries. The largest changes in individual solute to Cl mass ratios were a result of the Tantalus Creek inflow (I4, 2.9 km). Many of the mass ratios decrease from upstream from NGB to downstream from Tantalus Creek because the concentration of Cl is higher than most solutes in NGB geothermal waters. However, it is noteworthy that the As and Sb to Cl ratios substantially increase (Fig. 4) because As and Sb concentrations are extremely low in the waters upstream from NGB and are relatively high in geothermal waters from NGB. Downstream from the NGB reach, the mass ratios of As, B, Br, Cs, Li, Rb, and Sb to Cl are nearly constant (Fig. 4). The mostly constant

solute to Cl ratios suggest that these solutes, including Cl, come from sources with similar ratios and confirm that they do not undergo detectable attenuation or transformation. Downstream from the NGB reach, Mo and W to Cl ratios increase (Fig. 4) because there are inflows with higher solute to Cl ratios. Even though B, Cs, Li, Rb, and Br are from geothermal sources (Fig. 1), it has been demonstrated that their primary source is the NGB reach (Fig. 2) and that they are not attenuated (Fig. 3) in the Gibbon River; therefore, more detailed discussions about these solutes are not necessary. 4.2.1. Aluminum The low-pH inflows (I2, I3, I4, and I6) from NGB contributed 53% of the Al load to the Gibbon River (Fig. 2). Tantalus Creek (2.9 km) is the largest single contributor of the Al load to the Gibbon River, providing 52% of the dissolved load at the gage (Fig. 5). Between sites G2 (0.7 km) and G3 (2.6 km), there is an unsampled diffuse source of Al (10.5 kg/day), which accounts for nearly 23% of the Al loading in the NGB reach. The primary control on the concentration and speciation of dissolved Al in natural waters is pH, and Al is generally insoluble at circumneutral pH (Nordstrom, 2008). Nordstrom and Ball (1986) explained that Al begins to hydrolyze and precipitate when the pH of an acid, aluminum-rich solution approaches the pK1 for Al hydrolysis (5.0). However, when the low-pH inflows from NGB mix with the Gibbon River and are neutralized, 70 to 90% of the Al remained dissolved in solution at 0.2–0.4 mg/L, which is atypical for circumneutral pH waters. For some natural waters amorphous Al(OH)3, gibbsite, or halloysite may control Al concentrations (e.g., Hem et al., 1973; Nordstrom and Ball, 1986). Speciation computations using WATEQ4F (Ball and Nordstrom, 1991) revealed that Gibbon River water is

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of the meadows at Elk Park (G7, 6.1 km) and GGB (G9, 12.3 km), most of the particulate Al remains suspended. Hence, there is little attenuation of Al but some conversion of dissolved to particulate Al.

Fig. 1. Plot of the global range of trace element concentrations based on some of the largest rivers in the world (Gaillardet et al., 2004) and the dissolved concentration range for the Gibbon River.

uniformly undersaturated with respect to amorphous Al(OH)3, near saturation with respect to microcrystalline gibbsite, and supersaturated with respect to halloysite in the Gibbon River (Fig. 6). Fluoride concentrations (see Part I — McCleskey et al., 2010) are more than 10 times the Al concentrations in the Gibbon River, and 93 to 98% of the dissolved Al is complexed with F (Fig. 6). The remaining dissolved Al is present as OH complexes (data not shown). These results provide evidence that elevated F concentrations are responsible for maintaining Al at concentrations that appear to exceed Al solubility. As a consequence of Al–F complexing, more than 70% of the Al entering the Gibbon River reaches the Madison River as aqueous F complexes. The particulate Al load is 15–35% of the total Al load and with the exception Table 2 Dissolved trace element loads on September 12, 2009 in the Gibbon River at the USGS gage (06037100). Constituent

g/day

Constituent

g/day

Constituent

g/day

B Li Al Br As Fe Rb Cs Sr Mn Mo Ba W

170,000 90,000 52,000 33,000 30,000 21,000 14,000 7900 4900 4400 2700 1900 1100

Sb Be Zn U Y Ce Zr Nd La Tl Dy Gd Pr

1100 440 380 300 77 36 27 27 21 11 9 7 7

Sm Er Yb Pb Th Ho Tb Tm Lu Cd Hg Eu Re

6 6 6 5 5 2 1.3 1 0.9 0.9 0.8 0.5 0.3

4.2.2. Iron Iron is important geochemically because it affects the redox state and sorption of other solutes depending on its concentration, redox state, and form (dissolved, colloidal, or particulate) (e.g., Dzombak and Morel, 1990; Emett and Khoe, 2001). Fig. 7 is a plot of total dissolved Fe (Fe(T)) and Fe(II) concentrations and loads against downstream distance. The low-pH (b3.5) inflows from NGB contain up to 3 mg/L dissolved Fe and Fe(II)/Fe(T) ratios range from 0.16 to 0.58. Because the low-pH waters in NGB originate primarily from the oxidation of sulfur rather than pyrite and little Fe leaches from silicic volcanic rocks, the NGB inflows contain considerably less Fe than many acid-rock drainages with similar pH (Nordstrom and Alpers, 1999). In the Gibbon River, 59% of the dissolved Fe(T) is transformed or attenuated by instream processes (Fig. 3). At circumneutral pH, the Fe(II) oxidation rate is rapid and Fe hydrolysis and precipitation are expected to occur (e.g., Hem and Cropper, 1959; Singer and Stumm, 1970; Sung and Morgan, 1980). Once the low-pH waters from NGB are neutralized by Gibbon River water, Fe(II) oxidation and precipitation are observed within one kilometer (Fig. 7). Ninety-eight percent of the Fe exists as suspended Fe(III) particles at Elk Park, the most downstream site in the NGB reach. Saturation indices for ferrihydrite are consistently an order of magnitude or more supersaturated, indicating Fe colloids are likely forming along the lower portion of the NGB reach. The largest increase in dissolved Fe load is in the CP reach (Fig. 7C) where Fe(II)-rich springs discharge into the Gibbon River (Allen and Day, 1935). Hot springs in the CP reach have been found to contain up to 9.5 mg/L dissolved Fe(II) and precipitate ferrihydrite (Pierson et al., 1999; Pierson and Parenteau, 2000). Downstream from CP in the GGB reach, additional Fe oxidation and precipitation and some sedimentation of Fe occur (Fig. 7). Despite this evident oxidation, hydrolysis, and conversion to particulate form, most of the Fe remains in the water column and reaches the Madison River as suspended particles. Dissolved Fe concentrations in the Gibbon River may have varied due to diel processes (Gammons et al., 2005a); however, the Fe(III) photoreduction is expected to proceed slowly because the pH of the Gibbon River is well above the pH range of 2 to 3.5 where the maximum photoreduction rate occurs (David and David, 1976). Furthermore, the rate of Fe(II) oxidation is greater than the rate of Fe photoreduction at circumneutral pH (McKnight et al., 2001). Because the total recoverable Fe (dissolved and suspended particulate) concentration in the Gibbon River is fairly low (b0.37 mg/L), sorbtion to Fe colloids appears to be substantial only for those solutes present in trace concentrations (i.e., Hg and the REEs). Fig. 8 shows the fraction of dissolved As, Sb, Pb, and Cd as a function of the particulate Fe (total recoverable Fe (FeTR)–Fe(T)) concentration. Nearly all of the As and Sb are present in the water column in the dissolved form. As the particulate Fe concentration increases, the dissolved As fraction decreases slightly but Sb does not appear to be affected by particulate Fe (Fig. 8A and B). There is no clear trend for the dissolved fractions of Pb or Cd with respect to particulate Fe (Fig. 8C and D), but the dissolved fraction of Pb is low (b0.3) suggesting sorption to Fe colloids. 4.2.3. Arsenic Many geothermal waters contain high concentrations of As (Nordstrom, 2002; Webster and Nordstrom, 2003) including geothermal waters from YNP (e.g., Gooch and Whitfield, 1888; Stauffer and Thompson, 1984; McCleskey et al., 2005; Ball et al., 2006). Geothermal waters from NGB have some of the highest As concentrations in YNP, where we measured 14.6 mg/L As(T) in an unnamed spring in the Ragged Hills area of NGB in 2008. Total dissolved As concentrations reached a maximum of 0.16 mg/L in the Gibbon River and inflows from NGB contained up to 1.8 mg/L As

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Fig. 2. Percentage of dissolved load at the Gage for selected trace elements from the 5 reaches.

(Fig. 9A). The As load in the Gibbon River and its inflows is shown in Fig. 9B. Nearly 60% of the total As load in the Gibbon River was contributed by inflows in the NGB reach and 16% and 11% of the As load comes from CP and GGB reaches, respectively (Fig. 2). Tantalus Creek (17.5 kg/day) was the largest single contributor of As to the Gibbon River, accounting for nearly 58% of the total As load at the gage (Fig. 9C). Between sites G2 and G3 (0.7–2.6 km), there was an unsampled diffuse source of As (2 kg/day) which accounts for nearly 10% of the As loading in the NGB reach (Fig. 9C). While As generally emerges from hot springs as As(III) (Langner et al., 2001; Nordstrom et al., 2005), the As in the Gibbon River and inflows near the confluence with the Gibbon River existed primarily as As(V) (Fig. 10). Arsenic(V) concentrations were determined by subtracting As(III) concentrations from As(T) concentrations (Table 1). Arsenic(III) oxidizes rapidly after reaching the surface (Gihring et al., 2001; Langner et al., 2001; Inskeep and McDermott,

Fig. 3. Plot of the percentage of the dissolved load attenuated or transformed to particulates in the Gibbon River.

2005) as long as reduced S species (sulfide and thiosulfate), which are inhibitors of inorganic and microbial As oxidation (Cherry et al., 1979; Jackson et al., 2001; D'Imperio et al., 2007), have degassed or oxidized. Hence, the fate of dissolved As in the Gibbon River is controlled by As(V) geochemistry. Concurrent with Fe and Al precipitation, there is some loss of dissolved As (4.5 kg/day or 7% of the total As in the Gibbon River) in the lower parts of the NGB reach (Fig. 9C). The loss of only a small amount of dissolved As may be due to the low particulate Fe concentrations (Fig. 8A), little iron-rich sediments, circumneutral pH, and possible silica coatings on sediments resulting in decreased sorption capacity. Adsorption of As(V) by Fe oxides reaches a maximum at pH 3–4, and gradually decreases as pH increases (Hingston et al., 1971; Anderson et al., 1976). Nonetheless, Stauffer

Fig. 4. Plot of trace element to Cl mass ratio against downstream distance.

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Fig. 5. Plot of Al concentration, load, and change in load against downstream distance.

Fig. 7. Plot of Fe concentration, load, and change in load against downstream distance.

et al. (1980) claimed that “60% or more of the geothermal As flux in the Gibbon River drainage basin is removed by precipitation or sorption processes.” Stauffer et al. (1980) compared Cl/As mole ratios for the Gibbon River at Madison Junction (760) and key indicator springs in both GGB (400 ± 25) and NGB (543 ± 11). Because the Cl/As molar ratio at Madison Junction was much higher, they concluded that much of the geothermal As flux was removed. While it is likely that some of the As precipitated as As–S near the hot spring sources, Stauffer et al. (1980) did not include Flood Creek (1500) and Terrace Spring (815), which contain lower As concentrations than many of the

other inflows. Furthermore, Thompson (1979) concluded that very little of the total load of As at NGB appeared to be precipitated downstream. Downstream from the NGB reach, the Cl/As atomic ratios in the Gibbon River were found to be 840 ± 40 (or As/Cl mass ratio = 0.0025 ± 0.0001, Fig. 4), demonstrating that dissolved As is not significantly attenuated in the Gibbon River. Finally, for most of the river the dissolved As concentrations are about 90% of the total recoverable As concentrations and at the gage 100% of the As is dissolved (Fig. 9A and Table 1), suggesting that only a small amount of As is associated with suspended particulate material. The results of the present study demonstrate that nearly all the As that enters the Gibbon River reaches the Madison River as dissolved As(V), 58% of the As load comes from one tributary, Tantalus Creek, and that only about 7% of the dissolved As is lost to instream processes over 29 km of fluvial transport.

Fig. 6. Plot of saturation index for amorphous Al(OH)3(am), microcrystalline gibbsite(µC), and halloysite and percent of total Al present as F complexes against downstream distance for the Gibbon River samples only.

4.2.4. Antimony Antimony concentrations are elevated in many geothermal features in YNP (Stauffer and Thompson, 1984; Ball et al., 2002, 2006; McCleskey et al., 2005) and the highest Sb concentration we have measured was 0.38 mg/L in a hot spring from Norris Geyser Basin (Ball et al., 2002). Elevated Sb concentrations in the Gibbon River reflect the high Sb concentrations found in the hot springs (Fig. 1). Antimony concentrations reached a maximum of 6.6 µg/L in the Gibbon River and inflows from NGB contained up to 53 µg/L Sb (Fig. 11A). Nearly 70% of the total Sb load in the Gibbon River was contributed by inflows in the NGB reach and 12% and 11% of the Sb load comes from CP and GGB reaches, respectively (Figs. 2 and 11B). Tantalus Creek (0.53 kg/day) was the largest single contributor of Sb to the Gibbon River, accounting for nearly 50% of the total Sb load at the gage (Fig. 11C). Unlike As, just downstream from Tantalus Creek there was a substantial source of Sb (0.2 kg/day) that was not accounted for by sampled inflows (Fig. 11C). Similar to other geothermal areas around the world (Sakamoto et al., 1988), there is

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Fig. 8. Plot of the fraction of dissolved As, Sb, Pb, and Cd concentrations against particulate Fe concentration.

a positive relationship between As and Sb in the Gibbon River watershed (Fig. 12). Both As and Sb are found in the rhyolitic rocks in Yellowstone (Stauffer and Thompson, 1984) and Sb is often associated in arsenopyrite minerals (Craw et al., 2004).

The primary processes affecting dissolved Sb are sorption to suspended particulates or precipitation of stibnite (Sb2S3) (Wilson, 2009). Stibnite precipitation is likely near hot spring's sources where high concentrations of sulfide and Sb(III) are present (Wilson, 2009), especially in acid waters. However, nearly all of the Sb in the Gibbon River and its tributaries exist as Sb(V) (Table 1). Antimony is known to sorb onto Fe-oxyhydroxides, but in circumneutral waters this process is inconsequential (Ashley et al., 2006), and Sb(III) adsorption to particulate matter is greater than Sb(V) (Webster and Nordstrom, 2003). Consequently, Sb(V) often behaves conservatively in natural waters (Wilson, 2009) and in the Gibbon River very little Sb is attenuated or transformed to particulates (Fig. 11B). Similar to As, there is a small amount of dissolved Sb loss in the lower part of the

Fig. 9. Plot of As concentration, load, and change in load against downstream distance.

Fig. 10. Plot of dissolved As(V) concentration against dissolved As(T) concentration.

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Fig. 11. Plot of Sb concentration, load, and change in load against downstream distance.

Fig. 13. Plot of Hg concentration, load, and change in load against downstream distance.

NGB reach. However, nearly all of the Sb is in the dissolved phase (Fig. 11A) and Sb is not positively correlated with particulate Fe (Fig. 8B). Hence, nearly all of the Sb that enters the Gibbon River reaches the Madison River as dissolved Sb(V).

the Gibbon River reached a maximum of 13 ng/L just downstream from The Gap inflow (Fig. 13A). Streams in YNP that are not affected by geothermal inputs such as Secret Valley Creek contain ≤1 ng/L Hg. The Hg load (Fig. 13B) also reached a maximum in the NGB reach and unlike most other solutes entering the Gibbon River, only 31% of the Hg is accounted for by sampled inflows in the NGB reach (Fig. 13C). Phelps and Buseck (1980) measured soils with anomalously high Hg content that lie along a north–south trend across NGB and they suggest that Hg migration is controlled by a north–south fracture. In addition, McCleskey et al. (2005) measured 1520 ng/L Hg in a mud pot just north of the Gibbon River near this north–south line. It is plausible that this Hg anomaly extends to the north of NGB between sample sites G2 (0.7 km) and G4 (3.6 km). In the NGB reach, about 69% of the Hg (1.1 g/day) in the Gibbon River appears to come from this area and likely enters the Gibbon River via discharge from disperse thermal features. Flood Creek at 3.7 km (I5, 47 ng/L Hg) was the largest surface-water source of Hg to the Gibbon River (Fig. 13C). The Hg in Flood Creek appears to be coming from Nymph Lake and the West Nymph Creek Thermal Area (WNCTA). In September, 2006, we measured 30 ng/L Hg in the main WNCTA drainage, 78 ng/L Hg in the Nymph Lake drainage, and 59 ng/L Hg downstream from their confluence in Flood Creek, about 0.6 km upstream from I5. Sixty-four percent of the dissolved Hg that entered the Gibbon River was either transformed to suspended particles and/or attenuated by sorption to bed sediment and settling of suspended particles with sorbed Hg (Fig. 3). Nearly all of the loss of dissolved Hg occurred in the lower part of the NGB reach and in the CP reach. The substantial decrease in dissolved Hg load occurs in the lower part of NGB and CP reaches where dissolved Fe and Al are forming particulates. Sorption of Hg(II) on a natural Fe-oxyhydroxide precipitate and Al/Si-bearing flocculent material (Kim et al., 2004) may sequester Hg in the Gibbon River. Total recoverable samples were not collected for Hg in 2006; however, a sample collected from Elk Park (G7, 6.1 km) in 2008 contained 6 ng/L total dissolved Hg

4.2.5. Mercury Geothermal features are known sources of Hg (Nriagu, 1989; Barnes and Seward, 1997; King et al., 2006) and elevated Hg concentrations have been measured in YNP soils (Phelps and Buseck, 1980) and in several YNP geothermal waters including features in NGB (McCleskey et al., 2005; Ball et al., 2006). Inflows in the NGB reach have elevated Hg concentrations and the Hg concentration in

Fig. 12. Plot of total dissolved Sb concentrations against total dissolved As concentrations.

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149

and the total recoverable Hg was 22 ng/L, whereas a sample collected upstream from NGB had 1.6 ng/L total dissolved Hg and the total recoverable Hg was 2.3 ng/L. The 2008 Hg data suggest that a large proportion of Hg sorbs to suspended particles in the lower part of the NGB reach. Hence, substantial attenuation of Hg is probably not occurring, only sorption onto particles and continued transport downstream. Methyl-Hg (CH3–Hg) samples were also collected and the concentration range in the Gibbon River was 0.05 to 0.15 ng/L. The inflows with the highest methyl-Hg concentrations were an unnamed tributary near Elk Park (I7, 0.36 ng/L), Hazle Lake drainage (I3, 0.23 ng/L), and Flood Creek (I5, 0.22 ng/L). 4.2.6. Manganese Manganese concentrations and loads for the Gibbon River are shown in Fig. 14. Manganese concentrations in the Gibbon River are elevated compared to major rivers around the world (Fig. 1). Chocolate Pots is the major source of Mn (46%, Fig. 2) and Allen and Day (1935) measured 2 mg/L Mn and Pierson and Parenteau (2000) measured 1 mg/L Mn in the Chocolate Pots Hot Springs. The Mn concentrations in the Chocolate Pots Hot Springs were at least an order of magnitude greater than the Mn concentrations in the NGB inflows. Nearly all of the Mn that entered the Gibbon River along the CP reach (6.6 kg/day) was removed by the end of the GGB reach. Rhodochrosite (crystalline) was undersaturated in the Gibbon River downstream of CP and is not controlling the solubility of Mn. The well-known mounds at Chocolate Pots contain black streaks of what are thought to be manganese dioxide (Allen and Day, 1935; Pierson and Parenteau, 2000), which are a Mn sink. Manganese likely emerges from the Chocolate Pots Hot Springs as Mn(II) and rapidly oxidizes to Mn(III) and Mn(IV), hydrolyzes, and precipitates. The Mn oxidation process may be catalyzed by the existing manganese oxide surfaces coating the mounds (Wilson, 1980) and/or microbes (Nealson et al., 1988). The results for Mn indicate very little transformation from dissolved to suspended particles and, unlike Fe and Al, aqueous Mn appears to be removed to the bed sediment. 4.2.7. Rare earth elements The Rare Earth Elements (REEs: La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Tb, and Lu) are abundant in the felsic volcanic rocks found in YNP (Lewis et al., 1997). Upstream from NGB, REE concentrations in the Gibbon River were low and increased by about an order of magnitude in the NGB reach (Fig. 15A). Tantalus Creek and inflows in the CP reach were the primary sources of REEs in the Gibbon River (Fig. 15B and C). The REE elements are more soluble in acid waters, which accounts for the large REE load from Tantalus Creek and NGB (Lewis et al., 1997). Lewis et al. (1997) also found a positive relation between REE and Fe concentrations for several geothermal waters, and the CP reach, which had the largest increase in dissolved Fe load (Figs. 2 and 7), also had a large increase in REE load (Fig. 15C). Sixty percent of REEs appear to sorb to Fe and Al colloids and are likely transported as suspended particulate material (Fig. 3). Concurrent with Al and Fe precipitation as suspended particles (Figs. 5 and 7, respectively), a substantial portion of the dissolved REE load (260 g/day) was removed downstream from Tantalus Creek at 2.9 km (Fig. 15C). Sampling time and diel changes in temperature and pH, which can affect the partitioning of REE between dissolved and solid phases at neutral pH (Gammons et al., 2005b), may have influenced the results. Nonetheless, Fig. 16 shows a decreasing fraction of dissolved ∑REE concentrations with increasing particulate Fe concentration (FeTR–Fedis). The smallest fraction of dissolved/ total recoverable ∑REE (0.25) occurs at Elk Park which is the most downstream site in the NGB reach and was the site with the most particulate Fe (Fig. 16). For samples with pH values greater than 5, REEs have been shown to partition to hydrous ferrous oxides (Verplanck et al., 2004). In the Gibbon River, the association of REEs

Fig. 14. Plot of Mn concentration, load, and change in load against downstream distance.

with suspended Al particulate material is less clear than with Fe; nonetheless, Elk Park has the highest particulate Al (Fig. 16) and the lowest REEdis/REETR ratio.

Fig. 15. Plot of ∑REE concentration, load, and change in load against downstream distance.

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dissolved to the suspended particle phase as has been demonstrated in other studies (Sholkovitz, 1995; Gimeno Serrano et al., 2000). Alternatively, the REE composition for waters from Terrace Spring may be depleted in LREEs. However, in 2008 the Terrace Spring drainage ∑ REE concentration (0.5 µg/L) was about half that of the Gibbon River and because Terrace Spring's flow is a fraction of that of the Gibbon River, we suspect Terrace Spring has little affect on the REE pattern in Gibbon River. A negative Ce anomaly develops with downstream distance as Ce(III) oxidizes to the relatively insoluble Ce (IV), which leads to fractionation relative to La and Pr that do not oxidize (Moffett, 1994).

Fig. 16. Plot of the fraction of dissolved ∑ REE concentrations against particulate Fe and Al concentration.

North American Shale Composite (NASC; Haskin et al., 1968; Gromet et al., 1984) normalized dissolved REE patterns show negative Eu anomalies (Fig. 17). The negative Eu anomaly in waters from YNP is well documented (Lewis et al., 1997, 1998). Negative Eu anomalies in the fluids indicated the Eu has been decoupled from the REE series and enriched in altered rock as a result of ion-exchange or adsoption processes (Lewis et al., 1997, 1998). The REE pattern (Fig. 17) for the Gibbon River sample collected just downstream from Tantalus Creek (G4, 3.6 km) can be explained by dilution of Tantalus Creek by a factor of 12. Between G4 (3.6 km) and Elk Park (G7, 6.1 km) the ∑ REE decreased by a factor of 3 and very little fractionation of the REE occurred. The REE pattern in the Gibbon River just downstream from CP (G8, 8.2 km) is similar to that for G4 (3.6 km) suggesting that the REE compositions in waters from NGB and CP are similar and is consistent with the proposition, discussed in Part 1, that a substantial portion of the solute loading in the CP reach is emerging subsurface water from the NGB reach. In the LGR reach, the Terrace Spring REE composition is different than that of the upper Gibbon River. Between G9 (12.3 km) and G12 (28.7 km) fractionation of the REEs occurs as the LREEs (La to Sm) became depleted relative to the HREEs (Gd to Lu). The REE fractionation is most likely caused by the preferential removal of LREEs over HREEs from the

Fig. 17. Dissolved REE patterns (water concentration/North American shale composite (NASC) concentration) for Tantalus Creek and the Gibbon River.

4.2.8. Molybdenum and tungsten Tungsten concentrations in the Gibbon River are similar to major river concentrations around the world, however, Mo concentrations are elevated (Fig. 1). Molybdenum and W exhibit very similar chemical behavior, because their atomic radii are almost identical (Greenwood and Earnshaw, 1989). In waters with pH greater than 6.5, both metals form stable +6 oxidation state polymolybdates and polytungstates, respectively (Latimer and Hildebrand, 1965). The predominant forms in surface waters are the molybdate and tungstate oxy-anions (Johannesson et al., 2000; Seiler et al., 2005). In surface waters, both Mo and W show conservative behavior. Molybdenum and W concentrations in surface waters are generally low, below 1 and 10 µg/L, respectively (Fig. 1). However, their concentrations are often elevated and associated with each other in geothermal waters. It has been reported that concentrations of Mo in geothermal waters can be as high as 70 µg/L (Arnórsson and Ivarsson, 1985), and W as high as 300 µg/L (Kraynov, 1965). Typically, W concentrations increase as geothermal water temperature increases, from 20 °C to upwards of 300 °C. Molybdenum concentrations vary irregularly with increasing water temperature, possibly due to molybdenite (MoS2) geochemical solubility controls (Stefansson and Arnórsson, 2005).

Fig. 18. Plot of W concentration, load, and change in load against downstream distance.

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Data from this study show that in the Gibbon River, the dissolved W concentrations increase downstream by about a factor of 20, from about 0.28 to a high of 6.4 µg/L (Fig. 18A). The concentration of W increases sharply through the NGB reach, primarily due to high concentration geothermal input from Tantalus Creek (43.5 µg/L). Downstream from Gap inflow, the concentrations remain between 4 and 6 µg/L. The load continues to increase (Fig. 18B and C), attaining a maximum value of 1.2 kg/day downstream from the Secret Valley Creek inflow (18.3 km). The small decrease in W load at the farthest downstream sites in the LGR reach may be the result of sorption to non-suspended sediment matter and/or organic matter (Johannesson et al., 2000), or the possible uptake of W by biological components (Strigul et al., 2005). Total recoverable W concentrations are similar to dissolved concentrations (Table 1), with total recoverable being 4 to 25% higher than the dissolved concentration, depending upon the site. The largest difference occurs in the lower portion of the NGB reach, which is concurrent with the highest concentration of colloidal Fe. The load curves in Fig. 18B confirm this observation. Similar to W, Mo concentrations sharply increase in the NGB reach, but unlike W, only by a factor of about 3, ranging from 2 to 6.3 µg/L (Fig. 19A). However, 51% of the Mo load in Gibbon River enters between the last two sample sites, near Terrace Spring (27 km), in the LGR reach (Fig. 19B and C). Taking into account the total discharge from Terrace Spring (Allen and Day, 1935) and the Mo concentration in a 2008 sample collected from one of Terrace Spring's drainages (37 µg/L), only half of the Mo mass loading observed in 2006 would be accounted for by Terrace Spring. Therefore, either the Mo concentration in Terrace Spring is variable or there is another Mo source nearby. Total recoverable and dissolved concentration values are nearly identical, indicating that particulate transport for Mo is inconsequential. In the Gibbon River, the main sources of W and Mo are different and their chemical behavior varies indicating that identical physical or chemical processes do not occur for Mo and W.

Fig. 19. Plot of Mo concentration, load, and change in load against downstream distance.

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Fig. 20. Plot of Be concentration and load against downstream distance.

4.2.9. Beryllium Dissolved Be concentrations in the Gibbon River (Fig. 20A) are nearly 2-orders of magnitude greater than that of most major rivers (Fig. 1). The highest Be concentration (6.7 µg/L) was measured in the Secret Valley Creek sample. The Gibbon River Be load continually increases with downstream distance (Fig. 20B) with nearly 52% of the Be loading occurring in the LGR reach (Figs. 2 and 20C). Beryllium is a metal found in natural deposits as ores and has been found in high concentrations in areas of Mo ore deposits (Nordstrom, 2008). The Be and Mo loading profiles (Figs. 19B and 20B) are strikingly similar and appear to have similar source areas except that much less of the Be load comes from Tantalus Creek as that of Mo. Wood (1991, 1992) documented the importance of Be–F complexes for the speciation and transport of Be in hydrothermal fluids. With the exception of one sample from NGB, there is a positive relationship between Be and F concentrations (Fig. 21) in the Gibbon River and nearly all of its inflows, suggesting that Be–F complexes may be important in the

Fig. 21. Plot of Be concentrations against F concentrations.

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Gibbon River. Only 14% of the dissolved Be that enters the Gibbon River is transformed to particulates with most of the difference between dissolved and particulate Be occurring between Secret Valley Creek (18.2 km) and downstream from the Canyon Creek inflow (19 km). 4.2.10. Thallium Thallium concentrations in the Gibbon River are elevated compared to major, non-geothermal affected, rivers (Fig. 1). Thallium is known to substitute for K and Rb in potassium feldspars and to form numerous sulfide minerals. Lorandite (TlAsS2) is the most common Tl bearing mineral and thermodynamic calculations suggest that lorandite is often the phase controlling the solubility in hydrothermal fluids (Xiong, 2004). Thallium also is associated with the organic fraction in silica sinter that is actively depositing from geothermal systems (McKenzie et al., 2001). Thallium concentrations in the Gibbon River reached 0.13 µg/L just downstream from Tantalus Creek inflow (3.6 km), which had a high concentration of 0.94 µg/L (Fig. 22). Seventy-three percent of the Tl load in the Gibbon River comes from the NGB reach and 17% comes from the CP reach (Figs. 2, 22B, and C). Nearly 45% of the dissolved Tl load is transformed to particulates in the Gibbon River (Fig. 3), with most of the loss occurring in the lower section of the NGB reach and in the GGB and LGR reaches (Fig. 22C). Even though a substantial portion of Tl is attenuated in the Gibbon River, at the gage (G12, 28.7 km) nearly all of the Tl in the water column is in the dissolved form (Fig. 22A). 4.2.11. Barium Dissolved Ba concentrations in the Gibbon River (Fig. 23A) are low compared to Ba concentrations found in most major rivers (Fig. 1). The Ba concentrations are highest in the acid inflows from NGB (47– 134 µg/L) and are much lower in the circumneutral inflows and Gibbon River (b20 µg/L) (Fig. 23A). Fifty percent of the Ba load enters the Gibbon River from the acid inflows along the NGB reach and 23% enters along the CP reach (Figs. 2, 23B, and C). The low solubility of

Fig. 22. Plot of Tl concentration, load, and change in load against downstream distance.

Fig. 23. Plot of Ba concentration, load, and change in load against downstream distance.

barite often provides a solubility control of Ba concentrations in acidsulfate waters (Nordstrom, 2008). Barite saturation indices are plotted against SO4 and Ba concentrations in Fig. 24A and B, respectively. Barite is supersaturated in four of the high SO4 inflows from NGB (Fig. 24A) and barite solubility limits the Ba concentration in many of the acid-sulfate inflows from NGB. On mixing with the Gibbon River, Ba and SO4 are diluted causing barite to become undersaturated (Fig. 24C). Even though barite is undersaturated in the Gibbon River, there is a small loss of Ba load in nearly every river reach (Fig. 23C), and the dissolved Ba concentrations are slightly less than the total recoverable concentrations in the LGR reach (Fig. 23A). 4.2.12. Zinc Dissolved Zn concentrations are typically low (b0.05 mg/L) in YNP geothermal waters (Ball et al., 2001a, b, 2006; McCleskey et al., 2005) and the dissolved Zn concentrations in the Gibbon River reflect this. However, most of the Zn in the Gibbon River was in the particulate form. While our study was designed to study the effects of geothermal discharge on the Gibbon River, the data suggest that there may be an anthropogenic Zn input. Over the last 40 years, 2 to 3 million people have visited YNP annually (NPS, 2005). Most visitors drive through the park and their automobile tires and brakes may be a source of particulate Zn. Highway 89 runs adjacent to the Gibbon River from upstream from NGB to the Madison River. A number of investigators have found significant levels of Zn in runoff from urban areas, especially in highway runoff (e.g., Sansalone and Buchberger, 1997; Camponelli et al., 2005; Davis et al., 2007). Camponelli et al. (2005) found that roadway particulate matter transported during runoff events is a dominant source of Zn. Fig. 25A and B are plots of Zn concentration and load, respectively, against downstream distance. The dissolved Zn concentration and load are low and fairly constant over the entire study reach. However, the total recoverable load is much higher throughout the study reach. There are areas where the total recoverable load decreases, most notably is the middle to lower

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Fig. 24. Plot of barite S.I. against SO4 and Ba concentrations and against downstream distance.

part of the NGB reach, is a considerable distance from any roads. The largest increase in the total recoverable Zn load occurred at the most downstream site near Madison Junction, which is heavily traveled. To support this hypothesis, total recoverable samples would need to be collected from the inflows as well as upstream and downstream from any possible highway runoff. Furthermore, studies would need to include rain events which are more likely to mobilize the particulate roadway Zn. 5. Conclusion Even though the Gibbon River contains elevated trace element concentrations (e.g., As, Sb, Be, Tl, Mn, Mo, W) compared to most major rivers, it is an important natural resource and habitat for fisheries and wildlife in YNP. Consequently, knowledge of the source, speciation, redox state, and form (dissolved or particulate) of trace elements is central to understanding their fate and ecological effects. Geothermal inflows are the major source of trace elements in the Gibbon River. Even though their discharges are relatively small, inflows from the NGB reach, especially Tantalus Creek, are the largest

contributors of Al, As, B, Ba, Br, Cs, Hg, Li, Sb, W, and REEs to the Gibbon River. The bulk of the Fe and Mn load in the Gibbon River comes from the CP reach, although Tantalus Creek is also a major source of Fe. The LGR reach, probably Terrace Spring, is the primary source of Be and Mo. There is very little attenuation of trace elements in the Gibbon River because of low Fe concentrations and because SiO2 concentrations are potentially high enough (46–85 mg/L) to coat sediment surfaces, minimizing sorption. Consequently, most trace elements that enter the Gibbon River arrive at the Madison River primarily in the dissolved form including As and Sb. Notable exceptions are Fe, Al, Mn, Hg, and REEs. Upon entering the Gibbon River, Fe oxidizes and hydrolyzes, forming Fe precipitates. Although some settling occurs, most of the Fe reaches the Madison River as suspended particulate material. Unlike Fe, a substantial proportion of Mn leaves the water column. Because both the Fe (≤ 230 µg/L) and Mn (≤ 93 µg/L) concentrations are relatively low in the Gibbon River, their influence on other solutes is minimal. Furthermore, because settling of Fe precipitates is minimal and the sorption sites on existing bed sediments are likely occupied or coated with SiO2, the streambed is

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Fig. 25. Plot of Zn concentration and load against downstream distance.

not a continuous sink for solutes. While some Al precipitates in the lower part of NGB, the majority of the Al remains in solution as Al–F complexes and has little influence on other solutes. The solutes that appear to be affected by Fe (REEs and Hg) were present at very low concentrations (less than 1 µg/L). Sixty percent of the REEs appear to sorb to Fe colloids and are likely transported as suspended particulate material. In addition, a substantial loss of dissolved Hg downstream from NGB coincides with the increase in particulate Fe. Acknowledgements We thank David Roth and Dale Peart for providing chemical analyses for the REEs and Hg. P.L. Verpanck, D.A. Nimick, W.C. Evans, B.A. Kimball, and K. Walton-Day are thanked for their thoughtful comments and reviews. The use of trade, product, industry, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. References Allen, E.T., and Day, A.L., 1935. Hot springs of the Yellowstone National Park. Carnegie Institution of Washington Publication 466, 525pp. Anderson, M.A., Ferguson, J.F., Gavis, J., 1976. Arsenate adsorption on amorphous aluminum hydroxide. Journal of Colloid and Interface Science 54 (3), 391–399. Arnórsson, S., Ivarsson, G., 1985. Molybdenum in Icelandic geothermal waters. Contributions to Mineralogy and Petrology 90, 179–189. Ashley, P.M., Craw, D., Tighe, M.K., Wilson, N.J., 2006. Magnitudes, spatial scales and processes of environmental antimony mobility from orogenic gold–antimony mineral deposits, Australasia. Environmental Geology 51 (4), 499–507. Ball, J.W., Nordstrom, D.K., 1991. User's manual for WATEQ4F, with revised thermodynamic data base and test cases for calculating speciation of major, trace, and redox elements in natural waters. U.S. Geological Survey Open-File Report 91-0183. 193 pp. Ball, J.W., Nordstrom, D.K., Cunningham, K.M., Schoonen, M.A.A., Xu, Y., DeMonge, J.M., 2001a. Water-chemistry and on-site sulfur-speciation data for selected springs in Yellowstone National Park, Wyoming, 1994–1995. U.S. Geological Survey Open-File Report 98-574. 35 pp. Ball, J.W., Nordstrom, D.K., McCleskey, R.B., Schoonen, M.A.A., Xu, Y., 2001b. Waterchemistry and on-site sulfur-speciation data for selected springs in Yellowstone National Park, Wyoming, 1996–1998. U.S. Geological Survey Open-File Report 0149. 42 pp.

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