Diel stream geochemistry, Taylor Valley, Antarctica

HYDROLOGICAL PROCESSESHydrol. Process. (2012)Published online in Wiley Online Library(wileyonlinelibrary.com) DOI: 10.1002/hyp.9255

Diel stream geochemistry, Taylor Valley, Antarctica

Sarah K. Fortner,1,2* W. Berry Lyons1,2 and LeeAnn Munk31 Byrd Polar Research Center, The Ohio State University, Columbus, OH, USA2 School of Earth Sciences, The Ohio State University, Columbus, OH, USA

3 Department of Geological Sciences, University of Alaska Anchorage, Anchorage, AK, USA

*COhE-m

Co

Abstract:

Unlike temperate and polythermal proglacial streams, the proglacial streams in Taylor Valley (TV), Antarctica, are derivedprimarily from glacier surface melt with no subglacial or groundwater additions. Solute responses to flow reflect only theinteraction of glacial meltwater with the valley floor surrounding the stream channel. We have investigated the major, minor andtrace element 24-h variations of two proglacial melt streams, Andersen Creek and Canada Stream, originating from the CanadaGlacier in TV, Antarctica. Both streams exhibited diel mid-austral summer diurnal flow variation, with maximum flow beingmore than 50 times the minimum flow. Dissolved (< 0.4 mm) major, minor and trace solute behaviors through diel periods werestrongly controlled by the availability of readily solubilized material on the valley floor and hyporheic-biological exchanges.Anderson Creek had generally greater solute concentrations than Canada Stream because of its greater receipt of eolian sediment.Andersen Creek also acquired greater solute concentrations in the rising limb of the hydrograph than the falling limb because ofdissolution of eolian material at the surface of the stream channel coupled with minimal hyporheic-biological exchange.Conversely, Canada Stream had less available eolian sediment, but a greater hyporheic-biological exchange, which preferentiallyremoved trace and major solutes in the rising limb and released them in the falling limb. Given the dynamic nature of discharge,eolian, and hyporheic-biological processes, solute loads in TV streams are difficult to predict. Copyright © 2012 John Wiley &Sons, Ltd.

KEY WORDS diel; trace elements; streams; Antarctica; major ions

Received 7 July 2011; Accepted 13 January 2012

INTRODUCTION

Many studies of streams in the foreland of mountainglaciers have examined the relation between soluteconcentrations and discharge (e.g. Anderson et al., 2000;Brown et al., 2006; Mitchell and Brown, 2007). Proglacialmelt derived from temperate and polythermal glaciers havechemistries that reflect mixing from distinct quick and slowreservoirs on, within and underneath the glacier (Tranteret al., 1993; Brown, 2002). Downstream mixing withprecipitation, soil or groundwater further alters chemistry(Fairchild et al., 1999; Flowers, 2008) with groundwaterpotentially serving as a major source of proglacial solutevariation (Dzikowski and Jobard, 2011). Solute response inTaylor Valley (TV) proglacial streams may be easier todiscern because mixing is much less complex. Proglacialstreams in the TV only receive melt from the surface andshallow subsurface of glaciers (Fountain et al., 1999) withlittle precipitation (<10 cm swe a-1) (McKnight et al.,1999) and no groundwater (Runkel et al., 1998).Because the sun circles the horizon and affects distinct

glacial melt surfaces at different times, TV streamsexperience large changes in diurnal flow. Although flowvolumes vary, most TV streams exhibit similar relativeincreases or decreases in total flow over diurnal periods

orrespondence to: Sarah K. Fortner: Byrd Polar Research Center, Theio State University, 1090 Carmack Road, Columbus, OH 43210, USAail: [email protected]

pyright © 2012 John Wiley & Sons, Ltd.

(Conovitz et al., 1998). Surprisingly, little is known aboutthe response of major solutes and minor and traceelements to such large diel flow changes. Yet under-standing how elements vary in time and with flow is thekey to determining the processes that are most importantto the functioning of the streams as well as quantifyingelemental fluxes.In TV proglacial streams, meltwaters travel through

highly permeable unconsolidated channel material thatpromotes high solute exchange rates between the near-stream hyporheic zone and main channel compared withtemperate streams of similar discharge (Runkel et al.,1998; McKnight et al., 1999; Gooseff et al., 2002). Theeffects of hyporheic exchange on biogeochemical processesdepend on flow conditions, with high-flow enhancingchemical weathering but decreasing biotic uptake (Gooseffet al., 2002; Maurice et al., 2002). Solutes, such as H4SiO4,are rapidly added from silicate weathering within thehyporheic zone (Gooseff et al., 2002; Maurice et al., 2002;Gooseff et al., 2004a), and biotic uptake and sorption canremove solutes such as NO3

- and Li+ (Gooseff et al., 2002;Gooseff et al., 2004b). Presently, the understanding ofsolute behavior in the hyporheic zone of TV proglacialstreams is largely limited to evaluating tracer injections ofconservative or nutrient solutes or examining downstreamadditions or losses in stream geochemistry (Nezat et al.,2001; Gooseff et al., 2002; Gooseff et al., 2003; Gooseffet al., 2004b). An examination of diurnal discharge-concentration hysteresis response behavior may be the

S. K. FORTNER, W. B. LYONS AND L. MUNK

ideal way to determine the controls of solutes within thetwo-component (supraglacial melt, biotic-hyporheic inter-actions) proglacial streams. The hysteresis response ofsolutes to flow variation has been widely examined tounderstand mixing exchanges that occur within temperateand alpine streams (e.g. Evans and Davies, 1998; Nagorskiet al., 2003) and even within the hyporheic zone (Arntzenet al., 2006).In this study, we examine the diel controls of a number

of solutes in two TV streams that are derived from waterfrom one glacier. Although these streams are derivedfrom the same melt source, the western stream containsabundant eolian debris and very little visible biomass, andthe eastern stream contains less eolian material and isone of the most biologically rich streams in the entireMcMurdo Dry Valleys region (McKnight and Tate, 1997;Fortner et al., 2011). The primary objective of this studywas to examine the major distinctions between theconcentrations of major and trace solutes in these twostreams and to identify the processes responsible fortheir response to flow. Diel cycles of trace elementbehavior can elucidate important biogeochemical pro-cesses occurring within a stream system includinghydrological, biological and geochemical processes(McKnight and Bencala, 1988; Gammons et al., 2005;Nimick et al., 2011).

Site description

Taylor Valley (77� 00’S, 162� 52’ E) is part of thelargest ice-free expanse in Antarctica, the McMurdo Dry

Figure 1. Map of Taylor Valley, Antarctica, highlighting Canada Glacier pare also

Copyright © 2012 John Wiley & Sons, Ltd.

Valleys. TV spans 34 km from the outlet of the EastAntarctic Ice Sheet, Taylor Glacier, to the Ross Sea(Figure 1). The landscape consists of coarse-grained soils,exposed bedrock, cold-based mountain glaciers, ephem-eral streams and perennially ice-covered, closed-basinlakes (Fountain et al., 1999). Because the sun circles thehorizon and affects distinct glacial melt surfaces atdifferent times, TV streams experience large changes indiurnal flow. For example, eight daily hydrographsmeasured from five TV streams between 1990 and 1992all had daily peakflow to baseflow ratios exceeding 2 andthat reached up to 38 (Conovitz et al., 1998).This study is focused on two proglacial melt streams

derived from the Canada Glacier (~30 km2) in the AsgardRange (Figure 1). This glacier is situated less than 15 kmfrom the Ross Sea. Typical mean monthly temperaturesrange from �1.5 to �33 �C as recorded by themeteorological station on the Canada Glacier ablation atan elevation of 264 masl (1–2m above glacier surface)(Canada Glacier meteorological data available at: http://www.mcmlter.org).Canada Glacier presently acts as a watershed divide

with surface, terminus cliff and shallow subsurface meltdraining into two of the three major TV lake basins.Water is routed from the glacier to the west into AndersenCreek and then into Lake Hoare, whereas in the east,water flows into Canada Stream and then into LakeFryxell (Figure 1). Andersen Creek and Canada Streamhave the same gradient (0.05m/m) and similar lengths(1.4 km and 1.5 km) (Alger et al., 1997). Both streamsoverlay similar lithologies including bedrock of the

roglacial streams: Andersen Creek and Canada Stream. Glacial fed lakesnoted

Hydrol. Process. (2012)DOI: 10.1002/hyp

http://www.mcmlter.org


DIEL STREAM GEOCHEMISTRY, TAYLOR VALLEY, ANTARCTICA

following: Precambrian to Cambrian metasedimentsincluding marbles, schists and argillites and JurassicFerrar Dolerite (Hendy et al., 1979), overlain by Bonneylacustrine deposits and Quaternary Ross Sea drift andAlpine 1 glacial drift (Hall et al., 2000).Although sites overlay similar landscapes, previous

work has shown that Andersen Creek and the westernsupraglacial streams feeding it have greater concentra-tions of crustally derived elements than Canada Stream(Fortner et al., 2011). Foehn winds deliver more debris tothe western streams and glacier surfaces within the TVincluding Canada Glacier (Lyons et al., 2003; Fortneret al., 2005; Bagshaw et al., 2007). In addition to havingdistinct eolian loading, the two streams also are differentbecause Canada Stream travels further from the glaciermargin and has much more biomass than found inAndersen Creek (Alger et al., 1997). In fact, Canada Streamis considered an ecological hotspot, hosting some of themost abundant and diverse plant (e.g. bryophytes and algae)growth in the ice-free regions of Antarctica (McKnight andTate, 1997) and, because of this, has been designated by theAntarctic Treaty as an Antarctic Specially Protected Areathat requires special permission to access.

METHODS

Sampling and laboratory procedures

All stream samples were collected and processed usingultra-clean trace element protocols described in Gardnerand Carey (2004), including bottle cleaning, samplecollection, sample filtration and sample preparation. Watersamples were collected over a continuous 24-h period, inboth Canada Stream and Andersen Creek beginning 22December and 23 December 2007, respectively. StreampH and temperatures were measured in situ using aBeckman Coulter F200W field meter. Proglacial sampleswere collected and filtered (0.4mm) for dissolved con-centrations and acidified to 2% HNO3 v/v. Analysedelements include trace and minor elements: As, Cd, Cu, Fe,Mn, Mo and V as well as major ions (Ca2+, K+, Na+, Mg2+,Cl-, NO3

- and dissolved Si (e.g. H4SiO4).Minor and trace element concentrations were deter-

mined using a Thermo-Finnegan Element 2 SF-ICP-MSin low resolution at the Trace Element Research

Table I. ICP-SF-MS instrument detection limits (DL) are equal to thelements of the worst filter blank (WFB) also appear when greater thdissolved samples. Certified and measured concentrations for refere

standard deviation (RSD). We have also listed RSD value

ElementDissolved DL

(nM)WFB(nM)

TMRAIN-95 CertifiedConcentration (nM)

As 0.24 0.24 14.3� 3.3Cd 0.24 0.44 4.3� 1.1Cu 0.4 97.6� 14.6Fe 0.1 434� 65Mn 0.5 111� 2Mo 0.03 1.8� 0.1V 0.7 12.6� 2.4


Laboratory at The Ohio State University. The instrumentwas calibrated during each sample run using sixstandards, with the high and low standard bracketingthe concentrations examined. Elemental concentrationscorrected for drift using an internal Indium standard(90 nM). Certified reference standard TM-RAIN 95W

(trace element fortified rainwater) was analysed approxi-mately every ten samples, and one of the intermediatecalibration standards was chosen to verify calibration andanalysed every five samples (Table I). Filtration blankswere prepared by filtering deionized Milli-QW water intosample bottles used for collections. Filtration blanks wereoccasionally greater than the instrument detection limit(DL). Therefore, we have calculated the DL as three timesthe standard deviation of the blanks (Gabrielli et al.,2006) or the concentration of the highest filtration blank.Dissolved As was not reported for Andersen Creek, anddissolved Mo was not reported for Canada Stream, asthese elements were elevated in at least one filtrationblank suggesting potential contamination.TMRAIN-95W measurements were all similar to the

certified concentrations, except for As (Table I). Arsenicwas as much as 17% lower than the certified value.Relative standard deviation (RSD) values calculated fromTM-RAIN-95W, and our calibration verification standardshows that sample precision was within 10% for allelements, excluding As. Therefore, the reported Asconcentrations could be at least 10% and as much as20% lower than actual concentrations.Dissolved Si concentrations were determined using an

ICP-OES with sample precision� 8% as determined by therepeating calibration verification standard and measuringduplicate samples. Major ions (Ca2+, K+, Na2+, Mg2+, Cl-,and NO3

- ) were determined using a Dionex DX-120 ionchromatograph, using methods outlined in Welch et al.(1996). Major ion measurements have a precision of ≤ 5%as determined by analysing calibration standards.

RESULTS

Hydrology

During the entire 2007–2008 melt season, AndersenCreek mean daily flow ranged from 0 to 153 l/s, and meandaily flow in Canada Stream ranged from 0 to 163 l/s

ree times the standard deviation of the blanks. Concentrations ofan the detection limit to subtract from concentrations observed innce standard TM-RAIN 95 (n= 30) are listed as well as relatives from our check standard, used in the initial calibration

Measured TMRAIN-95(mean) (nM)

RSDTMRAIN-95

RSD CheckStandard

8.3–11.2 (9.5) 27 393.9–4.9 (4.3) 8.8 3.093–112 (98) 8.2 1.8

NA 2.9 4.1NA 3.1 4.7

1.4–1.8 (1.6) 9.9 2.412.6–13.8 (13.2) 5.5 6.3



(Figure 2). Daily mean flow conditions experiencedduring the entire melt season were similar to the rangein diel flow for both streams during our diel samplingcampaign. The Andersen Creek diel study began on 23December 2007 with flow ranging from 6 to 120 l/s,whereas the Canada Stream diel study, which began on 22December 2007, had daily flow ranging from 28 to 150 l/s(Figure 3). The TV diel studies were limited to one 24-hperiod from each stream because small drops in airtemperature result in the cessation of TV stream flow(Conovitz et al., 1998), and it was important to samplestreams during similar flow conditions. Peak flowoccurred between 17:00 and 19:00 local time in AndersenCreek and between 14:00 and 16:00 in Canada Stream,reflecting the different areas and aspects of the contrib-uting glacier melt and hyporheic surfaces exposed to thesun as well as the water travel times (Conovitz et al.,1998). Andersen Creek had lesser overall flow thanCanada Stream because Andersen Creek is more shieldedfrom the sun by the Canada Glacier (Figure 1). Althoughthe hyporheic extent was not measured in Andersen Creekand Canada Stream during this melt season, the observedwetted margin was at least 0.5m greater on CanadaStream than Andersen Creek during the diel study. It hasbeen noted that streams flowing further away from glaciershielding having greater hyporheic extents (Conovitzet al., 1998; Cozzetto et al., 2006). Furthermore, ourmeasurements revealed that diurnal temperatures reacheda greater maximum temperature in Canada Stream(9.4�C) than Andersen Creek (5.4�C) consistent withgreater hyporheic exchange (McKnight et al., 2004).Greater daily maximum temperatures have been observed

Figure 2. Mean Andersen Creek and Canada Stream daily flow during the2007–2008 melt season


in Canada Stream than Andersen Creek throughout thelong-term temperature trends for both streams (http://www.mcmlter.org). Additionally, Canada Stream hasgreater low flow than Andersen Creek, possibly suggest-ing there is greater water release from the hyporheic zoneinto Canada Stream than in Andersen Creek.

Proglacial stream solute geochemistry

Mean solute concentrations and pH values for AndersenCreek and Canada Stream are provided in Table II. Majorcations, Cl- and NO3

- all occurred at higher meanconcentrations in Andersen Creek than Canada Stream.In fact, NO3

- was below detection limits (0.02 mM) in allCanada Stream diel samples. Furthermore, all dissolvedtrace andminor elements measured at both sites occurred ingreater mean concentrations in Andersen Creek with theexception of Mn, which occurred at similar concentrationsin both streams. Only dissolved Si occurred at greater meanconcentrations in Canada Stream (13.1 mM) than AndersenCreek (10.9 mM). However, both streams had the samemean pH value (7.6), with Canada Stream having a greaterrange (6.6–8.2).The flow response of major ions was distinct between

the two proglacial streams. For Andersen Creek, Ca2+,K+, Mg2+, Na+, Cl-, NO3

- , and dissolved Si occurred attheir highest concentrations at low flow (Figure 4). Infact, a Pearson’s test revealed that in Andersen Creek, allthe aforementioned solutes had a significant negative(a= 0.05, p< 0.01) linear correlation with discharge. InCanada Stream, only Na+, Si and Cl- had a significantnegative linear correlation with discharge (Figure 4).However, these solutes did not respond to flow assubstantially as they did in Andersen Creek. Note thegreater range of concentrations exhibited in the AndersenCreek. Furthermore, in Canada Stream, Ca2+ and Mg2+

remained relatively constant in concentration throughchanging flow. Interestingly, in Canada Stream, K+ had asignificant positive (a= 0.05, p< 0.01) linear relationwith discharge.

DISCUSSION

Eolian proglacial stream chemistry

Because both Andersen Creek and Canada Streamoverlay similar bedrock lithologies and surficial geology,these are not considered a primary control of theirgeochemical differences. In the TV, the strongest winds(up to 37m/s) are southwesterly foehns routed from theEAIS toward the Ross Sea (Nylen et al., 2004; Speirs et al.,2008). The western portion of the glacier can act as abarrier to these winds and favor the deposition of eolianmaterial (Fortner et al., 2011). Lancaster (2002) reportsthat the Lake Hoare basin fed in part by the west sideof Canada Glacier receives 0.86 gm m-2a-1 of eoliansediment, whereas the ablation zone of Canada Glacieronly receives 0.43 gm m-2a-1. On Canada Glacier concen-trations of particulate-affiliate element (e.g. correlated withcalcium) in snow, supraglacial and proglacial decrease




Figure 3. Andersen Creek and Canada Stream diel flow (l/s), temperature (�C) and pH measurements


from west to east reflecting the prevalent winds (Fortneret al., 2011). Eolian processes also have been hypothesizedto deliver substantial loads of N and P to TV lake icesurfaces and eventually to the lakes themselves (Barrettet al., 2007). With the exception of Si, Andersen Creekhad greater mean solute concentrations than CanadaStream. It is highly likely that greater solute concentrationsreflect the greater availability of eolian material on thewestern side of Canada Glacier than the eastern side. Themean Ca2+ concentration of Andersen Creek (104.2mM)was more than twice the mean observed in Canada Stream(46.9mM), and the mean dissolved Fe concentration inAndersen Creek (258.5 nM) was more than four timesgreater than the mean observed in Canada Stream(58.0 nM) (Table II).

Table II. Mean concentrations of major cations and dissolved Si in mCanada Stream 2008 diel studies. Mean** and range of diel pH va

Stream samples. (*range provided for dissolved As with sev

pH Ca2+ K+ Na+ Mg2+ S

Andersen Creek 6.8-8.0 7.6 104.2 14.0 71.8 19.6 10Canada Stream 6.6-8.2 7.6 46.9 9.6 42.7 11.4 13


Eolian inputs may be more important in controlling TVsurface water geochemistry than the underlying geology.The importance of eolian particulate dissolution to soluteconcentrations has been illustrated in other locationsbesides the TV. For example, although the Park Range,Wind River Range and the Beartooth Range in the RockyMountains overlay granitic rock, they have calcite-richsurface water derived from the eolian deposition ofcarbonate-rich dust (Drever and Hurcomb, 1986; Mastet al., 1990). During droughts, winds deliver highereolian solute loads to high elevation lakes in the FrontRange of the Rocky Mountains (Turk and Spahr, 1990).Wind-exposed stream channels, like Andersen Creek,may be natural collectors of eolian material. For example,an abandoned TV stream east of Lake Fryxell (Figure 1)

M and As*, Cu, Fe, Mn, Mo and V in nM for Andersen Creek andlues are also given. NO3

- was below detection limit in all Canadaeral samples below detection; **mean calculated from H+)

i As Cu Fe Mn Mo V Cl- NO3-

.9 — 2.5 258.5 6.3 1.0 12.7 71.3 2.9

.1 <0.2-8.9 1.1 58.0 7.1 — 4.8 43.7 <0.02


Figure 4. Andersen Creek and Canada Stream major cation, dissolved Si, Cl- and NO3 - concentration (mM) versus discharge (l/s) for 2008 diel samples.Significant linear correlations are shown (a= 0.05, p< 0.01)


accumulated fine eolian debris post-abandonment thatproduced elevated solute loads when the channel wasreactivated (McKnight et al., 2007). We hypothesize thatthe higher overall concentrations of solutes in AndersenCreek with respect to Canada Stream suggest the greateravailability of eolian material in Andersen Creek than inCanada Stream. This is especially important, given theclose geographic proximity (< 5 km) of these two sites.Even over short distances, eolian deposition may createlarge differences in the availability of fresh material to besolubilized in melt water.It should be noted that not all solute concentrations

were dominated by solubilization of eolian deposition.For example, there were higher mean concentrations ofdissolved Si in Canada Stream than Andersen Creek,although there is clearly greater eolian delivery of freshaluminosilicate material to Andersen Creek. The primary


source of Si to TV streams is the dissolution ofaluminosilicate minerals within the hyporheic zone(Gooseff et al., 2002; Maurice et al., 2002). The lowerdissolved Si concentrations in Andersen Creek cannot becaused by potential biogenic uptake because this streamlacks abundant diatom-rich microbial mats (Espositoet al., 2006).

Diel geochemical cycling

In Andersen Creek, all major cations, dissolved Si, NO3- ,

and Cl- had a significant inverse correlation with discharge(Figure 4). This is consistent with trends observed in atemperate glacial melt streams where solutes are diluted byincreasing flow (Anderson et al., 2000). In Canada Stream,not all major solutes experienced dilution with increasingflow (Figure 4). TV streams with greater hyporheic-biotic



abundances discharge fewer nutrients into lakes(McKnight et al., 2004). In Canada Stream, NO3

- waslikely also removed by the algal mats and mosses. K+

concentrations significantly increased with increasingflow. Because it is a macronutrient, K+ might increasesimilar to other nutrients because of decreased hyporheic-biological removal at higher discharge (Gooseff et al.,2002; Maurice et al., 2002; Gooseff et al., 2004a).Alternatively, K+ can also be released from the hyporheiczone via silicate weathering (Maurice et al., 2002), butbecause dissolved Si decreased significantly with in-creased flow and increased hyporheic exchange, asilicate-weathering source of K+ is highly unlikely. Ca2+

and Mg2+ had no linear relation to flow. This may berelated to hyporheic weathering processes that will bediscussed with respect to hysteresis response.

Figure 5. Andersen Creek temperature, pH, major cation, and dissolved trasamples. Hysteresis depicted if present. Significant


To further understand the diel controls of temperature,pH, major cations, and dissolved minor and trace elementand their concentrations were plotted versus the rising andfalling limb of the diel hydrograph (Figures 5 and 6).Arrows indicate hysteresis rotation with clockwiserotation resulting from greater solute concentrations inthe rising limb and counterclockwise rotation resultingfrom greater solute concentrations in the falling limb. Inboth streams, many of the chemical constituents exam-ined show hysteresis with some having a significant linearrelation (/= 0.05, p< 0.01) with flow (Table III). Thedominantly clockwise hysteresis response of solutes inAndersen Creek mirrors alpine regions where earlysnowmelt flushes ions within the snow, soil andgroundwater (Williams et al., 1993; Campbell et al.,1995). Unfiltered and acidified (pH< 2) trace elements in

ce and minor element concentrations versus discharge (l/s) for 2008 diellinear correlations are shown (a= 0.05, p< 0.01)


Figure 6. Canada Stream temperature, pH, major cation, and dissolved trace and minor element concentrations versus discharge (l/s) for 2008 dielsamples. Hysteresis depicted if present. Significant linear correlations are shown (a= 0.05, p< 0.01)

Table III. Summarized relation of temperature, pH, summed major cations, dissolved As*, Cu, Fe, Mn, Mo** and V with flow inAndersen Creek and Canada Stream (*As and Mo** were not quantified in Andersen Creek and Canada Stream, respectively)

Andersen Creek Canada Stream

Parameter Linear relation Hysteresis Linear relation Hysteresis

Temperature None None None ClockwisepH None None None CounterclockwiseCations Negative Clockwise None CounterclockwiseAs NA NA None CounterclockwiseCu Negative Clockwise None NoneFe None Clockwise None CounterclockwiseMn None Clockwise Positive NoneMo Negative Clockwise NA NAV Negative Clockwise Positive Clockwise


Copyright © 2012 John Wiley & Sons, Ltd. Hydrol. Process. (2012)DOI: 10.1002/hyp


pristine streams and streams downstream of mining sitesin Montana, USA, showed clockwise hysteresis duringearly spring runoff flushing events (Nagorski et al.,2003). Conversely, solutes depleted in groundwater canexhibit counterclockwise hysteresis during alpine snowmelt(Stoddard, 1987; Bhangu and Whitfield, 1997). BecauseAndersen Creek contains abundant eolian-derived reactivesediment, rapid salt dissolution is likely the source of soluteadditions to Andersen Creek. Unlike temperate snowmeltresponse, there is no soil or groundwater flushing. Coolerstream temperatures (< 5.5 �C) and lack of hysteresis instream temperature suggests that rapid solute dissolutionoccurs. In the TV, it has been demonstrated that coolerstreams have less infiltration and hyporheic mixing thanwarmer streams (Cozzetto et al., 2006). Furthermore, inthese streams, pH does not appear to exert as strong of aninfluence on stream chemistry as flow. Both dissolved Moand V behaved conversely to their expected pH response. Inoxidized natural waters, dissolved Mo and V occur asoxyanions that adsorbed to particulate matter in acidic toneutral conditions and desorbed in basic conditions(Johannessen et al., 2000). However, both occurred atgreater concentrations in the rising limb of the hydrographwhen conditions were more acidic.Unlike the other solutes observed in Andersen Creek,

dissolved Fe and Mn did not decrease significantly withincreasing discharge. Yet these solutes both show the sameclockwise hysteresis as the other solutes in Andersen Creeksuggesting they are primarily derived from rapid dissol-ution. The lack of dilution with increasing discharge mayreflect the greater sensitivity of Fe andMn to solar radiation,redox and/or pH condition (e.g. McKnight and Bencala,1988; Gammons et al., 2005; Nimick et al., 2011). In theSnake River, Colorado, diurnal concentrations of dissolvedFe were greatest during the middle of the day correspondingto the greatest photosynthetically activated radiation(McKnight and Bencala, 1988).Canada Stream solute behavior was dominated by

counterclockwise hysteresis (Figure 6). Furthermore,solutes lacked a significant negative relation (/ = 0.05,p< 0.01) with flow with dissolved Mn and V having asignificant positive relation (Table III). Streamtemperature exhibited clockwise hysteresis in CanadaStream. Heat budget calculations for TV streamssuggested that the hyporheic zone has a greater coolingimpact on stream water in losing reaches than in gainingreaches (Cozzetto et al., 2006). Therefore, clockwisehysteresis of stream temperature is likely indicative ofhyporheic exchange with temperatures falling duringreturn flow with the receipt of cooler hyporheic waters.During peak summer flow, Green Creek, a TV streamwith abundant algal mats, had greater concentrations ofmajor ions and higher pH values within its hyporheiczone than within the stream itself (Maurice et al., 2002).Calcite-rich TV soils (Green et al., 1988) are likelyweathered within the hyporheic zone contributing greaterconcentrations of major solutes in the falling limb of thehydrograph when the weathered solutes return to thestream channel. As calcite is weathered, pH increases


with greater solute concentrations in the falling limbcompared with the rising limb of the hydrograph.In Canada Stream, both dissolved As and Fe occur at

lower concentrations during rising flow and exhibitcounterclockwise hysteresis (Table III). Although it couldbe that these elements are added via hyporheic weatheringin return flow, it may also be that removal occurs in therising limb. Counterclockwise hysteresis is exhibited bynutrients, including phosphate and particulate phosphate,in temperate streams in storm events that occur in thesummer or after early spring nutrient flushing (Hatchet al., 1999; Stutter et al., 2008). This is likely true inCanada Stream where dissolved Fe losses have beenassociated with biological uptake within the hyporheiczones of TV streams (Maurice et al., 2002) and PO4

3-

is known to be removed by algal mats (McKnight et al.,2004). Aquatic and terrestrial plants can take upAsO4

3-, similar in form to the nutrient PO43- (Tamaki and

Frankenberger, 1992; Robinson et al., 2003), so it isnot surprising that As has nutrient-type behavior similarto Fe.DissolvedMn had a significant positive relationwithflow

and no obvious hysteresis behavior (Table III). Incircumneutralwaters, dissolvedMn concentrations decreasewith increasing pH and increased microbial response (co-varying with pH) or to adsorption/co-precipitation withoxides (Brick and Moore, 1996). Because pH decreaseswith increased flow, and Mn increases, Mn is likelyincreasing in high-flow conditions in response to decreasedmicrobial exchange. The behavior of dissolved Cu is morecomplex with no obvious linear or hysteresis relation toflow, temperature or pH. It may be that because chemicalweathering, sorption and biological uptake all affect theconcentration of dissolved Cu in differing ways (Warrenand Zimmerman, 1994; Ren and Packman, 2005; Fernandezand Borrok, 2009), possibly generating a less predictablerelation between concentrations and flow. Finally, unlikeother dissolved solutes in Canada Stream, dissolved V had apositive relation with flow and exhibited clockwisehysteresis. Dissolved V occurred in greater concentrationsin the supraglacial streams feeding Canada Stream (Fortner,2008), suggesting that supraglacial, not hyporheic, watersare a source of V. Trace solutes may occur at lowerconcentrations in Canada Stream than in the glacial surfacemelt because of loading from westerly winds (Fortner et al.,2011). In this instance, an increase in flow would act as asource, rather than a dilutor of solutes. The clockwisehysteresis of V in Canada stream is consistent with theexplanation that V is gained from the rising flow associatedwith glacial melt rather than in the falling flow associatedwith hyporheic exchange. The conservative behavior ofdissolved V in oxic, circumneutral water (Shiller and Boyle,1987) also makes it unlikely that V is primarily weatheredfrom the hyporheic zone.

CONCLUSIONS

Landscape aspect and position are important to the spatio-temporal variations in geochemistry of TV streams.



Although the two streams in this study originate from thesame glacial source, overlay similar lithologies, and havesimilar lengths; they have very different biogeochemicalbehaviors. Solute response in TV proglacial streamsdoes not reflect similar processes observed in temperateand polythermal proglacial streams, where glacial meltincludes supraglacial, englacial and subglacial componentsand downstream additions of groundwater and precipita-tion occur. With little precipitation and no groundwater,solutes in TV proglacial streams respond to the abundanceof soluble material on the valley floor and the extent ofbiotic-hyporheic exchange. The greater receipt of eolianmaterial generated greater dissolved element concentra-tions within the western wind-exposed Andersen Creekthan the eastern lying Canada Stream. Hyporheic-biological processes affect the diel hysteresis behavior ofsolutes in TV streams. Little to no hyporheic exchange inAndersen Creek favors rapid dissolution in the rising limbwith respect to the falling limb, whereas greater hyporheicexchange in Canada Stream removes solutes in the risinglimb and releases them in the falling limb. The geochem-ical differences in these two streams suggest that even withsimilar diel flow variation, lithologies, and water source,TV solute concentrations are highly sensitive to variationsin eolian loading as well as hyporheic-biological processes.Results from this study suggest that hyporheic-bioticextent controls the diel response of solutes on the valleyfloor to changing glacial melt contributions. Becauseprevious research illustrates that TV stream ecosystemsexist largely within or adjoined to the hyporheic zone, morework is needed to separate the role eolian delivery plays inthe chemical loading of these streams. More work is alsoneeded to understand how solute response changesthroughout the melt season as the hyporheic extent varies.Building our understanding of the spatio-temporal relationof stream solutes versus flow is especially important forrelating solute delivery to biogeochemistry.

ACKNOWLEDGEMENTS

We thank John Olesik and Anthony Lutton for theirassistance in The Ohio State University Trace ElementResearch Lab. Special thanks to Kathy Welch, AprilJacobs and Gregg McElwee for their help with major ionanalyses. Thank you also to Josh Koch for providingimportant hydrological information and Michael Goosefffor his thoughtful discussions on the original manuscript.Thanks also to an anonymous reviewer who greatlyimproved the final manuscript. This work was supportedby NSF Grant ANT-0423595.

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Diel stream geochemistry, Taylor Valley, Antarctica

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