simple analytical models for interpretation of environmental tracer profiles in the vadose zone

HYDROLOGICAL PROCESSESHydrol[ Process[ 03\ 0492Ð0410 "1999#

Copyright © 2000 John Wiley & Sons, Ltd.Received July 1997

Accepted 14 June 1999

Simple analytical models for interpretation of environmentaltracer profiles in the vadose zone

Bhaskar Joshi0� and Charles Maule�1

0 Water Manaèment Consultants Inc[\ 1699 N[ Central Ave[\ Suite 299\ Phoenix\ AZ 74993\ USA1 Department of A`ricultural and Bioresource Enìneerin`\ Enìneerin` Buildin`\ 46 Campus Drive\ University of Saskatchewan\ Saskatoon

S6N 4A8\ Canada

Abstract]Di}use vadose zone soil!water ~ux is minuscule in semi!arid environments[ Measurements of soil suction and

hydraulic conductivity are prone to errors and their use leads to unreliable ~ux estimates[ Often\ unambiguous

environmental tracer pro_les are available in the unsaturated zone soil pro_le[ They can be used to obtain

robust estimates of the soil!water ~ux by applying simple analytical models[ Environmental tracers are very

suitable because they normally occur in small concentrations and do not disturb the natural ~ow system

signi_cantly[ They also provide integrated values of the ~ux over longer periods of time and in balance with

the local vegetation or land use patterns[ Current techniques enable small concentrations of these tracers to be

measured reliably[ In the present instance three di}erent tracer pro_les were used to obtain ~ux estimates by

using very simple models requiring minimal input data[ If tracer pro_les suggest that di}usion dominates the

transport process then the use of simple models is justi_ed[

The shape of the tracer pro_les in conjunction with the water contents and porosity data suggest that tracer

advection and dispersion was of minor importance[ Soil!water ~ux was _rst estimated by using the tritium

peak!migration and tritium mass!balance methods[ A heat di}usion analogy was also used to match the

observed tritium pro_le[ Chloride mass balance of the pro_le was used to obtain another ~ux estimate[ A

modi_cation of the chloride mass!balance method was also used to obtain advective and di}usive components

of moisture ~ux[ Simple piston ~ow models based on peak migration were used to obtain additional estimates

from chloride and nitrate pro_les[ The estimates obtained were of the same order of magnitude and within the

range reported for semi!arid regions in other parts of the world[ Copyright Þ 1999 John Wiley + Sons\ Ltd[

KEY WORDS vadose^ semi!arid^ soil!water ~ux^ tracers^ tritium^ chloride^ nitrate^ isotopes^ prairies^ massbalance^ peak migration^ advective^ di}usive

INTRODUCTION

The application of environmental tracer techniques in hydrology is well established[ Mazor "0864# categorizesthe salinity\ chloride content and detailed chemical analysis that are applied in hydrological studies as{classic| tracers[ The application of isotope tracers\ such as deuterium\ tritium\ oxygen!07 and carbon!03\has developed mainly since the 0859s along a path of its own[ Until the 0869s most studies on groundwaterdid not include chemical analyses in their surveys and interpretations[ However\ it is now recognizedthat hydrochemical and isotope approaches are equally powerful complementary aids in groundwaterinvestigations "Mazor\ 0864#[

It has been found that environmental tracers represent a spatially uniform input to the soil water andintegrate all of the processes that combine to a}ect water ~ow in the vadose zone "Allison et al[\ 0883#[ They

� Correspondence to] Dr B[ Joshi\ 1699 N[ Central Ave[\ Suite 299\ Phoenix\ AZ 74993\ USA[ E!mail] kisshÝgci!net[com

B[ JOSHI AND C[ MAULEł

Copyright Þ 1999 John Wiley + Sons\ Ltd[ Hydrol[ Process[ 03\ 0492Ð0410 "1999#

0493

allow a direct measurement of the displacement of water or solutes[ An additional advantage is that tracerdi}usivity is much less variable with change in water content and soil type than the di}usivity of soil water"Allison\ 0876#[ Most common ions have a binary di}usion coe.cient "D9# of 09−8 to 1×09−8 m1 s−0 inwater at 19 >C[ The di}usion coe.cient in soil matrix is normally 09) "clays# to 69) "sands# of this value"de Marsily\ 0875#[ The typical scale of variation of moisture di}usivity is much greater[ Philip "0858# gives anexample where moisture di}usivity of Yolo Light clay varied from 09−5 to 09−09 m1 s−0 between volumetricwater contents of 9=90 to 9=49[ Thus tracer behaviour represents a much more robust indicator of water movementin soil than the solution of equations of water ~ow\ especially in the unsaturated zone "Allison\ 0876#[

There are two principal ways in which tracers have been used in hydrological studies[ Firstly\ they areused for qualitative evaluations that include factors such as direction and nature of ~ow\ origin\ age\components of di}erent waters and seasonal variations[ Secondly\ and most often\ they are used to estimatemagnitude of moisture ~uxes[

Both natural and arti_cially applied tracers have been used in obtaining quantitative estimates of water~uxes[ As natural systems are voluminous and travel times are long\ the injection of tracers may not alwaysbe the best method[ Therefore\ the use of natural tracers has been more common in estimating ~uxes "Mazor\0864^ Vogel et al[\ 0852#[ The natural tracers used most commonly are deuterium\ tritium\ carbon!03\nitrogen!04\ oxygen!07\ carbon!02 and chlorine[ Among these\ carbon!03 and tritium are radioactive andtheir input concentrations to the hydrological cycle have been modi_ed greatly as a result of nuclear testing[The input of the other isotopes has also changed on a much longer time!scale as a result of climatic variations[

For estimation of magnitude of the soil!water ~ux in the vadose zone of arid and semi!arid regions it hasbeen suggested that di}usion may be the principal mode of solute transport "Barnes et al[\ 0883^ Joshi\0886#[ Where this is true it may be possible to obtain tracer migration velocity and associated water ~uxesby using simple analytical models[ The validity of using simple models needs to be justi_ed on a site!speci_cbasis by studying the temporal variation of variables such as water content "Joshi et al[\ 0886#[ The aim ofthis paper is to demonstrate the application of simple analytical models for estimation of vadose zone soil!water ~ux in the semi!arid Canadian Prairies[

SITE DESCRIPTION

The experimental area of the study reported here is located in the central part of the province of Saskat!chewan\ between 41> and 42> north and 095> and 097> west[ The province of Saskatchewan forms part ofthe physiographic area known as the Great Plains Province of the Interior Plains of North America[ Thegeneral large!scale topographic slope is to the north!east[ Two major rivers "the North and SouthSaskatchewan Rivers# provide external drainage in the area "Acton and Ellis\ 0867#[

The study was carried out on an instrumented plot at the University of Saskatchewan farms "KernenFarm# located about 01 km east of Saskatoon\ Canada[ It is located within the physiographic subsectionknown as the Saskatoon Plain\ which slopes from 409 m a[s[l[ from the edge of the South SaskatchewanRiver on the west to about 424 m a[s[l[ at the edge of the Strawberry Hills on the east[ The SouthSaskatchewan River is entrenched nearly 59 m into this plain and provides limited external drainage[ Thelocal landform and topography is characterized as undulating\ sandy to clayey glacio!lacustrine plains"Acton and Ellis\ 0867#[

Saskatoon has a continental climate characterized by a wide range in temperatures between summer andwinter as well as by short!term changes in the weather[ The mean annual precipitation is about 260 mm andthe lake evaporation about 607 mm "Wittrock et al[\ 0878#[ Roughly 29) of the annual precipitation occursas snow[ The mean monthly temperature ranges from −08=0 >C in January to ¦07=3 >C in July[

Soil `enesis\ landforms\ sur_cial deposits and land use

The Kernen Farm landscape is characteristically level to undulating glacio!lacustrine plain\ with minorareas of hummocky topography "Souster\ 0868#[ The farm is situated in the Dark Brown soil zone "Souster\

TRACER PROFILES IN THE VADOSE ZONE


0494

Figure 0[ Variation of sand content and clay content with depth

0868#[ The soils are classi_ed as silty clay to clay to heavy clay\ Rego and Orthic Dark Brown series of theSutherland Association "Souster\ 0868#[ The Sutherland Association has been characterized as moderately_ne to _ne textured\ weakly to moderately calcareous\ glacio!lacustrine deposits "Acton and Ellis\ 0867#[The Rego and Orthic Dark Brown series are moderate to low in organic matter\ neutral to mildly alkalinein reaction\ low in available phosphorous and high in available potassium "Acton and Ellis\ 0867#[ The bulkof the soils are either well or moderately well drained "Souster\ 0868#[ Some poorly drained soils occur inlocal depressed areas\ where drainage is restricted[ Salinity is not a serious problem\ although moderatelyhigh salt levels may occur in silty lacustrine materials "Acton and Ellis\ 0867^ Souster\ 0868#[ Gentlyundulating\ unpatterned to knoll and depressional lacustrine landforms predominate in this association"Acton and Ellis\ 0867#[ Figure 0 shows the variation of percentage sand and clay content with depth at thepresent experimental site[ These were obtained by the author from hydrometer analysis carried out on thesoil core samples collected during installation of the piezometers[

The experimental plot is ~at and gently inclined downwards from east to west\ with a slope of about 1)"Figure 1#[ In further discussion the eastern end of the plot is referred to as the {upper slope| position whereasthe western end\ near the bottom of the slope\ is called the {lower slope| position[ The bottom of the slope"about 29 m away from the lower slope position# is a local depression in the landscape where wateraccumulates after snowmelt and it is populated by Reed Canary grass[ This location will be referred as the{slough| in subsequent discussion[ Figure 1 also shows the location and brief description of instrumentationthat was installed to carry out the study[

Historical data on land use at Kernen Farm were obtained from Mr Kirk Bloomquist\ Farm Manager[The farm was handed over to the University of Saskatchewan in 0866 and no records of land managementare available prior to this[ The records available show that the area of the experimental plots remained



0495

Figure 1[ Stratigraphic section and site instrumentation "local bench mark � 099=99 m was a concrete culvert about 099 m south of thelower slope position#

fallow during 0866 to 0868 and 0870[ No crop was grown and no fertilizer or pesticides were used duringthese years[ During 0879 and 0871 to 0883 it was cropped with wheat[ Canola was grown in 0884 and peasin 0885[ During the period of this study\ a crop of spring wheat was seeded on 16 May and harvested on 7September 0883[ In 0884\ a crop of canola was seeded on 06 May and harvested on 5 September[

Geolo`y

The shallow stratigraphic section obtained from test hole data around the area "within a radius of 2 km#indicates 4 to 5 m of glacio!lacustrine clay and clay loam\ which is underlain by till up to a depth of about07 m[ An aquifer is encountered at around this depth and it is underlain by till material[ This sequence wasalso con_rmed from visual observations of auger and core samples collected while installing piezometersduring the present study "Figure 1#[ A Saskatchewan Research Council test hole section located about 1=14km north of the site "SRC No[ NW!05!97!26!3W2# indicates that the upper till is friable and fracture surfacesare stained with iron oxide[ Both the upper and lower layers of till appear to contain isolated silty lenses upto 9=4 m thick\ at varying depths "SRC No[ NW!05!97!26!3W2#[

The till deposits in this area are of Pleistocene age "Keller et al[\ 0875#[ Pleistocene glacial till deposits inthe Saskatoon area are divided into the Sutherland and Saskatoon Groups "Christiansen\ 0881#[ The tillmember underlying the glacio!lacustrine material at the study site has been classi_ed as the Floral Formationof the Saskatoon Group "Christiansen\ 0869#[ The Floral Formation is considered to include tills of twoseparate glaciations\ however the compositional di}erences are small to merit designation as stratigraphicalunits "Christiansen\ 0881#[ They are therefore simply called the lower and upper till[ Radiocarbon ages ofthese till units range from 27 999 to 07 999 years BP "Christiansen\ 0881#[ The last deglaciation occurredaround 09 999 years BP in the Saskatoon area "Remenda et al[\ 0885#[ The aquifer encountered at the lowerslope position of the study site is believed to be the Forestry Farm aquifer\ which is an intra!till aquiferlocated between the upper and lower Floral Formation tills[

Visual observations on core samples

A visual study of the soil core samples obtained during this study "during installation of the piezometers#showed that the upper 2 to 4 m of this glacial deposit is highly weathered at the site[ The depth of the



0496

weathered zone is indicated by a colour transition in the clay matrix from brown to grey at around thisdepth[ The A horizon is gleyed at the lower slope position[ The presence of profuse gypsum up to about 2m depth at this location suggests that e}ects of weathering extend down at least to this depth[ Gypsum waslast observed to a depth of about 4=4 to 5 m at upper and middle slope positions and to about 2 m at thelower slope position[

At the upper slope position isolated fossil root hairs were observed within the cores to a depth of about 4m[ At the middle slope position isolated root hairs were observed to 4 m depth[ Cores from the lower slopeposition showed evidence of root hairs to depths of 3 m[ Iron oxide stains were observed to about 00 mdepth at the upper and middle slope positions[ At the lower slope iron oxide stains were found at depths ofup to 6 m[ The in~uence of these features on ~ow and transport mechanisms has to be viewed in the light ofadditional evidence\ for example from solute pro_les "Keller et al[\ 0875#[

The studies of Keller et al[ "0875# and Fortin et al[ "0880# were carried out in clay till deposits located atabout 09 to 29 km north!west of this study site[ The shallow stratigraphy at these sites is very similar to thatat Kernen[ Both studies demonstrated that the sur_cial weathered zone\ extending down to a depth of 01 min the _rst case and 6 to 8 m in the second case\ was hydraulically active owing to the presence of fractures[Keller et al[ "0875# concluded that fractures were hydraulically active in the unweathered till as well[However\ the solute pro_le "tritium in this case# indicated that the unweathered till behaved like an equivalentporous medium because of matrix di}usion between _nely spaced fractures "Keller et al[\ 0875#[ Thus thein~uence of fractures on ~ow and transport mechanisms was di}erent than what one might expect on thebasis of evidence for presence of fractures and the hydraulic conductivity data[

Hydro`eolo`y

A regional hydrogeological section to the north of the study site "section BB| in _gures 01 and 24 ofChristiansen\ 0869# shows that the Strawberry Hills to the east of the study site serve as a major rechargearea[ The Strawberry Hills area provides direct recharge into the Forestry Farm aquifer\ which extends outin the shape of an elongated disc from the eastern bank of the South Saskatchewan River towards the eastand pinches out in the vicinity of Kernen Farm "_gures 06 and 26 of Christiansen\ 0869#[ Water ~ow in theaquifer is horizontal and in an oblique northerly direction towards the South Saskatchewan River\ alongwhich it outcrops in the form of a number of springs "_gure 26 of Christiansen\ 0869#[ The zone above theForestry Farm aquifer is also a recharge zone\ as there is no indication of artesian conditions[ The well!drained and productive soils at Kernen Farm are also indicative of recharge "Christiansen\ 0869#[

Groundwater enters the Forestry Farm aquifer by downward in_ltration through till and by lateralmovement along the interface between tills from Strawberry Hills[ The aquifer acts as an interceptor drainthat collects groundwater from the Strawberry Hills and diverts it north!westward towards the SouthSaskatchewan River "Christiansen\ 0869#[ The water level encountered in piezometers installed at the studysite is within the sur_cial clay and silt aquifer "Christiansen\ 0869# except for one deep piezometer "at 19 mdepth#\ which probably intercepts the Forestry Farm aquifer[ Sur_cial aquifers were deposited during orsubsequent to\ the _nal deglaciation of the Saskatoon area "about 09 999 years BP#[ Water in these aquifersoriginates as precipitation that has in_ltrated downward from the ground surface to the water table\ whichforms the upper surface of the sur_cial aquifers "Christiansen\ 0869#[

MATERIALS AND METHODS

The senior author carried out most of the chemical analyses[ Stable isotopes and tritium analysis werecarried out at the Environmental Isotope Laboratory\ University of Waterloo\ Ontario\ Canada[

Soil chloride measurements were carried out on saturated paste extracts "Carter\ 0882#[ An Orion Model85!06B Combination Chloride electrode with Orion MOdel 189A speci_c ion meter was used for allmeasurements[ The electrode has a range of 0=7 to 24 499 mg L−0 and a reproducibility of 21) "Orion\0889#[ The accuracy of these electrodes may be 9=0 mV with a decadal concentration change of 48 mV\ for



0497

univalent anions "Camann\ 0868#[ Sample and standards were equilibrated at room temperature prior tomeasurement[ A sample of _xed known concentration was used as a check with every series of measurements[Soil nitrate measurements were carried out by Enviro Test Laboratories\ Saskatoon[ The samples were airdried prior to submission[ Nitrate was determined colorimetrically and the root mean square deviation ofthese measurements is expected to be 6) with an interlaboratory error of 06)[

Tritium was measured directly by liquid scintillation counting "Drimmie et al[\ 0882# on the extractedsoil!water samples[ These measurements have a lower limit of detection of approximately 7 tritium units[

ESTIMATION OF SOIL!WATER FLUX IN THE VADOSE ZONE

The data collected were used to obtain an estimate of soil!water ~ux[ An estimate of medium! to long!term~ux "over a period of decades or more# was obtained from the tritium and chloride mass!balance approach[Migration of the chloride\ nitrate and tritium peaks was used to obtain an alternative estimate of ~ux at thepresent study site[

In general\ solute pro_les within the vadose zone may be utilized for estimation of soil!water ~ux in atleast three di}erent ways[

0[ Peak!migration methods] "i# the distance to a solute peak divided by the approximate time of its injectionprovides an idea of the microscopic velocity * also called the {percolation velocity|[ "ii# assuming asteady!state volumetric water content pro_le one may argue that a volume of water equal to that presentabove the peak at the present time must have been displaced[ This volume divided by the estimated timeof injection gives an estimate of the recharge ~ux[

1[ Mass!balance methods] the total mass of solute present in the pro_le "within a depth interval notin~uenced by the root zone and the water table# may be estimated[ The accession period and the inputfunction of the solute should be known[ Then one may equate the total amount of solute present in thepro_le to the amount that would accumulate if unit recharge "with a suitably estimated solute con!centration# had occurred[ This equation enables the mean annual recharge to be estimated[

2[ Pro_le!matching methods^ the qualitative features of a tracer pro_le may be matched to measured pro_lesby using simple Fickian di}usion models provided their use can be justi_ed based upon site conditions[

Note that all the solute methods rely on steady!state ~ow and spatially uniform solute input assumptions[They are rather simplistic tools for obtaining estimates of an elusive quantity[ The _rst two methods alsoassume piston ~ow but mass balance estimates do not explicitly impose such a restriction on the ~ow process[Table I provides details about the methods of ~ux estimation used in our study[ The various tracers usedand the ~ux parameters estimated are also listed[

Table I[ Methods of ~ux estimation

Tracer Method used Parameter estimated Time framea

Tritium Peak migration Percolation velocity Short termMass balance Mean annual recharge Long term

Pro_le matching Qualitative

Chloride Peak migration Percolation velocity Short termMass balance Mean annual recharge Long term

Nitrate Peak migration Percolation velocity Short term

aShort!term estimates cover a maximum period of 099 years[ Long!term estimates are for periods spanning several hundred to thousandsof years[



0498

ESTIMATES OF SOIL!WATER FLUX] TRITIUM DATA

Three di}erent methods\ "i# peak migration^ "ii# mass balance and "iii# pro_le matching\ were used forinterpreting tritium pro_les measured in the unsaturated zone[ The _rst two methods provide quantitativeestimates of soil!water ~ux whereas the third provides a qualitative con_rmation regarding the nature of thetransport process[ An implicit assumption in these methods is that the unsaturated zone is deep enough\ orthe recharge is small enough\ such that at least 20 years "0852Ð83# of recharge can be held above the watertable[ It is assumed that the major in~ux of tritium into the hydrological cycle occurred as a result of thethermonuclear tests conducted during 0851Ð52 "Thatcher\ 0854#[ It has to be recognized that estimatesobtained from these methods are limited by uncertainties in accurate measurement of tritium concentrationsin interstitial and precipitation waters as well as in evapotranspiration estimates[

Estimates of soil!water ~ux] tritium peak mi`ration

The position of tritium peaks in precipitation "0851Ð54 and 0847Ð48# were matched to those observed inthe soil pro_le[ The tritium peak at 1=17 m "Figure 2# was matched with the 0852 peak in precipitation[ It isassumed that tritiated water moves downward predominantly as a slug and completely displaces the residentmoisture in the pro_le[ It is assumed that an amount of water present in the pro_le above the fall!out peakmust have been displaced in the period since the peak was injected at the surface[

The depth pro_le for tritium present in interstitial soil water and the corresponding volumetric watercontent at the lower slope position is shown in Figure 2[ Owing to resource constraints\ samples could beanalysed only for one slope location[ The lower slope position was selected because it was expected that thebomb tritium peak would more likely be preserved at this location[ Rapid leaching at this location couldtransport moisture beyond depths likely to be in~uenced by direct evapotranspiration[

The volumetric water content at the time of sampling varied from 32) to 35) in the 039 to 117 cm depthinterval "Figure 2#[ Using this information a recharge ~ux of 04 mm year−0 was obtained[ It must be saidthat any bypass or _ssure ~ow past the 0=4 m depth will result in underestimation of the ~ux by this method[

The tritium mass balance method

The amount of tritium measured in the soil pro_le can be used to obtain an estimate of water ~ux throughthe vadose zone "Allison and Hughes\ 0863#[ The total amount of tritium held in the soil pro_le below the

Figure 2[ Pro_le of tritium concentration in soil water and corresponding volumetric water content



0409

root zone is calculated from measured concentrations in the soil and pro_le volumetric water contents[This is compared with the total amount of tritium that would be held if unit recharge had occurred[ Asuitable tritium input function of recharge water passing below the root zone is obtained from availablemeasurements of tritium levels in precipitation "International Atomic Energy Agency web site athttp]::www[iaea[or[at:programs:ri:gnip:gnipinfo[htmècont 2\ November 0885#[ The method assumes thatat least some tritiated water travels to a depth where it is not further in~uenced by evapotranspiration[ Thisis considered as recharge water and its tritium concentration needs to be estimated suitably[

The tritium mass balance in the vadose zone for the period 0842Ð83 is written as "Allison\ 0876#

MAR× s30

n�9

v"n#TI "n# exp"nl# � gz

9

Tsu"z#dz "0#

where MAR is the mean annual recharge "mm#\ v"n# is a weighting factor for the nth years tritium input"�P"n#:P

Þ#\ P"n# is the total precipitation in the nth year\ P

Þis the long!term total annual precipitation\ TI"n#

is the tritium concentration in water recharged below the root zone "TU# during year "n#\ taken as the annualaverage tritium input concentration^ Ts"z# is the tritium concentration held in the soil at depth "z#^ u"z# isthe volumetric water content at depth "z#^ l is the tritium decay constant "�9=9454 year−0#^ z is the depthbelow ground^ and n is the number of years elapsed from 0842 to 0883 "value of n�30#[

It is assumed that tritium stored in the pro_le before 0842 was negligible[ Equation "0# may be rearrangedto calculate the mean annual recharge "MAR# valid over the entire period of elevated tritium input resultingfrom thermonuclear testing

MAR�$g

z

9

TS"z#u"z#dz%s30

n�9

TI "n# exp"nl#

"1#

The mass balance method is robust because the estimates are independent of the distribution of tritium inthe pro_le and non!ideal percolation of water is not an issue[ Fewer samples need to be analysed becausedetailed depth discrimination in the tritium concentration pro_les is not very important[ Unlike the chloridemass balance method\ tritium mass balance uses a measured\ temporally variable input function[ The methodassumes that the unsaturated zone is deep enough to store the tritium input over the period 0842 to 0883[ Arough calculation using the average volumetric water content of the unsaturated zone pro_le and a rechargerate of 04 mm year−0\ shows that some tritiated water may already have moved into the saturated zone[This amount is not accounted for in the calculations[ Considering Equation "1# it becomes clear that such apossibility would result in underestimation of recharge by this method[

Using this technique\ recharge was estimated to be about 04 mm year−0[ We note that the tritium massbalance estimate is made over a short period of time and is more likely to be in~uenced by extreme events[

Tritium pro_le matchin`] a qualitative explanation of water movement

This approach assumes that some tritiated water moves rapidly to a depth una}ected by evaporation[ Itthen moves down by intergranular seepage[ This method is qualitative and relies upon matching themagnitude and:or location of the observed tritium peaks[ It is postulated that rapid transport of tritiumoccurs to about 0=4 m to 1=9 m depth and molecular di}usion dominates transport below this depth "Joshiet al[\ 0886#[

The analytical solution of heat ~ow due to Carslaw and Jaeger "Carslaw and Jaeger\ 0858^ p[ 51\ equation04# was used[ The solution is for conduction of a slug of heat energy into a medium of thermal di}usivity"k# that initially is at zero temperature[ Speci_cally it is stated that the region a³ z³ b initially is at a



0400

Figure 3[ Time series of tritium concentration in precipitation at Ottawa "IAEA\ Vienna#

constant temperature V\ and the regions 9³ z³ a and z× b are at zero\ and the surface z�9 is maintainedat zero for time t× 9[ The analytical solution for the transient temperature distribution "T# is given as

T�V

1 6erf"z−a#

1zkt¦erf

"z¦a#

1zkt−erf

"z−b#

1zkt−erf

"z¦b#

1zkt7 "2#

In this case we assumed that each year a 3!cm slug of water with a tritium concentration equal to that of theyearly average concentration in precipitation at Ottawa "http]::www[iaea[or[at:programs:ri:gnip:gnipinfo[htmècont 2#\ moves rapidly downwards to a depth of about 089 cm[ After that it travels by matrixdi}usion[ This occurs every year beginning from 0852 until 0883 and the e}ect of consecutive year|s tritiuminput is added[ Considering the typical late autumn volumetric water content at this depth it was calculatedthat a 3!cm slug would displace the resident moisture from 084 to 194 cm depth and then di}use outwards"049 cm−"9=93×099#:9=27�028=4 cm#[ A 3!cm slug was taken as reasonable and convenient input in viewof calculations from post!melt volumetric water content pro_les\ which showed that 12 to 37 mm water mayend up in the pro_le after snowmelt "Joshi\ 0886#[ The coe.cient of di}usivity of tritium in clay was takenas 0=76×09−8 m1 s−0[ This is within the range of published values "09−8 to 09−09 m1 s−0# for di}usion oftritiated water in soils "Schmalz and Polzer\ 0858#[

The period 0853Ð83 was chosen for the simulation because the post!0850 tritium pulse is the largestobserved "Thatcher and Ho}man\ 0852#[ Its sharp rise after decline from a smaller pulse in 0847 provides arelatively unambiguous marker "Figure 3#[ Schmalz and Polzer "0858# reported that only 2=4) of the totaltritium deposited over a 04 year period remained in the top 199 cm of a silty clay loam pro_le\ and the restwas lost by evapotranspiration and decay[ Decay for 04 years can account for a loss of only about 46)[Therefore the balance "about 32−2=4�28)# must be lost by some other process\ such as evapo!transpiration[ Thus 59) of the Ottawa concentrations should be taken as the concentration of the sluginput at the 084 to 194 cm depth[ The best _t to measured data\ however\ was obtained with 25) of theOttawa input being recharged into the soil\ with about 4) of this directly injected to depths of 2 m andbelow[ A variable injection function had to be assumed in order to _t the measured data and it is shown inFigure 4[ The period as well as percentage of direct injection at discrete depths ranging from 299 to 399 cmwas varied in order to obtain a good match with the observed tritium pro_le in the soil[ The amount injected



0401

Figure 4[ Injection function used for simulating the _eld measured tritium pro_le

constitutes about 4) of the 25) tritium input into the soil\ or roughly 0=7) of the tritium in precipitation"Figure 3#[

The results of this simulation for the period 0852Ð83 are shown in Figure 5[ The 0852 peak is wellpreserved as the tritiated water travels downward[ The simulated peak magnitude is about 36 TU and it islocated at a depth of about 191 cm[ These values are in good agreement with the _eld measured peakmagnitude of 36 TU and peak depth of about 117 cm[

The results of this simulation show that the observed tritium pro_le can be produced from the observedtritium input function and reasonable values of other parameters[ They support the idea of rapid transportthrough a shallow mixing zone and subsequent di}usion!dominated solute movement[

ESTIMATES OF SOIL!WATER FLUX] CHLORIDE DATA

Two di}erent methods\ "i# mass balance and "ii# peak migration\ were used for interpreting chloride pro_lesmeasured in the unsaturated zone[ A variation of the chloride mass balance method was also used to estimatesteady!state advective and di}usive ~ux[ All methods provide quantitative estimates of soil!water ~ux[ Therelative magnitude of steady!state advective and di}usive ~uxes gives qualitative con_rmation regarding thenature of the transport process[ It has to be recognized that estimates obtained from these methods arelimited by uncertainties in accurate measurement of chloride concentrations in interstitial and precipitationwaters[



0402

Figure 5[ Heat ~ow analogy for di}usion of _nite tritium slugs\ 0852Ð0883

The chloride mass balance method

If pedogenic origin of chloride is negligible then it may be shown from a mass balance of chloride in thesoil pro_le that

PCp �RCz¦DS "3#

where P is the precipitation "mm year−0#\ R is the drainage "recharge# below the maximum rooting depth\also in mm year−0\ Cp and Cz are the chloride concentrations in precipitation and drainage water respectively\and DS is the change in chloride storage within the root zone[ For deep\ relatively undisturbed\ pro_les asteady state may be assumed and DS may be negligible "Sharma and Hughes\ 0874#[ If the long!term averagevalues of Cp and P "i[e[ C

Þp and P

Þ# are known then the long!term average recharge "R

Þ# may be estimated as\

RÞ

�CÞ

pPÞ

CÞ

z

"4#

where CÞ

z is the long!term average concentration of water draining below the root zone[ Equation "4# makesthe average ~ux of chloride below the root zone equal to the average input of chloride from precipitation\assuming runo} to be negligible[

Depth!averaged chloride concentrations in the unsaturated zone pro_le as well as the groundwater wereused as values for C

Þz in the calculation of ~ux[ We see that in Equation "4# C

Þz indicates the average

concentration of chloride in the water draining below the root zone[ It has been suggested "Sharma andHughes\ 0874# that because usually there is uncertainty in estimating the exact rooting depth and alsowhether a steady state has been reached\ C

Þz should be estimated by several di}erent methods[

It is observed from Equation "4# that only concentrations of chloride are required[ As there exists aninverse relationship between recharge and chloride concentration in the soil pro_le\ sampling and analyticalerrors become less important in in~uencing the precision of recharge estimates obtained in areas of low soil!water ~ux "Allison and Hughes\ 0872#[ Another advantage is that the salt pro_le is established in equilibriumwith the climate and vegetation of an area\ resulting in a pattern that is characteristic of that ecosystem"McCown et al[\ 0865#[

The chloride mass balance method assumes "i# one!dimensional steady state\ vertical\ downward ~ow^ "ii#precipitation as the only source of chloride^ "iii# mean annual precipitation and chloride concentration of



0403

precipitation constant through time^ and "iv# steady!state chloride ~ux equal to the chloride accession ratein rainfall[

A variation of the chloride mass balance method "Gardner\ 0856^ Peck et al[\ 0870^ Scanlon\ 0880# hasbeen utilized to study the relative importance of steady!state advective and dispersive moisture ~uxes[ Thesteady!state advectiveÐdispersive solute ~ux may be expressed as

Js �−Ds

1c

1z¦cqw "5#

where Js is the mass ~ux density of the solute "ML−1 T−0#\ Ds "L1 T−0#\ is the hydrodynamic dispersioncoe.cient of the solute in the soil\ c is the solute concentration in soil water "ML−2#\ qw is the Darcian soilwater ~ux "L T−0# and z is the elevation[

Equation "5# may be rearranged to directly express the soil!water ~ux as

qw �0

c$Js¦Ds

1c

1z% "6#

In Equation "6# the _rst term on the right!hand side "after opening the brackets# denotes the advectivemoisture ~ux\ whereas the second term represents the dispersive ~ux[ The hydrodynamic dispersion coe.cient"Ds �Dm¦De# is comprised of the mechanical dispersion coe.cient "Dm# and the e}ective moleculardi}usion coe.cient "De#\ which is expressed as

De � g"L:Le#1D9 "7#

where g accounts for ion solid interaction e}ects and "L:Le#1 accounts for pore geometry e}ects "Porter et

al[\ 0859#[ Thus solute mass ~ux "kg m−1 s−0# �Dsuw"1c:1z#[Mechanical dispersion re~ects the in~uence of local velocity variations and soil heterogeneity[ Normally

Dm is negligible for ~ow velocities less than about 9=6 m year−0 "Scanlon\ 0880#[ Given maximum watercontents of about 39) this may mean Darcian velocities of about 09−7 m s−0 "Peck et al[\ 0870#[ Thecoe.cient De includes the e}ects of tortuosity and water content[ For silts\ sands and gravel it is primarilydependent on water content "Scanlon\ 0880#[ For chloride di}usion in clay soils empirical relationships _ttedto experimental data are available "Peck et al[\ 0870#[

If a steady!state situation is assumed with a constant solute ~ux equal to the rate of accession fromprecipitation\ Equation "6# may be used to obtain qw at any depth provided that the solute accession rate"Js# and the solute concentration in soil water "c# are known[

Estimates of soil!water ~ux] chloride mass balance method

The measured chloride concentrations in soil water at the three slope positions are shown in Figure 6[The chloride concentration in bulk precipitation was estimated to vary from 9=92 to 9=01 mg L−0 "Joshi\0886#[ Both these values "9=92 and 9=01 mg L−0# were used for C

Þp in estimating the ~ux from Equation "4#[

The long!term average annual precipitation for Saskatoon area is 260 mm year−0 "Wittrock et al[\ 0878#[This was the value used for P

Þin Equation "4#[ The depth!averaged chloride concentration in the pro_le was

calculated by excluding the top 0=4 m below ground level and about 0 m above the water table[ The depth!averaged chloride in the groundwater for about 1 m depth below the water table at the lower and middleslope positions was also calculated[

The drainage ~ux calculated from the pro_le chloride concentrations ranged from 9=05 to 0=95 mm year−0[Using the chloride concentrations in groundwater\ values ranging from 9=24 to 0=85 mm year−0 were obtained[Sharma and Hughes "0874# also obtained drainage ~uxes from groundwater chloride concentrations thatwere double those obtained from the depth!averaged chloride in the soil pro_le[ They explained the di}erenceon the basis of a simple partitioning model and estimated that roughly 49) of the transport occurredthrough preferential ~ow paths[ However their soil was 74) to 84) coarse sand and the average annual



0404

Figure 6[ Chloride concentrations in soil water

rainfall was 799 mm year−0[ The mean areal recharge rate they calculated was 005 mm year−0 "about 04)of the annual precipitation#[ Although preferential ~ow may be important at this site\ the recharge ~ux beingvery small "only about 9=0) to 9=1) of annual precipitation#\ a simple partitioning model may not beappropriate in this case[

A major question about chloride mass balance estimates\ especially in a continental area such as Sas!katchewan\ concerns the origin of chloride present in the soil pro_le[ Remenda et al[ "0885# suggest that thesource of chloride in Saskatchewan soils is presumably precipitation[ According to Remenda "0882# thechloride in the pro_le may be the result of continuous accumulation over time since deglaciation "about09 999 years BP#[ The close correspondence of chloride concentrations in the soil pro_le "31 to 60 mg L−0#and the groundwater "11 to 20 mg L−0# at this study site suggests that the chloride may indeed be meteoric"see Edmunds and Gaye\ 0883#[

A Na]Cl ratio near 9=45 would indicate oceanic origins "Blackburn and McLeod\ 0872#[ For the CreeLake data an average Na]Cl ratio of 9=35 over the period 0872Ð81 was obtained\ indicating possible terrestrialsources of chloride[ Junge and Werby "0847#\ however\ suggested that the ocean is the major source of Clin precipitation over the continental USA[ They concluded that deviation of the Na]Cl ratio from 9=45 maybe either by a loss of Cl caused by a decomposition of sea!spray particles or by additional Na "mineral dust#from the soil[

The magnitude and variation of yearly average chloride deposition is small at large distances from the seacoast "Joshi\ 0886#[ The chloride concentration in rainfall decreases dramatically with distance from thecoast but it can still be measurable at large distances[ Figure 7 shows the chloride concentration in pre!cipitation across Canada measured at precipitation chemistry monitoring stations of Environment Canada"Vet et al[\ 0877#[ One may argue that the uniformly low chloride concentrations in the soil pro_le at thepresent study site are a result of accession from the small amount present in precipitation "Remenda et al[\0885#[ However\ mining activity in Saskatchewan may provide local sources of Cl and the contribution tobulk precipitation from these sources may be considerable[ It is therefore suggested that the chlorideaccumulated in the pro_le may be of meteoric or anthropogenic origin[

Assuming rainfall to be the primary source of chloride it was calculated that roughly 3999 to 6999 yearswould be required to accumulate the total chloride load in the soil pro_le "Joshi\ 0886#[ The residence timeof water within the tills may range from a few hundred years at leached low!lying depressions to over 09 999years in unleached settings "Fortin et al[\ 0880#[ According to Christiansen "0881# the Saskatoon area became



0405

Figure 7[ Chloride concentration in precipitation across Canada "Vet et al[\ 0877#

ice!free about 01 999 to 09 999 years BP at the end of Pleistocene Epoch[ Thus one could assume thatmeteoric chloride accession to the sur_cial freshwater sediments began at about this time[

Another source of chloride could be manure application by early farmers[ Kernen\ however\ has beenmostly a crop farm and manure was probably not applied extensively[ There is no independent evidenceavailable to discount this possibility[ Chloride uptake by vegetation could have a signi_cant e}ect on thechloride accession during the past 76 years of cultivation[ However\ over a total period of 4999 to 09 999years required for accumulation of the pro_le chloride\ this period is very small[ Thus the in~uence ofchloride loss as a result of cultivation on the calculated vadose zone soil!water ~ux is expected to be minimal[

Steady!state advective and diffusive moisture ~uxes

The depth pro_les of advective soil!water ~ux obtained by using the _rst term on the right!hand side ofEquation "6# are shown in Figure 8[ The relationships given by Peck et al[ "0870# were used to compute thedi}usion coe.cient for chloride[ The value of Ds ranged from 1×09−09 to 6×09−7 m1 s−0[ The solute

Figure 8[ Steady state advective and di}usive moisture ~uxes



0406

concentration gradient "1c:1z# was obtained from the depth pro_les of chloride "Figure 7#\ whereas thevalue of Js was the same as indicated earlier "01=85×09−3 mg cm−1 y−0#[

It is clear that the highest moisture ~uxes occur in the shallow zone\ where chloride has been leached"2×09−00 to 8×09−00 m s−0#[ These ~uxes decrease sharply to about 3×09−01 to 5×09−01 m s−0 within thetop 1 m of the unsaturated zone because most of the soil water is evapotranspired from this zone[ Thecalculated ~uxes reach a minimum roughly at the chloride peak and then increase as the chloride con!centrations decrease[

Figure 8 shows the calculated di}usive moisture ~uxes "second term on the right!hand side of Equation6#[ Di}usive moisture ~uxes are upward above the chloride peak and downward below it[ The upwarddi}usive moisture ~ux ranges from a maximum of 0×09−01 m s−0 at the upper slope to a minimum of about0×09−02 m s−0 at the lower slope[ The maximum and minimum downward di}usive moisture ~uxes rangefrom about 0=4×09−01 m s−0 at the lower slope to about 1×09−02 m s−0 at the middle slope[ These ~uxesare only about an order of magnitude less than advective moisture ~uxes and suggest that\ in general\ thedi}usive moisture ~ux may be comparable in magnitude to the advective component[ In a study carried outin the Chihuahuan Desert of Texas\ Scanlon "0880# obtained advective moisture ~uxes that were two tothree orders of magnitude larger than the di}usive moisture ~uxes[ Note that unlike the di}usive ~ux thatvaries in direction\ the advective ~ux is always downward\ because this is a priori assumed in the chloridemass balance approach[

The Peclet number characterizes the magnitude of advective relative to di}usive transport[ In the presentcase it may be calculated as Pe�V1T:Ds\ where V denotes the porewater velocity\ T is the time spaninvolved "maximum 09 999 years in this case# and Ds is the hydrodynamic dispersion coe.cient[ Advectivetransport is negligible if Peð0[

In view of the very low advective velocity\ mechanical dispersion is negligible and Ds may be consideredequal to the e}ective di}usion coe.cient of chloride in soil water "see Peck et al[\ 0870#[ Speci_cally\ takingV�4=3×09−00 m s−0\ De �0=97×09−09 m1 s−0 "being typical for the middle slope position up to 0 m depth#and T�095 years corresponding to a depth of 9=34 m "Joshi\ 0886#\ a value of 9=08 for the Peclet number"Pe# is obtained[ This may be considered as a large value of the Peclet number for this ~ow system[ Thusadvection may be important in the sur_cial zone[ At depths between about 1=4 to 3 m the advective ~uxreaches a minimum[ The minimum value of V�3=0×09−01 m s−0 and De �3=86×09−09 m1 s−0 occurringat the middle slope gives Pe�9=90[ Roughly similar minimum values are obtained at the other two slopepositions[ Therefore the transport process may be dominated by di}usion at these greater depths[ An increasein the Peclet number occurs below about 3 m depth at all slope locations[ A maximum V�0=4×09−00 ms−0 and De �5=2×09−09 m1 s−0 just above the water table "c[ 4=1 m depth# at the middle slope gives aPe�9=29\ indicating an increased contribution of the advective component\ perhaps as a result of directinjection[ At the lower slope a value of Pe�9=96 is obtained at about 3=6 m depth "just below the watertable# whereas the upper slope Pe�9=06 at a depth of 3=3 m\ which is well above the water table[

Chloride peak mi`ration] back`round and justi_cation

As stated earlier\ it has to be considered that as a result of mining activities in and around Saskatoon theanthropogenic chloride input could have been substantial over short periods of time[ The KCl fall!out datafrom earlier studies carried out in this region varied from 9=96 to 9=29 g Cl m−1 month−0 "Buswell\ 0861^Van Beek et al[\ 0864^ personal communication from Ken Reid\ Potash Corporation of Saskatchewan\0884#[ The highest value of the dust fall!out is roughly 01 to 29 times the input from rainfall and of the sameorder as the atmospheric chloride accession reported from the coastal semi!arid regions of south!westernAustralia "Peck et al[\ 0870#[ Even after allowing for a 4) reduction as a result of crop uptake or loss it stillconstitutes a massive increase in input concentration[ During short periods this anthropogenic input wouldhave masked the input from meteoric water and may be the reason for the sharply de_ned bulges of chlorideobserved at all three slope locations[ During the period 0853 to 0860 there were at least six mines operatingin the vicinity of Saskatoon "Van Beek et al[\ 0864#[



0407

This dust fall!out from mines would dissolve with precipitation and move down the soil pro_le[ A lookat the temporal variations in water content pro_les revealed that the chloride bulges could result from adominantly vertical and rapid downward movement through the root zone and subsequent advectivedispersive ~ow "Joshi\ 0886#[ The higher lower limits to the zone of rapid transport were taken as 9=7 m and0=4 m respectively "Joshi\ 0886^ Joshi et al[\ 0886#[

It is possible that rapid ~ow below a certain depth allows transport without much change in the watercontent pro_le[ However\ the evidence presented earlier with regard to low advective moisture ~uxes "lowPeclet numbers# rules out such a possibility[ The observed solute peaks are smooth and nearly symmetric\which indicates that they are a result of a ~ow process where di}usion dominates and ~ow velocities are nothigh[

It is proposed that the chloride bulges result from the fraction of water that moves down rapidly viapreferred pathways through the root zone\ after episodes such as snow melt and heavy rainfall[ It thentravels by advectiveÐdispersive ~ow below this depth[

Calculated ~ux estimates usin` chloride peak mi`ration

In view of the possibility of anthropogenic chloride accession\ chloride peak migration provides a directmeans for another estimate of the soil!water ~ux in the study area[ From the dust fall!out data a prominentinput peak in 0861 was distinguished "Figure 09#[ Van Beek|s "0864# data suggest that the input peak wouldhave occurred in 0855[ Assuming that the chloride peak was injected 11 to 17 years ago\ percolation velocitiesas shown in Table II were estimated[

The estimates of percolation velocity are based on zero transport time in the _rst 9=7 m to 0=4 m depthand allow for a 19) increase in chloride ion velocity as a result of anion exclusion e}ects "Gee and Hillel\0877#[ The zone of rapid transport is assumed to be 9=7 m to 0=4 m deep\ as indicated earlier[ A summary ofthe estimates for percolation velocities and recharge obtained from the chloride and nitrate pro_les "nitratepro_les are not discussed here\ see Joshi\ 0886# is given in Table II[

An independent estimate of the recharge was made by considering that the peaks must have displaced atleast the amount of soil water present above them in the pro_le[ Any peak migration method using completedisplacement of resident moisture to estimate ~ux assumes that the existing water content pro_le has reacheda steady state[ This may not be true\ although it may be argued that because of the nearly uniform land use

Figure 09[ PCS chloride fallout data for Cory mine "personal communication\ Ken Reid\ Manager Environmental A}airs\ PCSSaskatoon#



0408

Table II[ Percolation velocities "m s−0# calculated from the chloride and nitrate peaks

Slope location Peak age

Chloride Nitrate

11 years 17 years 38 years 76 years

Upper 4=42E!09 to 0=25E!98 3=23E!09 to 0=95E!98 0=57E!09 0=42E!98Middle 1=29E!98 to 2=00E!98 0=70E!98 to 1=33E!98 5=59E!09 ÐLower 1=55E!98 to 2=36E!98 1=98E!98 to 1=61E!98 6=65E!09 Ð

Table III[ Recharge "mm year−0# estimates obtained from tritium\ chloride and nitrate pro_les

Slope location Method

Peak migration Mass balance

Chloride Nitrate Tritium Chloride Nitrate Tritium

Upper 8 to 00 00 Ð 9=05 Ð ÐMiddle 04 to 08 14 Ð Ð Ð ÐLower 27 to 37 02 04 1 Ð 04

for the past 099 years this may well be possible below rooting depth[ It was found that the water contentpro_le does not change very much below a depth of about 0=4 m\ hence the steady!state assumption may beconsidered reasonable below this depth "Joshi\ 0886#[ Using the volumetric water content pro_les "obtainedfrom cores# above the peaks at the time of sampling and a peak age of 11 years\ recharge estimates of 00\08 and 37 mm year−0 at the upper\ middle and lower slopes were obtained[ Using a peak age of 17 yearsgave values of 8\ 04 and 27 mm year−0 respectively[ The pro_le depth used for these calculations was from0=4 m to the top of the peak at all slope locations[

A summary of the estimates of recharge obtained from the tritium\ chloride and nitrate pro_les using thedi}erent methods described earlier is given in Table III[ The percolation velocities calculated from chloridepeaks were taken from Table II[ It is seen that the percolation velocities and Darcian ~ux estimates obtainedfrom the solute pro_les are within an order of magnitude[ This increases the con_dence that may be placedupon the estimates obtained at the present study site[

CONCLUSIONS

It has been shown by analysis of _eld data collected during this study that in at least some areas of the semi!arid Canadian Prairies the vadose zone soil!water ~ux below the root zone may be estimated reliably byusing simple analytical models and mass balance methods[ The estimates obtained by using di}erent tracersare within the same order of magnitude[ It was shown by an analysis of chloride age and associated Pecletnumbers that the use of simple models to estimate soil!water ~ux below the root zone is justi_ed at thisstudy site[ It is suggested that a variety of chemical and isotopic tracers\ as well as a suitable soil physical orhydrometoerological method\ should be considered when estimating the minuscule di}use vadose zone soil!water ~ux in semi!arid regions[



0419

REFERENCES

Acton DF\ Ellis JG[ 0867[ The soils of the Saskatoon Map Area 62!B Saskatchewan[ Extension Publication 295\ Saskatchewan Instituteof Pedology Publication S3\ Extension Division\ University of Saskatchewan] Saskatoon[

Allison GB[ 0876[ A review of some physical\ chemical and isotopic techniques available for estimating groundwater recharge[ InEstimation of Natural Groundwater Recharè^ D[ Reidel Pub[ Co] Norwell Ma\ USA[ NATO ASI Series C] 111] 38Ð61[

Allison GB\ Hughes MW[ 0863[ Environmental tritium in the unsaturated zone] estimation of recharge to an uncon_ned aquifer[ InIsotope Techniques in Groundwater Hydrolo`y[ Proceedings of Symposium held in Vienna\ International Atomic Energy Agency]Vienna^ 46Ð61[

Allison GB\ Hughes MW[ 0872[ The use of natural tracers as indicators of soil!water movement in a temperate semi!arid region[Journal of Hydrolo`y 59] 046Ð062[

Allison GB\ Gee GW\ Tyler SW[ 0883[ Vadose zone techniques for estimating groundwater recharge in arid and semi!arid regions[ SoilScience Society of America Journal 47"0#] 5Ð03[

Barnes CJ\ Jacobson G\ Smith GD[ 0883[ The distributed recharge mechanism in the Australian arid zone[ Soil Science Society ofAmerica Journal 47"0#] 20Ð39[

Blackburn G\ McLeod S[ 0872[ Salinity of atmospheric precipitation in the Murray Darling Drainage Division\ Australia[ AustralianJournal of Soil Research 10] 300Ð323[

Buswell JC[ 0861[ Chloride levels of plants sampled near potash mines[ BSc thesis\ Department of Soil Science\ University of Saskatchewan]Saskatoon[

Camann K[ 0868[ Workin` with Ion Selective Electrodes * Chemical Laboratory Practice[ Springer Verlag] New York[Carslaw HS\ Jaeger JC[ 0858[ Conduction of Heat in Solids[ Clarendon Press] Oxford[Carter MR[ "ed[# 0882[ Soil Samplin` and Methods of Analysis[ Canadian Society of Soil Science\ Lewis Publishers] Boca Raton\

Florida[Christiansen EA[ "ed[# 0869[ Physical Environment of Saskatoon[ Publication 00267\ National Research Council of Canada] Ottawa[Christiansen EA[ 0881[ Pleistocene stratigraphy of the Saskatoon area] an update[ Canadian Journal of Earth Science 18] 0656Ð0667[Coleman ML\ Sheperd TJ\ Durham JJ\ Rouse JE\ Moore GR[ 0871[ Reduction of water with zinc for hydrogen isotope analysis[

Analytical Chemistry 43] 882Ð884[De Marsily G[ 0875[ Quantitative Hydroèolo`y[ Academic Press * Harcourt Brace Jovanovich Publishers] San Diego\ CA\ USA[Drimmie RJ\ Heemskerk AR\ Johnson JC[ 0882[ Tritium Analysis[ Technical Procedure 0=9\ Rev 92\ Environmental Isotope Laboratory\

Department of Earth Sciences\ University of Waterloo] Ontario^ 17 pp[Edmunds WM\ Gaye CB[ 0883[ Estimating the spatial variability of groundwater recharge in the Sahel using chloride[ Journal of

Hydrolo`y 045] 36Ð48[Fortin G\ van der Kamp G\ Cherry JA[ 0880[ Hydrogeology and hydrogeochemistry of an aquiferÐaquitard system within glacial

deposits\ Saskatchewan\ Canada[ Journal of Hydrolo`y 015] 154Ð181[Gardner WR[ 0856[ Water uptake and salt distribution patterns in saline soils[ In Isotope and Radiation Techniques in Soil Physics and

Irriàtion Studies[ Proceedings of Symposium held in Aix!en!Provence\ France\ International Atomic Energy Agency] Vienna^ 224Ð239[

Gee GW\ Hillel D[ 0877[ Groundwater recharge in arid regions] review and critique of estimation methods[ Hydroloìcal Processes 1]144Ð155[

Joshi B[ 0886[ Estimation of diffuse vadose zone soil!water ~ux in a semi!arid reìon[ PhD dissertation\ Department of Agricultural andBioresource Engineering\ University of Saskatchewan] Saskatoon[

Joshi B\ Maule C\ De Jong E[ 0886[ Subsurface Hydrologic Regime and Estimation of Di}use Soil Water Flux in a Semi Arid Region[Electronic Journal of Geotechnical Enìneerin` Winter 0886[ Issue located at the following web site http]::geotech[civen[okstate[edu:ejge:ppr8691:index[htm

Junge CE\ Werby RT[ 0847[ The concentration of chloride\ sodium\ potassium\ calcium and sulfate in rain water over the UnitedStates[ Journal of Meteorolo`y 04"4#] 306Ð314[

Keller KC\ van der Kamp G\ Cherry JA[ 0875[ Fracture permeability and groundwater ~ow in clayey till near Saskatoon\ Saskatchewan[Canadian Geotechnical Journal 12] 118Ð139[

Lenore SC "ed[# 0878[ Standard Methods of Examination of Water and Wastewater[ American Public Health Association] Washington\DC[

Mazor E[ 0864[ Multitracing and multisampling in hydrological studies[ Interpretation of Environmental Isotope and HydrochemicalData in Groundwater Hydrolo`y\ Proceedin`s of an Advisory Group Meetin`\ International Atomic Energy Agency] Vienna^ 6Ð25[

McCown RL\ Murtha GG\ Smith GD[ 0865[ Assessment of available water storage capacity of soils with restricted subsoil permeability[Water Resources Research 01] 0144Ð0148[

Orion[ 0889[ Model 83!06B Chloride Electrode and Model 85!06B Combination Chloride Electrode Instruction Manual[ Orion ResearchIncorporated\ Laboratory Products Group] Boston\ MA[

Peck RJ\ Johnston CD\ Williamson DR[ 0870[ Analysis of solute distribution in deeply weathered soils[ A`ricultural Water Manaèment3] 72Ð091[

Philip JR[ 0858[ Theory of in_ltration[ Advances in Hydroscience 4] 104Ð185[Porter LK\ Kemper WD\ Jackson RD\ Stewart BA[ 0859[ Chloride di}usion in soils as in~uenced by moisture content[ Soil Science

Society of America Journal 13] 359Ð352[Remenda VH[ 0882[ Oriìn and mi`ration of natural `roundwater tracers in thick clay tills of Saskatchewan and the Lake A`àsiz clay

plain[ PhD thesis\ University of Waterloo] Ontario[Remenda VH\ van der Kamp G\ Cherry JA[ 0885[ Use of vertical pro_les of d07O to constrain estimates of hydraulic conductivity in a

thick\ unfractured aquitard[ Water Resources Research 21"09#] 1868Ð1876[



0410

Scanlon BR[ 0880[ Evaluation of moisture ~ux from chloride data in desert soils[ Journal of Hydrolo`y 017] 026Ð045[Schmalz BL\ Polzer WF[ 0858[ Tritiated water distribution in unsaturated soil[ Soil Science 097] 32Ð36[Sharma ML\ Hughes MW[ 0874[ Ground water recharge estimation using chloride\ deuterium and oxygen!07 pro_les in the deep

coastal sands of Western Australia[ Journal of Hydrolo`y 70] 82Ð098[Souster WE[ 0868[ Soils of the Kernen Crop Research Farm[ Publication M40\ Saskatchewan Institute of Pedology\ University of

Saskatchewan] Saskatoon[Thatcher LL\ Ho}man CM[ 0852[ Tritium fallout over North America from the Soviet Tests in 0850[ Journal of Geophysical Research

57"19#] 4788Ð4890[Van Beek CGEM\ Halstead EH\ Rennie DA\ Ballantyne AK[ 0864[ Movement and Accumulation of Salts in Soils around Potassium

Re_neries in Saskatchewan\ Report 35\ Saskatchewan Institute of Pedology\ University of Saskatchewan] Saskatoon[Vet RJ\ Sulko} WB\ Still ME\ Martin JB\ Kobelka WF\ Gaudenzi A[ 0877[ Canadian Air Precipitation Monitorin` Network "CAPMoN#\

Precipitation Chemistry Data Summary[ AQRB!77!90\ Environment Canada\ Atmospheric Environment Service] Ottawa[Vogel JC\ Ehhalt D\ Roether W[ 0852[ A survey of natural isotopes in South Africa[ Radioisotopes in Hydrolo`y\ Proceedin`s of

Symposium Tokyo[ International Atomic Energy Agency] Vienna^ 39Ð305[Wittrock V\ Begrand RM\ Wheaton EE[ 0878[ Saskatoon SRC climatolo`ical reference station summary\ 0877[ Technical Report 111\

Saskatchewan Research Council] Saskatoon^ 20 pp[

simple analytical models for interpretation of environmental tracer profiles in the vadose zone

Documents