Tracers Of Water Movement Research Articles

Determining thermal diffusivity using near‐surface periodic temperature variations and its implications for tracing groundwater movement at the eastern margin of the Tibetan Plateau

AbstractThe thermal diffusivity is the key parameter that controls near‐surface temperature where periodic temperature variation is progressively attenuated and delayed with depth. This article presents the results of apparent thermal diffusivity using temperatures recorded by a bedrock temperature measurement network in the fault zones of western Sichuan. High sensitivity temperature sensors (10−4 K) were installed at a maximum depth reaching 30 m. The apparent thermal diffusivities were deduced from both amplitude damping and phase shifting of annual temperature variations between two different depths. Under pure conduction, the thermal diffusivity determined through the phase method (αΦ) should be equivalent to that determined through the amplitude method (αA), whereas effects of the upward (downward) water flow are evidently reflected in the amplitude decay to make αΦ larger (lesser) than αA. The discrepancy between αΦ and αA can thus be a tracer of water movement or convective heat transfer. The calculated αΦ of the measurement stations varies from 1.22 × 10−6 to 3.00 × 10−6 m2/s, and the estimated αA ranges from 0.93 × 10−6 to 2.41 × 10−6 m2/s. Two regimes of heat transfer underground were suggested from the results. Conductive heat transport prevails over the nonconductive processes at five stations, which is characterized by αΦ coincident with αA for the same depth pair. On the contrary, the values of αΦ differ from αA at six stations in the intersection area of the Y‐shaped fault system, implying that convective heat transfer also plays a comparably important role. This finding is consistent with the hot springs distribution of the area. The results also indicate that water moves upward with an average Darcy velocity of approximately −1 × 10−7 m/s in this region. Our research provides new evidence for the hydrothermal activity in the fault zones at the eastern margin of the Tibetan Plateau.

Effect of Water Table Depth on Nutrient Concentrations Below the Water Table in a Spodosol

Water table depth manipulations as implemented in sugarcane fields of Southwestern Florida, USA, were hypothesized to influence the nutrient concentrations below the water table. Concentrations of phosphorus (P), potassium (K), nitrogen (N), and bromide (Br−) were monitored above and below the water table using a column leaching experiment. Three columns were packed with Immokalee soil (A, E, and Bh horizons) classified as a spodosol and fertilizers (NPK) were applied on the soil surface as solids using rates of 11 kg P ha−1, 166 kg K ha−1, and 200 kg N ha−1. A fourth column where fertilizer mixture and bromide were not added acted as a blank. Potassium was also applied as KBr with bromide used as tracer for water movement. Water table was maintained at 30 cm for 6 weeks and lowered to 50 cm deep for another 6 weeks. Samplers were placed in A, E, and Bh horizons and outlets were placed at 30 and 50 cm deep to obtain solutions for monitoring nutrients and tracer. Solution samplers placed in E and Bh horizons were located below the water table. Slightly elevated P, N, and K concentrations in E horizon for a 50-cm water table depth treatment were observed. For both water table treatments, minimal loss of applied N, P, and K below the water table was observed. The results of the study have shown that movement of nutrients below the water table is slow, and depends on the type of nutrients applied and the water table depth.

Specific Conductance as a Tracer of Preferential Flow in a Subsurface‐Drained Field

Core Ideas An agricultural subsurface drain was used to quantify preferential flow paths. High‐frequency specific conductance was a tracer of water movement through the soil. Preferential flow contributed up to 75% of the water in the subsurface drain. Most preferential flow events were probably through macropores or surface cracks. Specific conductance (SC), soil volumetric water content (VWC), and discharge were monitored on a subsurface agricultural drain for a 2‐yr period (2007–2008) to differentiate preferential flow paths from matrix flow paths. A major observation from the 2‐yr period was the fast SC decrease after relatively small rainfall events, often <5 mm. A total of 25 paired rainfall–SC events were classified, with an average preferential flow onset time (from the event start) after 1.7 h and maximum preferential flow after 2.4 h. A specific conductance end‐member mixing analysis (SC‐EMMA) was used to determine the volume of water that infiltrated through preferential flow pathways. The SC‐EMMA was used for 20 of the 25 paired rainfall–SC events; of the 20 classified events, the maximum preferential flow ranged from 11 to 75% of the total subsurface drain flow, with a mean maximum preferential flow of 31%. Overall, SC‐EMMA illustrated that a significant portion of the subsurface drain discharge can be attributed to preferential flow, mainly through macropores or other largely open preferential flow pathways. The other primary mechanism, antecedent moisture conditions shifts, could only be shown for four of the 25 classified events. Specific conductance as a tracer of preferential flow was shown to be an effective tool for distinguishing preferential flow to subsurface drains. Even during relatively dry periods, the SC had a substantial decrease shortly after a rainfall event contrary to the conventional idea that macropore flow starts only after all the smaller pores are saturated and surface ponding begins to occur.

Miniature External Sapflow Gauges and the Heat Ratio Method for Quantifying Plant Water Loss.

External sapflow sensors are a useful tool in plant ecology and physiology for monitoring water movement within small stems or other small plant organs. These gauges make use of heat as a tracer of water movement through the stem and can be applied in both a laboratory and a field setting to generate data of relatively high temporal resolution. Typical outputs of these data include monitoring plant water use on a diurnal time scale or over a season (e.g., in response to increasing water deficit during drought) to gain insight into plant physiological strategies. This protocol describes how to construct the gauges, how best to install them and some expected data outputs.

Effects of a Shielding Skirt for Prevention of Sea Lice on the Flow Past Stocked Salmon Fish Cages

The effect of a shielding skirt, a tarpaulin mounted from the surface down to 5 m depth around a net cage, on the flow pattern at a commercially stocked salmon cage was investigated. Dye was used as a tracer for water movement and the dye spreading was monitored using aerial images. Current meters were employed to investigate the flow close to the net inside and outside the cage. Tests were conducted with and without the shielding skirt. The focus was on the effectiveness of the shielding skirt to deflect water around the cage. This study shows that a shielding skirt can reduce horizontal flow components significantly inside a cage, which is related to a reduction of water exchange. The flow toward a cage is divided by a shielding skirt, i.e., some of the water is transported around the cage, while some is passing underneath the shielding skirt. Some water entering the fish cage from underneath the tarpaulin is transported toward the surface inside the cage. The use of a shielding skirt might not prevent interaction of the upper water layers inside and outside of a fish cage completely, but it has the potential to reduce the inflow of surface water into the cage, if deployed properly.

Interpreting seasonal convective mixing in Devils Hole, Death Valley National Park, from temperature profiles observed by fiber‐optic distributed temperature sensing

Devils Hole, a groundwater‐filled fracture in the carbonate aquifer of the southern Nevada Mojave Desert, represents a unique ecohydrological setting, as home to the only extant population of Cyprinodon diabolis, the endangered Devils Hole pupfish. Using water column temperatures collected with a fiber‐optic distributed temperature sensor (DTS) during four field campaigns in 2009, evidence of deep circulation and nutrient export are, for the first time, documented. The DTS was deployed to measure vertical temperature profiles in the system, and the raw data returned were postprocessed to refine the calibration beyond the precision of the instrument's native calibration routines. Calibrated temperature data serve as a tracer for water movement and reveal a seasonal pattern of convective mixing that is supported by numerical simulations of the system. The periodic presence of divers in the water is considered, and their impacts on the temperature profiles are examined and found to be minimal. The seasonal mixing cycle may deplete the pupfish's food supplies when nutrients are at their scarcest. The spatial and temporal scales of the DTS observations make it possible to observe temperature gradients on the order of 0.001°C m−1, revealing phenomena that would have been lost in instrument noise and uncertainty.

Differential Transport of Atrazine and Glyphosate in Undisturbed Sandy Soil Column

With increasing awareness and concern for environmental quality, it is important to study the fate of pesticides in the subsurface. Laboratory studies were conducted to determine the behavior of atrazine and glyphosate within the root zone of an undisturbed sandy soil in Jianghan Plain, central China. Chloride as a tracer for water movement was applied to the soil as KCl for 26 hours before pesticide application for another 160 hours. Glyphosate, atrazine, and Cl concentrations (conc.) were determined as a function of time in breakthrough curves (BTCs). Atrazine BTC was fitted better in convection-dispersion equation equilibrium model. For glyphosate, however, a two-site non-equilibrium model was chosen. Leaching rate of atrazine from sandy soil was much higher than that of glyphosate and it took longer for glyphosate to leach through the column due to stronger sorption and degradation to its major metabolite, AMPA (aminomethylphosphonic acid, CH6NO3P), which was detected (up to 8890 ng/l) in the final leachate.

Isotope Oxygen-18 as Natural Tracer of Water Movement in a Coarse Gravel Unsaturated Zone

The unsaturated zone of an aquifer serves as a water reservoir which discharges water and eventual pollution to the saturated zone for a relatively long period after the cessation of surface input. Effective protection of a water resource requires detailed knowledge of transport mechanisms through the unsaturated zone with regard to its protective function. The article presents the application of isotope methods in the study of groundwater transport processes in the unsaturated zone of Selniska Dobrava coarse gravel aquifer. Emphasis is given to the use of environmental isotopes as natural tracers in the study of groundwater dynamics in the unsaturated zone. The estimation of groundwater flow characteristics was based on experimental work in lysimeter. Based on long-time isotope investigations with the use of lumped parameter models, some water flow parameters (mean residence time, mean matrix flow velocity) in the unsaturated zone were calculated. The results were compared with tracing experiment results in the same lysimeter.

Isotopic composition of bare soil evaporated water vapor. Part II: Modeling of RUBIC IV experimental results

Stable water isotopes such as oxygen 18, are tracers of water movement within the soil–vegetation–atmosphere system. They provide useful information for a better understanding of evaporation and water vapor transport within soils. In part I of this paper, we presented a novel control experimental set-up under non steady conditions, dedicated to the measurement of the evaporation flux and corresponding isotopic composition from six bare soil columns. Data analysis raised several questions about the soil depth controlling the isotopic composition of the evaporated water vapor, suggesting different behavior before and after the appearance of back diffusion. Experimental data also suggested a time variable value of the kinetic fractionation factor. The present paper presents the modeling of the experimental results using the coupled heat, water and stable isotope transfer model SiSPAT_Isotope. Model results were used for investigating the above questions more in details. For this purpose, model parameters were calibrated for each soil column in order to reproduce the data. Then model results were inverted to estimate the kinetic fractionation factor. The results show that the hypothesis that the kinetic fractionation factor varies in time is plausible but the uncertainty is too large to derive firm conclusions. The largest uncertainty is found when the soil relative humidity is lower than one but water vapor is still negligible. When back diffusion has occurred, model results are the most robust and confirm that the isotopic composition of the evaporated water vapor is controlled by the soil isotopic composition of the liquid water at the peak. In this case, the retrieved kinetic fractionation factor is close to 18.9‰, corresponding to laminar flow.

SiSPAT-Isotope, a coupled heat, water and stable isotope (HDO and H 218O) transport model for bare soil. Part I. Model description and first verifications

Stable water isotopes, namely deuterium and oxygen 18, are tracers of water movement within the soil–vegetation–atmosphere system. They provide useful information for a better understanding of evaporation and transpiration processes as well as water vapour transport within soils. To better evaluate those potentialities and to identify possible lack of knowledge, a coupled heat, water and stable isotope transport model, called SiSPAT-Isotope was developed for bare soil. This paper presents the theoretical basis of the model, revisiting existing formulations encountered in the literature. An emphasis was put on the formulation of the kinetic fractionation factor, conditioning the resistance to isotope transport between the soil surface and the atmosphere, for which no agreement exists in the literature. The paper also presents first validation tests, showing the consistency of the model by comparison with existing analytical solutions. Sensitivity tests showed that the isotope concentration was very sensitive to the formulation of the resistance to isotope transport between the soil surface and the atmosphere, especially under saturated soil conditions. Only a comparison with existing data sets and further laboratory and field experiments, can help decide which formulation has to be used and in which conditions. Finally, an example of simulation under non-steady state conditions is also presented and discussed.

SiSPAT-Isotope, a coupled heat, water and stable isotope (HDO and H 218O) transport model for bare soil. Part II. Evaluation and sensitivity tests using two laboratory data sets

Stable water isotopes are tracers of water movement within the soil–vegetation–atmosphere system. They have the potential for a better understanding of water vapour transport within soils, evaporation and transpiration processes. To better understand those potentialities and possible lack of knowledge, a coupled heat-water and stable isotope transport model, called SiSPAT-Isotope was developed for bare soil. We presented the theoretical basis of the model in the first part of the paper, including a first validation of the likelihood of model results and a comparison with existing analytical solutions. In this companion paper, we go a step further by comparing the model results with two data sets collected on laboratory columns. In both cases, five soil columns were saturated and let drying during 173 and 253 days, respectively. At selected dates, one of the column was cut into slices and analysed to determine the volumetric water content, the deuterium and oxygen 18 concentrations profiles. The first data set was acquired on disturbed soil columns. The second one was collected on non-disturbed soil columns and it included a complete monitoring of atmospheric variables. It was not the case for the first one and a sensitivity analysis of model results to the air humidity was performed, showing its large influence on surface isotope concentrations. For both data sets, we also conducted a sensitivity analysis to the formulation of the kinetic fractionation factor, conditioning the resistance to isotope transport between the soil surface and the atmosphere, and to the value of soil tortuosity. The results showed that the model was able to reproduce the behaviour of the observed concentration profiles. A fair agreement between measured and calculated values was obtained for all profiles for the disturbed soil. Near surface concentrations were in general overestimated for the undisturbed soil, raising the question of possible influence of immobile water on concentrations values. We showed that soil tortuosity was mostly influential on the depth of the peak isotope concentration, which opens perspectives for its retrieval from the measurement of isotope concentration profiles. When only molecular diffusion was considered, the model was not able to reproduce the liquid slopes of the deuterium/oxygen 18 relationships at the beginning of the drying process. Results were more in agreement with the data when molecular diffusion combined with turbulent transfer were considered. Further laboratory and field experiments are, however, still required to derive a formulation of the kinetic fractionation factor adapted to drying soils and non-saturated conditions.

Particulate backscattering ratio at LEO 15 and its use to study particle composition and distribution

Particulate scattering and backscattering are two quantities that have traditionally been used to quantify in situ particulate concentration. The ratio of the backscattering by particles to total scattering by particles (the particulate backscattering ratio) is weakly dependent on concentration and therefore provides us with information on the characteristics of the particulate material, such as the index of refraction. The index of refraction is an indicator of the bulk particulate composition, as inorganic minerals have high indices of refraction relative to oceanic organic particles such as phytoplankton and detrital material that typically have a high water content. We use measurements collected near the Rutgers University Long‐term Ecosystem Observatory in 15 m of water in the Mid‐Atlantic Bight to examine application of the backscattering ratio. Using four different instruments, the HOBILabs Hydroscat‐6, the WETLabs ac‐9 and EcoVSF, and a prototype VSF meter, three estimates of the ratio of the particulate backscattering ratio were obtained and found to compare well. This is remarkable because these are new instruments with large differences in design and calibration. The backscattering ratio is used to map different types of particles in the nearshore region, suggesting that it may act as a tracer of water movement. We find a significant relationship between the backscattering ratio and the ratio of chlorophyll to beam attenuation. This implies that these more traditional measurements may be used to identify when phytoplankton or inorganic particles dominate. In addition, it provides an independent confirmation of the link between the backscattering ratio and the bulk composition of particles.

Dyes as tracers for vadose zone hydrology

Dyes are important tracers to investigate subsurface water movement. For more than a century, dye tracers have provided clues about the hydrological cycle as well as flow and transport processes in the subsurface. Groundwater contamination often originates in the vadose zone. Agrochemicals applied to the soil surface, toxic compounds accidentally spilled by human activities, and contaminants released from waste repositories leach through the vadose zone and can ultimately pollute groundwater resources. Dyes are an important tool to assess flow pathways of such contaminants. This review compiles information on dyes used as hydrological tracers, with particular emphasis on vadose zone hydrology. We summarize briefly different human‐applied tracers, including nondye tracers. We then provide a historical sketch of the use of dyes as tracers and describe newer developments in visualization and quantification of tracer experiments. Relevant chemical properties of dyes used as tracers are discussed and illustrated with dye intermediates and selected dye tracers. The types of dyes used as tracers in subsurface hydrology are summarized, and recommendations are made regarding the use of dye tracers. The review concludes with a toxicological assessment of dyes used as hydrological tracers. Many different dyes have been proposed as tracers for water movement in the subsurface. All of these compounds, however, are to some degree retarded by the subsurface medium. Nevertheless, dyes are useful tracers to visualize flow pathways.

Behavior of a surface applied radionuclide and a dye tracer in structured and repacked soil monoliths

There has been increasing evidence in recent years about the impact of soil structure on vadose zone hydrology and the distribution of surface applied chemical substances. We have carried out a combined dye and radionuclide tracer study on two monoliths from the same location, one structured and one repacked, as part of an ongoing study to investigate the link between preferential flow, leaching of surface applied substances and their distribution within the soil. A tracer solution containing 1300 Bq/L 58Co and 0.31 μmol/L Sulforhodamine B (SB) was added with roughly constant irrigation during a period of three weeks. The dye served as a tracer for water movement within the soil and thus allowed linkage of the radiotracer ( 58Co) with the flow pattern. Both were monitored in the outflow and measured within profile sections after monolith disassembly. Preferential flow in the structured monolith promoted the bypass and transport of both tracers, although transport was impeded at depths greater than 30 cm by compacted soil and reduced hydraulic conductivity. Eighty four percent of radiocobalt and 8% of SB were found in the upper 4 cm of the structured monolith. The homogenized monolith, on the other hand, showed mostly chromatographic infiltration and a more efficient soil filtering capacity with 91% of radiocobalt and 20% SB residing in the upper 4 cm. Furthermore no tracer was found in the outflow of the homogenized monolith during normal to high irrigation or at greater depth within the monolith. We have related flow characteristics and sorption of radiotracers by quantifying dye distributions and radionuclide activities throughout the profiles. Activities within the flow paths are up to 20-times higher than those measured in the soil matrix, and a fraction of radiocobalt follows the dye tracer in spite of cobalt’s low mobility. The dye can thus be used to trace radionuclide distribution within the soil block.

Fate of Atrazine in Sandy Soil Cropped with Sorghum

A field study was conducted to determine the fate of atrazine (6-chloro-N2-ethyl-N4-isopropyl-1,3,5-triazine-2,4-diamine) within the root zone (0 to 90 cm) of a sandy soil cropped with sorghum [Sorghum bicolor (L.) Moench] in Gainesville, Florida. Atrazine was uniformly applied at a rate of 1.12 kg ai. ha(-1) to a sorghum crop under moderate irrigation, optimum irrigation, and no irrigation (rainfed), 2 d after crop emergence. Bromide as a tracer for water movement was applied to the soil as NaBr at a rate of 45 kg Br ha(-1), 3 d before atrazine application. Soil water content, atrazine, and Br concentrations were determined as a function of time using soil samples taken from the root zone. Atrazine sorption coefficients and degradation rates were determined by depth for the entire root zone in the laboratory. Atrazine was strongly adsorbed within the upper 30 cm of soil and most of the atrazine recovered from the soil during the growing season was in that depth. The estimated half-life for atrazine was 32 d in topsoil to 83 d in subsoil. Atrazine concentration within the root zone decreased from 0.44 kg ai. ha(-1) 2 days after application (DAA) to 0.1 kg a.i. ha(-1) 26 DAA. Negligible amounts of atrazine (approximately 5 microg kg(-1)) were detected below the 60-cm soil depth by 64 DAA. Most of the decrease in atrazine concentration in the root zone over time was attributed to degradation. In contrast, all applied bromide had leached past the 60-cm soil depth during the same time interval.

Simulation of pesticide leaching at Vredepeel and Brimstone farm using the macropore model PLM

The distributions of bromide, bentazone and ethoprophos in the light-textured and unstructured soil at Vredepeel was simulated using the Pesticide Leaching Model (PLM). Distributions of all compounds were satisfactorily simulated using the data provided and without calibration. Since bromide is used as a tracer of water movement, this agreement indicates that PLM was able to model the movement and dispersion of water in the soil profile. However traces of bromide that remained near the soil surface were not predicted. Although PLM was designed to simulate concentrations of pesticide that reach drainage waters by preferential flow in structured soils, the model was still able to predict the distribution of the large proportion of bentazone and ethoprophos that remained in the topsoil at Vredepeel. The soil at Brimstone farm is a very highly structured, heavy, cracking-clay soil. PLM was used to simulate concentrations of isoproturon measured in samples of drainage water taken from the site. Simulated concentrations similar to those measured were obtained but only after extensive calibration of the model.

Convective water exchanges in a wind-sheltered littoral region of Eau Galle Reservoir, Wisconsin USA

Rates of convective water exchange were estimated for periods of differential cooling from a heat budget model, based on detailed changes in water temperature at stations positioned along the littoral slope of the macrophyte-occupied southwest embayment in Eau Galle Reservoir, Wisconsin. Differential cooling and convective water exchanges occurred nightly over a study period of 14 days in August, 1991. Although wind speeds were negligible during most of the nights, estimated rates of convective exchange (grand mean = 0.00066 m 3 m -1 s -1 ) were sufficient to result in a residence time of only ∼1 day in this embayment. Rates of convective exchange calculated via a heat budget model in 1991 were very similar in magnitude to rates measured in 1989 in another embayment of Eau Galle Reservoir using dye as a tracer for water movement. Our results suggest that substantial horizontal water movements and solute transport can occur in the absence of wind in vegetated littoral regions of lakes.

Effects of bioturbation by the lugworm Arenicola marina on cadmium uptake and distribution in sandy sediments

The effect of bloturbation by the lugworni Arenicola marina on uptake and distribution of cadnxum in sediment was assessed using laboratory sediment cores. Carner-free was added to the water phase each day. Bioturbation (irrigation) was measured using bromide (Br-) as a tracer for water movement. In cores without lugworms all Cd was found in the surface sediment where it continued to build up over 16 d of exposure. In cores containing lugworms a distinct peak of Cd was found both at the sediment surface and, after a few days, at the feeding pocket of the worm (10 to 15 cm depth). During the 16 d of exposure this subsurface: peak broadened and eventually Cd was found in all depths from top to feeding depth of the indiv~dual worm. Compared to sediment cores without worms, the presence of lugxeorms more than doubled the rate of removal of Cd from water to sediment. Thls was attributed to an ~ncreased turnover of sediment (due to feeding activity), an increased sediment surface area (due to fecal casts, head shaft, tube and irrigation of the whole burrow) and an increased contact of Cd-labelled water with potential binding sites in the sediment due to irrigation Exposure to 1 ppm Cd reduced the fract~onal ratcl at which lugworms removed Cd from the water (as 'F of Cd in the water). The total Cd flux to the sediment, however, was much greater due to the h g h e r Cd concentrations in the water Water fluxes estimated using Bras a solute tracer revealed a 10to 20fold increase in water exchange of the sediments when lugworms were present. This enhanced water flux was not affected by exposure of lugworms to 1 ppm Cd. The results indicate that the presence of bioturbating infauna influences both the uptake rates of trace metals in near-shore sediments and the distribution of those metals.

The transfer of reprocessing wastes from north-west Europe to the Arctic

The discharge of radioactive waste, from nuclear fuel reprocessing facilities, into the coastal waters of north-west Europe has resulted in a significant increase in the inventories of a number of artificial radionuclides in the North Atlantic. Radiocaesium, 90Sr and 99Tc, which behave conservatively in seawater, have been used widely as tracers of water movement through the North Sea, Norwegian Coastal Current, Barents Sea, Greenland Sea, Fram Strait, Eurasian Basin, East Greenland Current and Denmark Strait overflow. These studies are summarised in the present paper. It has been estimated that 22% of the 137Cs Sellafield discharge has passed into the Barents Sea, en route to the Nansen Basin, via the Bjomoya-Fugloya Section, with another 13% passing through the Fram Strait. This amounts to 14 PBq 137Cs. Quantifying the influx of other radionuclides has been more problematic. The inflowing Atlantic water now appears to be diluting waters in the Arctic Basin, which were contaminated in the late 1970s and early 1980s as a result of the substantial decrease in the discharge of reprocessing wastes. Sellafield (U.K.) has dominated the supply of 134Cs, 137Cs, 90Sr, 99Tc and Pu, whereas La Hague (France) has contributed a larger proportion of 129I and 125Sb.

Use of injected helium as a hydrological tracer

Abstract Helium has several characteristics which make it attractive for use as a tracer in hydrological studies. These include its inert nature, relatively high solubility in water (~ 1 %), low molecular diffusion in water, ready availability in commercial quantities, nontoxic nature, and low background atmospheric concentration. The use of helium as a tracer of water movement has become possible through the development of an instrument which takes advantage of the fact that at room temperature helium diffuses through a quartz glass membrane at a rate of three to four orders of magnitude greater than any other gas. This paper describes: (i) a set of experiments undertaken to compare breakthrough of helium with common salt (NaCl) tracer through laboratory sand columns; (ii) a set of groundwater tracing experiments conducted in a basaltic aquifer in Central O'ahur, Hawaii and (iii) two laboratory experiments undertaken to evaluate the applicability of helium instrumentation for the tracing of submerged plumes in open water conditions. The test results demonstrate that helium behaves as a conservative tracer during saturated flow through porous media. During unsaturated flow, exchange of helium with air entrained in the porous media reduces its usefulness. During submerged flow of a labelled plume, helium behaves like fluorescein in a relatively tranquil laboratory tank environment for hours but is gradually lost through the air-water interface, thus limiting the usefulness of helium in shallow plume tracing studies to short duration experiments.