Physiological condition and water source use of Sonoran Desert riparian trees at the Bill Williams River,Arizona, USA

We investigated the environmental water sources used in mid-summer by three Sonoran Desert phreatophytic riparian tree species, Salix gooddingii, Populus fremontii, and the exotic Tamarix spp., at sites that differed in water table depth. Salix gooddingii was most sensitive to water table decline, as evidenced by lower predawn water potentials. Although P. fremontii was less sensitive to water table decline than S. gooddingii, its leaf gas exchange was the most responsive to atmospheric water stress imposed by high leaf-to-air vapor pressure deficit. Tamarix spp. was least sensitive to water table decline and showed no reduction of predawn water potential over the measured range of depth to groundwater. Comparison between D/H of xylem and sampled environmental water sources suggest that S. gooddingii and P. fremontii used groundwater at most sites with no change in water source as depth to groundwater varied. In contrast, xylem D/H of Tamarix spp. was depleted in deuterium compared to groundwater at most sites, suggesting use of water from an unsampled source, or discrimination against deuterium during water uptake. This study highlights the difficulty in sampling all water sources in large-scale studies of riparian ecosystems with complex subsurface hydrogeology.     

Estimation of groundwater recharge via deuterium labelling in the semi-arid Cuvelai-Etosha Basin,Namibia

The stable water isotope deuterium (²H) was applied as an artificial tracer (²H₂O) in order to estimate groundwater recharge through the unsaturated zone and describe soil water movement in a semi-arid region of northern central Namibia. A particular focus of this study was to assess the spatiotemporal persistence of the tracer when applied in the field on a small scale under extreme climatic conditions and to propose a method to obtain estimates of recharge in data-scarce regions. At two natural sites that differ in vegetation cover, soil and geology, 500?ml of a 70?% ²H₂O solution was irrigated onto water saturated plots. The displacement of the ²H peak was analyzed 1 and 10 days after an artificial rain event of 20 mm as well as after the rainy season. Results show that it is possible to apply the peak displacement method for the estimation of groundwater recharge rates in semi-arid environments via deuterium labelling. Potential recharge for the rainy season 2013/2014 was calculated as 45 mm a^?1 at 5.6 m depth and 40 mm a^?1 at 0.9 m depth at the two studied sites, respectively. Under saturated conditions, the artificial rain events moved 2.1 and 0.5 m downwards, respectively. The tracer at the deep sand site (site 1) was found after the rainy season at 5.6 m depth, corresponding to a displacement of 3.2 m. This equals in an average travel velocity of 2.8 cm d^?1 during the rainy season at the first site. At the second location, the tracer peak was discovered at 0.9 m depth; displacement was found to be only 0.4 m equalling an average movement of 0.2 cm d^?1 through the unsaturated zone due to an underlying calcrete formation. Tracer recovery after one rainy season was found to be as low as 3.6?% at site 1 and 1.9?% at site 2. With an in situ measuring technique, a three-dimensional distribution of ²H after the rainy season could be measured and visualized. This study comprises the first application of the peak displacement method using a deuterium labelling technique for the estimation of groundwater recharge in semi-arid regions. Deuterium proved to be a suitable tracer for studies within the soil–vegetation–atmosphere interface. The results of this study are relevant for the design of labelling experiments in the unsaturated zone of dry areas using ²H₂O as a tracer and obtaining estimations of groundwater recharge on a local scale. The presented methodology is particularly beneficial in data-scarce environments, where recharge pathways and mechanisms are poorly understood.     

Stable isotopic and geochemical variability within shallow groundwater beneath a hardwood hammock and surface water in an adjoining slough (Everglades National Park,Florida, USA)

Data from a 10-month monitoring study during 2007 in the Everglades ecosystem provide insight into the variation of δ¹⁸O, δD, and ion chemistry in surface water and shallow groundwater. Surface waters are sensitive to dilution from rainfall and input from external sources. Shallow groundwater, on the other hand, remains geochemically stable during the year. Surface water input from canals derived from draining agricultural areas to the north and east of the Everglades is evident in the ion data. δ¹⁸O and δD values in shallow groundwater remain near the mean of?2.4 and?12 ‰, respectively. ¹⁸O and D values are enriched in surface water compared with shallow groundwater and fluctuate in sync with those measured in rainfall. The local meteoric water line (LMWL) for precipitation is in close agreement with the global meteoric water line; however, the local evaporation line (LEL) for surface water and shallow groundwater is δ D=5.6 δ¹⁸O+1.5, a sign that these waters have experienced evaporation. The intercept of the LMWL and LEL indicates that the primary recharge to the Everglades is tropical cyclones or fronts. δ deuterium to δ¹⁸O excess (D_ex values) generally reveal two moisture sources for precipitation, a maritime source during the fall and winter (D _ex>10 ‰) and a continental-influenced source (D _ex<10 ‰) in the spring and summer.     

Dating problems with selected mining lakes and the adjacent groundwater body in Lusatia,Germany

This study presents selected results, applying environmental tracers to investigate lake water–groundwater interactions at two study sites located in Lusatia, Germany. The focus of the investigations were two meromictic pit lakes and their adjacent aquifers. In order to follow hydrodynamic processes between lake and groundwater, mixing patterns within the lakes as well as ages of lake and groundwater, water samples of ground- and lake water were collected at three occasions, representing summer and winter conditions in the aquatic systems. The water samples were analysed for stable isotopes (deuterium, oxygen-18) and tritium and sulphurhexafluoride (SF₆ concentration). Lake water profiles of conductivity and ¹⁸O could validate the permanent stratification pattern of both the lakes. Groundwater data sets showed a heterogeneous local distribution in stable isotope values between rain and lake water. A two-component mixing model had been adopted only from ¹⁸O data to determine lake water proportions in the surrounding groundwater wells in order to correct measured tritium and SF₆ concentrations in groundwater samples. This procedure had been hampered by upstream-located wells indicating strong ¹⁸O enrichment in groundwater samples. However, rough groundwater ages were estimated. For both study sites, Piston flow ages between 12.9 and 27.7 years were calculated. The investigations showed the good agreement between two different environmental dating tools, considering the marginal data sets.     

δ13C and δD Values of Opuntia Atacamensis Depending on Different Environmental Conditions in the Atacama Desert of Northern Chile

Abstract

We analysed ¹³carbon and deuterium discrimination in Opuntia atacamensis Phil, at three different sites in the Atacama desert in Northern Chile: At the western Andean slopes, influenced by summer rainfall, in the very arid Chilean central valley, and at coastal fog mountains.

At the most arid site, the central valley, discrimination of ¹³C and D was less (δ-values less negative) and also discrimination more against deuterium. This is an aridity, not an altitude effect.

The differences in ¹³C content may be due to some carbon fixation via the C3 photosynthetic pathway at the more humid sites. Deuterium enrichment at the arid sites might be due to greater discrimination of HDO against H₂O during transpirational water loss.     

Isotopic composition in precipitation and groundwater in the northern mountainous region of the Central Valley of Costa Rica

The linkage between precipitation and recharge is still poorly understood in the Central America region. This study focuses on stable isotopic composition in precipitation and groundwater in the northern mountainous region of the Central Valley of Costa Rica. During the dry season, rainfall samples corresponded to enriched events with high deuterium excess. By mid-May, the Intertropical Convergence Zone poses over Costa Rica resulting in a depletion of ¹⁸O/¹⁶O and ²H/H ratios. A parsimonious four-variable regression model (r^2?=?0.52) was able to predict daily δ¹⁸O in precipitation. Air mass back trajectories indicated a combination of Caribbean Sea and Pacific Ocean sources, which is clearly depicted in groundwater isoscape. Aquifers relying on Pacific-originated recharge exhibited a more depleted pattern, whereas recharge areas relying on Caribbean parental moisture showed an enrichment trend. These results can be used to enhance modelling efforts in Central America where scarcity of long-term data limits water resources management plans.     

Stabile Isotope in den Interaktionen von Parasiten und Wirten bei Höheren Pflanzen

Abstract

An overview is given about the δ¹³C- and δ5D-values in the organic material of hemi- and full- parasitic higher plants and of their hosts.

Hemiparasites have to direct the content of the host xylem into their tissues by lowering their water potential. They achieve this by active water secretion or by lowering the stomatal resistance. In the latter case, the intercellular CO₂-concentration in the chlorenchyme of the parasite is increased. This causes a reduction of the ¹³C-content (δ¹³C-value of the parasite more negative than of the host). The dry matter of the mistletoes is always richer in deuterium than that of the host. The reason for this fact is unknown.

In the case hemiparasites and their hosts show differences in the ¹³CO₂-discrimination during the photosynthetic CO₂-fixation, an eventual transfer of organic material from host to parasite can be checked. By this way a holoparasitic mistletoe, Tristerix aphyllus, could be demonstrated.

In contrast to mistletoes on C3-hosts, such on CAM-hosts have a lower deuterium content in the dry mass than the hosts.

Holoparasites get all their organic material from the hosts and mirror, therefore, in their δ¹³C-values those of the hosts. Their deuterium content in the organic material is always higher than the one in the host. The reason is unknown.     

Soil water balance in the Lake Chad Basin using stable water isotopes and chloride of soil profiles

ABSTRACT

The Lake Chad Basin (LCB) is an endorheic transboundary catchment highly vulnerable to drought. For effective groundwater management, recharge areas need identification and replenishment quantification. At present, little research exploring unsaturated zone water flow processes and groundwater recharge are available. In this study, 12 vertical soil profiles were analysed for stable water isotopes and chloride concentration to estimate evaporation and groundwater renewal. Most δ¹⁸O and δ²H isotope profiles reveal typical arid environment patterns, with maximum enrichment at depths between 2.5 and 20?cm and depletion towards the surface (atmospheric influence) and depth (mixing and diffusion). Average annual dry season evaporation rates in Salamat and Waza Logone range from 5 to 30?mm, in Bahr el Ghazal and Northern Lake Chad from 14 to 23?mm. According to the chloride mass balance (CMB), the average annual recharge rate is estimated between 3 and 163?mm in Salamat and Waza Logone and less than 1 mm in Bahr el Ghazal and Northern Lake Chad. Based on the CMB results, potential recharge sites were identified, while estimated soil evaporation corresponds to plant water use at the initial growing stage, which is an important component in irrigation water management.     

Stable H and O isotope variations reveal sources of recharge in Dhofar,Sultanate of Oman

Due to the ability of stable water isotopes to characterize the origin of water and connected processes of groundwater recharge, we used the isotope variations of hydrogen and oxygen in different water sources for assessing the recharge process in the Dhofar region. δ¹⁸O and δ²H of precipitation, spring water, and groundwater cover a range from ?10 to +2 and from ?70 to +7?‰ (vs Vienna Standard Mean Ocean Water), respectively, and correlate in a linear relationship close to the Global Meteoric Water Line. No obvious evaporation processes are detected. A clear signal of the recent precipitation is given by the annual monsoon. The monsoon signal is confirmed by several springs existing in the south at the foot of the Dhofar mountains and sources at Gogub above 450?m and Tawi Atir at 650?m above sea level. They occur here first in the form of water intercepted by trees as stemflow and throughflow. The isotope signature of groundwater in the Dhofar mountains reflects the climatic conditions at the time of recharge and the lithological features of the limestone matrix. To the north, the isotope patterns of the groundwater are continuously depleted from the monsoon signal along the outcropping aquifer D (Lower Umm Er Radhuma). Here, a more negative signature towards the wells in the Najd desert region was observed. Cyclone water that flooded wadis in the Dhofar region occasionally, as observed in November 2011, falls isotopically into the same range as we observed in the fossil groundwater. Taking into account the different sources of precipitation and groundwater and thus a clear distinction of the isotopic composition of the water sources, we conclude a recharge process divided into a southward and a northward component in the Dhofar region.     

Turnover of hydrogen isotopes in lake sturgeon blood: implications for tracking movements of wild populations

Naturally occurring deuterium (²H) in biota can be used to trace movement, migration and geographic origin of a range of organisms. However, to evaluate movements of animals using δ²H measurements of tissues, it is necessary to establish the turnover time of ²H in the tissues and the extent of isotopic discrimination from different environmental ²H sources to those tissues. We investigated the turnover of ²H in lake sturgeon (Acipenser fulvescens) blood by manipulating both environmental water δ²H and diet δ²H over a four-month period. The half-life of deuterium in lake sturgeon blood was 37.9 days after an increase in the environmental water δ²H of +714?‰. However, no clear turnover in blood ²H occurred over the same period in a separate trial following a change of ?63.8?‰ or +94.2?‰ in diet. These findings suggest that environmental water ²H exchanges much faster with blood than diets and that blood δ²H values can be used to trace movements of sturgeon and other fish moving among isotopically distinct waters.     

Analysis of n(87Sr)/n(86Sr), δ88Sr/86SrSRM987 and elemental pattern to characterise groundwater and recharge of saline ponds in a clastic aquifer in East Austria

Elemental and isotopic pattern of n(⁸⁷Sr)/n(⁸⁶Sr) and δ⁸⁸Sr/⁸⁶Sr_SRM987 were used to characterise groundwater and recharge of saline ponds in a clastic aquifer in East Austria. Therefore, shallow, artesian and thermal groundwaters of the investigated aquifer along with rainfall and rivers were analysed using (MC) ICP-MS. The n(⁸⁷Sr)/n(⁸⁶Sr) ratio and elemental pattern changed with aquifer depth as a result of progressing bedrock leaching and dissolution with increasing groundwater residence time. The n(⁸⁷Sr)/n(⁸⁶Sr) ratio of shallow groundwater below saline ponds of 0.71019?±?0.00044 was significantly different from thermal groundwater of 0.71205?±?0.00035 (U, k?=?2). In contrast to previous theories, this result suggested no recharge of saline ponds by upwelling paleo-seawater. Isotope pattern deconvolution revealed that rainfall accounted to about 60% of the n(⁸⁷Sr)/n(⁸⁶Sr) ratio of shallow groundwater below saline ponds. The δ⁸⁸Sr/⁸⁶Sr_SRM987 values of groundwater decreased from about 0.25 ‰ in most shallow, to predominantly negative values of about –0.24 ‰ in artesian groundwater. This result indicated leaching and dissolution of weathered minerals. In turn, the δ⁸⁸Sr/⁸⁶Sr_SRM987 of deep thermal groundwater showed positive values of about 0.12 ‰, which suggested removal of ⁸⁶Sr from solution by carbonate precipitation. These results highlight the potential of δ⁸⁸Sr/⁸⁶Sr_SRM987 signature as an additional geochemical tracer.     

The exchange of hydrogen ions and of water molecules near the active site of cytochrome c

Three-pulse electron-spin-echo envelopes have been measured for frozen solution samples of horse heart ferric cytochrome c both before and after exchange against D₂0. The deuterium modulation pattern was enhanced relative to modulation patterns due to coupled ¹⁴N nuclei by dividing the envelope obtained with the nondeuterated sample into the envelope obtained with the deuterated sample. Measurements of the modulation depth were made by fitting single cycles of a decaying waveform having the free deuterium NMR period to early portions of the experimental quotient waveform. The observed modulation depth was compared with the depth calculated theoretically from X-ray crystallographic data. The good agreement obtained in this comparison demonstrates the reliability of the electron-spin-echo method as a means of studying the distance and/or distribution of exchangeable hydrogen nuclei in the vicinity of sufficiently well-characterized protein metal-ion active sites.     

Optimized Selection of Water Resource Allocation Schemes Based on Improved Connection Entropy in Beijing’s Southern Plain

Increased urbanization has caused problems such as increasing water consumption and the continuous deterioration of the groundwater environment. It is necessary to consider the groundwater quality in the water resource optimization system and increase the rate of reclaimed water development to reduce the amount of groundwater exploitation and achieve sustainable development of water resources. This study used the Daxing District, a region of Beijing’s southern plain, as an example to evaluate water quality by analyzing water quality data of surface and groundwater from 2012 to 2016 and actual water-use schemes from 2006 to 2016. Three groundwater extraction modes were set up based on NO₃–N concentrations, water resources were optimized under three extraction modes, and water resource optimization schemes were determined based on the improved connection entropy. The results show that (1) the surface water quality was poor, and the proportion of V₄ type water in the indexes of NH₃–N and chemical oxygen demand (COD) was the largest. The surface water can only be used for agricultural irrigation. The pollution sources contributing most to NH₃–N and COD were domestic and agricultural pollution sources. (2) The groundwater quality was good. The NO₃–N index was primarily type I–III water, accounting for 95.20% of the total samples. Severe NH₃–N pollution areas were mainly in the northern region, and most regional groundwater can be used for various purposes. (3) Taking 2016 as an example, three groundwater exploitation modes were set to optimize water resource allocation, and the results showed that the rate of groundwater development and NO₃–N pollution decreased significantly after optimization. (4) Connection entropy is an evaluation method that combines connection numbers and entropy, including identify, difference, and opposition entropy. As connection entropy being a kind of complete entropy, which can reflect the difference of the system in different states, based on the improved connection entropy, the connection entropies of optimal water resource allocation and actual water-use schemes were calculated. The connection entropy of groundwater exploitation mode 3 was less than that of groundwater exploitation modes 1 and 2 and actual water-use schemes from 2006 to 2016. Therefore, exploitation mode 3’s water resource optimization scheme was recommended. In the paper, satisfactory results have been obtained. As a kind of complete entropy, connection entropy has great research value in dealing with complex hydrological problems. This study’s research methods and outcomes can provide methodological and theoretical lessons for water management in freshwater-deficient areas.     

Depth profiling of D implanted into Ti at different temperatures

Depth proliles of 6.6 keV D⁺ implanted into titanium in the temperature range between 140 K and 500 K have been studied using the D(³He, α) H nuclear reaction.

At 140 K the trapped amount is close to 100% at low doses and reaches saturation at about 2 × 10¹⁸D/cm², whereas at room temperature no saturation could be reached up to 2 × 10¹⁹ D/cm². At higher temperatures the amount decreases until no deuterium could be detected in the surface layer above 500 K.

The depth profiles are strongly dependent on temperature. At 140 K the deuterium is found in a surface layer of about 2000 Å with a maximum ratio of deuterium to metal atoms of 2.5. At room temperature a hydride layer of TiD^1.8, forms. The thickness of the hydride layer depends on deuterium dose and extends to 1.5 μm at 2 × 10¹⁹ D/cm². At higher temperatures the atom concentrations are lower and the deuterium seems to diffuse deeply into the bulk.

These results are discussed in terms of diffusion of deuterium i n Ti and titanium hydride.     

Sensitive interferometer for determination of optical and thermal properties

A very sensitive interferometric technique is presented. It allows direct measurement of optical and thermal properties. The experimental set-up is very simple and acts essentially as an unfocused Fabry-Perot interferometer giving rise only to a central fringe. Measurement of (∂n/∂T)_p up to 10^-7 K^-1 is possible. Determination of (∂n/∂T)_p for some liquids, particularly for water and deuterium oxide, has been already performed and others, for ionic crystals, are under way.     

Tracing the pathways of Neotropical migratory shorebirds using stable isotopes: A pilot study

We evaluated the potential use of stable isotopes to establish linkages between the wintering grounds and the breeding grounds of the Pectoral Sandpiper (Calidris melanotos), the White-rumped Sandpiper (Calidris fuscicollis), the Baird's Sandpiper (Calidris bairdii), and other Neotropical migratory shorebird species (e.g., Tringa spp.). These species molt their flight feathers on the wintering grounds and hence their flight feathers carry chemical signatures that are characteristic of their winter habitat. The objective of our pilot study was to assess the feasibility of identifying the winter origin of individual birds by: (1) collecting shorebird flight feathers from several widely separated Argentine sites and analyzing these for a suite of stable isotopes; and (2) analyzing the deuterium and ¹⁸O isotope data that were available from precipitation measurement stations in Argentina. Isotopic ratios (δ¹³C, δ¹⁵N and δ³⁴S) of flight feathers were significantly different among three widely separated sites in Argentina during January 2001. In terms of relative importance in separating the sites, δ³⁴S was most important, followed by δ¹⁵N, and then δ¹³C. In the complete discriminant analysis, the classification function correctly predicted group membership in 85% of the cases (jackknifed classification matrix). In a stepwise analysis δ¹³C was dropped from the solution, and site membership was correctly predicted in 92% of cases (jackknifed matrix). Analysis of precipitation data showed that both δD and δ¹⁸O were significantly related to both latitude and longitude on a countrywide scale (p < 0.001). Other variables, month, altitude, explained little additional variation in these isotope ratios. Several issues were identified that will likely constrain the degree of accuracy one can expect in predicting the geographic origin of birds from Argentina. There was unexplained variation in isotope ratios within and among the different wing feathers from individual birds. Such variation may indicate that birds are not faithful to a local site during their winter stay in Argentina. There was significant interannual variation in the δD and δ¹⁸O of precipitation. Hence, specific locations may not have a constant signature for some isotopes. Moreover, the fractionation that occurs in wetlands due to evaporation significantly skews local δD and δ¹⁸O values, which may undermine the strong large-scale gradients seen in the precipitation data. We are continuing the research with universities in Argentina with a focus on expanding the breadth of feather collection and attempting to resolve the identified issues.     

Geochemical and isotopic evidences from groundwater and surface water for understanding of natural contamination in chronic kidney disease of unknown etiology (CKDu) endemic zones in Sri Lanka

Chronic kidney disease of unknown etiology (CKDu) is the main health issue in the dry zone of Sri Lanka. Despite many studies carried out, causative factors have not been identified yet clearly. According to the multidisciplinary researches carried out so far, potable water is considered as the main causative factor for CKDu. Hence, the present study was carried out with combined isotopic and chemical methods to understand possible relationships between groundwater; the main drinking water source, and CKDu in four endemic areas in the dry zone. Different water sources were evaluated isotopically (²H, ³H and ¹⁸O) and chemically from 2013 to 2015. Results revealed that prevalence of CKDu is significantly low with the groundwater replenished by surface water inputs. It is significantly high with the groundwater stagnated as well as groundwater recharged from regional flow paths. Thus, the origin, recharge mechanism and flow pattern of groundwater, as well as geological conditions which would be responsible for natural contamination of groundwater appear as the main causative factors for CKDu. Therefore, detailed investigations should be made in order to identify the element(s) in groundwater contributing to CKDu. The study recommends providing drinking water to the affected zones using water sources associated with surface waters.     

High-Pressure Hydrogen Isotopes Sources Based on Vanadium Hydride

Equilibrium pressures of protium and deuterium desorption over a two-phase area of monohydride-vanadium dihydride were measured. Temperature measurement range was 300–635 K and the pressure range 1–500 MPa. Obtained temperature-dependences of fugacities within the given measurement range are: lgf(MPa) = −2152/T+ 6.6 and lgf(MPa) = −2575/T + 7.4 for protium and deuterium, respectively. The values of enthalpy and entropy for vanadium dihydride phase formation were calculated from obtained relations. Using expressions obtained for fugacities and literature data on hydrogen imperfection the pressures, which can be obtained with vanadium dihydride employed in thermodesorption hydrogen sources, were estimated. Taking into account that due to deterioration in strength properties of the used structural materials, the heating temperature of the load-bearing body is limited to ∼973 K, maximal calculated pressure, which can be obtained with such sources as ≈1820 MPa for protium and ≈2220 MPa for deuterium. This revised version was published online in August 2006 with corrections to the Cover Date.     

Use of isotopes to study floodplain wetland and river flow interaction in the White Volta River basin,Ghana

Floodplain wetlands influence the timing and magnitude of stream responses to rainfall. In managing and sustaining the level of water resource usage in any river catchment as well as when modelling hydrological processes, it is essential that the role of floodplain wetlands in stream flows is recognised and understood. Existing studies on hydrology within the Volta River basin have not adequately represented the variability of wetland hydrological processes and their contribution to the sustenance of river flow. In order to quantify the extent of floodwater storage within riparian wetlands and their contribution to subsequent river discharges, a series of complementary studies were conducted by utilising stable isotopes, physical monitoring of groundwater levels and numerical modelling. The water samples were collected near Pwalugu on the White Volta River and at three wetland sites adjacent to the river using the grab sampling technique. These were analysed for ¹⁸O and ²H. The analysis provided an estimate of the contribution of pre-event water to overall stream flow. In addition, the variation in the isotopic composition in the river and wetland water samples, respectively, revealed the pattern of flow and exchange of water between the wetlands and the main river system.     

Secondary ion mass spectrometry measurements of deuterium penetration into silicon by low pressure RF glow discharges

Abstract

Using secondary ion mass spectrometry (SIMS) the penetration of deuterium into Si(100) substrates as a result of exposure to deuterium low pressure rf discharges has been determined as a function of exposure time, thermal contact of the Si wafers to the substrate electrode, substrate doping, and discharge pressure. For undoped (100) single crystal Si exposed without intentional heating to a 25 m torr D₂ plasma for 1 min the deuterium concentration in the near-surface region (0—30 nm) approaches 10²¹ at.cm^?3. It drops off with depth, but is still greater than 10¹⁷ at.cm.^?3 at a silicon depth of 200 nm. The large penetration depth, the observation that lowering the substrate temperature decreases the rate of deuterium uptake, and the dependence of deuterium penetration on the substrate doping type indicate that hydrogen diffusion is of primary importance. The presence of a 50 nm thick oxide layer on the Si substrate during plasma exposure lowers the deuterium near-surface concentration in the Si substrate by about three orders of magnitude, while the presence of 10 nm of thermal oxide reduces the deuterium uptake only insignificantly. Heavily B and As doped polycrystalline Si show less deuterium penetration, while undoped polycrystalline Si shows more deuterium uptake than undoped single crystal Si for the same plasma treatment.