Dilute Waters Research Articles

Responses of an Amazonian teleost, the tambaqui (Colossoma macropomum), to low pH in extremely soft water.

Our goal was to compare the internal physiological responses to acid challenge in an acidophilic tropical teleost endemic to dilute low-pH waters with those in nonacidophilic temperate species such as salmonids, which have been the subjects of most previous investigations. The Amazonian tambaqui (Colossoma macropomum), which migrates between circumneutral water and dilute acidic "blackwater" of the Rio Negro, was exposed to a graded low-pH and recovery regime in representative soft water (Na+ = 15, Cl- = 16, Ca2+ = 20 mumol L-1). Fish were fitted with arterial catheters for repetitive blood sampling. Water pH was altered from 6.5 (control) to 5.0, 4.0, 3.0, and back to 6.5 (recovery) on successive days. Some deaths occurred at pH 3.0. Throughout the regime, there were no disturbances of blood gases (O2 and CO2 tensions and contents) or lactate levels, and only very minor changes in acid-base status of plasma and red cells. However, erythrocytic guanylate and adenylate levels increased at pH's less than or equal to 5.0. Down to pH 4.0, plasma glucose, cortisol, and total ammonia levels remained constant, but all increased at pH 3.0, denoting a stress response. Plasma Na+ and Cl- levels declined and plasma protein concentration increased at pH 3.0, indicative of ionoregulatory and fluid volume disturbance, and neither recovered upon return to pH 6.5. Cortisol and ammonia elevations also persisted. Transepithelial potential changed progressively from highly negative values (inside) at pH 6.5 to highly positive values at pH 3.0; these alterations were fully reversible. Experimental elevations in water calcium levels drove the transepithelial potential positive at circumneutral pH, attenuated or prevented changes in transepithelial potential at low pH, and reduced Na+ and Cl- loss rates to the water during acute low-pH challenges. In general, tambaqui exhibited responses to low pH that were qualitatively similar but quantitatively more resistant than those previously documented in salmonids.

Microbial diversity of soda lakes.

Soda lakes are highly alkaline extreme environments that form in closed drainage basins exposed to high evaporation rates. Because of the scarcity of Mg2+ and Ca2+ in the water chemistry, the lakes become enriched in CO3(2-) and Cl-, with pHs in the range 8 to > 12. Although there is a clear difference in prokaryotic communities between the hypersaline lakes where NaCl concentrations are > 15% w/v and more dilute waters, i.e., NaCl concentrations about 5% w/v, photosynthetic primary production appears to be the basis of all nutrient recycling. In both the aerobic and anaerobic microbial communities the major trophic groups responsible for cycling of carbon and sulfur have in general been identified. Systematic studies have shown that the microbes are alkaliphilic and many represent separate lineages within accepted taxa, while others show no strong relationship to known prokaryotes. Although alkaliphiles are widespread it seems probable that these organisms, especially those unique to the hypersaline lakes, evolved separately within an alkaline environment. Although present-day soda lakes are geologically quite recent, they have probably existed since archaean times, permitting the evolution of independent communities of alkaliphiles since an early period in the Earth's history.

Genetic and temporal relations between formation waters and biogenic methane: Upper Devonian Antrim Shale, Michigan Basin, USA

Controversy remains regarding how well geochemical criteria can distinguish microbial from thermogenic methane. Natural gas in most conventional deposits has migrated from a source rock to a reservoir, rarely remaining associated with the original or cogenetic formation waters. We investigated an unusual gas reservoir, the Late Devonian Antrim Shale, in which large volumes of variably saline water are coproduced with gas. The Antrim Shale is organic-rich, of relatively low thermal maturity, extensively fractured, and is both source and reservoir for methane that is generated dominantly by microbial activity. This hydrogeologic setting permits integration of chemical and isotopic compositions of coproduced water and gas, providing a unique opportunity to characterize methane generating mechanisms. The well-developed fracture network provides a conduit for gas and water mass transport within the Antrim Shale and allows invasion of meteoric water from overlying aquifers in the glacial drift. Steep regional concentration gradients in chemical and isotopic data are observed for formation waters and gases; dilute waters grade into dense brines (300,000 ppm) over lateral distances of less than 30 km. Radiogenic ( 14C and 3H) and stable isotope ( 18O and D) analyses of shallow Antrim Shale formation waters and glacial drift groundwaters indicate recharge times from modern to 20,000 yr bp. Carbon isotope compositions of methane from Antrim Shale wells are typical of the established range for thermogenic or mixed gas (δ 13C = −47 to −56‰). However, the unusually high δ 13C values of CO 2 coproduced with methane (∼+22‰) and dissolved inorganic carbon (DIC) in formation waters (∼+28‰) require bacterial mediation. The δD values of methane and coproduced formation water provide the strongest evidence of bacterial methanogenesis. Methane/[ethane + propane] ratios and δ 13C values for ethane indicate: (1) the presence of a thermogenic gas component that increases basinward and (2) progressive bacterial oxidation of ethane as the Antrim Shale subcrop is approached. Multiple episodes of Pleistocene glaciation over northern Michigan appear critical to the development of these gas deposits. Loading of thick ice sheets may have provided hydraulic head that enhanced dilation of preexisting fractures and influx of meteoric water. The physical erosion cycle of repeated glacial advances and retreats exhumed the Antrim Shale around the northern margin of the Michigan Basin, subjecting it to near-surface physiochemical and biochemical processes. The chemical and hydrologic relations demonstrated in the Antrim Shale reservoir suggest a dynamic connection between Pleistocene glacial history of the midcontinent region and development of recoverable, microbially generated natural gas reserves.

Hot and cold CO 2-rich mineral waters in Chaves geothermal area (Northern Portugal)

In order to update the geohydrologic characterisation of Chaves geothermal area, coupled isotopic and chemical studies have been carried out on hot and cold CO 2-rich mineral waters discharging, in northern Portugal, along one of the major regional NNE-trending faults (the so-called “Verin-ChavesPenacova Depression”). Based upon their location, and chemical and isotopic composition, the analysed waters can be divided into two groups. The northern group belongs to the HCO 3/Na/CO 2-rich type, and consists of the hot spring waters of Chaves and the cold spring waters of Vilarelho da Raia. The δD and δ 18 O values show that these waters are of meteoric origin. The lack of an 18O shift indicates that there is no evidence of water/rock interaction at high temperatures. The southern group includes the cold spring waters of Campilho/ Vidago and Sabroso/Pedras Salgadas. Their chemistry is similar to that of the northern group but their heavier δD and δ 18O values could be attributed to different recharge altitudes. Mixing between deep mineralised waters and dilute superficial waters of meteoric origin might explain the higher 3H activity found in the Vidago and Pedras Salgadas mineral waters. Alternatively, they could be mainly related to shallow underground flowpaths. The δ 13C values support a deep-seated origin for the CO 2. The δ 37Cl is comparable in all the mineral waters of the study area, indicating a common origin of Cl. The 87Sr/ 86Sr ratios in waters seem to be dominated by the dissolution of plagioclases of granitic rocks.

Microbial Production and Modification of Gases in Sedimentary Basins: Constraints from Isotopic Compositions

Unconventional natural gas reservoirs, such as organic-rich shales and coalbeds, are gaining in economic significance worldwide. Many of these fields contain some portion of microbial methane, either enhancing or replacing thermogenic gas. Importantly, these microbes produce isotopic and compositional effects on the various gas components that often obfuscate their origin. An expanding data set for gases produced from Devonian black shales in the Michigan and Illinois basins, USA, has allowed for a detailed examination of the related chemical and isotopic compositional changes in gas-water systems that trace these processes. The Antrim Shale, within the northern margin of the Michigan Basin, has recently been shown to produce economic quantities of methane that is dominantly bacterial in origin, based on integrated chemical and isotopic analyses of formation waters and co-produced gas (Martini et al., 1996). The most compelling evidence for microbial generation is the correlation between deuterium in methane and coproduced water (Fig. 1). Exploration for economic microbial gas deposits has been linked to low thermal maturity of the host rock organic matter, development of an open, permeable fracture network, and hydrologic conditions that permit freshwater recharge. Further expansion in the Michigan and Illinois basins has allowed us to develop this hypothesis in areas with differing geologic histories and hydrologic settings. Expansion along the western and southern margins of the Michigan Basin at shallow depths within the Antrim Shale has yielded results that are very similar to those previously reported for the northern margin. Waters show evidence of meteoric influx (salinities increasing basinward from subcrop) and microbial activity. Gas chemistries suggest the occurrence of bacterial methanogenesis. In contrast, deeper, midbasin Antrim Shale development has proven unsuccessful. Here, waters show no signs of meteoric mixing, having salinities and stable isotope compositions (O and H) typical of basinal brines. The gases produced include significant volumes of ethane and propane. Importantly, the correlation between the deuterium in methane and that in co-produced waters is absent. These results suggest the gas produced is thermogenic. The isotopic effects of microbial activity are also seen in the 6a3C values of ethane. The 513C values for methane and ethane are plotted against the 51So values of co-produced waters in Fig. 2. The 6~80 values represent the influx of dilute waters, with the most negative values being from shallow wells near the subcrop of the shale, and the most positive values being from deeper wells within the basin. The methane values are invariant while those for ethane become increasingly higher as the ~lSo values of

Lithium in waters of a polar desert

Lithium (Li+) concentrations were measured in a series of stream and lake samples from a cold, dry desert, the McMurdo Dry Valleys (MDV) in Southern Victoria Land, Antarctica. Li+ geochemistry has been of great interest and utility, in part, because of its solubility and mobility during rockwater interactions. In general, the values determined for the streams and the dilute lake waters in this polar desert environment are similar to those found in temperate streams and lakes. The source of Li+ to these waters is a combination of marine aerosol and crustal weathering within the stream channels. The hypersaline hypolimnion of Lake Bonney has extremely high concentrations of Li+ which has been concentrated via a previous drawdown of the lake and its subsequent evapoconcentration. The different distributions of Li+ within the lakes is also due to past climatic changes and their effects on the chemical evolution of the lakes. The high relative mobility of Li+ controls its distribution within the aquatic systems of this cold, desert environment.

Geochemical exploration of the Chipilapa geothermal field, El Salvador

Results of the geochemical exploration of the Ahuachapán-Chipilapa area are presented. The procedure for interpreting the chemical composition of very dilute thermal waters is emphasized. Three groups of thermal waters are described, two with a geothermal brine component and one resulting from steam condensation. The model for one of the groups (Type 2) leads to predictions of temperature and chloride concentration that are reasonably close to those of the geothermal liquid feeding Chipilapa well CH-7B. In particular, it was predicted correctly that the salinities in the Chipilapa area would be considerably lower than those in the Ahuachapán field.It is shown that the simultaneous modeling of the carbon dioxide concentration and isotopic composition of fumarole steam allows discrimination between primary and secondary steam. The composition of all fumarole samples is described as steam originating from a single reservoir fluid at 250°C, and composition δ 18O = −4.1, δD = −46, CO 2 = 5 × 10 −5 molar fraction.The total discharge composition of CH-7B confirms the trend observed in the Ahuachapán field of decreasing reservoir salinities towards the east. Postulating the existence of a “deep” reservoir brine in the eastern (Chipilapa) section of the system, with lower salinity but otherwise similar temperature and isotopic composition to the Ahuachapán brine, allows for the generation of relatively simple models that explain the formation of the CH-7B brine, and the three groups of thermal waters. Type 1 waters are noteworthy in the sense that they result from a ternary mixture of meteoric water, geothermal brine and high-temperature steam condensate.The possibility that the east-west trend in salinity results from a process of dilution of brine with condensate from steam separated at very high temperatures is discussed. The distribution of the different types of hydrothermal manifestations delineates a lateral discharge system, with the steam upflow zone to the south of the study area, on the northern slope of the volcanic range, and thermal water discharges several kilometers to the north. It is deemed reasonable that exploratory drilling should be directed towards the southern edge of the geothermal system, as far as topography and the indicators of probable secondary permeability permit.

Modeling Organic Solutes in Peatland Soils Using Acid Analogs

AbstractDissolved organic carbon (DOC) dominates the chemistry of porewaters in many peatland soils. Yet modeling its contribution to acid‐base chemistry and to anionic charge has not been attempted for peatland porewaters. Using 3 yr of field data, we investigated the effectiveness of four analog organic acid models in describing the acid‐base chemistry of DOC in porewaters from two acidic (mean pH = 4.0–4.2), high‐DOC (mean DOC = 4.2–5.4 mmol CL−1) peatlands in southern Michigan. Although developed for dilute lake waters, we applied these models to porewaters of peatland soils. All sites exhibited a large deficit in anionic charge (mean = 229 µmolc L−1), which was strongly correlated with DOC (r2 = 0.82) and accounted for 70 to 80% of the total anionic charge. We, therefore, used charge balance to evaluate the models. The four models varied in effectiveness; variations in model organic anion accounted for between 50 and 84% of the variation in anion deficit. Representing organic acid anions with a triprotic acid analog model yielded the best results (r2 = 0.84, slope = 0.96), while a monoprotic acid model was least effective (r2 = 0.50, slope = 0.91). Mean charge densities of the DOC pool (44–52 εmolc mmol−1 DOC) varied little with differences in site characteristics (i.e., water levels and emergent plant communities) and were consistent with other studies. The triprotic acid model appears to be an effective analog for the acid‐base and ionic charge‐contributions of DOC in porewaters of acidic peatland soils.

Geochemistry of the rare earth elements in natural terrestrial waters: A review of what is currently known

The range of observed chemical compositions of natural terrestrial waters varies greatly especially when compared to the essentially constant global composition of the oceans. The concentrations of the REEs in natural terrestrial waters also exhibit more variation than what was reported in seawater. In terrestrial waters, pH values span the range from acid up to alkaline. In addition, terrestrial waters can range from very dilute waters through to highly concentrated brines. The REE concentrations and their behavior in natural terrestrial waters reflect these compositional ranges. Chemical weathering of rocks represents the source of the REEs to natural terrestrial waters and, consequently, the REE signature of rocks can impart their REE signature to associated waters. In addition, because of the typical low solubilities of the REEs, both surface and solution complexation can be important in fractionating REEs in aqueous solution. Both of these processes are important in all natural terrestrial waters, however, their relative importance varies as a function of the overall solution composition. In alkaline waters, for example, solution complexation of the REEs with carbonate ions appears to control their aqueous distributions whereas in acid waters, the REE signature of the labile fraction of the REEs is readily leached from the rocks. In circumneutral pH waters, both processes appear to be important and their relative significance has not yet been determined.

Environment of ore deposition in the Creede mining district, San Juan Mountains, Colorado; Part V, Epithermal mineralization from fluid mixing in the OH Vein

Detailed fluid inclusion studies on coarse-grained sphalerite from the OH vein, Creede, Colorado, have shown that the abrupt color changes between growth zones correspond to abrupt changes in the nature of the ore fluids. Within each growth zone, however, the composition of the fluids remained constant. The base of a distinctive orange-brown growth zone marks a sharp increase in both temperature and salinity relative to the preceding yellow-white zone. The orange-brown growth zone can be correlated along much of the vein and is believed to represent a time-stratigraphic interval. Along the vein, temperatures and salinities of fluid inclusions within this interval show a systematic decrease from about 285 degrees C and 11.5 wt percent NaCl equiv near the base of the vein to about 250 degrees C and 8 wt percent NaC1 equiv, respectively, near the top of the vein. The iron concentration of this sphalerite growth zone shows a similar pattern, decreasing from about 2.8 to 1.2 mole percent FeS.When plotted on an enthalpy-salinity diagram, the fluid inclusion data define a spatial trend indicating the progressive mixing of deeply circulating hydrothermal brines with overlying, dilute ground waters. The hydrothermal brines entered the OH vein from below at a temperature, salinity, and density of approximately 285 degrees C, 11.5 wt percent NaCl equiv, and 860 kg/m 3 , respectively, whereas the overlying ground waters appear to have been preheated to roughly 150 degrees C and had an assumed salinity of 0 wt percent and a density of 920 kg/m 3 . The greater density of the heated ground water promoted mixing with the hydrothermal brine within the open fractures, eausing sphalerite deposition. Although there were also episodes of boiling during vein mineralization, boiling appears unimportant for this sphalerite. Isotopic evidence and geochemical modeling studies also indicate that mixing was the depositional mechanism for sphalerite.An important aspect of the mixing hydrology of the Creede system involves an aquitard overlying the OH vein. This low permeability zone restricted the flow of ground water into the vein from above and forced the upwelling hydrothermal fluids to flow laterally along the vein. The mixing environment thus occurred along the interface between a deeply circulating hydrothermal convection cell and a topographically driven shallow ground-water system.

Chemical weathering of a soil chronosequence on granitoid alluvium: II. Mineralogic and isotopic constraints on the behavior of strontium

The use of strontium isotopes to evaluate mineral weathering and identify sources of base cations in catchment waters requires an understanding of the behavior of Sr in the soil environment as a function of time. Our approach is to model the temporal evolution of 87Sr/ 86Sr of the cation exchange pool in a soil chronosequence developed on alluvium derived from central Sierra Nevada granitoids during the past 3 Ma. With increasing soil age, 87Sr/ 86Sr of ammonium-acetate extractable Sr initially decreases from values typical of K-feldspar to those of plagioclase and hornblende and then remains constant, even though plagioclase and hornblende are absent from the soils after approximately 1 Ma of weathering. The temporal variation of 87Sr/ 86Sr of exchangeable Sr is modeled by progressively equilibrating Sr derived from mineral weathering and atmospheric deposition with Sr on exchange sites as waters infiltrate a soil column. Observed decreases in quartz-normalized modal abundances of plagioclase, hornblende, and K-feldspar with time, and the distinct 87Sr/ 86Sr values of these minerals can be used to calculate Sr flux from weathering reactions. Hydrobiotites in the soils have nearly constant modal abundances, chemistry, and 87Sr/ 86Sr over the chronosequence and provide negligible Sr input to weathering solutions. The model requires time and soil horizon-dependent changes in the amount of exchangeable Sr and the efficiency of Sr exchange, as well as a biologic cycling term. The model predicts that exchangeable Sr initially has 87Sr/ 86Sr identical to that of K-feldspar, and thus could be dominated by Sr leached from K-feldspar following deposition of the alluvium. The maximum value of 87Sr/ 86Sr observed in dilute stream waters associated with granitoids of the Yosemite region is likewise similar to that of the K-feldspars, suggesting that K-feldspar and not biotite may be the dominant source of radiogenic Sr in the streams. This study reveals that, when attempting to use Strontium isotopes to identify sources of base cations in catchment waters and biomass, both preferential leaching of Sr from minerals during incipient soil development and changing Sr exchange efficiency must be considered along with chemical contributions due to mineral dissolution.

Salinity relationships in a freshwater population of eastern mosquitofish

Tolerance limit to elevated ambient salinity, and plasma osmotic regulatory capabilities were evaluated in a freshwater population of Gambusia holbrooki. The upper tolerance limit of ambient salinity was found to be 25‰. Plasma osmotic concentrations trended sharply upward with increasing salinity, but in a stepwise fashion, unlike patterns in related, but more euryhaline species. These laboratory observations are consistent with field observations that natural populations of G holbrooki are generally restricted to fresh and dilute brackish waters.

Salinity relationships in a freshwater population of eastern mosquitofish

Tolerance limit to elevated ambient salinity, and plasma osmotic regulatory capabilities were evaluated in a freshwater population of Gambusia holbrooki. The upper tolerance limit of ambient salinity was found to be 25‰. Plasma osmotic concentrations trended sharply upward with increasing salinity, but in a stepwise fashion, unlike patterns in related, but more euryhaline species. These laboratory observations are consistent with field observations that natural populations of G holbrooki are generally restricted to fresh and dilute brackish waters.

Chemical evolution of waters during long term interaction with granitic rocks in northern Switzerland

As part of an assessment of crystalline rock as a potential host for a nuclear waste repository, water samples were collected from more than 50 locations from the crystalline basement where it is under sedimentary cover in Northern Switzerland and where it is at the surface in the Black Forest. These samples describe the changing chemistry of water in an extended flow system from dilute recharge waters far from chemical equilibrium with its host rock to saline waters at temperatures of 50 to 100°C with residence times far in excess of 105 a that have reached chemical equilibrium with their host rock. This unique set of samples allows an analysis of the chemical evolution of granitic waters from surficial waters far from equilibrium to almost equilibrated waters. Mobile ions, rare gases and isotopic data are used to estimate the extent of reaction between waters and their host rock. The evolution of controlled elements is interpreted as a function of this extent of reaction. Silica contents correspond to approximate equilibrium even in the recharge waters. The relative concentrations of Ca and especially Mg are significantly lower in the borehole waters than in recharge waters indicating a trend towards equilibrium. The Na/K ratios correspond to equilibrium only in the most evolved, older, waters which are shown to be at full equilibrium.

Geochemistry of the rare-earth elements in hypersaline and dilute acidic natural terrestrial waters: Complexation behavior and middle rare-earth element enrichments

Rare-earth element (REE) speciation was modelled in acid (2.9 ≤ pH ≤ 3.5), hypersaline groundwaters from Australia and from the Palo Duro Basin in Texas, USA, using a combined specific ion interaction (Pitzer model) and ion pairing model. The free metal ion species (i.e. Ln 3+) is the dominant form of dissolved REEs in these systems, accounting for 40–70% of the dissolved metal in groundwater from Lake Tyrrell (Victoria, Australia), 50–90% of the REEs in groundwater from Lake Gilmore (Western Australia), and always > 90% of each REE in the Texas groundwaters. (Lakes Tyrrell and Gilmore are actually dry lakes that act as groundwater discharge zones.) The abundance of the free metal ion species increases in these waters with increasing ionic strength and with decreasing pH. The free metal ion species is followed in abundance by REE-sulfate and REE-chloride complexes that account for: 20–50% and 10–15%, respectively, of the dissolved REEs in the groundwaters from Lake Tyrrell; 15–30% and 5–20%, respectively, in the groundwaters from Lake Gilmore; and < 3% and < 7%, respectively, in the Palo Duro Basin groundwaters. The groundwaters of the Lake Tyrrell system and the Palo Duro Basin are enriched in the middle REEs (MREEs) compared to both the light REEs (LREEs) and the heavy REEs (HREEs). (Only Nd, Sm, and Dy were determined in the Lake Gilmore groundwaters and, consequently, it is unclear whether these acid groundwaters are also enriched in the MREEs.) Previous investigators suggested that Fe-rich organic flocs, REE-phosphate complexation, and solid-liquid exchange reactions between terrestrial waters and MREE-enriched surface FeMn coatings, suspended particulates, or secondary mineral phases within aquifer materials, may promote the development of MREE enrichments in natural waters. We propose that organic colloids and REE-phosphate complexes are insignificant in acidic natural waters in regards to MREE enrichments. Instead, solid-liquid exchange reactions or dissolution of surface coatings, suspended particulates, and/or secondary phases as well as sulfate complexation, more likely controls the development of MREE enrichments in acidic natural terrestrial waters.

Rhenium, molybdenum, and uranium in groundwater from the southern Great Basin, USA: Evidence for conservative behavior

Dissolved Re, Mo, and U concentrations, and the concentrations of the major cations and anions, were measured in groundwaters from twenty-three springs in the southern Great Basin, USA, from June 1992 through March 1994. Rhenium concentrations ranged from 5 ± 1 pmol/kg to 190 ± 20 pmol/kg. The highest Re values were observed in the saline groundwater of Saratoga Spring in Death Valley and Cold Spring in Ash Meadows, whereas the lowest Re concentrations were found in Nevares Spring in Death Valley. The mean Re concentration for all of the spring waters sampled is 44 ± 33 pmol/kg. The concentrations of Re differs dramatically for groundwaters that discharge from the regional Paleozoic carbonate aquifer and for local groundwaters from felsic volcanic rocks. The mean Re concentration for groundwaters issuing from the carbonate aquifer is 37 ± 14 pmol/kg (which is similar to the average Re value reported for seawater, i.e., 39.8 ± 0.2 pmol/kg), whereas for the spring waters that discharge from the felsic volcanic aquifers, the mean Re concentration is 18 ± 3.5 pmol/kg. The overall mean concentrations of U and Mo in these groundwaters are 18 ± 12 nmol/kg and 120 ± 60 nmol/kg, respectively. Differences in the U and Mo concentrations for groundwaters from the carbonate aquifer and those from the volcanic aquifer are also observed such that the mean U and Mo concentrations in the carbonate groundwaters are 13 ± 5 nmol/kg and 106 ± 40 nmol/kg, respectively, and the mean U and Mo concentrations in the volcanic spring waters are 31.5 ± 4 nmol/kg and 94 ± 12 nmol/kg, respectively. By comparison, U and Mo concentrations reported for seawater are 13.9 nmol/kg and 107 nmol/kg, respectively.In the oxygenated groundwaters of the Great Basin, Re, Mo, and U appear to be acting conservatively, as in seawater, as evidenced by the covariance observed between Re, Mo, and U with chloride, sodium, and sulfate. Groundwaters discharging from the regional carbonate aquifer in Ash Meadows typically exhibit a URe ratio of about 300 while groundwaters that discharge in Death Valley from local felsic volcanic sources have ratios of about 1700. Waters in the remainder of the Death Valley springs are intermediate and may result from the mixing of the carbonate and volcanic derived waters. The Re, Mo, and U concentrations in addition to the major solute chemistry, indicates that dissolution of carbonate rocks is of primary importance in the groundwaters from Ash Meadows, whereas the weathering of felsic volcanic rocks contributes substantially to the chemical signatures of the Death Valley groundwaters. The differences between URe ratios and different aquifer materials suggest that there is a relationship between the dissolved URe ratios and the aquifer materials.Similar Re/Mo/U ratios for the groundwaters from the carbonate aquifer and seawater are strongly suggestive of quantitative uptake of these trace elements from seawater by carbonate mineral precipitation and subsequent quantitative release of these trace elements during dissolution of the carbonate rocks by groundwater. The substantially larger salinity normalized Re, Mo, and U concentrations in the groundwaters compared to seawater, rule out the possibility that these groundwaters represent simple mixing of dilute terrestrial waters and seawaters or reconstitution of evaporite deposits by groundwater dissolution.

Niche for Steam Stripping in Treating Dilute SOC-Contaminated Waters

As regulatory limits for contaminants in air and water become increasingly stringent, interest in steam stripping to remove synthetic organic compounds (SOCs) from industrial waters has increased. To identify situations in which steam stripping could be a cost-competitive option for treating waters contaminated with low concentrations (<10 mg/L) of synthetic organic chemicals, the performance and cost of steam-stripping towers were modeled, and a range of hypothetical contaminated waters was examined. The cost of steam stripping was compared to that of air stripping, liquid-phase carbon adsorption, and air stripping with off-gas adsorption. Steam stripping was found to be a highly specialized treatment technology that will not frequently be cost-effective, but it does have a small niche in the environmental remediation market. Steam stripping is cost-effective when site-specific factors significantly reduce capital or operating costs, or when the target chemical is only marginally volatile, adsorbable, and biodegradable, effectively making all other conventional treatment methods more expensive.

A 100 ka record of water tables and paleoclimates from salt cores, Death Valley, California

Sedimentary and petrographic features of evaporites and associated sediments from a 185 m deep core taken in Death Valley, CA, together with uranium-series dating have been used to reconstruct the history of water table fluctuations and climate changes in Death Valley for the past 100 ka. Death Valley has been arid during the Holocene (0–10 ka), with predominantly mudflat and saline pan subenvironments. A perennial lake, up to 90 m deep, existed in Death Valley from 10 to 35 ka. Saline pan and mudflat subenvironments dominated Death Valley from 35 to 100 ka. The chronology of changing subenvironments and water table fluctuations in Death Valley generally correlates with other climate records in the western US (Owens Lake and Searles Lake, CA, Browns Room cave calcite, NV), the marine oxygen isotope record, and the Vostok ice core record. Core intervals through saline pan sediments are composed of interbedded halite, chaotic muddy halite, and mud. The halite contains abundant vertical dissolution pipes, cemented with clear halite. These sediments record repeated flooding by dilute waters, dissolution of subaerially exposed surface salt crusts, deposition of mud from suspension, precipitation of halite during the saline lake phase, and cementation by diagenetic halite. Mudflat sediments consist of clayey silt, with sand patches and mud cracks, which document long periods of desiccation and the formation of efflorescent salt crusts from the evaporation of groundwater brines. Saline pan and mudflat deposits formed during periods when Death Valley was relatively arid, similar to the modern climate. Lacustrine deposits consist of mudhalite cycles, accumulated during the early lake stage, bedded thenardite (Na2SO4) and mud above, and a cap of massive halite formed during the latest lake stage, all of which record fluctuating salinities and lake levels in a perennial system. Such deposits document a relatively wet climate with a high ratio of water inflow to evaporation. Ostracodes in mud layers represent the least saline, deepest lake phases. Halite layers are made of fine grained cumulates and clear, vertically-oriented crystals precipitated during shallower, perennial lake stages. Of significance is the nearly complete absence of syndepositional dissolution of saline minerals in the lacustrine interval, indicating that accumulated salts were permanently protected from dissolution by saline lake waters. Such evidence strongly suggests that lakes existed continually, without desiccating, for 25 ka between 10 and 35 ka B.P.

Chemical and isotopic characteristics of fluids along the Cameroon Volcanic Line, Cameroon

Results of the chemical and isotopic analysis of the water and gases discharged from volcanic crater lakes and soda springs located along the Cameroon Volcanic Line were used to characterize and infer their genetic relationships. Variations in the solute compositions of the waters indicate the dominant influence of silicate hydrolysis. Na + (40–95%) constitutes the major cation in the springs while Fe 2+ + Mg 2+ (70%) dominate in the CO 2-rich lakes. The principal anion is HCO 3 (>90%), except in the coastal springs where Cl-predominates. Lakes Nyos and Monoun have FeMgCaHCO 3 − type signatures; the soda springs are essentially NaHCO 3 − type, while all other lakes show similar ionic compositions to dilute surface waters. Dissolved gases show essentially CO 2 (>90%), with small amounts of Ar and N 2, while CH 4 constitutes the principal component in the non-gassy lakes. Active volcanic gases are generally absent, except in the Lobe spring with detectable H 2S. Stable isotope ratio evidence indicates that the bicarbonate waters are essentially of meteoric origin. CO 2 ( δ 13C = −2 to −8% 0 and He ( 3He/ 4He = 1 to 5.6R a) infer a mantle contribution to the total CO 2. CH 4 has a biogenic source, while Ar and N 2 are essentially atmospheric in origin, but mixing is quite common.

EXPERIMENTAL INVESTIGATIONS OF THE WEATHERING OF SUSPENDED SEDIMENT BY ALPINE GLACIAL MELTWATER

The magnitude and processes of solute acquisition by dilute meltwater in contact with suspended sediment in the channelized component of the hydroglacial system have been investigated through a suite of controlled laboratory experiments. Constrained by field data from Haut Glacier d'Arolla, Valais, Switzerland the effects of the water to rock ratio, particle size, crushing, repeated wetting and the availability of protons on the rate of solute acquisition are demonstrated. These ‘free-drift’ experiments suggest that the rock flour is extremely geochemically reactive and that dilute quickflow waters are certain to acquire solute from suspended sediment. These data have important implications for hydrological interpretations based on the solute content of glacial meltwater, mixing model calculations, geochemical denudation rates and solute provenance studies.