Groundwater Upwelling Research Articles

Models of formation and activity of spring mounds in the mechertate-chrita-sidi el hani system, eastern Tunisia: implications for the habitability of Mars.

Spring mounds on Earth and on Mars could represent optimal niches of life development. If life ever occurred on Mars, ancient spring deposits would be excellent localities to search for morphological or chemical remnants of an ancient biosphere. In this work, we investigate models of formation and activity of well-exposed spring mounds in the Mechertate-Chrita-Sidi El Hani (MCSH) system, eastern Tunisia. We then use these models to explore possible spring mound formation on Mars. In the MCSH system, the genesis of the spring mounds is a direct consequence of groundwater upwelling, triggered by tectonics and/or hydraulics. As they are oriented preferentially along faults, they can be considered as fault spring mounds, implying a tectonic influence in their formation process. However, the hydraulic pressure generated by the convergence of aquifers towards the surface of the system also allows consideration of an origin as artesian spring mounds. In the case of the MCSH system, our geologic data presented here show that both models are valid, and we propose a combined hydro-tectonic model as the likely formation mechanism of artesian-fault spring mounds. During their evolution from the embryonic (early) to the islet (“island”) stages, spring mounds are also shaped by eolian accumulations and induration processes. Similarly, spring mounds have been suggested to be relatively common in certain provinces on the Martian surface, but their mode of formation is still a matter of debate. We propose that the tectonic, hydraulic, and combined hydro-tectonic models describing the spring mounds at MCSH could be relevant as Martian analogs because: (i) the Martian subsurface may be over pressured, potentially expelling mineral-enriched waters as spring mounds on the surface; (ii) the Martian subsurface may be fractured, causing alignment of the spring mounds in preferential orientations; and (iii) indurated eolian sedimentation and erosional remnants are common features on Mars. The spring mounds further bear diagnostic mineralogic and magnetic properties, in comparison with their immediate surroundings. Consequently, remote sensing techniques can be very useful to identify similar spring mounds on Mars. The mechanisms (tectonic and/or hydraulic) of formation and evolution of spring mounds at the MCSH system are suitable for the proliferation and protection of life respectively. Similarly, life or its resulting biomarkers on Mars may have been protected or preserved under the spring mounds.

Effect of low‐permeability layers on spatial patterns of hyporheic exchange and groundwater upwelling

AbstractBed form‐induced hyporheic interactions are characterized by a nested system of flow paths that continuously exchange water, solutes, momentum, and energy. At the local scale, sediment heterogeneity plays a key role in the hydrodynamics and potential for biogeochemical transformations within the hyporheic zone. This manuscript explores the role of low‐permeability sedimentary layers on the interplay between bed form‐induced hyporheic exchange and groundwater upwelling. A hydrodynamic conceptualization that sequentially couples fully‐turbulent flow in the water column and Darcian flow in the sediment is used. Low‐permeability layers are characterized by long residence times and solute accumulation. Furthermore, these layers induce hydrodynamic sequestration due to the relocation and, in some cases, emergence of new stagnation zones. Spatial patterns of residence time distributions and flushing intensities indicate that the interface of the low‐permeability layers has the potential to be a hot spot for biogeochemical transformations and flow acceleration near such interface can increase the mobilization capacity for the products of redox chemical and microbial processes. A discussion about the possible implications that hydrodynamic changes have on the biogeochemistry of hyporheic zones is presented; however, further biogeochemical experimentation and modeling are needed to validate these arguments.

Hyporheic Exchange and Nutrient Uptake in A Forested and Urban Stream in the Southern Appalachians

The hyporheic exchange (HE) is defined as the interaction between stream water and groundwater, where the stream water passes back and forth between the active channel and subsurface flow paths (Runkel, 1998). The zone of this exchange is characterized by saturated pore spaces, under sand or gravel stream beds (Hancock, 2002) and near the adjacent banks of the stream (Ryan, 2010), that contain some amount of water from the main stream channel (Boulton, Welty, & Larson, 2010). An indication of channel complexity within streams (Grimm, 2005), this transitional zone exposes surface water solutes to alternating oxic and anoxic conditions as they are mixed within the groundwater flow system (Lautz & Siegel, 2007). This plays a crucial role in stream ecosystem functioning with regard to physical characteristics (e.g. stream temperature), biogeochemical processes, (Ryan, 2010), and nutrient cyclings, which ultimately control the water quality of the stream (Lautz & Siegel, 2007). HE is driven by many physical attributes. Parent lithology of watersheds affects HE by controlling sediment porosity and hydraulic conductivity (Morrice, Valett, Dahm, & Campana, 1997). In addition, bed topography (i.e.dunes and ripples in sediments) drives HE through changes in local hydraulics (Harvey & Bencala 1993). Stream slope, morphology, and bed form (e.g. pool-step sequence, channel sinuosity, etc) also influence HE (Wondzell, 2005). As a result, extent of HE depends on a wide variety of factors including, but not limited to, sedimentporosity and hydraulic conductivity, channel morphology, as well as strength of groundwater upwelling, discharge, and size of the channel (Hancock, 2002). Size of HE in the vertical and lateral directions can range anywhere from a few centimeters to tens of meters depending on all of the above stated factors (Kasahara & Hill,2000). From a hydrological perspective, the hyporheic zone also has the potential to reduce peak discharge during storm events (Kasahara & Hill, 2002), a quality of particular importance in urban areas with extensive impervioussurfaces prone to storm runoff. The ecological significance of HE is even greater than just hydrologic flux. HE brings oxygen and other substrates in and flushes wastes out (Hancock, 2002). This process lends itself to a buffer having the potential to impede pollutant transport within both surface water flow paths as well as groundwater (Hester & Gooseff, 2010). HE increases the contact time of stream water with chemically reactive sediments and microbial communities, which creates hot spots for biogeochemical processes (Findlay, 1995).Given the permeable nature of hyporheic sediments, as nutrients flow through the hyporheic zone, it is reactively filtered (Trimmer et al., 2012). Hyporheic zones also provide a means for nitrogen (N) and other nutrients to be temporarily stored before they are lost downstream (Reidy & Clinton, 2004). This longer residence time for materials and reactive filtration allows for nutrient processing and plays a crucial role in regulating theconcentrations and forms of N exported downstream (Ensign & Doyle, 2006).

Fine-Scale in Situ Measurement of Riverbed Nitrate Production and Consumption in an Armored Permeable Riverbed

Alteration of the global nitrogen cycle by man has increased nitrogen loading in waterways considerably, often with harmful consequences for aquatic ecosystems. Dynamic redox conditions within riverbeds support a variety of nitrogen transformations, some of which can attenuate this burden. In reality, however, assessing the importance of processes besides perhaps denitrification is difficult, due to a sparseness of data, especially in situ, where sediment structure and hydrologic pathways are intact. Here we show in situ within a permeable riverbed, through injections of (15)N-labeled substrates, that nitrate can be either consumed through denitrification or produced through nitrification, at a previously unresolved fine (centimeter) scale. Nitrification and denitrification occupy different niches in the riverbed, with denitrification occurring across a broad chemical gradient while nitrification is restricted to more oxic sediments. The narrow niche width for nitrification is in effect a break point, with the switch from activity "on" to activity "off" regulated by interactions between subsurface chemistry and hydrology. Although maxima for denitrification and nitrification occur at opposing ends of a chemical gradient, high potentials for both nitrate production and consumption can overlap when groundwater upwelling is strong.

Geometry, stratigraphy and evidences for fluid expulsion within Crommelin crater deposits, Arabia Terra, Mars

Conical mounds and furrows are widely interpreted as the morphological evidences of fluids expulsion on the martian surface. In the Crommelin crater (equatorial Arabia Terra) furrows and conical mounds are exhumed within light-toned equatorial layered deposits (ELDs). Aim of this paper is to describe these landforms and discuss their potential relations with water upwelling in Crommelin area.A comparative study of some of the morphologies hosted in the Crommelin area deposits have been performed by using multiple datasets (CTX, HRSC, MOLA, HiRISE). Then examples of spring and conical mounds on Earth was examined for comparison with analog structures on Mars. In this work thickness and geometries of the crater filling sediment packages have been calculated. Stratigraphic contacts and relations have been also reported in Crommelin area revised geological map, and mound clusters, potentially fluid-related morphologies, from Crommelin, Firsoff and Southern crater have been detailed.The morphometric and morphological analyses revealed that mounds and other structures occur where the ELDs are thicker and crudely layered. In addition, orthorectified imagery and high-resolution topography indicated the presence of conical mounds within the upper portion of ELDs near the craters rims. Mounds show apical holes and are linked to elongated structures resembling veins and dikes. Elongated structures (furrows) and concentric strata pattern that we refer to as ridge-and-through, were described inside to Crommelin crater. MOLA-based DEMs revealed that these morphologies developed within a flat topography and are inconsistent with gravitative processes.The results suggest that the inferred sediments package was likely part of an extensive zone of groundwater upwelling. This long-wavelength flow controlled water and sediments supply into the study area, probably during a major climate shift. Fluid expulsion processes were recognized as a relevant process in the formation of these morphologies. Mounds, furrows and related structures could be linked with deep fracture systems generated during the impact that trigger the potential upwelling of groundwater, at some point after the impact itself.As a consequence, groundwater upwelling could be expected in other craters on Mars with Crommelin-like topographic and geological setting.

Dissolved Oxygen Dynamics at the Sediment–Water Column Interface in an Urbanized Stream

This manuscript reports findings on sediment oxygen demand (SOD), gross primary production (GPP), net daily metabolism (NDM), and stream reaeration in an urbanized stream, the Jordan River, in Utah. The river has two segments; the Lower Jordan River, which is impaired for dissolved oxygen (DO) and the Upper Jordan River, which is fast flowing with coarse sediments and has no DO impairment. Summer SOD values for the Lower Jordan River ranged from a high 2.2 g DO/m2 per day to a low of 0.97 g DO/m2 per day with most of the sampled sites in the Lower Jordan River having SOD values greater than 1 g DO/m2 per day. SOD values correlated well with volatile solids in surface sediments of the Lower Jordan River. The Upper Jordan River showed SOD values as high as 3.0 g DO/m2 per day, which was attributed to hyporheic exchanges or groundwater upwelling. All sampled sites exhibited high SOD values in winter. A modified chamber method was employed to estimate community respiration (CR24), GPP, and NDM, while characterizing both the water column and benthos. In summer 2010, the sediment tray primary production (TPP) ranged from 1.0 to 7.4 g DO/m2 per day. In winter 2011, TPP ranged from 0.7 g DO/m2 per day to a high value of 5.6 g DO/m2 per day. NDM values indicated that the Upper Jordan River is a year round source of in-stream produced organic matter to the downstream Lower Jordan River with the majority of organic matter produced in the benthos. Reaeration measurements showed that the potential for reaeration is much higher in the mid-sections of the Jordan River, where the river has increased flow velocities due to topography, decreased depths, and a less uniform bottom.

Groundwater resource sustainability in the Wadi Watir delta, Gulf of Aqaba, Sinai, Egypt

The Wadi Watir delta, in the arid Sinai Peninsula, Egypt, contains an alluvial aquifer underlain by impermeable Precambrian basement rock. The scarcity of rainfall during the last decade, combined with high pumping rates, resulted in degradation of water quality in the main supply wells along the mountain front, which has resulted in reduced groundwater pumping. Additionally, seawater intrusion along the coast has increased salinity in some wells. A three-dimensional (3D) groundwater flow model (MODFLOW) was calibrated using groundwater-level changes and pumping rates from 1982 to 2009; the groundwater recharge rate was estimated to be 1.58 × 106 m3/year. A variable-density flow model (SEAWAT) was used to evaluate seawater intrusion for different pumping rates and well-field locations. Water chemistry and stable isotope data were used to calculate seawater mixing with groundwater along the coast. Geochemical modeling (NETPATH) determined the sources and mixing of different groundwaters from the mountainous recharge areas and within the delta aquifers; results showed that the groundwater salinity is controlled by dissolution of minerals and salts in the aquifers along flow paths and mixing of chemically different waters, including upwelling of saline groundwater and seawater intrusion. Future groundwater pumping must be closely monitored to limit these effects.

Mixing of surface and groundwater induced by riverbed dunes: Implications for hyporheic zone definitions and pollutant reactions

[1] The hyporheic zone is often defined as where mixing of surface water and groundwater occurs in shallow sediments beneath and adjacent to rivers. This mixing is credited with creating unique biogeochemical conditions that can attenuate contaminants from either upstream surface water or groundwater under gaining conditions. However, reactions of contaminants upwelling from groundwater may be more dependent on such mixing than contaminants from surface water. We numerically modeled mixing between hyporheic flow paths induced by riverbed dunes and flow paths of adjacent upwelling of deeper groundwater. Results show that only 12.7% or less tracer mass upwelling from deeper groundwater dispersed across into hyporheic flow paths originating in surface water. The spatial extent of a mixing-defined hyporheic zone was smaller than a hyporheic zone defined as hydrologic flow paths leaving and returning to surface water. Mixing-dependent reactions will therefore be localized within a thin mixing zone yet vary considerably with site conditions. For example, mixing in homogeneous sediments was controlled most by variation in hydraulic conductivity and upwelling flow rate which primarily affected mixing zone length. By contrast, introduction of heterogeneity increased mixing primarily by increasing mixing zone thickness, consistent with studies of flow focusing in aquifers. Finally, dispersivity is a critical parameter for which data are needed for shallow sediments. Our results help clarify hyporheic zone definitions and potential for mixing-dependent reactions. In particular, the biogeochemically reactive portion of riverbed sediments from the perspective of upwelling contaminants does not necessarily spatially coincide with more traditional hydrologic conceptions of the hyporheic zone.

Dynamics, chemical properties and bioavailability of DOC in an early successional catchment

Abstract. The dynamics of dissolved organic carbon (DOC) have been intensively studied in mature ecosystems, but little is known about DOC dynamics and the significance of DOC as a substrate for microbial activity in early-successional catchments. We determined the concentration, chemical composition, source, radiocarbon age, and bioavailability of DOC along the hydrological flow path from soil solution to a downstream pond in a recently constructed catchment (Chicken Creek Catchment, Germany). Soil solution, upwelling ground water, stream water, subsurface water in an alluvial fan, and pond water all had high DOC concentrations (averages: 6.0–11.6 mg DOC L–1), despite small carbon stocks in both vegetation and soil of the catchment. Solid-state CPMAS 13C NMR of DOC in upwelling ground water revealed a higher proportion of aromatic compounds (32%) and a lower proportion of carbohydrates (33%) than in pond water (18% and 45%, respectively). The average 14C age of DOC in upwelling ground water was 2600 to 2900 yr, while organic matter of the Quaternary substrate of the catchment had a 14C age of 3000 to 16 000 yr. Both the 14C age data and 13C NMR spectra suggest that DOC partly derived from organic matter of the Quaternary substrate (about 40 to 90% of the C in the DOC), indicating that both recent and old C of the DOC can support microbial activity during early ecosystem succession. However, in a 70 day incubation experiment, only about 11% of the total DOC was found to be bioavailable. This proportion was irrespective of the water type. Origin of the microbial communities within the catchment (enriched from soil, stream sediment or pond water) also had only a marginal effect on overall DOC utilization.

Incubation, hatching and survival of eggs of Atlantic salmon (Salmo salar) in spawning redds influenced by groundwater

Many west coastal and northern Norwegian rivers run through deep, confined valleys with permeable layers of glacial and alluvial deposits. Groundwater flows through these permeable layers and enter lakes and rivers as underwater seepage and springs. Groundwater inflow to inland Norwegian rivers may constitute 40–100% of total water discharge during low flow periods in late summer and winter. Juvenile salmonids may take advantage of groundwater upwellings and actively seek out such patches. In regulated rivers groundwater influx may create refuges during low flow or hydropeaking episodes. The importance of groundwater for salmon redd site selection and egg survival is also clear, although less known and documented in regulated rivers. Eggs of Atlantic salmon ( Salmo salar ) are deposited in redds in river bed gravels lacking fine sediments and with high oxygen levels. Egg development is therefore dependent on the interaction of a number of environmental factors such as groundwater influx, oxygen and temperature. Atlantic salmon in the regulated River Suldalslågen, Western Norway, spawn relatively late compared to other Norwegian rivers, with a peak in early January. Newly emerged fry are found from the end of May to the beginning of June, i.e. “swim up” one month earlier than expected using models for egg and alevin development and river water temperatures. The most plausible explanation is that groundwater has a higher and more stable temperature than surface river water. In field experiments, fertilized salmon eggs were placed in boxes close to natural spawning redds in the river bed at sites influenced and those not influenced by groundwater. A difference of up to 40 days in 50% hatching was found, and “swim up” occurred at the end of May in boxes influenced by groundwater. Preliminary studies have revealed that groundwater also plays an important role in survival of salmon eggs in the River Suldalslågen when dewatered in winter. Eggs placed in boxes in groundwater seepage areas during winter in the dewatered river bed survived even when covered by ice and snow. The survival from fertilization until 30 April, one month before hatching, was 91%, the same survival as found for eggs placed in boxes in the wetted river bed. However, mortality from fertilization to hatching was higher compared to the eggs placed in wetted river bed, 57 and 91% respectively. Groundwater creates a horizontal and vertical mosaic of temperatures in spawning redd areas leading to potentially greater variation in spawning sites, time of hatching and “swim up”. This is likely to increase egg survival during low flow periods in regulated rivers. In conclusion, the interaction between groundwater and surface river water should therefore be considered when managing fish populations in regulated rivers.

Groundwater influence on the aeolian sequence stratigraphy of the Mechertate–Chrita–Sidi El Hani system, Tunisian Sahel: Analogies to the wet–dry aeolian sequence stratigraphy at Meridiani Planum, Terby crater, and Gale crater, Mars

A multidisciplinary study of the watershed and depressions of the Mechertate–Chrita–Sidi El Hani (MCSH) system in eastern Tunisia shows that groundwater upwelling and/or seepage toward the modern surface is important in the shaping of its geomorphologic features and sediment outcrops. Along the watershed of the system, groundwater is downward enriched with evaporitic minerals. These minerals precipitate as cement and protect the sediment outcrops from aeolian erosion. The water table is the limiting control on erosion and deposition, and also influences the succession of sediment along the system. The water table further determines the local base level, which controls the deposition within depressions. With increasing humidity at the limit of the capillary fringe, the landscape of the evaporative system is organized according to three sedimentary types: (1) unconsolidated sediment of aqueous and/or aeolian origin that is eroded and transported toward depressions (away from groundwater interactions), (2) consolidated sediment that is also aqueous and/or aeolian in origin and is protected from aeolian erosion by groundwater influence, and (3) sedimentary filling of depressions located within accumulation zones. These sediments are organized along a lateral, basinward profile. Here we show that during periods of relative water table fall, sediments from the watershed prograde to cover the sabkha basin fill. The rise and fall of the water table and the connected base level result in the deposition of genetically-related progradational and retrogradational sequences. We propose that these genetic sequences can be useful to interpret the sequence stratigraphy at three locations on Mars where sedimentary formations were probably controlled by direct groundwater influence: Meridiani Planum, Terby crater, and Gale crater. At Meridiani Planum, the exposed stratigraphic sequence of the Burns formation starts with deposition of dry aeolian sediment derived from a former watershed. Then, due to the rise of the water table, wet sediments of a sabkha rest atop the dry aeolian cycle to comprise a retrogradational sequence. At Terby and Gale craters, an opposite stratigraphic sequence starts with the wet deposition of the sabkha fill. Then, due to the fall of the water table, the dry aeolian sedimentation progrades atop to the sabkha fill to comprise a progradational sequence. We conclude that the various stratigraphic sequences at the MCSH system, described here, represent different possible analog scenarios for diverse depositional sequences on Mars, in all cases involving groundwater activity.

Spatial patterns of groundwater‐lake exchange – implications for acid neutralization processes in an acid mine lake

AbstractExchange of groundwater and lake water with typically quite different chemical composition is an important driver for biogeochemical processes at the groundwater‐lake interface, which can affect the water quality of lakes. This is of particular relevance in mine lakes where anoxic and slightly acidic groundwater mixes with oxic and acidic lake water (pH < 3). To identify links between groundwater‐lake exchange rates and acid neutralization processes in the sediments, exchange rates were quantified and related to pore‐water pH, sulfate and iron concentrations as well as sulfate reduction rates within the sediment. Seepage rates measured with seepage meters (−2.5 to 5.8 L m‐2 d‐1) were in reasonable agreement with rates inverted from modeled chloride profiles (−1.8 to 8.1 L m‐2 d‐1). Large‐scale exchange patterns were defined by the (hydro)geologic setting but superimposed by smaller scale variations caused by variability in sediment texture. Sites characterized by groundwater upwelling (flow into the lake) and sites where flow alternated between upwelling and downwelling were identified. Observed chloride profiles at the alternating sites reflected the transient flow regime. Seepage direction, as well as seepage rate, were found to influence pH, sulfate and iron profiles and the associated sulfate reduction rates. Under alternating conditions proton‐consuming processes, for example, sulfate reduction, were slowed. In the uppermost layer of the sediment (max. 5 cm), sulfate reduction rates were significantly higher at upwelling (>330 nmol g‐1 d‐1) compared to alternating sites (<220 nmol g‐1 d‐1). Although differences in sulfate reduction rates could not be explained solely by different flux rates, they were clearly related to the prevailing groundwater‐lake exchange patterns and the associated pH conditions. Our findings strongly suggest that groundwater‐lake exchange has significant effects on the biogeochemical processes that are coupled to sulfate reduction such as acidity retention and precipitation of iron sulfides. Copyright © 2012 John Wiley & Sons, Ltd.

Streambed nitrogen cycling beyond the hyporheic zone: Flow controls on horizontal patterns and depth distribution of nitrate and dissolved oxygen in the upwelling groundwater of a lowland river

Biogeochemical turnover in hyporheic zones is known to have the potential to affect the chemical signature of surface water cycling through shallow streambed sediments. This study investigates the impact of streambed physical properties on the fate of nitrate and dissolved oxygen in groundwater upwelling through the streambed of a lowland river. For analyzing depth‐dependent patterns and zonation of nitrogen concentrations, diffuse gel probes in shallow (top 15 cm) streambed sediments have been deployed in a nested setup together with multilevel minipiezometers for streambed sediments of 15–150 cm. Spatial heterogeneity of groundwater upwelling was controlled by patterns of low‐conductivity peat and clay strata that caused locally confined conditions, suggesting increased streambed residence times. Nitrate concentrations in the upwelling groundwater changed by up to 68.06 mg L−1 within the top 15 cm of streambed sediments and by up to 107.47 mg L−1 at depths of 15–150 cm, indicating that significant nitrogen turnover was not restricted to shallow streambed sediments. Intensive reduction of nitrate concentrations was found, in particular, in vicinity of low‐conductivity streambed strata. The coincidence of confined groundwater upwelling and reduced oxygen concentrations at these locations suggests that increased residence times and associated depletion of dissolved oxygen create conditions favorable for nitrate reduction. Our results highlight that increased nitrogen turnover at aquifer‐river interfaces is not necessarily limited to shallow streambed zones, where surface water is mixing with groundwater, but can affect upwelling groundwater in reactive hot spots that extend to greater streambed depths and beyond hyporheic mixing zones.

Groundwater activity on Mars and implications for a deep biosphere

The subsurface of Mars could potentially have contained a vast microbial biosphere. An evaluation of the possibility of groundwater upwelling, which might provide clues to subsurface habitability, reveals evidence in the deep McLaughlin crater for clays and carbonates that probably formed in an alkaline, groundwater-fed lacustrine setting.

Determination of Nitrate Pollution Sources in the Marano Lagoon (Italy) by using a Combined Approach of Hydrochemical and Isotopic Techniques

Due to increased pollution by nitrate from intensive agricultural and other anthropogenic activities the Marano lagoon (northeast Italy) and part of its catchment area have been investigated, applying a combined approach of hydrochemical and isotopic techniques. Thus, to identify and characterize the potential multiple-sources of nitrate pollution the isotopic compositions of nitrate (δ15N, δ18O, and Δ17O), boron (δ11B), water (δ2H and δ18O), and sulphate (δ34S and δ18O), as well as the chemical composition of different water types have been determined. In the monitoring program water samples from the lagoon, its tributary rivers, the groundwater upwelling line, groundwater, sewage, and open sea on a quarterly interval from 2009 to 2010 have been collected and analyzed. Coupling isotopic and hydrochemical results indicate that the nitrate load in the lagoon was not only derived from agriculture activities but also from other sources such as urban wastewaters, in situ nitrification, and atmospheric deposition. However, none of the samples showed the isotopic characteristics of synthetic fertilizers.

Mineralogy of saline perennial cold springs on Axel Heiberg Island, Nunavut, Canada and implications for spring deposits on Mars

In recent years evidence for spring deposits on Mars has been mounting. It seems increasingly likely that groundwater upwelling and surfacing as springs may be responsible for some mineral deposits on Mars’ surface. In order to more easily detect and better understand potential spring deposits on Mars, it is pertinent that we gain a better understanding of the distribution of minerals at cold spring systems on Earth. Here, we report on the detailed mineralogy and distribution of precipitates in crusts and sediments of three non-volcanic perennial saline cold spring systems associated with gypsum/anhydrite diapirs on Axel Heiberg Island, Canada: Wolf spring (WS; also known as Lost Hammer), Colour Peak springs (CP), and Gypsum Hill springs (GH). At these sites permafrost, frigid winter temperatures, and arid atmospheric conditions approximate conditions of present-day, as well as past, Mars. Mineralogy of the three springs is dominated by halite (NaCl), calcite (CaCO3), gypsum (CaSO4·2H2O), thenardite (Na2SO4), mirabilite (Na2SO4·10H2O), and elemental sulfur (S°). Minerals at WS are more sodium-rich than at the other two sites, and water salinity is much higher, suggesting water flows through halite in the subsurface. Mirabilite is likely deposit at WS during winter months and dehydrates to thenardite during summer months. Elemental sulfur is typically associated with gypsum, and may be related to microbial metabolism. Spring sediments are home to thriving microbial communities in winter and summer months, and presumably year round. If spring systems did exist on the surface of Mars, they may represent environments capable of supporting microbial life. It is not known to what extent mineral crusts in cold saline spring systems on Earth preserve evidence of microbial life, or if they ever did on Mars. Therefore, studying terrestrial saline spring mineral deposits such as those on Axel Heiberg Island may help us to better understand cold spring precipitation on Mars and guide us in the search for minerals that may have been precipitated in spring systems and that may contain evidence of life. Additionally, spectral data from Europa indicates the presence of mirabilite. While the depositional environment on Europa differs from Axel Heiberg Island, the springs may still be a good mineralogical analogue, given the precipitation of mirabilite by the upwelling of cold, salty subsurface water, in a cold, semi-arid desert environment.

Surface water–groundwater interaction at restored streams and associated reference reaches

AbstractStream restoration goals include improving habitat and water quality through reconstruction of morphological features found at analogous, pristine stream reaches. Enhancing hyporheic exchange may facilitate achieving these goals. Although hyporheic exchange at restoration sites has been explored in a few previous studies, comparative studies of restored versus reference or control streams are largely absent. We hypothesized that restoration cross‐vanes enhance hyporheic exchange, resulting in biogeochemical alteration of stream water chemistry in the streambed. Two streams restored using cross‐vanes to control erosion and improve habitat were compared with their associated reference reaches, which provided the basis for the restoration design. Thirteen temperature profile rods with vertically stacked sensors were installed at each site for 2 weeks. Heat tracing was used to quantify vertical flux in the streambed from the diurnal temperature fluctuations in the subsurface. Stream water and bed pore waters from mini‐piezometers were analysed for ion and nutrient chemistry. In general, mean vertical flux rates through the streambed were small throughout reference sites (−0.3 to 0.3 m/day) and at most locations at restored sites. Immediately adjacent to cross‐vanes, vertical flux rates were larger (up to 3.5 m/day). Geochemistry of pore waters shows distinct differences in the sources for the reference and restored sites. Strong downwelling zones adjacent to cross‐vanes showed high dissolved oxygen (10.75 mg/l) and geochemistry in the streambed similar to surface water. Reference sites had lower dissolved oxygen in the streambed (0.66–5.14 mg/l), and geochemical patterns suggest a mixture of discharging groundwater and surface water in the hyporheic zone. Restored sites also clearly show sulfate and nitrate reduction occurring in the streambed, which is not observed at the reference sites. The stream restoration sites studied here enhance rapid hyporheic exchange, but upwelling of groundwater has a stronger influence on streambed geochemistry at reference sites. Copyright © 2012 John Wiley & Sons, Ltd.

Geologic relationships between gray hematite, sulfates, and clays in Capri Chasma

We used emissivity spectra from the Thermal Emission Spectrometer (TES) to identify the signature of crystalline gray hematite in Capri Chasma. Geologic units associated with major concentrations of hematite were then mapped using HiRISE, CRISM, and CTX images from the Mars Reconnaissance Orbiter (MRO). Along the northern portion of the Interior Layered Deposit (ILD), a lower polyhydrated sulfate (PHS) unit lies beneath a thicker kieserite unit, above which is a thinner upper PHS. An exposure at the thickest central portion of the ILD reveals additional sulfates, including a middle PHS, a mixture of lower hydration states PHS, and an intercalated unit comprised of kieserite and szomolnokite. We interpret these compositional transitions to reflect either changes in aqueous chemistry (e.g., iron levels and salinity) during groundwater upwelling events or successively buried layers of dust, ice and volcanic aerosols laid down over obliquity cycles. In addition to these sulfates, we identified a few small mounds along the chasma floor composed of either mixtures of ferric hydroxysulfate and Fe/Mg‐smectites, or possible opal, leached clays, and Fe/Mg‐smectites. Gray hematite is strongly spatially correlated to kieserite‐bearing slopes within the ILD and mantled PHS along the northern chasma floor. These results are consistent with sulfate and hematite formation found elsewhere on Mars, including Meridiani Planum, Aram Chaos, and several other chasmata and chaos regions within Valles Marineris.

Investigating patterns and controls of groundwater up-welling in a lowland river by combining Fibre-optic Distributed Temperature Sensing with observations of vertical hydraulic gradients

Abstract. This paper investigates the patterns and controls of aquifer–river exchange in a fast-flowing lowland river by the conjunctive use of streambed temperature anomalies identified with Fibre-optic Distributed Temperature Sensing (FO-DTS) and observations of vertical hydraulic gradients (VHG). FO-DTS temperature traces along this lowland river reach reveal discrete patterns with "cold spots" indicating groundwater up-welling. In contrast to previous studies using FO-DTS for investigation of groundwater–surface water exchange, the fibre-optic cable in this study was buried in the streambed sediments, ensuring clear signals despite fast flow and high discharges. During the observed summer baseflow period, streambed temperatures in groundwater up-welling locations were found to be up to 1.5 °C lower than ambient streambed temperatures. Due to the high river flows, the cold spots were sharp and distinctly localized without measurable impact on down-stream surface water temperature. VHG patterns along the stream reach were highly variable in space, revealing strong differences even at small scales. VHG patterns alone are indicators of both, structural heterogeneity of the stream bed as well as of the spatial heterogeneity of the groundwater–surface water exchange fluxes and are thus not conclusive in their interpretation. However, in combination with the high spatial resolution FO-DTS data we were able to separate these two influences and clearly identify locations of enhanced exchange, while also obtaining information on the complex small-scale streambed transmissivity patterns responsible for the very discrete exchange patterns. The validation of the combined VHG and FO-DTS approach provides an effective strategy for analysing drivers and controls of groundwater–surface water exchange, with implications for the quantification of biogeochemical cycling and contaminant transport at aquifer–river interfaces.

Advection Dominated Transport of Polycyclic Aromatic Hydrocarbons in Amended Sediment Caps

Typical sand caps used for sediment remediation have little sorption capacity to retard the migration of hydrophobic contaminants such as PAHs that can be mobilized by significant groundwater flow. Laboratory column experiments were performed using contaminated sediments and capping materials from a creosote contaminated USEPA Superfund site. Azoic laboratory column experiments demonstrated rapid breakthrough of lower molecular weight PAHs when groundwater seepage was simulated through a column packed with coarse sand capping material. After eight pore volumes of flow, most PAHs measured showed at least 50% of initial source pore water concentrations at the surface of 65 cm capping material. PAH concentration in the cap solids was low and comparable to background levels typically seen in urban depositional sediment, but the pore water concentrations were high. Column experiments with a peat amendment delayed PAH breakthrough. The most dramatic result was observed for caps amended with activated carbon at a dose of 2% by dry weight. PAH concentrations in the pore water of the activated carbon amended caps were 3-4 orders of magnitude lower (0.04 ± 0.02 μg/L for pyrene) than concentrations in the pore water of the source sediments (26.2 ± 5.6 μg/L for pyrene) even after several hundred pore volumes of flow. Enhancing the sorption capacity of caps with activated carbon amendment even at a lower dose of 0.2% demonstrated a significant impact on contaminant retardation suggesting consideration of active capping for field sites prone to groundwater upwelling or where thin caps are desired to minimize change in bathymetry and impacts to aquatic habitats.