Stream Groundwater Research Articles

Detection of Strobilurin Fungicides in Trout Streams within an Agricultural Watershed

The use of strobilurin fungicides in agriculture has increased steadily during the past 25 years, and although strobilurins have minimal water solubility, they regularly appear in surface waters, at times in concentrations approaching toxic levels for aquatic life. The present study examined concentrations of strobilurin fungicides in designated trout streams draining an agricultural watershed in southeastern Minnesota, USA, where fungicides may have contributed to a recent fish kill. Water samples (n = 131) were analyzed for the presence of five different strobilurin fungicides (azoxystrobin, fluoxastrobin, picoxystrobin, pyraclostrobin, trifloxystrobin). Samples were collected via grab and automated sampling during baseflow and stormflow events throughout an entire crop-growing season from sites on each of the three forks of the Whitewater River. Detection frequencies for the five strobilurins ranged from 44 to 82%. Fluoxastrobin and pyraclostrobin concentrations were above known toxic levels in 3% and 15% of total samples analyzed, respectively. The highest concentrations were detected in mid-summer (mid-June to mid-August) samples, coincident with likely strobilurin applications. Lower concentrations were present in water samples collected during the nonapplication periods in spring and fall, suggesting groundwater–stream interactions or steady leaching of fungicides from watershed soils or stream sediments. Further study is required to determine strobilurin concentrations in sediments, soils, and groundwater. Better tracking and guidance regarding strobilurin use is necessary to adequately protect aquatic life as fungicide use continues to increase.

Stream groundwater inputs generate fine‐scale variation in brook trout phenology and growth across a warming landscape

Abstract Climate change is increasing global atmospheric temperatures, which can reduce abundance and cause range shifts in species that are sensitive to warming. However, fine‐scale thermal heterogeneity can drive highly variable local responses to climate change, especially in freshwater environments that differ in groundwater inputs and geomorphology. We used temperature data collected during 2012–2021 from 10 small, pristine streams in eastern Canada to characterise thermal variation at a small spatial scale (~25 km2). We then used relationships between daily air and stream temperatures to reconstruct stream temperature since 1980, and assessed how thermal variation influenced the phenology and growth of brook trout (Salvelinus fontinalis). Air–stream temperature relationships varied considerably among streams despite their close proximity, with predicted summer temperatures differing up to 9.5°C between warmer rainfall‐dominated streams and cooler groundwater‐dominated streams. Rainfall‐dominated streams warmed more than twice as fast as groundwater‐dominated streams across all seasons since 1980, with nearly four‐fold differences in rates of warming evident during summer months. Fine‐scale thermal heterogeneity also shaped brook trout phenology, as juveniles in rainfall‐dominated streams were estimated to hatch and emerge much later (~70 and 40 days, respectively) and experience faster phenological shifts than in groundwater‐dominated streams. Relationships between juvenile brook trout size and accumulated degree‐days were positive, but slopes differed over two‐fold and did not vary systematically based on stream hydrology, suggesting more idiosyncratic impacts of warming on early growth. Collectively, our study illustrates how species responses to climate change in freshwater environments can be consistent in direction but vary substantially in magnitude owing to the influence of groundwater. Future climate change is likely to increase the thermal stress experienced by brook trout populations in warmer rainfall‐dominated streams, while potentially benefiting those in groundwater‐dominated streams where current temperatures are often suboptimal. Observed differences in the rates and ecological impacts of warming among streams suggest that fine‐scale thermal variation must be considered when forecasting effects of future climate change on stream fish population dynamics.

Range of application of heat pump systems on various natural refrigerants

GROUNDING: The utilization of heat pumps (variation of vapor compressing machines) for heat transfer between different temperature levels is a promising development trend, considering low cost of heat energy, environmental friendliness of working mediums, economically sufficient solutions and low cost maintenance. Heat pumps are used for heating in building structures where low potential heat sources are wastewater streams, groundwater streams, air, heat of the soil. It is also possible to use low potential heat of heat emissions from industrial plants, that can be cost effectively in terms of production resources usage.
 AIMS: Selection of the refrigerant and its composition in order to provide operational stability for heat pumps at temperature levels from 48 to 95 ̊C with minimum energy consumption for the most widespread thermodynamical cycles.
 MATERIALS AND METHODS: Standard thermodynamic cycles of heat pumps were simulated using Aspen HYSYS software. Further optimization and parameter selection were performed using MATLAB module Global Optimization Toolbox.
 RESULTS: In compliance with demanded design parameters the results of each working medium simulation were obtained. Energy efficient parameters of the common heat pumps thermodynamical cycles were determined.
 CONCLUSIONS: According to exergy analysis of the thermodynamical cycles it has been determined that mixed refrigerants, pentane and ammonia are the most suitable and energy efficient working fluids for heat pumps.

Wildfire-induced shifts in groundwater discharge to streams identified with paired air and stream water temperature analyses

Within the western United States, increasingly severe and frequent wildfires may alter the magnitude, timing, and quality of water exported from burned areas by streams. Post-fire hydrologic studies often focus on peak stream flow responses to shifts in runoff generation or on annual streamflow yield response to changes in evapotranspiration following fire. However, the magnitude and duration of wildfire effects on groundwater recharge, changes in subsurface routing, and consequences for stream low flows sourced predominately by baseflow are poorly understood. Here, we demonstrate an approach using the amplitude and phase of paired annual air and stream water temperature signals to broadly identify changes in watershed subsurface flow contributions after fire. Watersheds were classified using pre-fire temperature data, as having air-coupled (i.e., reduced apparent groundwater signature), deep groundwater, or shallow groundwater stream temperature signals. Changes in pre- and post-fire paired air and stream water temperature metrics were compared for locations (n = 17) spanning a large range of physiographic and climatic conditions across the western United States. Pre- and post-fire comparisons were computed by quantile using bootstrapped confidence intervals (ci = 95), as well as in aggregate using Kruskal-Wallis and post-hoc Dunn tests. Statistical comparisons of pre- and post-fire temperature metrics suggest that overall, watersheds classified as having minimal groundwater influence are the most likely to experience fire-induced subsurface hydrologic change. More specifically, watersheds classified as having air-coupled or shallow groundwater signals experienced increases in the magnitude of groundwater discharge, with more stable annual thermal regimes post-fire that are less-coupled to ambient air temperature. These findings form the basis of a conceptual framework for watershed resistance to subsurface hydrologic change following fire that can be broadly applied as a first approximation for water management, impacts on aquatic habitat, and post-wildfire response planning.

Hydrologic and environmental thresholds in stream fish assemblage structure across flow regimes

The characteristic pattern of variation in flow magnitude, frequency, duration, timing, and rate of change defines the flow regime of rivers and streams and is a key driver of ecosystem processes in fluvial ecosystems. Understanding how freshwater biotic assemblages change across gradients of hydrology and anthropogenic-source disturbance in different streamflow regimes is crucial to managing for sustainable environmental flows and watershed conservation. We compiled long-term (1916–2016) occurrence records for fishes collected in the Ouachita-Ozark Interior Highlands and West Gulf Coastal Plain streams, together with hydrologic metrics calculated from daily streamflow data measured at USGS stream gauging stations (n = 111), to examine important drivers and thresholds for fish assemblage turnover in groundwater (GW), runoff (RO), and intermittent (INT) flow regimes. We also examined the importance of spatial gradients (latitude, longitude, elevation, drainage area) and anthropogenic-source stressors (Hydrologic Disturbance Index; HDI) for fish assemblage turnover using a gradient forest modeling approach. Watershed fragmentation was of high importance for fish assemblage turnover in RO and INT streams, while changes in dam storage were more important for fishes in GW streams. Hydrologic metrics describing seasonal and stochastic properties of daily streamflow (Mag6) were most important for fish assemblage turnover in INT streams. Timing of high flow events had significantly higher importance compared to flow magnitude, duration, and frequency metrics, especially for fish assemblages in GW and INT streams. The frequency and timing of low flow events had high importance for fish assemblage turnover across all stream flow classes, while the magnitude of low flows and the magnitude and rate of change of average flows was most important for INT stream fish assemblages. In addition to benefiting multi-species conservation and management actions through identification of local and regional flow-ecology relationships generalized across different flow regimes, the results of this study provide a better understanding of complex nonlinear threshold effects, which is critical to anticipating changes in aquatic ecosystems and communities.

Control of the Remediation of Anoxic AMD Groundwater by Sulphate Reduction in a Subsoil Reactor

Groundwater containing high amounts of products of pyrite weathering as a consequence of lignite mining flows into receiving waters for a number of years. Iron hydroxides causing turbidity and silting will strongly affect the river Spree for many decades. In addition to liming acidic surface waters and the conventional treating of mine waters, microbial sulphate reduction of the inflowing anoxic AMD groundwater is tested for long-term remediation. During a pilot project at Lusatia / Germany, glycerin as a carbon source and nutrient solutions of N and P are infiltrated into an anoxic AMD groundwater stream by lances. Planning and operations were carried out based on the model as proposed below. Doi: 10.28991/HEF-2022-03-03-02 Full Text: PDF

Meteorological and hydrological data from the Alder Creek watershed, SW Ontario

Abstract. Data for small to mid-sized watersheds are seldom publicly available, but may be representative of diverse types of hydrological contexts when assessing patterns. These types of data may also prove valuable for informing numerical experimentation and practical modelling. This paper presents data collected in the Alder Creek watershed, located within the Grand River basin in Ontario, Canada. The Alder Creek watershed provides source water from the aquifers of the Waterloo Moraine for multiple well fields that supply the cities of Kitchener and Waterloo. Recharge rates and human impacts on streamflow are important topics for the watershed, and many numerical models of the area have been constructed. In order to support these types of analyses, field equipment was deployed within the watershed between 2013 and 2018 to monitor groundwater levels, stream stage, soil moisture, soil temperature, rainfall, and other weather parameters. The available data are described, complementary information is presented, and examples of possible analyses are cited and illustrated. The data presented and described in this paper are available at https://doi.org/10.20383/101.0178 (Wiebe et al., 2019).

Commercial‐scale remediation of per‐ and polyfluoroalkyl substances from a landfill leachate catchment using Surface‐Active Foam Fractionation (SAFF®)

AbstractThis article presents the results from a commercial‐scale field trial of the Surface‐Active Foam Fractionation (SAFF) process for the removal of per‐ and polyfluoroalkyl substances (PFAS) from a landfill leachate catchment at the Telge Recycling plant, Sweden. There have been 23 sampling events for PFAS influent and effluent concentrations over the course of 10 months, during which approximately 80,000 m3 of leachate feed has been successfully treated without the need for complex pretreatment. The contracted throughput was 330 m3 per day (120,000 m3/year), but, in practice, it varied between 200 m3 and 500 m3 per day depending upon the inventory of the upstream leachate catchment. Over the trial period, it was demonstrated that SAFF was successful in removing ≥98.7% perfluorooctane sulfonate (PFOS), ≥99.7% perfluorooctanoic acid (PFOA), and ≥98.8% perfluorohexane sulfonate (PFHxS) from the feed stream without using absorbent media or chemical amendment consumables, including the partial/significant removal of other PFAS species. The reported removal percentages are constrained by the limit of reporting (LOR) of analytical testing of the “treated stream”; the actual removal percentages could be higher as detailed by a single sampling event “I” included herein. The mean concentrations of the treated stream were ≤2.34 ng/L PFOS, ≤1.28 ng/L PFOA, and ≤1.00 ng/L PFHxS; the contractual criteria requirement was to reduce PFOS to <50 ng/L. The results are concordant with those obtained by Burns et al. (2021) who demonstrated that SAFF technology removed ≥99.8% PFOS, ≥99.8% PFOA, and ≥98.4% PFHxS from a PFAS‐contaminated groundwater stream at the Army Aviation Centre Oakey military base in Australia. The present study extends what was learned from the previous Australian groundwater study in that there is more complex chemistry associated with the leachate feed stream arising from landfill receipt of domestic, commercial, and industrial waste to the landfill cells. In addition, the climatic dependency that was considered by Burns et al. (2021) is explored in a colder environment and is found to be practically insignificant with respect to PFAS removal. Burns et al. (2021) asserted that nearly complete PFAS removal is achieved if the Brusseau adsorption coefficient is greater than approximately 1 µm. The present study extends this analysis to demonstrate that removal percentages fall to approximately 0 at an adsorption coefficient of 0.02 µm with a functional form of a sigmoid on semi‐log axes. A full set of third‐party laboratory test certificates are provided in the Supporting Information.

Limited roles of anthropogenic activities on arsenic mobilization in groundwater from the Yinchuan Basin, China

Arsenic (As) pollution in groundwater is an extremely concerning issue all over the world, because it has brought many negative health effects on people. However, the impact of anthropogenic activities on the formation of high As groundwater is poorly understood. Seventy-nine groundwater samples and seven surface water samples were taken along two transects in the Yinchuan Basin, China, to trace effects of anthropogenic activities on distribution of high As groundwater by using artificial sweeteners. The sampling campaign showed that, in 47% of samples, As concentrations exceeded the WHO drinking water guideline (10 μg/L). Both acesulfame and sucralose were detected in the groundwater samples, and concentrations in samples from the transect of the upper stream of regional groundwater were generally higher than those from the transect of the middle stream. Both acesulfame and sucralose in all studied groundwater samples had the detection rate (DR) > 7 and the detection frequency (DF) > 90%, indicating that they can be used as tracers to reflect anthropogenic activities. Higher As groundwater samples generally had lower concentrations of the artificial sweeteners and vice versa, showing that the influence of anthropogenic activities on high As concentration was limited. Geological processes are the main reason for the formation of high As groundwater. High As groundwaters were characterized by moderate reducing conditions, and the reductive dissolution of Fe(III) hydroxides led to the release of the adsorbed As into groundwater. Additionally, As desorption was another process to mobilize As under the conditions of elevated pH and/or high HCO3−. This study provides an insight into relative contribution of anthropogenic activities and hydrogeochemical conditions to As enrichment in groundwater, and highlights the necessity in protecting low As groundwater highly vulnerable to human activities in high As-groundwater areas.

A dynamic saline groundwater system mapped beneath an Antarctic ice stream

Antarctica's fast-flowing ice streams drain the ice sheet, with their velocity modulated by subglacial water systems. Current knowledge of these water systems is limited to the shallow portions near the ice-bed interface, but hypothesized deeper groundwater could also influence ice streaming. Here, we use magnetotelluric and passive seismic data from Whillans Ice Stream, West Antarctica, to provide the first observations of deep sub-ice stream groundwater. Our data reveal a volume of groundwater within a >1-kilometer-thick sedimentary basin that is more than an order of magnitude larger than the known subglacial system. A vertical salinity gradient indicates exchange between paleo seawater at depth and contemporary basal meltwater above. Our results provide new constraints for subglacial water systems that affect ice streaming and subglacial biogeochemical processes.

Lateral squeezing effects on cement-slag-bentonite slurry wall performance

Abstract in English Cement-slag-bentonite slurry walls are self-hardening structures, and they are mainly used to retard contamination transport into the groundwater stream. Whilst permeability of a mixture is an initial criterion in slurry wall design and material selection, long-term performance is mainly influenced by curing ages and stress-state caused by adjacent soil. In this study, the steady-state of effective stresses at 7 days and 28 days of curing age is predicted. The effect of the modulus of horizontal subgrade reaction, interface friction, and transition of the earth pressure from at-rest to the active condition was applied to develop the model. Unlike the quantities that the geostatic model presented, this method gives a slight decrease of stresses after a certain depth, and the trend is in good agreement with trends provided by previous studies. Furthermore, the predicted stresses are then applied to estimate the permeability of the wall at each depth and compare it with those obtained in the laboratory. Finally, predicted effective stresses stay lower than geostatic stress, and the slurry wall consolidation along with the sidewalls’ lateral squeezing leads to keeping the stress state under control.

Biodegradation Model of Dissolved Organic Matter during River Bank Filtration, at Al-Qurain City, Sharkyia Governorate, Egypt

Riverbank filtration is carried out at natural conditions and may occur by lowering the groundwater stream under the surface water levels either by hydraulic boundaries such as a bank of channels or by groundwater abstraction at pumping wells. In addition, the mixing of the infiltrated river water with groundwater at the pumping outlet well and the bank filtrate's retention time have been studied and identified as one of the critical parameters that determine the efficiency of riverbank filtration and water quality. RBF water results of pH, conductivity, TDS, hardness, color, alkalinity, nitrate, nitrite, phosphate, silica, sulphate, chloride, and turbidity were complying with The Egyptian Ministry of Health and WHO guidelines. The present study showed that groundwater's iron and manganese data in the study region did not comply with Egyptian regulation (Fe more than 0.3 mg/l and Mn more than 0.4 mg/l). The river surface water quality results did not comply with Egyptian regulation in some parameters, such as microbiological parameters (total bacterial count more than 5000 CFU/ml). The examination of river surface water samples was positive in total coliform fecal coliform examination. The study has shown that the water quality results from the RBF water had high water quality, especially in values of Fe & Mn and also microbiological parameters. The correlation coefficient between DOC recorded, and DOC estimated was very strong (r was 0.94).

The Multiscale TROPIcal CatchmentS critical zone observatory M‐TROPICS dataset III: Hydro‐geochemical monitoring of the Mule Hole catchment, south India

AbstractDespite the importance of tropical ecosystems for climate regulation, biodiversity, water and nutrient cycles, only a few Critical Zone Observatories (CZOs) are located in the tropics. Among these, most are in humid climates, while very few data exist for semi‐arid and sub‐humid climates, due to the difficulty of estimating hydro‐geochemical balances in catchments with ephemeral streams. We contribute to fill this gap by presenting a meteorological and hydro‐geochemical dataset acquired at the Mule Hole catchment (4.1 km2), a pristine dry deciduous forest located in a biosphere reserve in south India. The dataset consists of time series of variables related to (i) meteorology, including rainfall, air temperature, relative humidity, wind speed and direction, and global radiation, (ii) hydrology, including water level and discharge at the catchment outlet, (iii) hydrogeology, including manual (monthly) and/or automated (from 15 min to hourly) groundwater levels in nine piezometers and (iv) geochemistry, including suspended sediment content in the stream and chemical composition of rainfall (event based), groundwater (monthly sampling) and stream water (storm events, 15 min to hourly frequency with an automatic sampler). The time series extend from 2003 to 2019. Measurement errors are minimized by frequent calibration of sensors and quality checks, both in the field and in the laboratory. Despite these precautions, several data gaps exist, due to occasional access restriction to the site and instrument destruction by wildlife. Results show that large seasonal and interannual variations of climatic conditions were reflected in the large variations of stream flow and groundwater recharge, as well as in water chemical composition. Notably, they reveal a long‐term evolution of groundwater storage, suggesting hydrogeological cycles on a decadal scale. This dataset, alone or in combination with other data, has already allowed to better understand water and element cycling in tropical dry forests, and the role of forest diversity on biogeochemical cycles. As tropical ecosystems are underrepresented by Critical Zone Observatories, we expect this data note to be valuable for the global scientific community.

Impact of climate change on groundwater resource in a region with a fast depletion rate: the Mississippi Embayment.

Mississippi Embayment (ME) is one of the fastest groundwater depletion regions around the world, while the impacts of climate change on groundwater resources in the region are complex and basically unknown. Using the U.S. Geological Survey’s Mississippi Embayment Regional Aquifer Study (MERAS) model, such a challenge was addressed through the base, wet, and dry simulation scenarios. Over the 137-year simulation period from 1870 to 2007, the cumulative aquifer storage depletions were 1.70 × 1011, 1.73 × 1011, and 1.67 × 1011 m3, respectively, for the base, dry, and wet scenarios. As compared with that of the base scenario, the aquifer storage depletions were only 1.76% more for the dry scenario and 1.8% less for the wet scenario. A multiple regression analysis showed that the aquifer storage depletion rate was controlled more by the groundwater pumping and stream leakage rates and less by the groundwater net recharge rate. Groundwater table variation in the forest land was much smaller than in the crop land. Results suggested that groundwater pumping rather than climate change was a key driving force of groundwater depletion in the ME. Our findings provide a useful reference to water resource managers, foresters, and farmers in the ME and around the world when developing their groundwater supply strategies.

Assessing Stream-Aquifer Connectivity in a Coastal California Watershed

We report the results of field and laboratory investigations of stream-aquifer interactions in a watershed along the California coast to assess the impact of groundwater pumping for irrigation on stream flows. The methods used include subsurface sediment sampling using direct-push drilling, laboratory permeability and particle size analyses of sediment, piezometer installation and instrumentation, stream discharge and stage monitoring, pumping tests for aquifer characterization, resistivity surveys, and long-term passive monitoring of stream stage and groundwater levels. Spectral analysis of long-term water level data was used to assess correlation between stream and groundwater level time series data. The investigations revealed the presence of a thin low permeability silt-clay aquitard unit between the main aquifer and the stream. This suggested a three layer conceptual model of the subsurface comprising unconfined and confined aquifers separated by an aquitard layer. This was broadly confirmed by resistivity surveys and pumping tests, the latter of which indicated the occurrence of leakage across the aquitard. The aquitard was determined to be 2–3 orders of magnitude less permeable than the aquifer, which is indicative of weak stream-aquifer connectivity and was confirmed by spectral analysis of stream-aquifer water level time series. The results illustrate the importance of site-specific investigations and suggest that even in systems where the stream is not in direct hydraulic contact with the producing aquifer, long-term stream depletion can occur due to leakage across low permeability units. This has implications for management of stream flows, groundwater abstraction, and water resources management during prolonged periods of drought.

Chloride load dynamics along channelized and intact reaches in a northeastern United States urban headwater stream

Sodium chloride has long been used for winter deicing, although its legacy use has resulted in rising chloride concentrations in urban watersheds. Persistently high chloride levels impair drinking water resources and threaten the health of aquatic life and vegetation. In urban areas, chloride fate and transport is impacted by human modification of the environment, including increased impervious surface cover and disconnection of stream corridors from riparian groundwater. We couple continuous streamflow records with weekly chloride concentration data over two water years to create continuous chloride load estimates at three locations along a degraded, urban stream in upstate New York with contrasting channelized and intact reaches. Our results show that degraded reaches characterized by channelized, armored banks and minimal groundwater connection deliver chloride loads closer to chloride application rates in the surrounding watershed. In contrast, stream–groundwater interactions in intact reaches adjacent to riparian floodplains, including surface water losses to subsurface flow paths, result in stream chloride loads that are 50% less than those delivered from upstream channelized reaches. These findings show that longitudinal chloride load estimates along a stream channel can be valuable in identifying the timing and magnitude of chloride sources and sinks, which may be common but less apparent in urban environments.

Identifying and quantifying groundwater inflow to a stream using 220Rn and 222Rn as natural tracers

Study regionNoseong Stream watershed in Nonsan, Chuncheongnam-do, South Korea. Study focusThis study aims to identify and quantify groundwater inflow to a stream based on the spatial and temporal distributions of 220Rn and 222Rn activities in stream water and groundwater. Groundwater–stream water exchange fluxes were estimated on the basis of 222Rn mass balance approaches under losing and gaining stream conditions, and groundwater inflow type was identified using a spatial survey of 220Rn in stream water. New hydrological insights for the regionThe 222Rn activities at 20 stations along the stream during four sampling campaigns were higher at high altitudes than low altitudes, regardless of the season. At two sections, which appeared to be gaining systems, the groundwater inflow rates were estimated to be 6.5 × 102 and 4.0 × 102 m3 d–1. At another stream section, where groundwater inflow to the stream and stream water leakage into groundwater may alternatingly occur, the groundwater inflow and stream water leakage were 1.5 × 102 and 2.5 × 104 m3 d–1, respectively. A spatial survey of 220Rn along the stream indicates that groundwater may dominantly discharge to the stream water as point sources rather than diffuse seepage.

Groundwater–Stream Connectivity Mediates Metal(loid) Geochemistry in the Hyporheic Zone of Streams Impacted by Historic Mining and Acid Rock Drainage

High concentrations of trace metal(loid)s exported from abandoned mine wastes and acid rock drainage pose a risk to the health of aquatic ecosystems. To determine if and when the hyporheic zone mediates metal(loid) export, we investigated the relationship between streamflow, groundwater–stream connectivity, and subsurface metal(loid) concentrations in two ~1-km stream reaches within the Bonita Peak Mining District, a US Environmental Protection Agency Superfund site located near Silverton, Colorado, USA. The hyporheic zones of reaches in two streams—Mineral Creek and Cement Creek—were characterized using a combination of salt-tracer injection tests, transient-storage modeling, and geochemical sampling of the shallow streambed (<0.7 m). Based on these data, we present two conceptual models for subsurface metal(loid) behavior in the hyporheic zones, including (1) well-connected systems characterized by strong hyporheic mixing of infiltrating stream water and upwelling groundwater and (2) poorly connected systems delineated by physical barriers that limit hyporheic mixing. The comparatively large hyporheic zone and high hydraulic conductivities of Mineral Creek created a connected stream–groundwater system, where mixing of oxygen-rich stream water and metal-rich groundwater facilitated the precipitation of metal colloids in the shallow subsurface. In Cement Creek, the precipitation of iron oxides at depth (~0.4 m) created a low-hydraulic-conductivity barrier between surface water and groundwater. Cemented iron oxides were an important regulator of metal(loid) concentrations in this poorly connected stream–groundwater system due to the formation of strong redox gradients induced by a relatively small hyporheic zone and high fluid residence times. A comparison of conceptual models to stream concentration–discharge relationships exhibited a clear link between geochemical processes occurring within the hyporheic zone of the well-connected system and export of particulate Al, Cu, Fe, and Mn, while the poorly connected system did not have a notable influence on metal concentration–discharge trends. Mineral Creek is an example of a hyporheic system that serves as a natural dissolved metal(loid) sink, whereas poorly connected systems such as Cement Creek may require a combination of subsurface remediation of sediments and mitigation of upstream, iron-rich mine drainages to reduce metal export.

Use of environmental isotopes to assess groundwater pollution caused by agricultural activities

ABSTRACT This work applied environmental isotope techniques to validate the results of previous studies on recharge sources in a rural area in central Chile (34.3° S and 71.3° W) and discern the origin of nitrate contamination in wells. Stream water and groundwater samples were taken during three surveys, two during spring snowmelt and one in low-water conditions. Chemical analyses included major cations and anions, isotope analyses included 18O-H2O; 2H-H20; 3H-H20; 18O-NO3 − and 15N-NO3 −. The stable isotope data show that surface water and deep groundwater present depleted isotope values associated with recharge from the Andes Mountains and that shallow groundwater has more enriched isotope values that reflect the contribution of local recharge from rainwater infiltration. Depleted isotope values observed in shallow groundwater show the effect of recirculated river water used for irrigation. These results are consistent with the conceptual groundwater model developed in previous studies. Some wells have nitrate concentrations above the allowable limit for drinking water. The stable nitrogen isotopes indicate that nitrate is associated mainly with urea and ammoniacal fertilizers, and nitrate is attenuated by denitrification. The results of this study are relevant to improving management of groundwater resources used for drinking water.

Numerical modelling of the impacts of water abstraction for hydraulic fracturing on groundwater–surface water interaction: a case study from northwestern Alberta, Canada

ABSTRACT The temporal dynamics of groundwater–surface water interaction under the impacts of various water abstraction scenarios are presented for hydraulic fracturing in a shale gas and oil play area (23 984.9 km2), Alberta, Canada, using the MIKE-SHE and MIKE-11 models. Water-use data for hydraulic fracturing were obtained for 433 wells drilled in the study area in 2013 and 2014. Modelling results indicate that water abstraction for hydraulic fracturing has very small (<0.35%) negative impacts on mean monthly and annual river and groundwater levels and stream and groundwater flows in the study area, and small (1–4.17%) negative impacts on environmental flows near the water abstraction location during low-flow periods. The impacts on environmental flow depend on the amount of water abstraction and the daily flow over time at a specific river cross-section. The results also indicate a very small (<0.35%) positive impact on mean monthly and annual groundwater contributions to streamflow because of the large study area. The results provide useful information for planning long-term seasonal and annual water abstractions from the river and groundwater for hydraulic fracturing in a large study area.