Deep Groundwater Sources Research Articles

GEOPHYSICAL INDICATORS OF AUFEIS IN THE ANMANGYNDA RIVER (MAGADAN REGION)

Giant aufeis fields are the indicators of water exchange processes in the permafrost zone. The study of aufeis dynamics is relevant to assessing the state of the cryosphere in a changing climate. The Anmangynda aufeis which forms upstream of the Kolyma River basin, was as large as 6.8 km2in the last century and is considered representative of the mountainous territories in the northeast Russia. In recent decades, there have been significant changes in the aufeis formation regime that require updating the understanding of the cryosphere processes. The historical observational data obtained in 1962-1990 for the Anmangynda aufeis allows using it as the present-day object of research.The main goal of geophysical research in 2021-2022 was to study the structure of the Anmangynda aufeis and aufeis glade to determine its genesis and development processes. The main tasks were to identify the boundary between frozen and unfrozen rocks, to reveal groundwater discharge channels, and to assess the aufeis thickness distribution. There were carried out georadar survey using an antenna unit with central frequency of 250 MHz and ground-based capacitively coupled electrical resistivity tomography. It was found that by April 5, 2021, the maximum ice thickness was 4.35 m with an average value of 1.35 m, and the volume of aufeis was 3.56 million m3. By means of georadar, there were performed identification and drilling verification of the groundwater discharge channels from alluvium to aufeis surface, located in the stream beds. There is geophysical evidence of deep bedrock groundwater sources. Based on the electrical resistivity tomography data, there were identified large and locally freezing river taliks, from which the water is squeezed onto the ice surface. It is recommended to conduct further interdisciplinary research to clarify the geophysical results obtained.

A Study of Groundwater Aquifers in Tumbur Village Wer Tamrian District Tanimbar Islands District

Water is a primary human need that must be met, but as time increases, the rate of population growth means that water needs are increasingly not being met. The geoelectric method is a geophysical method that utilizes electrical properties to interpret the earth's subsurface. The main aim of the geoelectric method is to find the resistivity value of a rock. The higher the resistivity value, the more difficult it is for the rock to carry an electric current, and vice versa. For this reason, one solution to meet the needs of the Lorulun Village community is to search for groundwater aquifers using one of the methods that can be used, the geoelectric resistivity method. The data collection and analysis method used in this research is to conduct a survey at the location to review and see the conditions directly at the research location. Identification To determine the existence of a water-bearing layer at a certain depth, we can use geophysical methods, namely the geoelectric resistivity method, to obtain an overview of the soil layers below the surface. Apart from that, it can also predict the potential for deep and shallow groundwater in the research area. The problem in this research is analyzing deep groundwater sources based on the characteristics and implementation of geoelectric results and the aim of this research is to conduct a survey and design deep groundwater wells based on the characteristics and implementation of geoelectric results in Tumbur Village, Wer Tamrian District. The data is processed based on the apparent resistivity equation, so that the apparent resistivity value (ρa) is obtained by entering the values ∆V, I, a, and K into the Microsoft Excel program. Then processed using RES2DINV software. The water source is at two points, namely geoelectric drilling points 01 and 02, respectively, where the aquifer is found. The casing screen installation process is placed at 3 meters and 12 meters. The use of gravel packs from a depth of 2 to 12.5 meters is to protect the drilled wall hole from landslides and also act as a filter for mud or other materials entering the screen. and with a depth of ± 15 meters, the resistivity shows a brackish water aquifer. This is caused by the influence of seawater intrusion By conducting a survey and designing a deep-ground water well based on the characteristics and implementation of geoelectric results in Tumbur Village, Wer Tamrian District,

Groundwater travel times predict DOC in streams and riparian soils across a heterogeneous boreal landscape

Dissolved organic carbon (DOC) in surface waters is an important component of the boreal landscape carbon budget and a critical variable in water quality. A dominant terrestrial DOC source in the boreal landscape is the riparian zone. These near stream areas play a key role in regulating DOC transport between land and aquatic ecosystems. The groundwater dynamics at this interface have been considered a major controlling variable for DOC export to streams. This study focuses on the regulating role of groundwater levels and mean travel times (MTT) on riparian DOC concentrations and, subsequently, stream DOC. This is done by comparing them as explanatory variables to capture the spatial and intra-annual variability of the stream and riparian groundwater DOC. We used a physically based 3D hydrological model, Mike SHE, to simulate DOC concentrations of the riparian zones for 14 sub-catchments within the Krycklan catchment (Sweden). The model concept assumes that DOC concentrations will be higher in groundwater moving through shallow flow paths. In the model, this can be linked to the position of the groundwater table at a point of observation or the travel time, which will generally be shorter for water that has travelled through shallow and more conductive soil layers. We compared the results with both observed stream and groundwater concentrations. The analysis revealed that the correlation between modelled and observed annual averages of stream DOC increased from r = 0.08 to r = 0.87 by using MTT instead of groundwater level. MTT also better captured the observed spatial variability in riparian DOC concentrations and more successfully represented seasonal variability of stream DOC. We, therefore, suggest that MTT is a better predictor than groundwater level for riparian DOC concentration because it can capture a greater variety of catchment heterogeneities, such as variation in soil properties, catchment size, and input from deep groundwater sources.

Exploring a Climate Gradient of Midwestern USA Agricultural Landscape Runoff Using Deuterium (δD) and Oxygen-18 (δ18O)

Intensive agricultural activities have altered the hydrology of many Midwestern USA landscapes. Drain tiles (subsurface corrugated and perforated flexible tubing) has changed how and when water is discharged into the streams. Stable isotopes of oxygen (oxygen-18) and hydrogen (deuterium) were used to investigate hydrologic characteristics of three intensively managed agricultural landscapes in southern Minnesota (MN) and South Dakota (SD). Monthly δD and δ18O samples were collected across a climatic gradient from March 2016 to March 2018. Local meteoric water lines were established for the comparison of precipitation and evaporation magnitude from different sources at each location. These included vadose zone, phreatic zone, deep groundwater, tile drain, and river source waters. Two end-member hydrograph separation was performed at each site on selected dates to partition the shallow groundwater tile drainage contribution to streamflow. A lumped parameter modeling approach was applied to each dataset to investigate the mean transit time of water through different zones. Local meteoric water lines demonstrated differences in isotopic signatures due to the climate gradient to show the impact of low humidity and less rainfall. The hydrograph separation results showed that, from west South Dakota to eastern Minnesota, tile drains contributed about 49%, 64%, and 50% of the watershed streamflow. Precipitation took an average of 9 months to move through different pathways to end up in groundwater and an average of 4 months to end up in tile drains. This study confirms the important role tile drains play in the intensively managed fields and watersheds of Midwestern agriculture.

Antibiotic Resistance Profile and Chemical Quality Assessment of Groundwater Sources from Periurban Area of Bucharest, Romania

Twenty-two groundwater sources mainly used for drinking purpose in Bucharest peri-urban area were investigated for assessment of physico-chemical and microbiological quality with a view to determining its potential risk to public health. Results of chemical analysis revealed that nitrites, sulphates and chlorides were below the permissible levels, while 63.64% of the analysed groundwater sources exceeded the maximum admissible concentration for nitrates, with concentration variations ranging from 67.27 to 523.19 mg/L. The bacteriological analysis showed that in about 63% of groundwater sources total coliform, faecal coliform and enterococci have exceeded the threshold limits recommended by the Drinking Water Directive 98/83/EC and the Romanian Law. Another aim of the study was to investigate the prevalence of antibiotic resistance among Gram-negative strains isolated from groundwater sources. There observed the resistance to many antibiotics, particularly: ticarcillin (80%), aztreonam (29%), gentamicin (11%), imipenem (9%), ceftriaxone (9%), ceftazidime (3%) and ciprofloxacin (3%). Significant higher resistance rates were observed in strains isolated from shallow groundwater sources as compared with strains isolated from deep groundwater sources. Pseudomonas sp. (26%) isolates with multiple-drug resistance (MDR) were encountered. The results of the study revealed a bacteriological contamination and high levels of nitrate concentrations in most of the groundwater samples, which could pose an important risk to human health.

Antibiotic Resistance Profile and Chemical Quality Assessment of Groundwater Sources from Periurban Area of Bucharest, Romania

Twenty-two groundwater sources mainly used for drinking purpose in Bucharest peri-urban area were investigated for assessment of physico-chemical and microbiological quality with a view to determining its potential risk to public health. Results of chemical analysis revealed that nitrites, sulphates and chlorides were below the permissible levels, while 63.64% of the analysed groundwater sources exceeded the maximum admissible concentration for nitrates, with concentration variations ranging from 67.27 to 523.19 mg/L. The bacteriological analysis showed that in about 63% of groundwater sources total coliform, faecal coliform and enterococci have exceeded the threshold limits recommended by the Drinking Water Directive 98/83/EC and the Romanian Law. Another aim of the study was to investigate the prevalence of antibiotic resistance among Gram-negative strains isolated from groundwater sources. There observed the resistance to many antibiotics, particularly: ticarcillin (80%), aztreonam (29%), gentamicin (11%), imipenem (9%), ceftriaxone (9%), ceftazidime (3%) and ciprofloxacin (3%). Significant higher resistance rates were observed in strains isolated from shallow groundwater sources as compared with strains isolated from deep groundwater sources. Pseudomonas sp. (26%) isolates with multiple-drug resistance (MDR) were encountered. The results of the study revealed a bacteriological contamination and high levels of nitrate concentrations in most of the groundwater samples, which could pose an important risk to human health. Keywords: bacterial resistance, groundwater, antibiotics, nitrate, waterborne diseases

Biodiversity value of remnant pools in an intermittent stream during the great California drought

Abstract In many intermittent streams, remnant pools persist after flow ceases and provide refuge for aquatic organisms able to tolerate stagnant water conditions. The conservation value of these pools may be greatly under‐appreciated, especially in regions with a Mediterranean climate, where perennial streams have been substantially modified or disturbed by human activities. Fish, amphibians, aquatic reptiles, and aquatic invertebrates were sampled from 15 remnant pools and three seeps at Coyote Creek, California, USA, in the late summer of 2014, during the height of the most intense drought that California has experienced in 500 years. Patterns of vertebrate and invertebrate species richness and community composition were compared with abiotic factors (e.g. water quality and habitat size). Thirteen vertebrate species and 172 invertebrate taxa were identified from remnant pools and seeps. Overall vertebrate richness and composition were not correlated with abiotic factors, but fish species richness increased with remnant pool size and depth. Invertebrate taxon richness increased with pool size. Invertebrate community composition differed by habitat type (pool versus seep) and gradients in composition were correlated with several abiotic factors (e.g. pool size, substrate, and canopy cover). Remnant pools at Coyote Creek supported a full assemblage of native fishes and numerous imperilled taxa, including California red‐legged frogs and California floater mussels. Nearly all native fishes and imperilled taxa are absent from artificially perennial and urbanized reaches of Coyote Creek just a few kilometres downstream of the study area. Remnant pools in intermittent streams should be a focus of conservation efforts in regions with a Mediterranean climate, especially during extreme droughts. Native fauna adapted to harsh intermittent flow regimes can thrive in these habitats, whereas non‐native taxa may fare poorly. Furthermore, remnant pools supported by deep groundwater sources, such as those along geological faults, may provide both ecological refuge and evolutionary refugia for freshwater biota.

Examining the role of sub-foundation soil texture in chlorinated vapor intrusion from groundwater sources with a two-layer numerical model

In this study we investigate the role of the sub-foundation soil texture in determining groundwater source-to-indoor air attenuation factors. A three-dimensional numerical model was used to simulate a series of two-layer scenarios, involving different sub-foundation and deep soil textures, foundation types and groundwater source depths. The results indicate that if the sub-foundation soil permeability is larger than 10-11 m2, the convection dominates the soil gas transport into the building, and the indoor air concentration increases by half an order of magnitude with one order of magnitude increase of the sub-foundation soil permeability. Otherwise, diffusion plays a more important role and the sub-foundation soil texture does not cause significant variation of indoor air concentration. We found that, independently from the deep soil texture, the capillary fringe offers the main resistance to vapor transport. In these cases, the deep soil texture could induce at most half an order of magnitude of variation in total effective diffusion coefficient in deep soil as well as groundwater source-to-indoor air attenuation factors. Finally, we found that, as the thin capillary zone represents the higher resistance to upward soil gas flow, groundwater source depth has little influence in determining the chlorinated vapor intrusion risk.

Deep urban groundwater vulnerability in India revealed through the use of emerging organic contaminants and residence time tracers

Demand for groundwater in urban centres across Asia continues to rise with ever deeper wells being drilled to avoid shallow contamination. The vulnerability of deep alluvial aquifers to contaminant migration is assessed in the ancient city of Varanasi, India, using a novel combination of emerging organic contaminants (EOCs) and groundwater residence time tracers (CFC and SF6). Both shallow and intermediate depth private sources (<100 m) and deep (>100 m) municipal groundwater supplies were found to be contaminated with a range of EOCs including pharmaceuticals (e.g. sulfamethoxazole, 77% detection frequency, range <0.0001–0.034 μg L−1), perfluoroalkyl substances (e.g. PFOS, range <0.0001–0.033 μg L−1) as well as a number of pesticides (e.g. phenoxyacetic acid, range <0.02–0.21 μg L−1). The profile of EOCs found in groundwater mirror those found in surface waters, albeit at lower concentrations, and reflect common waste water sources with attenuation in the subsurface. Mean groundwater residence times were found to be comparable between some deep groundwater and shallow groundwater sources with residence times ranging from >70 to 30 years. Local variations in aquifer geology influence the extent of modern recharge at depth. Both tracers provide compelling evidence of significant inputs of younger groundwater to depth >100 m within the aquifer system.

Water quality assessment of shallow and deep boreholes in Ekpan community, Effurun, Delta State, Nigeria

Twelve (12) groundwater samples (six from shallow and six from deep boreholes) were randomly collected in Ekpan community and environs, Delta State, Nigeria, for water quality/safety assessment. All samples were collected in replicates and transferred to the laboratory within 24 h of collection. Soil samples were collected in well-labelled sterilised polythene bags. The samples were subjected to laboratory analysis. Descriptive statistics was used to explore data, while Pearson correlation (r) was used to determine the relationships of the physicochemical and microbial parameters. The test of homogeneity in mean variance of the parameters (with the single-factor analysis of variance ANOVA) was used to determine possible differences between the shallow and deep groundwater sources. pH, temperature and biological oxygen demand (BOD) varied from 6.00 to 6.66 (6.22 ± 0.04), 24.00 to 25.10 (24.50 ± 0.09) mg/l and 2.50 to 5.82 (4.15 ± 0.21) mg/l, respectively. Salinity and total hardness varied from 3.00 to 79.40 (32.24 ± 5.74) % and 4.50 to 97.69 (37.84 ± 7.20) mg/l, while NO3− and SO42− varied from 0.03 to 1.35 (0.67 ± 0.11) and 1.80 to 71.35 (13.97 ± 4.03) mg/l. The heavy metals Pb, Cd, Cr, Mn and Hg ranged from 0.01 to 0.15 (0.07 ± 0.01), 0.01 to 0.64 (0.25 ± 0.05), 0.02 to 0.11 (0.08 ± 0.01), 0.04 to 0.16 (0.10 ± 0.01) and 0.0001 to 0.00039 (0.0002 ± 0.00001) mg/l, respectively, while total coliform counts ranged from 1.90 × 105 to 4.90 × 105 cfu/ml. pH correlated significantly with Cd, Ni, Mn and As, with Pearson correlation r > 0.43, while total coliform counts were influenced by temperature, electrical conductivity EC, total dissolved solids TDS, BOD, K, Mg, SO42− and NO3−, with Pearson correlation r > 0.7. While Hg is averagely at contaminant level, Pb, Cd, Mn, Cr, BOD and total coliform values exceeded the recommended values of World Health Organization WHO guidelines for drinking water quality, and thus constitute pollutants. Relative water quality (and hence water safety) averagely increases with depth of the boreholes (and by implication, the depth to the aquiferous units). The major contributors to heavy metal load are essentially surface/near-surface-based geologic and anthropogenic activities. The predominant effect of natural filtration (during infiltration/recharge through precipitation) is evident and is most likely enhanced by appreciable presence of fines (clay and silt) at variable horizons.

Unusual metabolic diversity of hyperalkaliphilic microbial communities associated with subterranean serpentinization at The Cedars.

Water from The Cedars springs that discharge from serpentinized ultramafic rocks feature highly basic (pH=~12), highly reducing (Eh<-550 mV) conditions with low ionic concentrations. These conditions make the springs exceptionally challenging for life. Here, we report the metagenomic data and recovered draft genomes from two different springs, GPS1 and BS5. GPS1, which was fed solely by a deep groundwater source within the serpentinizing system, was dominated by several bacterial taxa from the phyla OD1 ('Parcubacteria') and Chloroflexi. Members of the GPS1 community had, for the most part, the smallest genomes reported for their respective taxa, and encoded only archaeal (A-type) ATP synthases or no ATP synthases at all. Furthermore, none of the members encoded respiration-related genes and some of the members also did not encode key biosynthesis-related genes. In contrast, BS5, fed by shallow water, appears to have a community driven by hydrogen metabolism and was dominated by a diverse group of Proteobacteria similar to those seen in many terrestrial serpentinization sites. Our findings indicated that the harsh ultrabasic geological setting supported unexpectedly diverse microbial metabolic strategies and that the deep-water-fed springs supported a community that was remarkable in its unusual metagenomic and genomic constitution.

Groundwater Recharge Quantification from Historical Rainfall Records and Salinity Profiling in the RAMSAR Listed Verlorenvlei Catchment, South Africa

The Verlorenvlei RAMSAR listed wetlands in the Sandveld of South Africa are threatened by the effects of salinization coupled with low rainfall. The lack of surface water throughout most of the year suggests that the wetlands may be fed by deeper groundwater sources. The Verlorenvlei River feeds into the wetlands and has four major tributaries which will form the basis of this study. A number of recharge techniques have been implemented in the Sandveld, but little research has characterised the groundwater of the tributaries of the Verlorenvlei River and their contribution to the wetlands. The Chloride Mass Balance technique and stable isotopes will be used to estimate the recharge occurring in these sub-catchments, with tritium and radiocarbon providing time constraints. These results can be compared to longer-term rainfall records to predict future fluctuations in groundwater availability. Eight rainfall collection points have been established throughout the catchment, with corresponding deep boreholes to be sampled on a regular basis. Preliminary results show that the shallow groundwater is more saline than the corresponding deep sources, with the exception of the fresh Krom Antonies tributary which is thought to be the main input source for the Verlorenvlei River.

Performance and Acceptance of Novel Silver-Impregnated Ceramic Cubes for Drinking Water Treatment in Two Field Sites: Limpopo Province, South Africa and Dodoma Region, Tanzania

Diarrheal disease and environmental enteropathy are serious public health concerns in low-income countries. In an effort to reduce enteric infection, researchers at the University of Virginia developed a new point-of-use (POU) water treatment technology composed of silver-impregnated porous ceramic media. The ceramic is placed in a 15 L plastic container of water in the evening and the water is ready to drink in the morning. The purpose of this study was to assess field performance and local acceptance of technology in two communities in Limpopo Province, South Africa, and one community in Dodoma Region, Tanzania. Performance was determined by coliform testing of treated water. Acceptance was determined using data from 150 household surveys and a nine-day structured observational study at a local primary school. At the primary school, 100% of treated water samples had no detectable levels of total coliform bacteria (TCB) in buckets filled by researchers. For all treated school buckets, 74% of samples achieved less than or equal to 1 CFU/100 mL and 3.2 average log reduction of TCB. Laboratory experiments with highly contaminated water diluted to lower turbidity achieved 4.2 average log reduction of TCB. Turbid water (approximately 10 NTU) only achieved 1.1 average log reduction of TCB; turbidity and organic material may have interfered with disinfection. The Tanzania primary school (deep groundwater source) had less turbid water and achieved 1.4 average log reduction of TCB; however, it did have high chloride levels that may have interfered with silver disinfection. The surveys revealed that the majority of people retrieve, store, and dispense water in ways that are compatible with the new technology. The willingness-to-pay study revealed potential customers would be willing to pay for the technology without subsidies. The results of this study indicate that this novel silver-impregnated ceramic POU water treatment technology is both effective and appropriate for use in the study communities.

Prevalence of Legionella in premise plumbing in Hungary

Legionella is one of the emerging concerns of water quality in built water environments. Premise plumbing systems are among the recognised sources of infection. In the present study, colonisation of hot water networks in health care facilities, schools, hotels, private residences, office and industrial buildings was investigated. Data was analysed in connection with building and premise plumbing characteristics. Over 60% of all buildings were colonised by Legionella; counts were over 1000 CFU/L in 49%. The most prevalent type was Legionella pneumophila serogroup 2–14, isolated from 75% of the positive samples. Centrally produced hot water was found to be a key risk factor (46% of the samples were positive vs. 16% in individual systems); within this group the type of the building was less relevant. Colonisation levels in schools were similar to hotels or hospitals, representing a previously underestimated risk setting. Systems supplied by water from deep groundwater sources were significantly less likely to be colonised than more vulnerable sources (bank-wall filtration, surface water abstraction or karstic water; 28% vs. 51% positive), regardless of the type of treatment applied, including the presence of disinfection. The aggravating effect of larger, more complex and older buildings on colonisation was also confirmed.The present study represents the first baseline analysis, pre-empting regulation or monitoring requirements for Legionella. The prevalence of legionellae and the identified risk factors are indicative for other settings lacking targeted interventions. The statistically confirmed risk factors can serve as indicators for preliminary risk assessment and the prioritisation of interventions.

Sources, sinks and long-term cycling of iodine in the hyperarid Atacama continental margin

The Atacama region in northern Chile hosts the driest desert on Earth and is the world’s premier iodine production province. The origin of iodine enrichment in Atacama is controversial and fundamentally different processes have been invoked over the years that involve marine, eolian and more recently deep sedimentary fluid and groundwater sources. As a result of the very limited geochemical iodine data in Atacama and the western South American margin, the origin of iodine enrichment in this region still remains elusive. In this study, we present a comprehensive survey of iodine concentrations and isotopic ratios (129I/I) of different reservoirs in the Atacama Desert of northern Chile, including nitrate soils, supergene copper deposits, marine sedimentary rocks, geothermal fluids, groundwater and meteoric water. Nitrate soils along the eastern slope of the Coastal Cordillera are found to have mean iodine concentrations of at least three orders of magnitude higher than the mean crustal abundances of ∼0.12ppm, with a mean concentration of ∼700ppm. Soils above giant copper deposits in the Central Depression are also highly enriched in iodine (100’s of ppm range), and Cu-iodide and iodate minerals occur in the supergene enrichment zones of some of these deposits. Further east in the Precordillera, Jurassic sedimentary shales and limestones show above-background iodine concentrations, the latter averaging ∼50ppm in the southern portion of the study area. The highest iodine concentrations in fluids were measured in groundwater below nitrate soils in the Coastal Range (∼3.5–10ppm) and in geothermal waters (1–3ppm) along the volcanic arc. Although highly variable, the iodine isotopic ratios (129I/I) of Jurassic marine sedimentary rocks (∼300–600×10−15), nitrate soils (∼150–1500×10−15) and waters (∼215×10−15) are consistently low (<1500×10−15), indicating that recent anthropogenic additions are almost negligible in most surficial and deeper reservoirs. Geochemical mixing models reveal that the measured 129I/I ratios in Atacama are in agreement with multiple sources of iodine that include variable contributions from old organic iodine sources (i.e., marine sedimentary rocks) and younger fluids such as pore waters, geothermal fluids and meteoric waters. Our results show that the large variation observed in the iodine isotopic ratios of different reservoirs (129I/I from 150 to 1580×10−15) is indicative of significant mixing and circulation of fluids of meteoric, sedimentary and volcanic origin along the Chilean continental margin in the last 30 million years. We conclude that this protracted and large-scale fluid flow was driven by tectonic uplift and highly influenced by the climatic history of the Atacama Desert. The combination of such factors has played an unforeseen role in transporting and accumulating iodine and other soluble components in the Atacama region, and is evidence that elemental remobilization is a key process in the overall crustal cycle of iodine over scales of millions of years.

Potential maps for the hydrogeologic prerequisites of the installation of deep geothermal doublets and groundwater source heat pump systems in Budapest, Hungary

Budapest is famous for its thermal springs and spas and outstanding thermal water resources. In the 21st century renewable energy utilization — including the use of geothermal energy — became the focus of interest. Improving the use of the different forms of geothermal energy requires the assessment of their possibilities. The potential for deep geothermal doublet systems for direct heating in Budapest was evaluated based on the temperature conditions, the depth and reconnaissance of the carbonate reservoir. NW Buda is not appropriate for thermal water exploration. SW and SE Budapest have better temperature conditions but the lithology of the reservoir is uncertain. Beneath Pest the thermal water is well exploitable. It is obvious from the map of the region that the area is promising; however, due to the hydraulic continuity of the system, reinjection is desirable. Considering the reliability of the employed data the geothermal potential map is suitable only for general orientation and guidance. The geoth...

Storm‐event flow pathways in lower coastal plain forested watersheds of the southeastern United States

AbstractThe landscape of the coastal plain of the southeastern United States is rapidly changing due to urbanization and climate‐change‐related impacts. In addition to the forecasted population increase, this region could experience significant changes in precipitation patterns making watershed management very challenging. In order to establish baseline data, storm‐event flow pathways were studied in three lower coastal plain (LCP) forested lowland watersheds of the southeastern United States between 2010 and 2011. Two of the watersheds had clay loam subsoils while the third had sandy soils throughout the profile. Stream flow and water samples from water‐table wells, piezometers, lysimeters, and rain gauges were analyzed for ion concentrations; ion trends were assessed using principal components analysis; and chemical hydrograph separation was performed for nine storm events using end‐member mixing analysis. End‐members consisted of lower concentration rainwater; a near‐stream source (riparian or streambed groundwater); and a distant or deep groundwater source. Storm‐event stream water on the clayey sites was composed primarily of rainwater (45–67% by volume) and shallow groundwater (21–55%), with small inputs from deep (below the clay‐rich soil horizon) groundwater (0.2–21%). At the sandy site, a greater proportion was groundwater (56–61%), with smaller inputs from rainwater (28–33%) and soil water (6–16%). Dry antecedent soil moisture (ASM) conditions and larger storms resulted in greater rainwater contribution at the clayey sites. Shallow groundwater was an important contributor even in dry ASM conditions, perhaps due to the high specific retention of the soils. The results from this study will inform researchers about stormwater routing in forested, shallow water table watersheds and provide land managers with baseline data as they plan stormwater mitigation practices.

Dissolved organic matter (DOM) concentration and quality in a forested mid-Atlantic watershed, USA

Understanding the quantity and quality of dissolved organic matter (DOM) in potential watershed sources is critical for explaining and quantifying the exports of DOM in stream runoff. Here, we examined the concentration and quality of DOM for ten watershed sources in a 12 ha forested catchment over a two-year period. DOM composition was evaluated for: throughfall, litter leachate, soil water (zero and tension), shallow and deep groundwater, stream water, hyporheic zone, and groundwater seeps. DOM quality was measured using a suite of optical indices including UV–visible absorbance and PARAFAC modeling of fluorescence excitation-emission matrices (EEMs). DOM concentrations and quality displayed a pronounced trend across watershed sources. Surficial watershed sources had higher DOM concentrations and more humic-like DOM with higher molecular weight whereas deeper groundwater sources were rich in % protein-like fluorescence. The greater % contribution of protein-like fluorescence in groundwater suggested that a larger fraction of groundwater DOM may be bioavailable. DOM for wetland groundwater was more aromatic and humic-like than that at the well-drained riparian location. Principal component analyses (PCA) revealed that the differences in surficial watershed compartments were dictated by humic-like components while groundwater sources separated out by % protein-like fluorescence. Observations from optical indices did not provide any conclusive evidence for preferential association of dissolved organic carbon (DOC) or dissolved organic nitrogen (DON) with any particular DOM quality pools.

Joint interpretation of hydrological and geophysical data: electrical resistivity tomography results from a process hydrological research site in the Black Forest Mountains, Germany

AbstractThe use of electrical resistivity tomography (ERT; non‐intrusive geophysical technique) was assessed to identify the hydrogeological conditions at a surface water/groundwater test site in the southern Black Forest, Germany. A total of 111 ERT transects were measured, which adopted electrode spacings from 0·5 to 5 m as well as using either Wenner or dipole‐dipole electrode arrays. The resulting two‐dimensional (2D) electrical resistivity distributions are related to the structure and water content of the subsurface. The images were interpreted with respect to previous classical hillslope hydrological investigations within the same research basin using both tracer methods and groundwater level observations. A raster‐grid survey provided a quasi 3D resistivity pattern of the floodplain. Strong structural heterogeneity of the subsurface could be demonstrated, and (non)connectivities between surface and subsurface bodies were mapped. Through the spatial identification of likely flow pathways and source areas of runoff, the deep groundwater within the steeper valley slope seems to be much more connected to runoff generation processes within the valley floodplain than commonly credited in such environmental circumstances. Further, there appears to be no direct link between subsurface water‐bodies adjacent to the stream channel. Deep groundwater sources are also able to contribute towards streamflow from exfiltration at the edge of the floodplain as well as through the saturated areas overlying the floodplain itself. Such exfiltrated water then moves towards the stream as channelized surface flow. These findings support previous tracer investigations which showed that groundwater largely dominates the storm hydrograph of the stream, but the source areas of this component were unclear without geophysical measurements. The work highlighted the importance of using information from previous, complementary hydrochemical and hydrometric research campaigns to better interpret the ERT measurements. On the other hand, the ERT can provide a better spatial understanding of existing hydrochemical and hydrometric data. Copyright © 2009 John Wiley &amp; Sons, Ltd.

Assessing the value of Cl− and δ18O data in modelling the hydrological behaviour of a small upland catchment in northeast Scotland

Model simulation of Cl− and δ18O in stream waters has been investigated as a means of improving interpretation of catchment-scale hydrological processes. The procedure has been evaluated for a small upland catchment which is one of the UK Environmental Change Network sites. Precipitation and stream samples have been analysed for hydrochemical determinands since the mid 1990s and, since November 2004, measurement of δ18O has also been undertaken. A conceptual hydrological model STREAM (STorage REsidence times And Mixing) was applied to the catchment to simulate the hydrology and responses of Cl− and δ18O. Results from model simulations confirmed that the catchment generally behaves as a well-mixed system. The feasibility of flow contributions from a deep groundwater source and infiltration excess runoff was examined, in addition to the apparently dominant shallow groundwater response. The ability to estimate mean residence times and draw strong conclusions about catchment processes was limited by the range of uncertainties in the experimental data and modelling. Integration of the tracer data in the model was found to be of value for probing model sensitivities and developing hypotheses that inform the design of further field experimentation. In this way, the modelling provides key feedback within a catchment learning framework.