Hydrogeological Connectivity Research Articles

Hydrogeological characterization of karst springs of the white (Proteus anguinus anguinus) and black olm (Proteus anguinus parkelj) habitat in Bela krajina (SE Slovenia)

The springs west of Črnomelj, in SE Slovenia, are the habitat of the black (Proteus anguinus parkelj) and the white olm (Proteus anguinus anguinus). Some of these springs are also the only known habitat in the world of endemic species of black olm. A steady decline in olm populations has been observed in this area over the past decades. Owing to the rapid runoff and groundwater flow high-resolution monitoring is essential in providing better insight into the hydrogeological characterization of the catchment area of springs. Specific factors and critical parameters of water behind said olm degradation have not yet been defined. Because the olm’s environment is largely aquatic, one potential critical parameter could be the higher water temperatures (>12 °C) or higher nitrate concentration (>9.2 mg/l). The six-month observation of the springs (July – December 2021) point to water temperature as a potential critical parameter since the water temperature of the springs exceeded 12 °C in months July and August. Nitrate concentrations could also be a second critical parameter in the degradation of the olm’s habitat. Maximum nitrate concentrations above 9.2 mg/l throughout much of the observation period (except for Dobličica spring). Due to less agricultural activity in December in the spring catchment area and a higher dilution rate due to reduced evapotranspiration and increased effective precipitation during this time of the year, the nitrate concentrations are decreased. The results of the measured parameters of groundwater could show the hydrogeological connection between the Otovski and Pački breg springs and between Šotor, Jamnice and Dobličica. The Obršec spring has an independent catchment area. A detailed estimation of the springs catchment area is possible due to a detailed geologic map. It is necessary to determine the origin of the nitrate (nitrate isotope analysis), to quantify the threshold values of the critical parameters, to define precisely all the causes of the olm deterioration, and to make proposals for appropriate measures to limit or even stop the decline of the olm population.

Unravelling geological controls on groundwater flow and surface water-groundwater interaction in mountain systems: A multi-disciplinary approach

Mountain water resources are considered to be the world’s water towers. Still, despite their importance for downstream societies and ecosystems and their vulnerability to climate change, they remain poorly understood – It is the case in particular of mountain groundwater systems. Their complexity makes them difficult to conceptualize, while their remoteness makes them difficult to study, both observationally and instrumentally. Understanding mountain hydrogeological systems is mostly limited by the lack of characterization of the subsurface geologic framework and by the limited understanding of the role of geological structures on groundwater flow and on surface water-groundwater interaction. Removing methodological barriers is therefore a necessary step for improving the understanding of mountain hydrogeological systems.To tackle this problem, we develop a comprehensive multi-disciplinary approach to gain insights into the hydrogeological role of geological structures in ungauged mountain catchments. The methodology consists of several complementary methods: (1) geological mapping at multiple scales; (2) a geophysical study including on-ground Electrical Resistivity Tomography (ERT) and, gravimetry transects, and a UAV-based magnetic survey; (3) hydraulic data, including a 9 km long transect of streamflow measurements in the recession period, the long-term Normalized Difference Vegetation Index (NDVI), and varied hydric markers (e.g., a thermal spring and a puddle). The methodology is tested in the Parque Nacional del Río Clarillo, an ungauged catchment in the Andes Mountains (≈130 km2) that is illustrative of the complexity of mountain hydrosystems featuring fault zones, weathered zones, intrusive rocks, and volcano-sedimentary successions.An increase of approximately 50% in the streamflow is observed over a short distance of 1 km. Such a localized and significant increase in the baseflow is not related to any superficial supply and can only be explained by groundwater exfiltration. Based on the multiscale geological mapping and geophysical survey, a regional N-S fault and a secondary set of E-W local faults are identified in the vicinity of the resurgence area, which conjointly are likely to export groundwater from a neighbouring subcatchment up to the resurgence area. Downstream of the resurgence area, no significant change in the baseflow is observed, corresponding to the presence of an impermeable granitic pluton identified by the geological and geophysical mapping. Finally, a fractured zone in the Andean foothills is identified in the volcanic unit, which coincides with a perennial thermal spring, indicating upwelling flow and hydrogeological connectivity between the mountain block and the alluvial basin.The results strongly support the ability of the proposed methodology to identify geological structures that substantially impact the evolution of the baseflow through the catchment. The complementary multi-disciplinary methods are used innovatively to infer the link between geological and hydrogeological structures. The methodology does not aim to fully characterize the geological framework of the catchment but pragmatically focuses on hydrogeologically pertinent structures that may impact baseflow and consequently catchment management.

Особенности экологической и безопасной ликвидации вертикальных выработок шахт Прокопьевско-Киселевского угольного района Кузбасса

Liquidation of the vertical shafts at hazardous production facilities — mines closed by dry or wet methods, in standard situations does not present any particular difficulties. The most complex, but environmentally friendly in technical and technological terms is the development and implementation of the combined method for the liquidation of hazardous mines of the Prokopyevsko-Kiselevsky coal district of Kuzbass with the depleted space of spent powerful coal seams opened by vertical shafts. This is related to the fact that these mines have, as a rule, common boundaries of mountain allotments and either a direct hydraulic or hydrogeological connection. It is established that the mines of the Prokopyevsko-Kiselevsky coal district form two hydraulically connected groups of mines: northern and southern. When they are closed and flooded, there is a flow of groundwater from one depleted space of the mine to another — neighboring, with the danger of water leaving at the lowest point on the earth surface. The combined method provides for flooding of the liquidated mines to a certain level, the level of which is regulated by installation in one of the vertical shafts of submersible pumps. After establishing the fact of complete flow of water and stabilization of the depression funnel, the dewatering complex is dismantled and the trunk, in which it was mounted, is eliminated. On the example of the Ziminka mine and the mine named after K.E. Voroshilov, the technical solutions, and the technological schemes for the safe liquidation of vertical shafts of pits and wells are shown. Liquidation is carried out by backfilling with non-combustible material with the preliminary erection of water-resistant insulating jumpers in the horizontal workings, and the installation of floor shelves in the long part and mouth.

Molecular genetic analysis of stygobiotic shrimps of the genus <em>Xiphocaridinella</em> (Crustacea: Decapoda: Atyidae) reveals a connection between distant caves in Central Abkhazia, southwestern Caucasus

Based on the morpho-genetic study of stygobiotic shrimps from the genus Xiphocaridinella Sadowsky, 1930 (Crustacea: Decapoda: Atyidae), a hydrogeological connection of a number of distant caves in Central Abkhazia of the southwestern Caucasus is satisfied, which indicates the possibility of using biospeleological studies in some cases to identify karst hydrosystems together with traditional hydrogeological methods. Moreover, a new stygobiotic atyid shrimp from the genus Xiphocaridinella, X. kelasuri sp. n., is described based on morphology and analysis of mitochondrial cytochrome oxidase I DNA sequences from three distant caves. The new species is genetically divergent from relatives and phylogenetically related to Xiphocaridinella smirnovi Marin, 2020, described from the Besletka (=Tskaro) Cave. Recently, the number of described speciesof the genus Xiphocaridinella from Caucasus has increased to 13 species, while the diversity of Xiphocaridinella found in the Besletka (=Tskaro) Cave is increasing to 3 species, which is higher than in any other known cave where Troglocaris-like shrimps have been discovered.

Spatio-Temporal Variations of Hydrochemical and Microbial Characteristics in Karst Water in Samcheok, South Korea

This study analyzed the hydrochemical characteristics and microbial communities of karst water in Samcheok, Korea, and compared water quality results to identify the seasonal characteristics and hydrogeological connectivity of the study areas of Hamaengbang-ri, Gyogok-ri, Yeosam-ri, and the downtown area of Samcheok. Field survey and water quality analysis were performed in July 2019, February 2020, and April 2020. Hydrochemical analysis of karst water (groundwater and surface water) showed that most samples were comprised of Ca-HCO3 and that water–rock interactions were a dominant factor compared to precipitation and evaporation (crystallization). For seasonal characteristics, water–rock interactions appeared more active in the dry season than in the rainy season. Calcite weathering was dominant in the dry season, whereas dolomite weathering dominated the rainy season. Moreover, the saturation indexes for the dry and rainy seasons were less than and greater than 0, respectively, corresponding to an unsaturation (oversaturation) state; thus, white precipitate distributed in the study areas was deposited in the rainy season. Finally, as a result of analyzing the hydraulic characteristics between regions, hydrogeological similarities were identified between Hamaengbang-ri and Yeosam-ri, and between Gyogok-ri and downtown Samcheok, which suggested hydrogeological connectivity between each of the pairs.

Identifying septic pollution exposure routes during a waterborne norovirus outbreak - A new application for human-associated microbial source tracking qPCR

In June 2017, the Pennsylvania Department of Health (PADOH) was notified of multiple norovirus outbreaks associated with 179 ill individuals who attended separate events held at an outdoor venue and campground over a month period. Epidemiologic investigations were unable to identify a single exposure route and therefore unable to determine whether there was a persistent contamination source to target for exposure mitigation. Norovirus was detected in a fresh recreational water designated swimming area and a drinking water well. A hydrogeological site evaluation suggested a nearby septic leach field as a potential contamination source via ground water infiltration. Geological characterization revealed a steep dip of the bedrock beneath the septic leach field toward the well, providing a viral transport pathway in a geologic medium not previously documented as high risk for viral ground water contamination. The human-associated microbial source tracking (MST) genetic marker, HF183, was used as a microbial tracer to demonstrate the hydrogeological connection between the malfunctioning septic system, drinking water well, and recreational water area. Based on environmental investigation findings, venue management and local public health officials implemented a series of outbreak prevention strategies including discontinuing the use of the contaminated well, issuing a permit for a new drinking water well, increasing portable toilet and handwashing station availability, and promoting proper hand hygiene. Despite the outbreaks at the venue and evidence of ground water contamination impacting nearby recreational water and the drinking water well, no new norovirus cases were reported during a large event one week after implementing prevention practices. This investigation highlights a new application for human-associated MST methods to trace hydrological connections between multiple fecal pollutant exposure routes in an outbreak scenario. In turn, pollutant source information can be used to develop effective intervention practices to mitigate exposure and prevent future outbreaks associated with human fecal contaminated waters.

A three-dimensional stratigraphic model of the Mississippi River Delta, USA: implications for river deltaic hydrogeology

A three-dimensional stratigraphic model was constructed of the upper 50 m of the Mississippi River Delta, southeastern USA. The model is used to understand hydrogeological connections among the Mississippi River, adjacent interdistributary bays and groundwater systems, and to understand how stratigraphic settings affect potential anthropically induced subsidence and erosion in the region. This study uses 619 geotechnical borings throughout the area along with the multiple-indicator natural neighbor (MINN) interpolation method to construct the model. Based on available data, the study focused on the Mississippi River reach from Head of Passes (river mouth) to Jesuit Bend (108 km upstream), covering an area of approximately 1,800 km2 and ranging in elevation from 3 to −46 m. The model shows typical basal coarse-grained sand bodies overlain by 10-m-thick blanket clay, which is interbedded frequently with silty and sandy sediments and occasionally with peat and organic clay. Sands are most abundant between elevations −10 and −35 m. The Mississippi River main channel incises the underlying sands, thereby providing pathways for river–groundwater exchange. Increased hydrologic loads may propagate along the flow paths potentially giving rise to high pore-water pressure and a resultant increase in land subsidence and thus local erosion of natural and local flood-control levees. This method of analysis may apply to other deltaic regions similarly subject to anthropically accelerated subsidence and erosion.

Ordenamiento territorial, agua subterránea y participación sociopolítica en Bacalar, Quintana Roo, México

A partir de un estudio interdisciplinario sobre la participación sociopolítica en la formulación del Programa de Ordenamiento Ecológico Local (POEL) de Bacalar, analizamos las motivaciones y dificultades para considerar la "vocación natural” de este territorio, es decir, la capacidad que tiene para sustentar las actividades de los diversos seres vivos que lo habitan, partiendo del hecho de que se trata de un sistema kárstico. Para incluir dicha consideración, el equipo de investigación implementó una estrategia de investigación-acción (IA) que consistió en elaborar un modelo de conectividad hidrogeológica y sumarse a las gestiones para la configuración de este instrumento de política pública. Desde un enfoque socioambiental, la investigación incluyó técnicas etnográficas como entrevistas, observación participante y diario de campo. Los resultados muestran que algunas de las representaciones territoriales de los actores son incompatibles con las características del sistema kárstico y plantean la necesidad de una política participativa, orientada a la construcción de una visión común del territorio mediante procesos de socialización del conocimiento entre los actores y los sectores involucrados. Entre las limitantes de la IA se encontró que, a pesar de lograr la convergencia de sectores, se mantuvo la dinámica inercial que hasta ahora ha impedido la entrada en vigor del POEL en un espacio cada vez más codiciado y en riesgo para el ecosistema y quienes lo habitan.

Hydrogeological characterization of an alpine aquifer system in the Canadian Rocky Mountains

Groundwater storage in alpine regions is essential for maintaining baseflows in mountain streams. Recent studies have shown that common alpine landforms (e.g., talus and moraine) have substantial groundwater storage capacity, but the hydrogeological connectivity between individual landforms has not been understood. This study characterizes the hydrogeology of an alpine cirque basin in the Canadian Rocky Mountains that contains typical alpine landforms (talus, meadow, moraines) and hydrological features (tarn, streams, and springs). Geological, hydrological, and hydrochemical observations were used to understand the overall hydrogeological setting of the study basin, and three different geophysical methods (electrical resistivity tomography, seismic refraction tomography, and ground penetrating radar) were used to characterize the subsurface structure and connectivity, and to develop a hydrogeological conceptual model. Geophysical imaging shows that the talus is typically 20–40 m thick and highly heterogeneous. The meadow sediments are only up to 11 m thick but are part of a 30–40-m-thick accumulation of unconsolidated material that fills a bedrock overdeepening (i.e. a closed, subglacial basin). A minor, shallow groundwater system feeds springs on the talus and streams on the meadow, whereas a deep system in the moraine supplies most of the water to the basin outlet springs, thereby serving as a ‘gate keeper’ of the basin. Although the hydrologic functions of the talus in this study are substantially different from other locations, primarily due to differences in bedrock lithology and geomorphic processes, the general conceptual framework developed in this study is expected to be applicable to other alpine regions.

Inter-aquifer connectivity between Australia’s Great Artesian Basin and the overlying Condamine Alluvium: an assessment and its implications for the basin’s groundwater management

Coal seam gas (CSG), or coal bed methane, developments in sedimentary basins such as the Great Artesian Basin (GAB) in Australia, have the potential to impact on aquifers overlying and underlying the target coal formations. The extent to which this may occur depends upon the degree of hydrogeological connectivity between the coal formations and the surrounding aquifers or aquifer systems, with general implications for groundwater management. In southeast Australia, one such aquifer system, the Condamine Alluvium (CA), overlies the Walloon Coal Measures (WCM), which is a formation of the GAB and also a target for CSG production. To investigate the connectivity between the two systems, multiple lines of investigation were employed involving field investigations, data gathering and analysis (including reinterpretation of geology, multivariate hydrochemistry analysis, regional water-level mapping, drilling and coring across the contact zone, multiple piezometer installations, long-term pumping tests, groundwater-level monitoring and local-scale modelling). The study found a low level of connectivity between the GAB and the overlying CA. A layer of undifferentiated basement clay (referred to as the ‘transition zone’)—a mixture of alluvial clay and weathered basement—provides an effective impediment to flow across the CA and the underlying GAB formations. Results from the study potentially have wider application across the GAB and sedimentary basins where younger alluvial sediments associated with river systems frequently overlie the erosional surface.

Combining hydrodynamics, hydrochemistry, and environmental isotopes to understand the hydrogeological functioning of evaporite-karst springs. An example from southern Spain

This work adopts a multicriteria approach, combining diverse karst hydrogeology techniques, to investigate the functioning of evaporite-karst systems, which are normally less studied due to the poor quality of their water resources. The applicability of using several methods was also verified. In view of previous experience at a pilot site within southern Spain, the natural responses of the main discharge point of the system of study (Lower Anzur spring) were controlled by continuous monitoring of the discharge rate, water temperature, and electrical conductivity. Water samples were collected for chemical analysis and for the determination of intrinsic fluorescence, water stable isotopes (δ18O, δ2H) and tritium (3H) concentrations. Physico-chemical data were statistically examined applying principal component analysis (PCA) and trend analysis tests (Mann-Kendall and Sen’s slope). The system shows a clear karstic functioning, highly dependent on concentrated recharge, and influenced by a limited drainage capacity of the conduit network. The piston-flow effects at the beginning of floods indicate a contribution to the drainage of deep ascending flows through the saturated zone. Subsequent drops in temperature and mineralization values in the water drained by the spring, as well as a recent infiltration deduced from the signature of intrinsic fluorescence and stable isotopes, point to a good hydrogeological connection from the recharge areas to the spring. Later restoration of the initial values of mineralization —in a much shorter time than those of temperature— reveals a faster geochemical evolution of the recently infiltrated groundwater, which may be a distinctive trait of evaporite karst aquifers. Lastly, the high solute content of the spring water in depletion conditions, with ascending trends of mineralization and temperature observed during several dry years as a consequence of lower recharge contribution, together with the tritium activity of selected samples, suggest the existence of an old component partly responsible for the spring base flow. Thus, groundwater would be linked to gravity-driven regional flows, but also to recent conduit flows. All the results obtained led us to devise a hydrogeological conceptual model to precisely reflect the functioning of the studied system. The results presented here demonstrate the advantages of using diverse techniques when investigating evaporite karst aquifers.

Hydrochemical and isotopic characterization of carbonate aquifers under natural flow conditions, Sierra Grazalema Natural Park, southern Spain

Abstract We used hydrogeochemical techniques and environmental isotopes (δ 18 O and δ 2 H) to characterize karst aquifers without a well-known hydrogeological conceptual model. The selected study area corresponds to carbonate outcrops located in the Sierra Grazalema Natural Park (SGNP) in southern Spain. The combination of high rainfall, large areas of carbonate outcrops and the high permeability of the outcropping rocks means that the SGNP is a strategic water reserve in a region that periodically suffers from a scarcity of water. There are still many uncertainties regarding the hydrogeological functioning of these aquifers, such as the groundwater flow paths, the identification of recharge areas and a possible hydrogeological connection with adjacent systems. The objectives of this work were: (1) to gain an insight into the hydrogeochemistry of groundwater in the SGNP aquifers; (2) to identify the recharge areas of the main springs of the karst system; and (3) to contribute to our understanding and conceptualization of the SGNP aquifers. Our results show marked differences in the chemical composition of the groundwater, which can be classified into three main groups: CaHCO 3 waters (southern sector); Ca–MgHCO 3 waters (northern sector); and those with higher SO 4 2− , Na + and/or Cl − concentrations. These hydrochemical differences are principally dependent on the mineral composition of the rocks the groundwater flows through and comes into contact with. These results also shed light on the recharge areas associated with the main springs and seem to corroborate a possible net groundwater flow from the eastern part of the SGNP (Sierra del Endrinal) towards carbonate outcrops situated several kilometres to the SE.

Basin characterization and determination of hydraulic connectivity of mega basins using integrated methods: (The case of Baro-Akobo and mega watershed beyond)

Despite being the longest river and the fourth in drainage area, Nile River has the lowest discharge per unit areas among the top ten rivers of the world. Understanding the hydrologic significance of the regional litho-stratigraphy and structures help to better understand the hydrodynamics. This work is aimed at characterizing the Baro-Akobo-Sobbat sub-basin of Nile and determine trans-basin flows. Integrated method is used to characterize the basin and determine the Baro-Akobo-Sobbat sub-basin's relationship with African Mesozoic Rifts. Oil and water well drilling logs; aeromagnetic, gravity and vertical electrical sounding data; and various study reports are used to establish regional lithostratigraphic correlations and determine trans-regional hydrogeological connectivity. A total of 633 samples collected from wells, springs, rivers, lakes, swamps and rain water are analysed for their chemical, stable isotopes, tritium and radon properties. The Baro-Akobo river basin is commonly presumed to have good groundwater potential, particularly in its lowland plain. However, it has poor exploitable groundwater potential and recharge rate due to the extensive clay cover, limited retention capacity and the loss of the bulk of the groundwaters through regional geological structures to the deep seated continental sediments; presumably reaching the hydraulically connected African Mesozoic Rifts; mainly Melut and Muglad. The deep underground northward flows, along Nile River is, presumably, retarded by Central African Shear Zone in the Sudan.

Hydrogeological characterization of the Salinas-Los Hoyos evaporitic karst (Malaga province, S Spain) using topographic, hydrodynamic, hydrochemical and isotopic methods

The Salinas-Los Hoyos karst system is a geological diapiric structure formed by materials of diverse nature (clays, sandstones, evaporites, volcanic rocks, dolostones, etc.) placed between Malaga and Granada provinces (S Spain). The abundance of evaporite rocks (gypsum, anhydrite and halite) and their high solubility contribute to the development of exokarstic features (dolines, uvalas, sinkholes). Grande and Chica lakes are dolines located in the western border of the diapir that are intersected by the piezometric level. Close to the first wetland is the Aguileras spring, which is the main discharge point of the west sector of the system. To assess the wetland-spring relation and the general functioning of the system, the geomorphologic framework has been analyzed and hydrogeological controls have been performed, consisting in limnimetric and discharge logging and in situ measurements of physico-chemical parameters (EC and water temperature). Furthermore, spring, wetland and rain water samples have been taken for subsequent chemical and isotopic analysis. Preliminary results show that wetland water level and spring discharge follow a similar trend, consistently with the inertia of the system. However, their hydrochemical evolution and isotopic values differ, thus wetland groundwater interaction has not been fully determined. Nevertheless, present research suggests that the hydrogeological connection would be more likely during wet periods, when the water table is at higher altitude. Key words: Evaporitic (karst) aquifer, Hydrological and hydrogeological behaviours, Natural responses, South Spain, Wetlands.

Hydrogeological characterization of the Asmari limestone aquifer, Anar anticline, Zagros Region, Iran

The Anar anticline is located in the Zagros Region, south of Iran. The anticline comprises of the Asmari Formation which is sandwiched between two impermeable formations, the Pabdeh–Gurpi Formation at the bottom and the Gachsaran Formation at the top. There are several freshwater resources (e.g., spring, lake, qanat, and pumping wells) around this anticline without clear known hydrogeological connection of which to the Anar anticline. The comprehensive hydrogeological studies, including the use of the APLIS method, karst hydrogeology, hydrochemistry, and stable isotopes data of the lakes and surrounding springs, were carried out in the study area. Results show that the anticline has no hydrogeological connection with the Haft Barm Lakes, but hydrogeologically, there is potential for hydraulic connection with the Chehel Cheshmeh Spring. The study shows that the catchment area of the Mashayekh and Deh Gerdoo Springs is located in the northeast and a part of the southwest flank of the Anar anticline. Mean annual recharge rate in the Asmari limestone aquifer is estimated less that 38.5 % based on the APLIS approach that confirmed by water balance.

Isolation, Migration, and Local Recruitment Drive Persistence of Cutthroat Trout in Tributaries near American Falls Reservoir

AbstractWe analyzed 67 SNPs to describe the genetics of Yellowstone Cutthroat Trout Oncorhynchus clarkii bouvieri in seven tributaries near American Falls Reservoir, Idaho. We detected Yellowstone Cutthroat Trout in all but one site despite significant historical stocking of Rainbow Trout O. mykiss. Three of four relatively low‐elevation sites near the reservoir contained Yellowstone Cutthroat Trout in sympatry with early‐generation hybrids and Rainbow Trout yet contained no physical barriers to admixture. A posteriori assignment tests suggested that migrants from a nearby headwater population in Ross Fork Creek and possibly recruitment by local‐origin Yellowstone Cutthroat Trout with fluvial or adfluvial life histories drive persistence in these sites. In contrast, hybridization was rare or absent in headwater populations and was associated with complete or apparent physical isolation. We also compared genetic diversity of our samples with Yellowstone basin Yellowstone Cutthroat Trout and Bear River Bonneville Cutthroat Trout O. c. utah to examine possible historical gene flow resulting from hydrogeological connections during the Pleistocene. Multivariate analysis showed that most genetic variation among individuals was explained by divergence of Yellowstone basin Yellowstone Cutthroat Trout from our samples and Bear River Bonneville Cutthroat Trout, which supports recent mtDNA studies and a possible change in taxonomic nomenclature. Our results indicate that, due to relative isolation and downstream emigration, headwater populations are critical to the persistence of Yellowstone Cutthroat Trout and thus loss of such populations would likely threaten the subspecies throughout the region. Management actions to reduce threats from established, nonnative Rainbow Trout populations will likely have to be multifaceted and may include a combination of targeted removal of Rainbow Trout and hybrids and the use of physical barriers to prevent further dispersal.Received April 19, 2015; accepted February 7, 2016 Published online May 31, 2016

Assessing groundwater recharge in an Andean closed basin using isotopic characterization and a rainfall-runoff model: Salar del Huasco basin, Chile

Closed basins are catchments whose drainage networks converge to lakes, salt flats or alluvial plains. Salt flats in the closed basins in arid northern Chile are extremely important ecological niches. The Salar del Huasco, one of these salt flats located in the high plateau (Altiplano), is a Ramsar site located in a national park and is composed of a wetland ecosystem rich in biodiversity. The proper management of the groundwater, which is essential for the wetland function, requires accurate estimates of recharge in the Salar del Huasco basin. This study quantifies the spatio-temporal distribution of the recharge, through combined use of isotopic characterization of the different components of the water cycle and a rainfall-runoff model. The use of both methodologies aids the understanding of hydrological behavior of the basin and enabled estimation of a long-term average recharge of 22 mm/yr (i.e., 15 % of the annual rainfall). Recharge has a high spatial variability, controlled by the geological and hydrometeorological characteristics of the basin, and a high interannual variability, with values ranging from 18 to 26 mm/yr. The isotopic approach allowed not only the definition of the conceptual model used in the hydrological model, but also eliminated the possibility of a hydrogeological connection between the aquifer of the Salar del Huasco basin and the aquifer that feeds the springs of the nearby town of Pica. This potential connection has been an issue of great interest to agriculture and tourism activities in the region.

How can we be sure fracking will not pollute aquifers? Lessons from a major longwall coal mining analogue (Selby, Yorkshire, UK)

ABSTRACTDevelopment of shale gas by hydraulic fracturing (‘fracking’) is opposed by campaigners who propose (inter alia) that freshwater aquifers could be polluted by upward migration of fractures and any fluids they contain. Prima facie hydrogeological analysis of this proposition has been undertaken. For it to occur, two conditions must be satisfied: (i)sufficient hydraulic interconnection (i.e., a continuous permeable pathway); and(ii)a sustained driving head, oriented upwards.With regard to (i), shale gas developers have a major vested interest in avoiding creating such hydraulic connection, as it would result in uneconomically excessive amounts of water needing to be pumped from their wells to achieve gas production. In relation to (ii), nominal upward hydraulic gradients will typically only be developed during fracking for periods of a few hours, which is far too brief to achieve solute transport over vertical intervals of one or more kilometres; thereafter, depressurisation of wells to allow gas to flow will result in downward hydraulic gradients being maintained for many years. The proposition is therefore found to be unsupportable. Albeit for contrasting motivations, developers and environmental guardians turn out to have a strong common interest in avoiding inter-connection to aquifers.A powerful illustration of the potential long-term effects of fracking is provided by the hydrogeological history of underground coal mining in the UK. Where large-scale mining proceeded from the surface downwards, major hydraulic inter-connection of shallow and deep zones resulted in widespread water pollution. However, where new mines were developed at depth without connections to shallow old workings (as in the Selby Coalfield, Yorkshire), complete hydraulic isolation from the near-surface hydrogeological environment was successfully maintained. This was despite far greater stratal disruption and induced seismicity than shale gas fracking could ever produce. The lesson is clear: without hydrogeological connectivity to shallow aquifers, shale gas fracking per se cannot contaminate shallow ground water.

Hydrogeochemical and isotopic evidence for flow paths of karst waters collected in the Heshang Cave, Central China

Understanding of hydrological processes in caves is important to help us interpret paleoclimate records from speleothems. In this study, we integrated hydrogeological and hydrogeochemical properties to characterize the hydraulic behavior of karst waters in the Heshang Cave, Central China. Using geological and topographical analyses, we identified regional watershed boundaries and hydrogeological connections that were controlled by anticlinal geometry and faults. Water samples were collected from the Heshang Cave and potential recharge sites. Geochemical data of c(Sr2+)/c(Ca2+) and c(Mg2+)/c(Ca2+) ratios suggest that the drainage system in Heshang Cave consists of two flow paths. For vadose waters, including drip water and rimstone pool water, c(Sr2+)/c(Ca2+) ratio ranges from 0.000 6 to 0.001 1, and c(Mg2+)/c(Ca2+) ratio ranges from 0.97 to 1.1, indicating that recharge was mainly from rainfall infiltration through the overlying Cambrian dolomite stratum. In contrast, slope current and underground river waters have higher c(Sr2+)/c(Ca2+) ratios (values from 0.002 2 to 0.002 8), and lower c(Mg2+)/c(Ca2+) ratios (values from 0.50 to 0.64). These waters show homogeneous isotopic composition (δ18O: −7.15‰–−6.95‰; δD: −52.73‰–−51.31‰), implying recharge of allogeneic water from the Xiaoer River via karst conduits that pass through Ordovician limestone and Cambrian dolomite stratum.

3D gravity inversion and Euler deconvolution to delineate the hydro-tectonic regime in El-Arish area, northern Sinai Peninsula

Sinai Peninsula occupies a part of the arid zone belt of northern Africa and southwestern Asia. The largest ephemeral stream in the Sinai Peninsula is called Wadi El-Arish, which winds down northward to the Mediterranean Sea. The delta of Wadi El-Arish has been built by the heavy floods of the Wadi. The Quaternary aquifer is the main water supply of the delta of Wadi El-Arish and its vicinities. The combined action of aridity and extensive pumping from the Quaternary aquifer led to a noticeable increase in groundwater salinity. The hydrochemistry and isotope hydrology confirm that the Quaternary aquifer is recharged by an old saline groundwater from the Pre-Quaternary. A hydrogeological connection between Quaternary and Pre-Quaternary aquifers in the form of fault(s) should exist to explain the hydro-tectonic regime of this area. The Bouguer gravity map shows the high gravity anomaly of the doubly plunging anticline of Risan Aniza Mountain to the south of El-Arish area, which is a part of the Syrian Arc System of northern Sinai Peninsula. A 3D density contrast model, 3D Euler deconvolution, horizontal derivative and least square separation have been performed. The findings showed that (1) two deep regional faults extending NE–SW, surround the Risan Aniza anticline, and (2) two deep local N–S faults are in the area of Delta Wadi El-Arish. These deep faults are proposed to bring the deep Cretaceous aquifer into contact with the shallow Quaternary aquifer and work as a hydrogeological connection between both aquifers. The present hypothesis has some geological evidences from the subsurface lithology of the nearby wells.