Deep Groundwater Research Articles

Anaerobic methane-oxidizing activity in a deep underground borehole dominantly colonized by Ca. Methanoperedenaceae.

The family Ca. Methanoperedenaceae archaea mediates the anaerobic oxidation of methane (AOM) in different terrestrial environments. Using a newly developed high-pressure laboratory incubation system, we investigated 214- and 249-m deep groundwater samples at Horonobe Underground Research Laboratory, Japan, where the high and low abundances of Ca. Methanoperedenaceae archaea have been shown by genome-resolved metagenomics, respectively. The groundwater samples amended with 13 C-labelled methane and amorphous Fe(III) were incubated at a pressure of 1.6MPa. After 3-7 days of incubation, the AOM rate was 45.8 ± 19.8nM/day in 214-m groundwater. However, almost no activity was detected from 249-m groundwater. Based on the results from 16S rRNA gene analysis, the abundance of Ca. Methanoperedenaceae archaea was high in the 214-m deep groundwater sample, whereas Ca. Methanoperedenaceae archaea was undetected in the 249-m deep groundwater sample. These results support the in situ AOM activity of Ca. Methanoperedenaceae archaea in the 214-m deep subsurface borehole interval. Although the presence of Fe-bearing phyllosilicates was demonstrated in the 214-m deep groundwater, it needs to be determined whether Ca. Methanoperedenaceae archaea use the Fe-bearing phyllosilicates as in situ electron acceptors by high-pressure incubation amended with the Fe-bearing phyllosilicates.

Global analysis of the correlation and propagation among meteorological, agricultural, surface water, and groundwater droughts

Groundwater drought monitoring relies on ground observation data, which cannot be used to reflect large-scale droughts in groundwater resources. The Gravity Recovery and Climate Experiment Satellite (GRACE) improved the situation and provided a new solution for groundwater drought research. However, the propagation relationship among global different drought types has not been fully explored. We employed CRU precipitation data, MERR2 reanalysis soil moisture data, GLDAS and GRACE data to calculate SPI (Standardized precipitation index), SSI (Standardized soil moisture index), SRI (Standardized runoff index), and GDI (Groundwater drought index), characterizing meteorological, agricultural, surface water and groundwater droughts, respectively. The Pearson correlation coefficient was adopted to study the propagation time of these four types of droughts. The results showed that the average propagation times for the different drought types are meteorological drought to surface water drought (3.5 months), meteorological drought to agricultural drought (5.7 months), agricultural drought to groundwater drought (12.97 months), surface water drought to groundwater drought (13.78 months), and meteorological drought to groundwater drought (14.47 months) from longest to shortest. (2) Climate conditions had a significant impact on the propagation time of different drought types. Low temperatures in cold climates resulted in the longest drought propagation time, while dry summer climates in temperate climates reduced drought propagation time. There were weaker propagation relationships in arid climates. In tropical climates, precipitation may not be the main driving factor for drought propagation. (3) Different land cover types show significant differences in the propagation of groundwater droughts, with forests having a longer propagation time from meteorological drought to agricultural drought or surface water drought than grassland and cropland, and forests having the shortest propagation time when meteorological drought, agricultural drought, and surface water drought is propagated to groundwater drought. Woody plants have deeper root systems than herbaceous plants and can draw up deeper groundwater. Forests have greater water storage capacity and weaker groundwater recharge than grasslands and croplands, resulting in forests being more resistant to agricultural and surface water droughts and less resistant to groundwater droughts during meteorological droughts. This study can help to clarify the propagation laws among different drought types and understand the internal mechanisms that affect the development of drought during the water cycle.

Investigating river–aquifer interactions using heat as a tracer in the Silala river transboundary basin

AbstractThis article reviews scientific studies in which heat was used as a natural tracer to investigate stream–aquifer interactions in the Silala River in Chile and provide evidence that was used to support a legal dispute between Chile and Bolivia over the status and use of the waters of this watercourse. Streambed temperature time series at various locations downstream of the Chile‐Bolivia international border showed that water flows downwards through the streambed sediments, from the river towards the fluvial aquifer. These findings are consistent with hydraulic head measurements performed at the study site. Additionally, fiber‐optic distributed temperature sensing (FO‐DTS) methods were employed to observe river temperatures with a spatial resolution of the order of 0.5 m in a river reach of ~1.3 km. FO‐DTS technology allowed detection of various warm springs that discharged their waters into the Silala River, as well as the location of an artesian well that supplies the river with ~90 L/s of deep groundwater at ~20 °C. The results provided improved understanding of the Silala River hydrogeology, and were used to calibrate and validate a groundwater model of the system, reported elsewhere. Both methodologies demonstrated that the river is indeed a system of surface waters and groundwaters interacting as a unitary whole, a key aspect of the definition of an international watercourse, and generated valuable scientific evidence to support a major international legal dispute.This article is categorized under: Science of Water > Hydrological Processes Science of Water > Methods

Magmatic fluid input controlling the geochemical and isotopic characteristics of geothermal waters along the Yadong-Gulu rift, southern Tibetan Plateau

Geothermal resources, regarded as sustainable green energy, are attracting increasing attention. The southern Tibetan Plateau possesses the most abundant intermediate-high geothermal resources in China and has enormous potential for geothermal exploration. Geothermal waters from the Yadong-Gulu Rift (YGR), which is considered as the most active geothermal belt of the plateau, are studied based on hydrochemical and isotopic characteristics to understand the spatial variations of fluid origin, evolution, and circulation mechanism as well as heat sources. The hydrochemical characteristics of cold springs and surface waters are consistently characterized by Ca-HCO3 dominated (Ca-HCO3 and Ca-HCO3·SO4) waters while those of geothermal springs present extensive variability with Na-Cl dominated (Na-Cl·HCO3, Na-HCO3·Cl, Na·Ca-Cl·HCO3) and Na-HCO3 waters. The main geochemical processes controlling the geothermal springs are combinations of silicate weathering, carbonate dissolution, and cation exchange. The characteristics of trace alkali metals and B indicate they undergone common/similar deep process and the potential input of magmatic degassing. The δD and δ18O values suggest that cold springs and surface waters are recharged by meteoric water, and geothermal springs are replenished by meteoric water, snow-melt, and magmatic fluid. The mass balance model reveal that dominant carbon sources for geothermal waters can be deeply derived CO2 (i.e., magmatic source and metamorphic source), contributing from 77% to 99%. Based on empirical chemical geothermometers, Si-Enthalpy mixing model, and geothermometrical modelling, the calculated reservoir temperatures are highly variable (137-312 °C). The circulation depths of geothermal waters are 2.45-6.85 km. A conceptual model is proposed to reveal the deep groundwater circulation.

Implications of a short carbon pulse on biofilm formation on mica schist in microcosms with deep crystalline bedrock groundwater.

Microbial life in the deep subsurface occupies rock surfaces as attached communities and biofilms. Previously, epilithic Fennoscandian deep subsurface bacterial communities were shown to host genetic potential, especially for heterotrophy and sulfur cycling. Acetate, methane, and methanol link multiple biogeochemical pathways and thus represent an important carbon and energy source for microorganisms in the deep subsurface. In this study, we examined further how a short pulse of low-molecular-weight carbon compounds impacts the formation and structure of sessile microbial communities on mica schist surfaces over an incubation period of ∼3.5 years in microcosms containing deep subsurface groundwater from the depth of 500 m, from Outokumpu, Finland. The marker gene copy counts in the water and rock phases were estimated with qPCR, which showed that bacteria dominated the mica schist communities with a relatively high proportion of epilithic sulfate-reducing bacteria in all microcosms. The dominant bacterial phyla in the microcosms were Proteobacteria, Firmicutes, and Actinobacteria, whereas most fungal genera belonged to Ascomycota and Basidiomycota. Dissimilarities between planktic and sessile rock surface microbial communities were observed, and the supplied carbon substrates led to variations in the bacterial community composition.

Dissolved Organic Matter Sources in High Arsenic Groundwater From a Sand‐Gravel Confined Aquifer

AbstractSources of dissolved organic matter (DOM) triggering arsenic enrichment in deep confined groundwater is a highly debated issue. Along these lines, the spectroscopic and molecular characteristics of DOM were monitored in both shallow unconfined and deep confined groundwater from the Songnen Basin, China. Results demonstrated that deep groundwater with higher dissolved arsenic concentrations was characterized by more abundant labile organic compounds than shallow groundwater. The three‐end‐member mixing model estimated that shallow groundwater had more fraction of surface water, while deep groundwater was primarily recharged by lateral groundwater flow. Groundwater DOM sources were estimated from the fluorescence index (FI) values, which suggests that shallow groundwater DOM was primarily sourced from surface water with stronger terrestrial signatures. However, deep groundwater DOM was mainly sourced from in situ sedimentary organic matter release or by‐products from microbial activity with stronger microbial signatures. Higher values of degradation index (I_deg) indicate that deep groundwater DOM had undergone greater degradation extents than the shallow one. The microbial DOM degradation in anoxic environments mainly occurred via a pathway where more saturated and low‐molecular‐mass compounds were preferentially degraded to produce more mid‐molecular‐mass compounds with unsaturated, aromatic, and microbial signatures. This explained the significant positive correlations between groundwater arsenic concentrations and FI and I_deg values. A stronger DOM degradation state in deep groundwater was conducive to more arsenic enrichment than that in the shallow one. This work successfully identified distinct sources of shallow and deep groundwater DOM, and proposed a paradigm of DOM processing pathways during arsenic enrichment under anoxic environments.

Enhancing urban runoff modelling using water stable isotopes and ages in complex catchments

AbstractIncreased urbanization, coupled with the projected impacts of climatic change, mandates further evaluation of the impact of urban development on water flow paths to guide sustainable land‐use planning. Though the general urbanization impacts of increased storm runoff peaks and reduced baseflows are well known; how the complex, non‐stationary interaction of the dominant water fluxes within dynamic urban water stores sustain streamflow regimes over longer periods of time is less well quantified. In particular, there is a challenge in how hydrological modelling should integrate the juxtaposition of rapid and slower flow pathways of the urban ‘karst’ landscape and different approaches need evaluation. In this context, we utilized hydrological and water stable isotope datasets within a modelling framework that combined the commonly used Hydrologic Engineering Center Hydrological Modelling System (HEC‐HMS) urban runoff model along with a simple hydrological tracer module and transit time modelling to evaluate the spatial and temporal variation of water flow paths and ages within a heavily urbanized 217 km2 catchment in Berlin, Germany. Deeper groundwater was the primary flow component in the upper reaches of the catchment within fewer urbanized regions, while the addition of wastewater effluent in the mid‐reaches of the catchment was the dominant water supply to sustain baseflow in the lower main stem stream, with additional direct storm runoff and shallow subsurface contributions in the more urbanized lower reaches. Water ages from each modelling approach mirrored flow contributions and water age mixing potential in subsurface storage; with older average water and lower young water contributions in less urbanized sub‐catchments and younger average water and higher young water contributions in more urbanized regions. The results from the first step towards more integrated tracer‐aided hydrologic modelling tools for similar peri‐urban catchments, given the potential limitations of simpler model frameworks. The results have broader implications for assessing the uncertainty in evaluating urban impacts on hydrological function under environmental change.

Politicising land subsidence in Jakarta: How land subsidence is the outcome of uneven sociospatial and socionatural processes of capitalist urbanization

Jakarta is sinking dramatically because of land subsidence, which in turn increases its vulnerability to tidal flooding. The explanation of land subsidence’s causes and the design of solutions is led by geoscientists and engineers, who tend to treat it as largely a technical problem. This paper takes issue with this. It sets out to contribute to politicizing land subsidence by analysing it as part of the sociospatial and socionatural transformations that characterize processes of urbanization. We propose an approach that allows showing how subsidence happens through urbanization’s interconnected moments of horizontal concentration, vertical extension, and differentiation – the weight of the built environment, the expansion of deep groundwater wells, and the remaking of the city (and beyond). By investigating the sociospatial correlation between land subsidence and the development of buildings, and the temporal correlation between land subsidence and the increase of groundwater wells we illustrate how land subsidence is intrinsic to (post-) New Order capitalism (1965–1998 and 1998-now). We also show that it proceeds in uneven ways: those who cause subsidence are not the ones who suffer most from it. Through a serious treatment of soil–water dynamics, our socionatural theorization also helps appreciate how urbanization is always co-shaped by interactions between human and non-human processes.

Hydrogeochemical and microbial signatures of deep and shallow groundwater near the enhanced geothermal system in response to the earthquake

Hydrogeochemical and microbial signatures of deep and shallow groundwater near the enhanced geothermal system in response to the earthquake

Modern and fossil seawater identification using ground- and pore-water dating from the western coast of the Miura Peninsula, Japan

Deep groundwater flow in coastal areas has attracted considerable attention in the context of radioactive waste disposal and CO2 storage from transportation point of view. It is important to show the stability of groundwater flow for a long time, which relates to identify modern and fossil seawater in coastal area. Borehole investigation was conducted at a coastal area along the west side of the Miura Peninsula in Japan, where is a typical of the accretionary wedge environments. As part of this investigation, groundwater ages have been evaluated based on dating ground- and pore-water samples (obtained by groundwater pumping and rock core squeezing, respectively) from three boreholes of up to 500 m deep. At the borehole locations, the Miura Group, which consists of sandstone and siltstone, is observed to depths of ∼200 m and the Hayama Group, which primarily consists of mudstone, is observed below ∼200 m. In the Miura Group, 14C was abundant; high-Cl samples showed high 14C and low 36Cl/Cl, equivalent to modern seawater. In the underlying Hayama Group, where the low hydraulic conductivity of the formation means that the assessment was based almost solely on porewater samples, the Cl concentration below a depth of 300 m was close to that of seawater and 36Cl/Cl was close to in situ secular equilibrium (as estimated from rock properties). Furthermore, 4He was abundant in the Hayama Group, and an observed shift in δ37Cl is inferred to have been controlled simply by diffusion. The results indicate that the groundwater in the Miura Group is modified modern seawater, while the porewater in the Hayama Group is fossil seawater. Thus, groundwater dating, using a combination of 14C, 36Cl, and 4He, is a useful tool for the identification of modern and fossil seawater in coastal areas.

Microbial Contributions to Iodide Enrichment in Deep Groundwater in the North China Plain.

Microorganisms play crucial roles in the global iodine cycling through iodine oxidation, reduction, volatilization, and deiodination. In contrast to iodate formation in radionuclide-contaminated groundwater by the iodine-oxidizing bacteria, microbial contribution to the formation of high level of iodide in geogenic high iodine groundwater is poorly understood. In this study, our results of comparative metagenomic analyses of deep groundwater with typical high iodide concentrations in the North China Plain revealed the existence of putative dissimilatory iodate-reducing idrABP1P2 gene clusters in groundwater. Heterologous expression and characterization of an identified idrABP1P2 gene cluster confirmed its functional role in iodate reduction. Thus, microbial dissimilatory iodate reduction could contribute to iodide formation in geogenic high iodine groundwater. In addition, the identified iron-reducing, sulfur-reducing, sulfur-oxidizing, and dehalogenating bacteria in the groundwater could contribute to the release and production of iodide through the reductive dissolution of iron minerals, abiotic iodate reduction of derived ferrous iron and sulfide, and dehalogenation of organic iodine, respectively. These microbially mediated iodate reduction and organic iodine dehalogenation processes may also result in the transformation among iodine species and iodide enrichment in other geogenic iodine-rich groundwater systems worldwide.

Research on prevention and control methods of land subsidence induced by groundwater overexploitation based on three-dimensional fluid solid coupling model—a case study of Guangrao County

Land subsidence is an environmental geological phenomenon with slowly decreasing ground elevation, The North China Plain is one of the areas with the most serious land subsidence in China, and Guangrao County is one of the subsidence centers. This paper is based on the hydrogeological and engineering geological data of Guangrao County, the groundwater monitoring data for many years and the land subsidence monitoring data, systematically analyzes the dynamic characteristics of groundwater, the distribution and evolution of land subsidence, and the correlation between groundwater exploitation and land subsidence development in different layers of this area. Based on Biot porous medium consolidation theory, establishes a three-dimensional fluid solid coupling numerical model of land subsidence in Guangrao County, restores the development process of land subsidence, predicts and analyzes the subsidence evolution law under different groundwater exploitation schemes, and proposes targeted prevention and control measures. The research results show that: the shallow groundwater forms a cone of depression with Guangbei Salt Field as the center, and the deep groundwater forms an elliptical regional cone of depression with the urban area as the center. The ground is gradually formed two small settlement areas with the urban area of Guangrao County and Guangbei Salt Field as the settlement center, and there is a trend of interrelated expansion. The three-dimensional fluid solid coupling model of land subsidence accurately restored the development process of land subsidence in the study area, predicted that under the current groundwater exploitation conditions, by 2040, the settlement of Guangrao urban settlement center will increase to 1,350 mm, forming a large regional funnel centered around the urban area, and gradually developing and expanding around. Prohibition of groundwater exploitation in the main funnel area is a more reasonable and effective exploitation plan to prevent the development of land subsidence.

Characteristics of dissolved N2O and indirect N2O emission factor in the groundwater of high nitrate leaching areas in northwest China

Numerous studies have demonstrated high concentrations of dissolved N2O and indirect N2O emission factors in groundwater affected by agriculture. However, the characteristics of seasonal and vertical dimensional difference in groundwater in high nitrate leaching areas are relatively lacking. We monitored the concentrations of dissolved and wellhead N2O of 23 groundwater wells over a one year period to understand the seasonal characteristics of dissolved and wellhead N2O concentrations and indirect N2O emission factors (EF5) of the shallow and deep groundwater in a high nitrogen leaching area and analyze the reasons for their differences. The mean dissolved N2O concentration in groundwater was 9.71 (9.03) μg/L, which was 1.5-fold higher during the wet season relative to the dry season. Furthermore, the leaching of soil N2O caused by rainfall and irrigation could be a pivotal factor affecting seasonal variation in the dissolved N2O. Shallow wells were found to have higher dissolved and wellhead N2O concentrations compared with deep wells in all seasons. The low wellhead N2O concentrations during the dry season were attributed to the seasonal decrease of the groundwater table and dissolved N2O concentrations. We concluded that indirect N2O emission factors did not vary in the vertical dimension but were higher during the wet season than that during the dry season. In addition, the mean indirect N2O emission factor in the groundwater was 0.025 %, which was one order of magnitude below the current IPCC value (0.25 %). Thus, we proposed that such a low indirect N2O emissions factor could imply a low indirect N2O emission potential in groundwater with high dissolved oxygen and nitrogen loads. Our study further indicated that seasonal differences in dissolved N2O concentrations and indirect N2O emission factors should be considered when estimating the potential emissions of dissolved N2O in groundwater.

Hydrogeological Study in Tongchuan City Using the Audio-Frequency Magnetotelluric Method

Tongchuan City, located in Shaanxi Province, northwest China, has limited groundwater resources. Rational planning and exploitation of groundwater are crucial to the sustainable development of the city, for which investigating the distribution of groundwater is the premise. Traditional resistivity sounding methods are often used to detect groundwater; however, these methods are not applicable in the study area where thick Quaternary loess is extensively distributed. In this study, we arranged five audio-frequency magnetotelluric (AMT) profiles to detect the deep clastic rock groundwater and carbonate karst fissure groundwater in Tongchuan. Firstly, we analyzed the electromagnetic interference (EMI) noises in Tongchuan City, revealing that the main EMI is power frequency interference (PFI). We used the dictionary learning processing technology to suppress the PFI. Secondly, the two-dimensional (2D) nonlinear conjugate gradient method was employed to invert a 2D electrical structure model for the area shallower than 1 km. We analyzed the characteristics of the electrical structure and its geological significance. Lastly, the three-dimensional (3D) electrical structure model of the study area was inverted using the 3D nonlinear conjugate gradient method, and the spatial distribution characteristics of the water-bearing strata were further analyzed. The results show that the PFI in urban environment can be suppressed by the dictionary learning processing technology. In Tongchuan city, the distribution of clastic rock fissure water is controlled by folds and faults, as well as the thickness of sandstone layers, and that of the carbonate karst fissure water is mainly controlled by faults. On this basis, we infer that the water-bearing areas are in the middle east and south of the study area.

BRIDGE methodology–based quality standards to assess aquifer chemical status in the southwest Bengal Basin, Bangladesh

Assessment of natural background levels (NBLs) of compositional groundwater parameters helps to identify the potential threats to groundwater resources. This study is the first attempt to apply the pre-selection-based BRIDGE (Background cRiteria for the IDentification of Groundwater thrEshold) methodology to calculate the NBLs and threshold values (TVs) of major groundwater constituents in the southwest Bengal Basin, Bangladesh. A database consisting of 78 groundwater samples was used to assess the NBLs and associated TVs of the major groundwater parameters (EC, Ca2+, Mg2+, Na+, K+, Cl-, NO3-, SO42-, PO43-, Mn2+, and Fe2+). NBLs were derived based on 90th and 97.7th percentiles. The status of regional groundwater resources was assessed by applying 90th percentile NBL on a regional dataset (n = 196). Results revealed the "poor" chemical status of shallow aquifers denoting heavy deterioration of the groundwater quality due to anthropogenic interventions. Nitrate contamination and salinization were identified as the major threats to the deep groundwater of the southwest Bengal Basin. Finally, to verify the chemical status of groundwater in aheavily urbanized area, derived TVs were applied throughout the experimental site Khulna. Twenty-five deep groundwater samples were collected for this purpose. Though most of the parameters exhibited "good" chemical status, nitrate demonstrated anthropogenic groundwater contamination in Khulna City. Thus, the developed TVs would provide an early warning system of pollution. On a national scale, it is expected to facilitate the sustainable groundwater management of the country and contribute to achieving the Sustainable Development Goals (SDG) of the United Nations (UN) in Bangladesh.

Evaluation of Groundwater Quality for Irrigation in Deep Aquifers Using Multiple Graphical and Indexing Approaches Supported with Machine Learning Models and GIS Techniques, Souf Valley, Algeria

Irrigation has made a significant contribution to supporting the population’s expanding food demands, as well as promoting economic growth in irrigated regions. The current investigation was carried out in order to estimate the quality of the groundwater for agricultural viability in the Algerian Desert using various water quality indices and geographic information systems (GIS). In addition, support vector machine regression (SVMR) was applied to forecast eight irrigation water quality indices (IWQIs), such as the irrigation water quality index (IWQI), sodium adsorption ratio (SAR), sodium percentage (Na%), soluble sodium percentage (SSP), potential salinity (PS), Kelly index (KI), permeability index (PI), potential salinity (PS), permeability index (PI), and residual sodium carbonate (RSC). Several physicochemical variables, such as temperature (T°), hydrogen ion concentration (pH), total dissolved solids (TDS), electrical conductivity (EC), K+, Na2+, Mg2+, Ca2+, Cl−, SO42−, HCO3−, CO32−, and NO3−, were measured from 45 deep groundwater wells. The hydrochemical facies of the groundwater resources were Ca–Mg–Cl/SO4 and Na–Cl−, which revealed evaporation, reverse ion exchange, and rock–water interaction processes. The IWQI, Na%, SAR, SSP, KI, PS, PI, and RSC showed mean values of 50.78, 43.07, 4.85, 41.78, 0.74, 29.60, 45.65, and −20.44, respectively. For instance, the IWQI for the obtained results indicated that the groundwater samples were categorized into high restriction to moderate restriction for irrigation purposes, which can only be used for plants that are highly salt tolerant. The SVMR model produced robust estimates for eight IWQIs in calibration (Cal.), with R2 values varying between 0.90 and 0.97. Furthermore, in validation (Val.), R2 values between 0.88 and 0.95 were achieved using the SVMR model, which produced reliable estimates for eight IWQIs. These findings support the feasibility of using IWQIs and SVMR models for the evaluation and management of the groundwater of complex terminal aquifers for irrigation. Finally, the combination of IWQIs, SVMR, and GIS was effective and an applicable technique for interpreting and forecasting the irrigation water quality used in both arid and semi-arid regions.

Secondary salinization of soils and ways to prevent downstream of the Amu Darya

In the history of irrigated agriculture there are many cases when due to severe soil salinity the yield was so low that it did not justify the costs incurred for cultivation of crops. Such lands were classified as unsuitable and were left without use for crops. Lands from suitable ones turned into unsuitable ones and were also often left out of use for irrigated crops, thus, among the old irrigated land masses there were many fallow lands, fallow fields and other vacant lands. The growth of salinity of irrigated soils in the Central Asian republics in the last 30-35 years has become almost ubiquitous. Both old and new irrigation systems bear heavy losses from growing soil salinity. More often secondary salinization in irrigated soils begins to appear even at relatively deep groundwater (3.5-4) in the form of seasonal (during summer) spot salinization of soils on microrelief elevations, on spots of irrigated fields bare from cultural vegetation.

In Search of Portable Water Supplies within a Brine and Mine Water-Invaded Region for Serving Some Communities Around Ishiagu, Afikpo and Environs in Abakaliki Basin, Southeast Nigeria

The study investigates the hydrogeochemical characteristics of some towns in the Abakaliki Basin, comprising, Ishiagu, Aka Eze, Amaseri, Afikpo and Okposi communities, with the aim of sourcing for portable water in the area. The basin is underlain by Albian sediments, essentially shales, in the lowlands, which were affected by low-grade metamorphism that had produced slates. The highlands comprise basic intrusives from episodes of magmatism and metallic ore mineralisation. Injection of brines into the aquifer system and low, seasonal aquifer recharge from rainfall results in poor water quality in the area. The study analyzes the geochemical distribution in water sources in the area and identifies sources of pollutants to guide the better choice of portable water. Results of hydrogeochemical analysis of both surface and groundwater from the communities were compared with World Health Organization to identify portable water locations in the area. While the salt lake at Okposi is the main source of brine intrusion in the study area, the Pb/Zn mine at Ishiagu is the main source of mine-water pollution in the study area. Most chemical parameters, (especially Cl-, Na+, Ca2+, Mg2+, SO42-, HCO3-) maintain high concentrations within the salt lake area, with the values declining away from the salt lake. The main anthropogenic source of pollution in the area, especially at Ishiagu, is the indiscriminate surface mining of lead-zinc without proposer waste management practices. Possible sourcing for portable water in the study area includes a deep borehole at Ishiagu, away from lead-zinc intrusives. At the Okposi axis, searching for portable water in boreholes should target shallower aquifers that do not communicate with the deeper-seated brine zones, likewise targeting zones farther away from these brine-invaded areas. A controlled pumping rate could potentially ensure that the cone of depression was not low enough to reach the brine zone at depth. In addition, desalination could also potentially render the salt water drinkable if properly handled to eliminate the high concentration of salts in the water to the level of acceptable limit by the WHO. Based on the study, the best area to target for portable water in the study area is Afikpo, with most geochemical elements naturally occurring within WHO’s standard concentration while portable water could be harnessed in areas further away from mining sites, especially at deep groundwater.

Revisiting Mt Fuji’s groundwater origins with helium, vanadium and environmental DNA tracers

Known locally as the water mountain, for millennia Japan’s iconic Mt Fuji has provided safe drinking water to millions of people via a vast network of groundwater and freshwater springs. Groundwater, which is recharged at high elevations, flows down Fuji’s flanks within three basaltic aquifers, ultimately forming countless pristine freshwater springs among Fuji’s foothills. Here we challenge the current conceptual model of Fuji being a simple system of laminar groundwater flow with little to no vertical exchange between its three aquifers. This model contrasts strongly with Fuji’s extreme tectonic instability due to its unique location on top of the only known continental trench–trench–trench triple junction, its complex geology and its unusual microbial spring water communities. On the basis of a unique combination of microbial environmental DNA, vanadium and helium tracers, we provide evidence for prevailing deep circulation and a previously unknown deep groundwater contribution to Fuji’s freshwater springs. The most substantial deep groundwater upwelling has been found along Japan’s most tectonically active region, the Fujikawa-kako Fault Zone. Our findings broaden the hydrogeological understanding of Fuji and demonstrate the vast potential of combining environmental DNA, on-site noble gas and trace element analyses for groundwater science.

Salt accumulation in soils under furrow and drip irrigation using modified waters in Central Iran

The objectives of this study were i) to characterize the water and soils under different managements, ii) to evaluate the sustainability of using hypersaline soils and water, and iii) to assess possible solutions to prevent more degradation of soil and water resources. Field and laboratory analysis of the samples using eight pedons and 128 surface samples taken from grid in four pre-determined land uses; pistachio orchard abandoned, pistachio orchard with furrow irrigation, wheat and maize cropping with furrow irrigation, pistachio orchard with drip irrigation. The study area, 170 ha, comprised two distinct soil parent materials including marls (max. ECe >100 dS/m) and alluviums (max. ECe >60 dS/m). Abandoning lands caused salinity increasing due to lack of leaching by irrigation water. The maximum increase of soil salinity was in the abandoned land use (EC e =98 dS/m), where trees had been removed and there is no irrigation, followed by pistachio plantation land use (EC=11 to 34 dS/m), and wheat and maize cropping land use (EC=11-19 dS/m). The minimum rise in soil salinity was in the drip irrigation due to mixing freshwater with saline water and therefore better water quality (EC=3 dS/m at surface layer and 17 dS/m in next layer). Land use change to agriculture increased the need for irrigation and because of arid climate it mainly supplied by groundwater from deep wells. Using deep groundwater due to rock-water reaction and increasing salinity, decreased water quality in furrow irrigation and therefore it had more significant effect on soil salinity compare to drip. Comparison of the mean values of soil salinity indicators in 2018 showed that salinity has increased by 3-6 times in the furrow irrigation and at least two-fold in the drip irrigation, compared to 2002. The calculated salinity indicators also proved the soil and water resources had been degraded and present land use types are not sustainable. Possible solutions could be to minimize land use change to agriculture, to use drip irrigation with mixed saline and freshwater, and to remove salt crusts from the soil surface.