Shallow Samples Research Articles

A comparison of time-varying propensity score vs sequential stratification approaches to longitudinal matching with a time-varying treatment

BackgroundMethods for matching in longitudinal cohort studies, such as sequential stratification and time-varying propensity scores, facilitate causal inferences in the context of time-dependent treatments that are not randomized where patient eligibility or treatment status changes over time. The tradeoffs in available approaches have not been compared previously, so we compare two methods using simulations based on a retrospective cohort of patients eligible for weight loss surgery, some of whom received it.MethodsThis study compares matching completeness, bias, coverage, and precision among three approaches to longitudinal matching: (1) time-varying propensity scores (tvPS), (2) sequential stratification that matches exactly on all covariates used in tvPS (SS-Full) and (3) sequential stratification that exact matches on a subset of covariates (SS-Selected). These comparisons are made in the context of a deep sampling frame (50:1) and a shallow sampling frame (5:1) of eligible comparators. A simulation study was employed to estimate the relative performance of these approaches.ResultsIn 1,000 simulations each, tvPS retained more than 99.9% of treated patients in both the deep and shallow sampling frames, while a smaller proportion of treated patients were retained for SS-Full (91.6%) and SS-Selected (98.2%) in the deep sampling frame. In the shallow sampling frame, sequential stratification retained many fewer treated patients (73.9% SS-Full, 92.0% SS-Selected) than tvPS yet coverage, precision and bias were comparable for tvPS, SS-Full and SS-Selected in the deep and shallow sampling frames.ConclusionTime-varying propensity scores have comparable performance to sequential stratification in terms of coverage, bias, and precision, with superior match completeness. While performance was generally comparable across methods, greater match completeness makes tvPS an attractive option for longitudinal matching studies where external validity is highly valued.

Identification of groundwater nitrate sources and its human health risks in a typical agriculture-dominated watershed, North China.

Identifying nitrate sources and migratory pathways is crucial for controlling groundwater nitrate pollution in agricultural watersheds. This study collected 35 shallow groundwater samples in the Nansi Lake Basin (NLB) to identify groundwater nitrate sources and potential health risks. Results showed that NO3- concentration in 62.9% of groundwater samples exceeded the drinking water standard (50 mg/L). Hierarchical cluster analysis (HCA) was used to classify the sampling points into three groups based on hydrochemical and isotopic data. Groups A and C were situated in the eastern recharge and discharge regions of Nansi Lake, while Group B was located in the Yellow River floodplain west of the lake. Hydrochemical data and nitrate stable isotopes (δ15N-NO3- and δ18O-NO3-) indicated that elevated NO3- primarily originated from soil organic nitrogen (SON) in Group A, while manure and sewage (M&S) were the primary sources in Groups B and C samples. Microbial nitrification was identified as the primary nitrogen transformation process across all groups. The source apportionment results indicated that SON contributed approximately 40.1% in Group A, while M&S contributed about 53.9% and 81.2% in Groups B and C, respectively. The Human Health Risk Assessment (HHRA) model indicated significant non-carcinogenic risks for residents east of Nansi Lake, primarily through the oral pathway, with NO3- concentration identified as the most influential factor by sensitivity analysis. These findings provide new perspectives on identifying and handling groundwater nitrogen pollution in agriculture-dominated NLB and similar basins that require enhanced nitrogen contamination management.

Mechanism of Subsurface Deformation Transmission and Geomechanical Response Inversion in Carbon Capture and Storage Project: Integrating Small Baseline Subset-Interferometric Synthetic Aperture Radar, Mechanical Experiments, and Numerical Simulation

Summary In the context of carbon capture and storage (CCS) engineering, ensuring the stability of the caprock is paramount to mitigating CO2 leakage, thus constituting a pivotal engineering challenge in CO2 geological sequestration. With the injection of CO2, pore pressure accumulates within the reservoir, bringing forth risks including diminished effective stress within the formation, surface deformation, occurrence of microseismic events, and potential caprock failure. Therefore, it is necessary to explore the geomechanical issues in CCS projects. This study focuses on the Daqingzijing in the Jilin Oilfield as the study area, utilizing the small baseline subset (SBAS)-interferometric synthetic aperture radar (InSAR) method to conduct a deformation time-series analysis in the well group area under injection and production conditions. The results reveal variations in deformation sensitivity among the sites, with surface displacements correlated to fluid injection and production, demonstrating temporal delays. At the H79 North block, the time effect is relatively minimal, with rapid propagation of formation deformation. Surface displacement in the H46 block appeared 4 months later than behind cumulative fluid volume changes. By conducting triaxial creep tests on shallow mudstone samples from the Songliao Basin under various triaxial stress states, a constitutive creep equation for caprock rocks was obtained. The numerical models of elastic and creep constitutive equations were established. The results show that the creep model exhibits superior accuracy by comparing with InSAR monitoring data (the root mean square error values of elastic and creep constitutive geomechanical models were 6.7 mm and 1.7 mm, respectively). Additionally, based on the experimental and simulation results, this study explores the transfer mechanisms of formation deformation and the inverse relationship between deformation and pore pressure. This study provides theoretical support for the geomechanical safety analysis in corresponding CCS projects.

Investigating dominant factors of coliform contamination in shallow groundwater: A logistic regression and AHP approach

Shallow groundwater is a crucial source of clean water in developing countries like Indonesia. However, population growth has led to declining water quality due to inadequate infrastructure. This study aimed to identify dominant factors contributing to coliform contamination in shallow groundwater, addressing the lack of detailed statistical and multicriteria analyses in previous large-scale studies. The study was conducted in a densely populated urban area in Yogyakarta, Indonesia, and total coliform measurements from 42 groundwater samples were used as the independent variable. There are 14 dependent variables, categorized into three aspects: infrastructure (e.g., well type, well depth, wall of well, DEWATS type, well distance to the septic tank, latrine, and other contaminant sources); specific (e.g., population density and land use); and intrinsic (e.g., groundwater level, rainfall, soil type, and slope). Those parameters were statistically analyzed using logistic regression with IBM SPSS 26 software, and supported by the Analytical Hierarchy Process (AHP) that was employed using Expert Choice software to prioritize the factors. The results showed that 83.3% of the shallow groundwater samples exceeded the acceptable limits for total coliform, with key factors including well's proximity to other contamination sources, slope, distance from septic tanks, groundwater level, and population density. These findings highlight the importance of considering complex environmental factors in managing groundwater quality, particularly in developing countries. It is recommended that local authorities implement stricter regulations and infrastructure improvements to mitigate contamination risks.

Surface soil sampling underestimates soil carbon and nitrogen storage of long-term cover cropping

Cover cropping is a promising management practice for soil health and climate change mitigation by improving soil organic carbon (SOC) and total nitrogen (TN) stocks. However, limited studies focused on deeper soil layers (>30 cm depth) where soil C is more stable than that in surface soil (≤30 cm depth). Here, deep soil sampling was conducted in a 15-year cover cropping experiment, in a horticulture-grain system on sandy loam soil. The SOC and TN stocks were expressed on an equivalent soil mass basis using a cubic spline model. Overall, long-term cover cropping had significantly greater SOC and TN stocks by 22 % (95 %CI: 5–43 %) and 26 % (95 %CI: 6–49 %), respectively in the 0–120 cm depth, compared to no cover cropping. Additionally, the mean SOC and TN sequestration rate (0–30 cm depth) was 0.53 Mg C ha−1 yr−1 and 0.06 Mg N ha−1 yr−1, respectively. However, if only 0–15 cm depth was evaluated, long-term cover cropping did not significantly affect SOC and TN stocks. These results indicated that shallow sampling (<15 cm depth) may not provide comprehensive information on the effect of long-term cover cropping on soil C and N storage. To better understand the mechanism of bulk soil C and N storage, we investigated their distribution between particulate and mineral-associated organic matter pools (POM and MAOM). We found POM pool was the main store of bulk SOC and TN stocks in surface soils while it was the MAOM pool in deeper soil layers, without soil texture change with soil depth. These findings indicated that soil C and N sources for bulk SOC and TN accrual differed in surface and deeper soils. Our study demonstrated that long-term cover cropping can facilitate SOC accumulation in the soil below 15 cm deep, which calls into question carbon capture protocols that focus on shallow soil depths.

An Improved Physics-Based Dual-Band Model for Satellite-Derived Bathymetry Using SuperDove Imagery

Shallow water bathymetry is critical for environmental monitoring and maritime security. Current widely used statistical models based on passive optical satellite remote sensing often rely on prior bathymetric data, limiting their application to regions lacking such information. In contrast, the physics-based dual-band log-linear analytical model (P-DLA) can estimate shallow water bathymetry without in situ measurements, offering significant potential. However, the quasi-analytical algorithm (QAA) used in the P-DLA is sensitive to non-ideal pixels, resulting in unstable bathymetry estimation. To address this issue and evaluate the potential of SuperDove imagery for bathymetry estimation in regions without prior bathymetric data, this study proposes an improved physics-based dual-band model (IPDB). The IPDB replaces the QAA with a spectral optimization algorithm that integrates deep and shallow water sample pixels to estimate diffuse attenuation coefficients for the blue and green bands. This allows for more accurate estimation of shallow water bathymetry. The IPDB was tested on SuperDove images of Dongdao Island, Yongxing Island, and Yongle Atoll. The results showed that SuperDove images are capable of estimating shallow water bathymetry in regions without prior bathymetric data. The IPDB achieved Root Mean Square Error (RMSE) values below 1.7 m and R2 values above 0.89 in all three study areas, indicating strong performance in bathymetric estimation. Notably, the IPDB outperformed the standard P-DLA model in accuracy. Furthermore, this study outlines four sampling principles that, when followed, ensure that variations in the spatial distribution of sampling pixels do not significantly impact model performance. This study also showed that the blue–green band combination is optimal for the analytical expression of the physics-based dual-band model.

Differences in Nitrogen Sources and Contributions in Shallow Groundwater in Plateau Lake Area with Different Climate Types

Clarifying the concentration, major sources, and contribution differences of nitrogen in shallow groundwater in plateau lake areas with different climate types can provide a novel direction for the control of nitrate （NO3-） pollution in regional groundwater. Taking the shallow groundwater around Erhai Lake in the subtropical monsoon climate zone and Chenghai Lake in the dry-hot valley area of the Jinsha River as the research objects, using hydrochemical indexes and multi-isotope techniques （δ15N-NO3-, δ18O-NO3-, δ18O-H2O, and δ2H-H2O） combined with the stable isotope （SIAR） model； the differences in nitrogen concentration in shallow groundwater around Erhai Lake and Chenghai Lake were analyzed, the sources of NO3- were identified, and the contribution rates of each pollution source were calculated. The results showed that water quality of more than 33% and 5% of shallow groundwater sampling points around Erhai Lake and Chenghai Lake was worse than the groundwater Class Ⅲ quality requirements （GB/T 14848） of 20 mg·L-1 for nitrate nitrogen （NO3--N）, respectively. The δ18O-H2O and δ2H-H2O in shallow groundwater around Erhai Lake and Chenghai Lake were parallel to the global and Chinese atmospheric precipitation lines, and a large intercept was present, indicating that atmospheric precipitation was not the major recharge source of groundwater in the two regions. The contribution rate of different NO3- sources in shallow groundwater around Erhai Lake was the highest for soil organic nitrogen （53.77%）, followed by nitrogen fertilizer （21.75%） and manure and sewage （21.55%）, and atmospheric deposition nitrogen （2.93%） was the lowest. Denitrification occurred in the transformation process of nitrogen in groundwater. The contribution rate of different NO3- sources in shallow groundwater around Chenghai Lake was manure and sewage （44.88%） &gt; soil organic nitrogen （37.03%） &gt; nitrogen fertilizer （16.17%） &gt; atmospheric deposition nitrogen （1.92%）, and nitrification occurred in the transformation process of nitrogen in groundwater. The climate type significantly affected the shallow groundwater level, altering the migration and transformation process of nitrogen, thereby affecting the nitrogen concentration in groundwater and the contribution of NO3- as the chief source. However, the major source of NO3- was not affected by the climate type； however was more affected by land use, agricultural activities, and manure treatment methods.

Hydrochemical characterization and health risk assessment of shallow groundwater in a northern coalfield of Anhui Province, China

In a global context, the hydrochemical characteristics of shallow groundwater in coalfields exhibit high degrees of diversity and complexity that are rooted in the intricate interplay of geological variations, diverse climatic conditions, and extensive human activities. The specific types and concentrations of ions, such as Ca2+, Cl−, and NO3−, show stark differences across geographical regions. Given the crucial roles of coalfields as energy suppliers, the potential environmental contamination risks posed by mining activities to groundwater cannot be overlooked as such pollution directly impacts human health and ecological safety. This study focuses on the Huainan coal mining area in northern Anhui Province (China), where shallow groundwater samples were systematically collected and analyzed to determine the hydrochemical characteristics and ascertain the water quality status. By integrating hydrogeochemical analysis techniques with inverse modeling methods, it was revealed that the groundwater in this region is predominantly HCO3-Ca type, exhibiting weak alkaline characteristics. The formation mechanisms are primarily governed by silicate rock weathering and mineral dissolution–precipitation processes, albeit with discernible influences from human activities. PHREEQC simulations were used to further confirm the precipitation tendencies of minerals like calcite, dolomite, and fluorite as well as the significant dissolution characteristics of halite. The inverse modeling pathway analysis reveals specific hydrochemical processes along different paths: paths I and IV are notably dominated by Ca2+ dissolution–precipitation and cation exchange–adsorption processes, whereas paths II and III are closely associated with the precipitation of calcium montmorillonite as well as dissolution of kaolinite, calcite, quartz, and mineral incongruents. Moreover, evaluations based on the entropy-weighted water quality index (EWQI) indicated overall positive trends of the groundwater quality indicators within the Huainan mining area, reflecting the effectiveness of regional water quality management efforts and providing a scientific basis for future water quality protection and improvement strategies. In summary, this study not only deepens our understanding of the groundwater chemistry in the Huainan coal mining area but also underscores the importance of scientifically assessing and managing groundwater resources to address the environmental challenges potentially arising from coal mining activities.

Isotope characterisation of groundwater resources in uranium impacted Fazilka, Punjab

AbstractGroundwater is the most reliable source for freshwater supplies in India and abroad. Population rise has affected the groundwater resources both in terms of quality and quantity. Punjab, being an agrarian state, is highly dependent on groundwater resources for both irrigation and drinking purposes. Recent studies have indicated presence of uranium in groundwater especially in southwestern parts of Punjab. In this research, water samples were collected from Fazilka district of Punjab for evaluating the water quality focussing uranium and identifying source and recharge processes of groundwater. Uranium concentration was found in both shallow and deep groundwater samples. Inter-ionic correlations signify that alkalinity and electrical conductivity of the water samples control the uranium mobilization from the aquifer matrix. Isotopic systematics demonstrate that groundwater recharge is mainly through rainwater infiltration.

Targeting Shallow Subsurface Sampling for Mars at Oxia Planum Using Fluvial Erosion–Deposition Modeling

A model-based surface fluvial erosion and deposition approach was adapted to Martian conditions to forecast the potential locations for shallow subsurface sampling by the Rosalind Franklin ExoMars rover at Oxia Planum. While remote and on-site images show only the surface visible features, former fluvial-related accumulation sites might be hidden. During the fluvial activity, most accumulation-related areas are interesting with regard to clay-like sediments, which could adsorb organics effectively—such sites could be identified by modeling. By applying the SIMWE fluvial erosion/deposition model, substantial variability in accumulation and deposition-dominated areas with their specific pattern and spatial distribution could be outlined, indicating that sophisticated targeting of future sampling could use such a model-based approach. At the main valley-like feature, former water flow tracks were identified, as well as deposition-dominated locations, which are the best targets for shallow subsurface sampling. Joint evaluation of safety aspects like slope angle and loose sand dunes with scientific aspects provide the best sampling locations. Such model-based targeting is important as by using only orbital images, these locations could not be identified.

Morphological, hydrogeochemical and sedimentological analysis of hypersaline Sambhar Lake, India: An analog to understand evaporitic paleolake basins on Mars

In the recent decade of astrobiological exploration of the Martian surface, there has been a shift from identifying habitable environments to finding markers indicative of biological activity. It requires a prior understanding of the physical and geochemical environment of the setting to decipher whether the conditions were conducive. Generally, quiescent surroundings of lacustrine basins are considered one of the best targets for the preservation of any biological signatures. However, due to logistical limitations, the geochemical information available is mostly restricted to small areas on the surficial level (or in the subsurface in case of layered deposits or impact craters) where sufficient satellite coverage is available and, in some areas, where rovers/landers have been deployed. In this context, terrestrial lacustrine basins offer valuable insights into the environment required for the formation of the minerals observed on the Martian surface.This study was carried out within Sambhar Lake located in the arid/semiarid climatic zone within the Thar desert. It is a hypersaline playa that has undergone several cycles of desiccation and re-filling, sharing its climate-controlled history with that of several paleolakes on Mars. We conducted physicochemical analysis of the samples collected from the lake and its surrounding area and compared our results with samples from the Curiosity rover (at Gale crater) and to those of the studies carried out in basalt-rich parent settings of Iceland. Our results suggest that Sambhar Lake is a Na-Cl type brine with climate-driven hydrology. The shallow cores and rock samples indicated that the area is rich in evaporites. We propose that even the sites with different parent material may be crucial in understanding the geological evolution of paleolakes on Mars and that Sambhar is a great example to study tectono-geomorphic evolution and the climate-induced transition of a lacustrine basin to a playa. Additionally, the lake is also desirable to study extremophiles and their adaptation to changing environmental variables for future planetary missions, including but not limited to, Mars.

Hydrogeochemical characteristics and agricultural suitability of shallow groundwater quality in a concentrated coalfield area of Huaibei Plain, China.

Groundwater is one of the chief water sources for agricultural activities in an aggregation of coal mines surrounded by agricultural areas in the Huaibei Plain. However, there have been few reports on whether mining-affected groundwater can be adopted for agricultural irrigation. We attempted to address this question through collecting 71 shallow groundwater samples from 12 coal mining locations. The Piper trilinear chart, the Gibbs diagram, the proportional coefficient of major ions, and principal component analysis were examined to characterize the source, origin, and formation process of groundwater chemical composition. The suitability for agricultural irrigation was evaluated by a final zonation map that establishes a comprehensive weighting model based on analytic hierarchy process and criteria importance though the intercriteria correlation (AHP-CRITIC). The results revealed that the groundwater was classified as marginally alkaline water with a predominant cation of HCO3- and anion of Na+. Total hardness, total dissolved solids, sulfate (SO42-), sodium (Na+), and fluoride (F-) were the primary ions that exceeded the standard. The results also indicated that the dominant hydrochemical facies were Ca-HCO3 and Na-Cl. The dissolution of carbonate, silicate, sulfate minerals, along with cation exchange, were the main natural drivers controlling the hydrogeochemical process of groundwater. The zonation map suggested that 43.17%, 18.85%, and 37.98% of the study area were high, mediate, and low suitability zones, respectively. These results from this study can support policymakers for better managing groundwater associated with a concentration of underground coal mines.

Defying the flat-Earth myth: Soil organic carbon monitoring in topographically complex temperate pasture landscapes

Soil sampling design to capture the spatiotemporal variability of soil organic carbon (SOC) stocks in complex landscapes is challenged by the influence of topographical features on primary production, animal behaviour, and carbon and nutrient return to grasslands. Here we explore a range of approaches for streamlining the sampling process using measures of SOC stock data (2003, 2020, 2021) from a long-term hill-country fertilizer experiment. The stepwise procedure included a) evaluation of sampling efficiency between stratified and random soil sampling designs to capture spatial variability of SOC stocks, b) semi-parametric regression analysis to evaluate the representativeness of certain strata (e.g. medium slopes), c) exploring the appropriateness of using shallow SOC stock estimates to represent the full sampling depth, and d) the use of a process-based model to determine expected SOC stock changes and temporal variability to estimate the number of representative soil samples required to achieve a significant minimum change. Our analyses suggest that a) the stratified sampling design was more efficient reflected in the number of samples required to identify 5 % deviation in SOC stocks, b) estimates obtained on the medium slope were a reasonable approximation of the SOC stocks and its spatial variation across the farmlets, c) shallow (0–75 mm) SOC stock estimates from an adjusted regression model offered an accurate inference of its vertical distribution (0–300 mm), and d) the Grass-NEXT model provided insights on where more intensive sampling is required to detect a significant minimum change in SOC stocks over time. Tailored, stratified soil sampling and context-specific strategies, such as using representative strata and shallow sampling as effective steps for estimating SOC stocks and addressing data gaps, are crucial for simplifying monitoring and minimizing the cost of on-farm soil sampling designs in topographically complex landscapes covered by long-term pastures.

Shallow Groundwater Around Plateau Lakes： Spatiotemporal Distributions of Dissolved Carbon and Its Driving Factors

Dissolved carbon in groundwater plays an important role in carbon cycling and ecological function maintenance, and its concentration level affects the migration and transformation of pollutants in groundwater. To understand the spatiotemporal variation characteristics of dissolved carbon and its driving factors in shallow groundwater around plateau lakes, variations in the concentrations of dissolved organic carbon （DOC）, inorganic carbon （DIC）, and total carbon （DTC） and their driving factors in shallow groundwater （n = 404） around eight plateau lakes were analyzed. The results indicated that the average values of ρ（DOC）, ρ（DIC）, and ρ（DTC） in shallow groundwater around plateau lakes were 8.23, 49.01, and 57.84 mg·L-1, respectively, with the ρ（DOC） in 79.0% of shallow groundwater samples exceeding 5 mg·L-1. There were no significant differences in the DOC, DIC, and DTC concentrations between rainy and dry seasons, whereas the change in dissolved carbon concentrations in shallow groundwater were strongly affected by the intensity of agricultural intensification and the depth of groundwater table； the DOC, DIC, and DTC concentrations in shallow groundwater from facility agricultural regions （SFAR）, cropland fallow agricultural regions （CFAR）, and intensive agricultural regions with deeper groundwater tables （DIAR） were significantly reduced by 25.8% - 56.6%, 14.0% - 32.9%, and 16.6% - 36.7%, respectively, compared with those in intensive agricultural regions with shallower groundwater tables （SIAR）. Additionally, the dissolved carbon concentrations in shallow groundwater from DIAR were significantly lower than those of SFAR and CFAR. RDA revealed that physicochemical factors in water and soil significantly explained the changes in the dissolved carbon concentrations. Moreover, the dissolved carbon concentrations in shallow groundwater around Yilong Lake were significantly higher than those of other lakes, whereas that of Chenghai Lake was significantly lower than that of other lakes. Our study highlights that agricultural intensification intensity and groundwater table depth jointly drove the variations in dissolved carbon concentrations in shallow groundwater around plateau lakes. The study results are expected to provide a scientific basis for understanding the carbon cycle in plateau lake areas with underground runoff flowing into lakes and evaluating the attenuation of pollutants by dissolved carbon in shallow groundwater.

Water-use characteristics of Populus euphratica trees in response to flood and groundwater depth in desert oasis

Populus euphratica, as the dominant species in arid desert area, plays an important role in maintaining the stability of desert ecosystem. However, P. euphratica water-use characteristics at different sizes and the effects of flooding and groundwater depth on water use remain unclear. In this study, the hydrogen and oxygen isotope compositions of xylem water, soil water, and floods were measured and coupled with the MixSIAR model to investigate the water-use patterns of P. euphratica at different sizes, flood periods (before, during, and after floods), and groundwater depths in the Taklimakan Desert hinterland. The carbon isotope composition of P. euphratica leaves was determined to investigate the water-use efficiency (WUE) of P. euphratica. The water-use patterns of P. euphratica at different sizes were consistent because of its reproductive mode (aswxual root tiller reproduction). P. euphratica showed a greater degree of ecological plasticity during different flood periods. Before the flood, the main water sources for P. euphratica were deep-soil-layer (140–220 cm) and near-groundwater-layer (220–300 cm). During the flood, it could absorb the flood directly, reducing water absorption from deep-soil-layer and near-groundwater-layer. After the flood, it resumed water absorption from deep-soil-layer and near-groundwater-layer. P. euphratica water absorption patterns differed at different groundwater depths. In the shallow and middle groundwater depth sample plots, the water sources were the deep-soil and near-groundwater layers, and the population of P. euphratica grew well. In the deep sample plot, water absorption was mainly near the groundwater layer, and the P. euphratica population showed a decreasing trend, further explaining the degradation of P. euphratica in terms of water-use patterns. WUE is related to the growth stage of P. euphratica and the water conditions of the living environment; the more mature the P. euphratica, the more deficit the water conditions, and the higher the WUE. This study provides a basis for maintaining the stability of P. euphratica forests in arid deserts and for water allocation.

Carbon evolution and mixing effects on groundwater age calculations in fractured basalt, southwestern Idaho, U.S.A.

Using hydrochemical and isotopic compositions of springs and wells, we trace carbon from critical zone carbon dioxide (CO2) into groundwater of the semi-arid Reynolds Creek Experimental Watershed - Critical Zone Observatory, southwestern Idaho, USA. Dissolved inorganic carbon (DIC) concentrations, pH and stable isotope tracers of carbon for DIC (δ13CDIC), are used to show that most groundwater evolves under open system conditions, moving carbon into the groundwater and acting as a carbon sink. However, one sample (−10.94‰ δ13CDIC, 6,350 14C years before present (yrs. BP)) may have evolved under closed system conditions with a higher partial pressure of critical zone CO2 than present-day soils. By characterizing the carbon cycle, we show that (1) carbon evolution is primarily under open-system conditions, (2) shallow groundwater samples are generally less mixed and more recent (10 to 70 3H yrs. BP) than deeper groundwater samples (1,469 to 6,350 14C yrs. BP), and (3) the older portion of the groundwater may be even older than the calculated 14C ages, as indicated by the mixing of age tracers in intermediate wells. Our global conception of the deep critical zone should include carbon cycling of critical zone CO2 in old groundwater. Characterizing the deep critical zone in a semi-arid weathered silicate watershed improves our global understanding of carbon, nutrient and water cycling.

Evaluation of nitrate in shallow groundwater at Pasirkoja of Bandung City, Indonesia, using the pollution index and the nitrate pollution index methods

Pasirkoja is an old residential area in Bandung City currently densely populated. Some people in Pasirkoja use shallow groundwater for washing and bathing, and some for cooking. Pollutants very easily pollute shallow groundwater, and nitrate is one of the pollutants found in shallow groundwater in residential areas. The water quality status was determined using the pollution index (PI) method based on a Decree of the Minister of Environment Number 115 of 2003 and the nitrate pollution index (NPI) to ascertain the shallow groundwater quality in Pasirkoja of Bandung City, Indonesia. The variables used in the PI method were pH, turbidity, total dissolved solids (TDS), nitrate, and nitrite, while the NPI method used the nitrate parameter. Shallow groundwater samples were taken during the rainy season and dry season. Based on the PI method, the results showed that the quality status of shallow groundwater at the research location is mostly lightly polluted in the rainy and dry seasons. Meanwhile, based on the NPI method, most are clean (not polluted). Differences in the quality status of shallow groundwater depend on the environmental conditions around which shallow groundwater samples were taken. The research results also showed that, based on the PI method, nitrate is not the main parameter that determines pollution at the research location.

Re-description of Chevalia aviculae Walker, 1904, five new species and new records of Chevaliidae from Australia and New Zealand (Crustacea: Peracarida: Amphipoda: Senticaudata)

The amphipod family Chevaliidae Myers &amp; Lowry, 2003 (Amphipoda: Senticaudata) contains two genera: Chevalia Walker, 1904 (13 species), and Bryoconversor Lörz, Myers &amp; Gordon, 2014 (1 species). Chevalia is a marine genus with a cosmopolitan distribution in circumtropical and temperate waters. Prior to this study, records of Chevalia from Australian waters were limited. Here, we describe five new species of Chevalia from Australian waters, C. bardi sp. nov., C. burrewarra sp. nov., C. csiro sp. nov., C. freycinet sp. nov. and C. sprightly sp. nov. The original description of Chevalia aviculae no longer adequately defined the species and is redescribed based on syntypic material from East Cheval Paar, Sri Lanka. Additionally, new distribution records are provided for the New Zealand species Bryoconversor tutus Lörz, Myers &amp; Gordon, 2014. Material reported is from both shallow and deep-water samples from 1–660 m depth. The prevalence of various gender and intersex states within specimens of chevaliids is discussed. An updated key to the 19 world species of Chevaliidae and a field guide to the seven known Australian and New Zealand species is provided.

Natural Hydrogen in the Northern Perth Basin, WA Australia: Geospatial Analysis and Detection in Soil Gas for Early Exploration

The scope of this work is to empirically check and prove the practical applicability of the Primordially Hydridic Earth (PHE) concept for early exploration of the resources of naturally occurring hydrogen. With the PHE concept postulates interpreted within the local geological, tectonic, petrological and geophysical context, the reconnaissance plan, as well as the field exploration and data acquisition programs, were put together and implemented in the field. The results obtained from the surface (&amp;lt;1m deep) soil gas survey performed in Western Australia (WA) resulted in values of hundreds of ppm H&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;, including three samples with a concentration of hydrogen exceeding the gas sensor detection limit of 2,000 parts per million (ppm) (the all-Australia record). Similarly, several of the shallow soil samples used for obtaining headspace gas extracts yielded dozens % H&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;, which was established utilizing Gas Chromatography (GC) technology. The latter tests established the all-Australia record of 58.3% (norm.) H&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; concentration from 15 m depth, being the highest reading from the area of research. At one location, a concentration of He exceeding 8,000ppm was detected in a 1m surface soil gas sample analyzed by the independent lab. The most important outcome was finding natural hydrogen where it was expected and predicted. On the other hand, H&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; concentrations exceeding the natural background of 1-3ppm were not detected in the soil gas readings outside of the areas identified using the PHE concept as a theoretical foundation. It may be stated that overall, the practical application of the PHE concept along with the thoroughly planned utilization of carefully selected exploration techniques brings satisfactory results.

Rare earth elements and yttrium (REY) in fjord waters: Comparison between seawater in the Trondheimfjord (Norway), its local riverine REY sources and the North Atlantic

The rare earth elements and yttrium (REY) are critical resources increasingly released into the environment due to their pivotal role for an ever-growing number of high-tech products and processes. Fjords, worldwide and particularly in Norway, are not only of high importance for biodiversity but they also have great economic value. Knowledge on the distribution of REY in Norwegian coastal and riverine waters is, however, surprisingly scarce. We here report REY data for water samples from depth profiles from ten stations in the Trondheimfjord, one of Norway’s largest fjords, several Norwegian rivers, and two wastewater treatment plants in Trondheim.Our results show that water from different locations in the Trondheimfjord yield similar REY concentrations that correlate well with dissolved organic carbon. The deepest sample at each station shows the lowest REY concentrations. The shale-normalised (SN) REY patterns of the fjord waters resemble those of North Atlantic seawater, but can be distinguished from open-ocean water by the smaller fractionation between light and middle REY (PrSN/TbSN ≥ 0.5). Stations in the vicinity of a river mouth show considerably higher REY concentrations at shallow depths. The respective REYSN patterns resemble the typically flat patterns of boreal rivers that are often rich in nanoparticles and colloids (NPCs). The REYSN patterns of the four rivers investigated (Nidelva, Orkla, Gaula, Stjørdalselva) show the features of the shallow(er) fjord water samples but have even higher REY concentrations. Ultrafiltration (< 1 kDa) data for the Nidelva corroborate that the typical “REYSN seawater signature” is in fact already present in freshwater where it is, however, usually hidden by the REY associated with NPCs. The local wastewater treatment plants release anthropogenic Gd (from contrast agents used in magnetic resonance imaging) into the Trondheimfjord, but this signal is immediately diluted and thus is not observed in the REYSN patterns of the fjord water. However, our results in general suggest that the slightly elevated Gd/Tb ratios observed in almost all fjord waters relative to North Atlantic marine water may rather be due to the presence of anthropogenic Gd in the southern North Sea and the Baltic Sea, corroborating that anthropogenic Gd can be applied as a sensitive far-field watermass tracer.