Water Profiles Research Articles

Twenty years of studying the origins and fate of atmospheric mercury over the Mediterranean Sea.

This study provides a review of 13 oceanographic campaigns between 2000 and 2017 to measure Hg in the Mediterranean, highlighting major findings from measurement and modelling activities during the Med-Oceanor program. The initial campaigns showed that high concentrations of RGM could be found far from industrial source regions and the observed daily variation in concentration, with peaks at midday and lower concentrations during darkness gave the first indications that photochemically mediated oxidation reactions were producing RGM in the MBL. Later atmospheric chemistry modelling studies showed the feasibility of Hg oxidation by bromine containing oxidants, which are released as a result of the acidification of sea salt aerosols in the Marine Boundary Layer (MBL). Spatial and seasonal variations of DGM were observed at different depths in the water column, with average DGM concentrations higher in the West and East Mediterranean deep and intermediate waters, than in overlaying Atlantic waters. DGM in water profiles typically increased with depth, together with nutrients and decreasing oxygen, indicating a possible bacterial and/or geogenic origin. Using measured DGM and meteorological variable values Hg fluxes can be calculated. When these are included in regional and global models they suggest that the net Hg evasion from the Mediterranean is around 30Mgyr-1. Repetition of these campaigns should be an extremely high priority, both to continue to monitor changes in atmospheric and aquatic Hg species concentrations, but also to perform RGM detection methodology intercomparisons so that the historical data is adequately contextualised and may be used to evaluate temporal trends.

Modified Green-Ampt model for infiltration analysis in loess area and its parameter determination and verification

Water infiltration into soil is important in geotechnical engineering. The classical Green-Ampt (GA) infiltration model is widely used in soil infiltration due to its physical significance, but it ignores the actual unsaturated layer in the infiltration process and has some deficiencies. Thus, the present study established a modified GA infiltration model (MLGA model) using Darcy’s infiltration law and continuity equation to fully consider the variation characteristics of the soil water profile in the infiltration process. The Philip model and the GA model have the same physical basis. By combining the internal relationship between the infiltration rate and cumulative infiltration of the two models, the expression of matrix suction of the MLGA model was obtained. The existing measured data was used to verify the correctness and applicability of the MLGA model. Finally, the sensitivity analysis of the critical parameters of the model was performed. The results showed that the MLGA model is reliable and can be used for water infiltration analysis in loess sites. When the MLGA model is used to calculate the infiltration depth, the maximum relative error between the calculated value and the measured data is less than 10%, and the average relative error is 5.54%, which indicates that the model has a high calculation accuracy. The average error of the MLGA model is 24.47% of the Kostiakov model and 80.42% of the existing modified GA model (LGAM model). Sensitivity analysis of the saturated permeability coefficient, initial water content, saturated water content, and matrix suction was performed using the single-factor disturbance method. The influence of each parameter on infiltration depth was summarized, and the sensitivity of each parameter was quantitatively evaluated, which revealed that saturated water content is a highly sensitive parameter. When using the MLGA model to calculate infiltration depth, the accuracy of saturated water content should be ensured first. Finally, the difference between the MLGA model and the LGAM model in describing the whole process of water infiltration is discussed, and the influence mechanism of critical parameters on the water infiltration process is deeply analyzed. The established MLGA model provides theoretical support for further study of the loess water infiltration mechanism.

Effect-based analysis of endocrine effects in surface and ground water with focus on progestagenicity using Arxula yeast-based reporter gene assays.

The use of effect-based methods in water monitoring for identifying risks to aquatic organisms and human health is important for aiding regulatory decisions. In the past decades, the database on monitoring, especially in surface waters, has grown as this aquatic environment is openly exposed to various contamination sources. With regard to endocrine disruption, estrogenic and androgenic effects have been primarily investigated. Here, yeast-based bioassays emerged as potent tools, offering sensitivity to environmentally relevant concentrations and high robustness. The objectives of this study were to investigate further endocrine endpoints and extend the monitoring to ground waters. The inclusion of progestagenic effects is crucial due to their multifaceted roles in various functions of organisms. Hence, three different Arxula-yeast hormone screens (estrogen, androgen, and progesterone receptors) were applied, revealing simultaneous exposure to diverse endocrine effects in surface and ground water matrices. Although effect profiles in surface waters showed mainly activation of hormone receptors, in-ground water samples inhibitory effects clearly predominate. Although toxicological thresholds are not yet legally binding, they are essential for effective regulatory measures and risk management to ensure the good ecological status of aquatic ecosystems. The results were compared with effect-based trigger values for ecological as well as human risk assessment depending on the sample matrix, none of which were exceeded.

Aquasearch: Enhancing Green Environmental Proteomics via MALDI-TOF-based Sewage Water Profiling

Aquasearch: Enhancing Green Environmental Proteomics via MALDI-TOF-based Sewage Water Profiling

Quantitatively tracing the decomposition of endogenous particulate organic carbon during sinking in (sub-)deep reservoirs: Using radiocarbon isotopes Δ14C.

The rapid expansion of reservoirs, coupled with increasing eutrophication, has profoundly influenced regional and global carbon cycles. To precisely assess the carbon sink potential of reservoirs, it is crucial to quantify the decomposition of endogenous particulate organic carbon (POC) during the deposition and sinking of particulate matter in reservoirs. This is particularly important in the context of rising temperatures and intensified human activities. In this study, the Hongfeng Reservoir, an artificial reservoir in a karst basin on the Yunnan-Guizhou Plateau in China, was selected as a representative reservoir to systematically explore the sources and evolution of endogenous POC in (sub-)deep reservoirs. Particulate matter and water samples were collected from inflowing rivers and reservoir water profiles to analyze the content of POC, stable isotope of POC (δ13CPOC), radioisotope of POC (Δ14CPOC), particulate nitrogen, and chlorophyll concentrations. The results revealed significant differences in POC content and carbon isotope signatures between riverine and reservoir particulate matter, primarily due to distinct POC sources. Riverine particulate matter exhibited C/N ratios of 10.4 to 18.4, δ13CPOC values of -29.3 ‰ to -26.1 ‰, and Δ14CPOC values of -282 ‰ to -183 ‰, in contrast, particulate matter in the reservoir's surface water had C/N ratios of 5.1 to 6.9, δ13CPOC values of -34.6 ‰ to -31.3 ‰, and Δ14CPOC values of -162 ‰ to -143 ‰. From the surface to the bottom of the reservoir water profile, the C/N ratio of particulate matter gradually increased, Δ14CPOC became increasingly negative, and δ13CPOC exhibited varying trends across different water profiles. The combined analysis of chlorophyll and other variables demonstrated that Δ14CPOC is the most reliable indicator for tracing the source and decomposition process of POC during particulate matter sinking in the reservoir. Quantitative estimates based on Δ14CPOC indicated that the contribution of endogenous POC decreased from 73-85 % in the surface water to 41-57 % in the bottom water, with 74.7-75.4 % of endogenous POC decomposed during the sinking process, suggesting that only a small fraction of endogenous organic matter could reach the reservoir bottom and was ultimately buried in sediments. Future research should focus on quantifying the fate of endogenous organic matter decomposition products to enhance understanding of reservoirs' carbon sink potential.

Flood analysis using the HEC-RAS software for Antakya Altınçay Creek

Flood is one of the most important disasters in the world. Floods, common in our country, are the second disaster after the earthquake in terms of loss of life and property caused by natural disasters and the first among climatic disasters. The district of Antakya is located where streamflow has a high flow coefficient. Because of flooding in Altınçay Creek which flows through the center of Antakya into the Orontes River, flood studies need to be carried out and the necessary precautions taken to prevent flooding. In this study, peak discharges for 2, 5, 10, 25, 50, and 100-year return periods of Altınçay Creek passing through residential areas in Antakya were determined by SCS and DSI synthetic methods. Using these estimated peak discharges the water profile along the Altınçay Creek route has been simulated using HEC-RAS software, and the flood risk areas were determined on cross-sections basis. As a result, flood risk was not observed in peak discharge for return periods of 2, 5 and 10 years. However, flood events were observed at 16, 51, and 73 different cross sections in peak discharges for return periods of 25, 50, and 100 years respectively. To reduce flood damage, it was suggested that the cross-sectional areas having flood risk must be increased.

Morphological Characteristics and Annual Population Dynamics of Microcystis (Cyanobacteria) in Nanwan Reservoir (Xinyang, China)

Microcystis, a key genus of bloom-forming cyanobacteria in freshwater ecosystems, has garnered significant research interest due to its species diversity and population dynamics. This study investigated the water profiles and Microcystis populations at six stations in the Nanwan Reservoir (Xinyang, China) throughout 2022 to elucidate the morphological characteristics of Microcystis, analyze its population density patterns, and identify key environmental factors influencing its dynamics. The reservoir was classified as mesotrophic during most of the study period. Seven common Microcystis species were identified, including M. botrys, M. smithii, M. wesenbergii, M. firma, M. novacekii, M. aeruginosa, and a species suspected to be M. flos-aquae. The spatial and temporal distribution analyses revealed a bimodal fluctuation in Microcystis densities, with a monthly occurrence across stations except in August. The highest density, 1.71 × 107 cells/L, was recorded in May, while the lower densities were observed from July to September. The Mantel test results indicated that the nitrogen levels, particularly NO3−-N, were the primary factors influencing the Microcystis density. Additionally, both the reservoir bays and dam areas exhibited a high risk of Microcystis blooms. Effective management of nitrogen inputs, enhanced monitoring, and appropriate gate operations are recommended to mitigate the risk of Microcystis blooms in the Nanwan Reservoir.

Water Sorption Properties and Hydrothermal Stability of Al-Containing Metal-Organic Frameworks CAU-10 and MIL-96 Studied Using Quasi-Equilibrated Thermodesorption.

A novel experimental technique, quasi-equilibrated temperature-programmed desorption and adsorption (QE-TPDA), was used to study the water sorption properties and hydrothermal stability of aluminum trimesate MIL-96 and aluminum isophthalate CAU-10, which have been selected due to their remarkable sorption properties. The QE-TPDA profiles of water observed for MIL-96 and CAU-10 confirmed the hydrophilic nature of these materials. Complex QE-TPDA profiles indicate that water sorption in MIL-96 follows a three-step pore filling mechanism. The shape of single desorption peaks in the QE-TPDA profiles for CAU-10 confirms that water sorption involves a reversible phase transition. Based on the QE-TPDA profiles, the water adsorption heat was determined: 45-46 kJ/mol for CAU-10 and 43-56 kJ/mol for MIL-96, in the latter case depending on the adsorption extent. Hydrothermal stability tests revealed that MIL-96 retained its stable porosity-related sorption capacity for water after hydrothermal treatment up to 290 °C. Gradual changes in the QE-TPDA profiles due to the hydrothermal treatment above 290 °C, with decreasing the high-temperature desorption peak and increasing the low-temperature one, indicate minor structural changes occurring in this material. Only after 410 °C treatment was fast degradation of MIL-96 observed. CAU-10 exhibited high and unchanged hydrothermal stability up to 400 °C.

Well water contaminants and colorectal cancer in North Dakota.

This study aims to identify common contaminants in well water linked to an increase in colorectal cancer (CRC) incidence rates in North Dakota (ND) counties. County-specific incidence rates for CRC were obtained from the ND Statewide Cancer Registry. Corresponding demographic, agricultural, and geophysical data were obtained from population-based sources. Associations between well water contaminants and CRC incidence were examined for 16 counties in ND with complete well water profiles between 1997-2019. Data were analyzed by multiple linear regression. Iron in well water exhibited a significant positive association with CRC incidence (4.75, P = 0.001), and barium exhibited a small, but significant negative association (-0.06907, P = 0.01). Residents in counties in ND with prevalent well water usage contaminated with iron may be at higher risk for CRC.

Controlling parameters of co-current and counter-current imbibition in naturally fractured reservoirs

Naturally fractured formations are complex petroleum reservoirs that are poor candidates for waterflooding due to difficulties in controlling sweep. Injected water can readily propagate through the fracture system, bypassing the hydrocarbon stored in the matrix. Instead, such systems rely on spontaneous imbibition (SI) from the matrix into the extensive fracture gathering system. SI is a crucial recovery mechanism that relies on capillary pressure-dominated fluid movement. SI can occur through two modes, co-current (COSI) and counter-current (COUSI), depending on the relative direction of fluid movement in response to prevailing boundary conditions. Analytical solutions that incorporate the diffusivity coefficient, which combines relative permeability and capillary pressure curves, are used to describe co-current and counter-current imbibition mechanisms. The perturbation method is one approach in solving these analytical equations. In-situ water saturation profiles, ascertained through experimental CT scanning, serve as validation benchmarks for both co-current and counter-current models. The understanding of the SI process can give more details about the fracture-matrix interactions and the exchange function. Sensitivity studies with respect to the parameterization of the driving force for imbibition, capillary pressure, and the resistive forces, captured in relative permeability curves, can guide experimental study planning and aid in inverse problem analysis in the characterization of naturally fractured reservoirs. The results of a parametric study show that capillary pressure curve parameters, such as capillary entry pressure and capillary exponent, significantly affect the position of the waterfront which indicates the imbibition rate. In addition, the water relative permeability exponent has greater impact on both shape and position of water profile than other relative permeability parameters. The nonwetting phase parameters, like oil endpoint relative permeability and oil exponent, have the least influence on water saturation profile.

Automatic Identification and Suppression of Random Noise and Methods for Profile Splicing in the Sub-Bottom Profile of Deep Water

The complex topography of deep sea presents numerous challenges for the accurate exploration of sub-bottom profiles. These include real-time tracking of seafloor reflectors, acquisition and storage of deep-sea long-term reflection data, and splicing of successive profiles. Based on the actual survey data of deep sea, we have developed automatic positioning and noise suppression algorithms, namely the double-difference threshold of proximity points. Furthermore, we have created automatic algorithms, namely content expansion and group data moving, based on extremum in seafloor’s depth. These have been designed to automatically suppress the random noise and effectively splice the sub-bottom profile data in deep water. The aforementioned processing techniques facilitate the enhancement of the quality of deep-water sub-bottom profile data, thereby enabling the provision of a comprehensive and successively long profile for interpretation in the context of deep-water sub-bottom profile data.

Integrating short- and full-length 16S rRNA gene sequencing to elucidate microbiome profiles in Pacific white shrimp (Litopenaeus vannamei) ponds.

Despite their immense economic value as a key aquaculture species, the production of Pacific white shrimp (Litopenaeus vannamei) faces significant challenges from intensive farming practices and disease outbreaks. Routine microbial profiling for disease surveillance could be a promising approach to anticipate and control disease outbreaks. To achieve this, accuracy in microbial profiling in shrimp ponds is crucial for enabling targeted action and prevention. Extensive documentation emphasizes that, beyond biological factors (related to the host, diet, or health status during the rearing period), technical elements, including sequencing techniques significantly influence bacterial community profiling. This study investigated the influence of short- and long-read sequencing of 16S rRNA genes on the microbial profiles in shrimp intestines, water, and sediments. The origin of the samples (intestine or environmental) in shrimp culture ponds primarily drove the observed differences in core microbial species. The ecological niches accounted for 56% of bacterial community variations in culture ponds. Both sequencing approaches showed consistent results in identifying higher-rank taxa and assessing alpha and beta diversity. However, at the species level, full-length 16S rRNA gene sequences provided better resolution than V3-V4 sequences. For routine microbial profiling in shrimp culture ponds, our study suggests that short-read sequences were sufficient for determining overall bacterial community.IMPORTANCEThis interdisciplinary study investigated the influence of sequencing techniques on bacterial communities profiling within Pacific white shrimp (Litopenaeus vannamei) ponds. By integrating aquaculture, microbiology, and environmental science, we revealed the role of ecological niches and factors like salinity and pH on microbiota diversity and composition in shrimp intestines, pond water, and sediment. Additionally, we compared the taxonomic resolution using partial versus full-length 16S rRNA gene sequences, highlighting the value of longer amplicons for precise identification of key taxa. These findings provide novel insights into microbial dynamics underlying environmental effects in shrimp aquaculture. Comprehensive characterization of the pond microbiome could lead to management strategies that promote shrimp health and productivity. Furthermore, the potential of a multi-omics approach for integrating complementary data streams to elucidate environment-microbiome-host interactions was highlighted.

Investigating ultra-high dose rate water radiolysis using the Geant4-DNA toolkit and a Geant4 model of the Oriatron eRT6 electron linac

Ultra-high dose rate FLASH radiotherapy, a promising cancer treatment approach, offers the potential to reduce healthy tissue damage during radiotherapy. As the mechanisms underlying this process remain unknown, several hypotheses have been proposed, including the altered production of radio-induced species under ultra-high dose rate (UHDR) conditions. This study explores realistic irradiation scenarios with various dose-per-pulse and investigates the role of pulse temporal structure. Using the Geant4 toolkit and its Geant4-DNA extension, we modeled the Oriatron eRT6 linac, a FLASH-validated electron beam, and conducted simulations covering four distinct dose-per-pulse scenarios – 0.17 Gy, 1 Gy, 5 Gy, and 10 Gy – all featuring a 1.8 µs pulse duration. Results show close agreement between simulated and experimental dose profiles in water, validating the eRT6 model for Geant4-DNA simulations. We observed important changes in the temporal evolution of certain species, such as the earlier fall in hydroxyl radicals (\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{ \\bullet } \ ext{O}\ ext{H}$$\\end{document}) and reduced production and lifetime of superoxide (\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\ ext{O}}_{2}^{{\\bullet\\:}-}$$\\end{document}) with higher dose-per-pulse levels. The pulse temporal structure did not influence the long-term evolution of species. Our findings encourage further investigation into different irradiation types, such as multi-pulse configurations, and emphasize the need to add components in water to account for relevant cellular processes.

Outcomes in Randomized Clinical Trials Testing Changes in Daily Water Intake

Several public recommendations exist regarding the amount of daily water intake, yet the supporting evidence is not clear, and benefits of increasing water consumption are not well-established. To summarize evidence from randomized clinical trials (RCTs) pertaining to the health-related outcomes associated with increased or decreased daily water consumption. A systematic search of PubMed, Web of Science, and Embase was performed up to April 6, 2023. Studies were included if they aimed to assess the impact of daily water consumption by any defined amount on any health-related outcome. Of 1464 records screened, 18 (1%) eligible studies were included in the review. Among eligible studies, 15 (83%) were parallel group RCTs, and 3 (16%) were crossover studies. Interventions in these studies consisted of a recommendation to alter the daily amount of water intake by a specific amount for a predefined period ranging between 4 days and 5 years, while the control groups were mostly asked to maintain their usual intake habits. The studies assessed various populations. Recurring primary end points included weight loss, fasting blood glucose level, headache, urinary tract infection, and nephrolithiasis. Consuming additional water was associated with greater weight loss (range, 44%-100% more than control conditions) and fewer nephrolithiasis events (15 fewer events per 100 participants over 5 years). Single studies suggested benefits related to migraine prevention, urinary tract infection, diabetes control, and hypotension. Ten studies (55%) reported at least 1 positive result, and 8 studies (44%) reported negative results. This systematic review found that there is a limited number of clinical trials in the literature assessing the benefits of increasing water intake related to a large variety of health outcomes. While the quality and quantity of evidence is limited, a small number of studies suggested benefits of water intake on weight loss and nephrolithiasis, while single studies raised the possibility of benefits for patients with migraine, urinary tract infection, diabetes, and hypotension. Given the low cost and low adverse-effect profile of water, further well-designed studies should assess benefits in these specific conditions.

Evaluating drinking water treatment residuals as an in-situ capping material for metal-contaminated sediments

This study evaluated drinking water treatment residuals (DWTR) as an in-situ capping material for metal-contaminated sediments using Gust-chamber experiments. Metal release from non-capped and DWTR-capped sediments was measured under increasing shear stress (τ) from 0.05 to 0.4 Pa. Fathead minnow (FHM) juveniles (Pimephales promelas) were exposed to water from these sediments in 96-h bioassays to assess DWTR's efficacy in reducing metal toxicity. Sand was used as an inert capping material for comparison. Diffusive gradients in thin films (DGT) assessed DWTR's impact on vertical metal concentration profiles in sediment pore water and overlying water, with concentrations determined by ICP-MS. Without capping, increasing τ raised metal concentrations in the overlying water from 45 to 95 mg/L for Cd and Zn, 4–10 mg/L for Cu, and 2–4 mg/L for Pb. Sand capping reduced these levels, with Cd and Zn ranging from 4 to 21 mg/L, Cu from 0.26 to 0.63 mg/L, and Pb from 0.051 to 0.23 mg/L. DWTR capping significantly lowered metal concentrations in the overlying water, with Cd ranging from 1 to 8 μg/L, Zn from 30 to 40 μg/L, Cu from 2.5 to 5 μg/L, and Pb from 1 to 2 μg/L. Therefore, beyond the physical barrier effect, the DWTR cap immobilizes metals through other mechanisms such as sorption and precipitation. Bioassays showed that DWTR significantly decreased metal toxicity to FHM, while sand-capped and non-capped sediments caused 100% mortality. DGT confirmed DWTR reduced metal fluxes at the sediment-water interface by up to two orders of magnitude.

Elucidating Wettability Alteration on Clay Surface Contacting Mixed Electrolyte Solution: Implications to Low-Salinity Waterflooding

Summary Many mechanisms have been proposed in the literature to explain wettability alteration at low-salinity waterflooding (LSWF). Some of these mechanisms include electrical double layer (EDL) expansion, multi-ion exchange, and cation hydration. However, no consensus has been reached on which one is the key mechanism in low-salinity enhanced oil recovery (EOR). Moreover, the mechanisms by which low-salinity flooding can enhance oil recovery are poorly understood. Parameters such as salinity, electrolyte type, oil components, and presence of clay minerals are often associated with the degree to which the injection of low-salinity water increases oil production. Therefore, an investigation of the geochemistry of the clay/fluid interface is crucial to understand the role of petrophysical properties such as wettability on oil production. We use molecular dynamics (MD) to (i) quantify the impacts of different types of oil components, electrolytes, and its mixture at varying ionic strengths on interfacial properties and (ii) investigate wettability alteration by means of water adsorption quantification. We investigate the brine/clay and oil/brine/clay interfacial interactions involved in the adsorption of ions and water molecules onto the clay surface. Clay is represented by illite, and brine is composed of water molecules and different electrolyte types such as NaCl, CaCl2, and their mixtures at varied concentrations. The oil components investigated in this work include decane (C10H22), decanoic acid (CH₃(CH₂)₈COOH), and sodium decanoate (C10H19NaO2). These components were selected to represent the range of oil molecules typically found in reservoirs, which include nonpolar, polar, and charged polar molecules. Initially, we set up systems composed of different ion composition and salinity to investigate the effect of these parameters on EDL structure and water adsorption. Then, we created systems composed of mixed electrolyte and different oil components to verify the impacts of these molecules on the oil/brine/clay interface. Finally, we increased the NaCl concentration in the system containing sodium decanoate to investigate the role of Na in wettability alteration. MD simulations were performed at 330 K, and particle density profiles of water, hydrocarbon, and ions inside the illite nanopores were computed. We observed that the ion composition and salt concentration of the systems composed of clay minerals and brine do not result in significant changes in the adsorption planes of cations. For the same systems, we also computed the number of water molecules per unit cell in each hydration layer. We observed that the change in the thickness of these hydration layers is also very small. The results showed that nonpolar-charged hydrocarbon molecules have the lowest mobility, suggesting that this component has a more intense interaction with the illite surface compared with other hydrocarbons. Additionally, snapshots of the simulation indicate that calcium preferentially forms bridges with sodium decanoate molecules compared with other organic components. Despite being widely known as an efficient method for achieving EOR, the underpinning mechanism for wettability alteration at LSWF is still not fully understood. The outcomes of this work improve our understanding of the key parameters affecting interactions at the oil/rock/brine interface during LSWF.

Combining low- and high-frequency microwave radiometer measurements from the MOSAiC expedition for enhanced water vapour products

Abstract. In the central Arctic, high-quality water vapour observations are sparse due to the low density of meteorological stations and uncertainties in satellite remote sensing. Different reanalyses also disagree on the amount of water vapour in the central Arctic. The Multidisciplinary drifting Observatory for the Study of the Arctic Climate (MOSAiC) expedition provides comprehensive observations that are suitable for evaluating satellite products and reanalyses. Radiosonde observations provide high-quality water vapour estimates with a high vertical but a low temporal resolution. Observations from the microwave radiometers (MWRs) on board the research vessel Polarstern complement these observations through high temporal resolution. In this study, we demonstrate the high accuracy of the combination of the two MWRs HATPRO (Humidity and Temperature Profiler) and MiRAC-P (Microwave Radiometer for Arctic Clouds – Passive). For this purpose, we developed new retrievals of integrated water vapour (IWV) and profiles of specific humidity and temperature using a neural network approach, including observations from both HATPRO and MiRAC-P to utilize their different water vapour sensitivity. The retrievals were trained with the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis version 5 (ERA5) and synthetic MWR observations simulated with the Passive and Active Microwave radiative TRAnsfer tool (PAMTRA). We applied the retrievals to synthetic and real observations and evaluated them with ERA5 and radiosondes launched during MOSAiC, respectively. To assess the benefit of the combination of HATPRO and MiRAC-P compared to single MWR retrievals, we compared the errors with respect to MOSAiC radiosondes and computed the vertical information content of the specific humidity profiles. The root mean squared error (RMSE) of IWV was reduced by up to 15 %. Specific humidity biases and RMSE were reduced by up to 75 % and 50 %, respectively. The vertical information content of specific humidity could be increased from 1.7 to 2.4 degrees of freedom. We also computed relative humidity from the retrieved temperature and specific humidity profiles and found that RMSE was reduced from 45 % to 15 %. Finally, we show a case study demonstrating the enhanced humidity profiling capabilities compared to the standard HATPRO-based retrievals. The vertical resolution of the retrieved specific humidity profiles is still low compared to radiosondes, but the case study revealed the potential to resolve major humidity inversions. To what degree the MWR combination detects humidity inversions, also compared to satellites and reanalyses, will be part of future work.

Defining and Mitigating Flow Instabilities in Open Channels Subjected to Hydropower Operation: Formulations and Experiments

A thorough literature review was conducted on the effects of free surface oscillation in open channels, highlighting the risks of the occurrence of positive and negative surge waves that can lead to overtopping. Experimental analyses were developed to focus on the instability of the flow due to constrictions, gate blockages, and the start-up and shutdown of hydropower plants. A forebay at the downstream end of a tunnel or canal provides the right conditions for the penstock inlet and regulates the temporary demand of the turbines. In tests with a flow of 60 to 100 m3/h, the effects of a gradually and rapidly varying flow in the free surface profile were analyzed. The specific energy and total momentum are used in the mathematical characterization of the boundaries along the free surface water profile. A sudden turbine stoppage or a sudden gate or valve closure can lead to hydraulic drilling and overtopping of the infrastructure wall. At the same time, a PID controller, if programmed appropriately, can reduce flooding by 20–40%. Flooding is limited to 0.8 m from an initial amplitude of 2 m, with a dissipation wave time of between 25 and 5 s, depending on the flow conditions and the parameters of the PID characteristics.

Hydrogeochemical Insights into the Sustainable Prospects of Groundwater Resources in an Alpine Irrigation Area on Tibetan Plateau

The Tibetan Plateau is the “Asia Water Tower” and is pivotal for Asia and the whole world. Groundwater is essential for sustainable development in its alpine regions, yet its chemical quality increasingly limits its usability. The present research examines the hydrochemical characteristics and origins of phreatic groundwater in alpine irrigation areas. The study probes the chemical signatures, quality, and regulatory mechanisms of phreatic groundwater in a representative alpine irrigation area of the Tibetan Plateau. The findings indicate that the phreatic groundwater maintains a slightly alkaline and fresh status, with pH values ranging from 7.07 to 8.06 and Total Dissolved Solids (TDS) between 300.25 and 638.38 mg/L. The hydrochemical composition of phreatic groundwater is mainly HCO3-Ca type, with a minority of HCO3-Na·Ca types, closely mirroring the profile of river water. Nitrogen contaminants, including NO3−, NO2−, and NH4+, exhibit considerable concentration fluctuations within the phreatic aquifer. Approximately 9.09% of the sampled groundwaters exceed the NO2− threshold of 0.02 mg/L, and 28.57% surpass the NH4+ limit of 0.2 mg/L for potable water standards. All sampled groundwaters are below the permissible limit of NO3− (50 mg/L). Phreatic groundwater exhibits relatively good potability, as assessed by the entropy-weighted water quality index (EWQI), with 95.24% of groundwaters having an EWQI value below 100. However, the potential health risks associated with elevated NO3− levels, rather than NO2− and NH4+, merit attention when such water is consumed by minors at certain sporadic sampling locations. Phreatic groundwater does not present sodium hazards or soil permeability damage, yet salinity hazards require attention. The hydrochemical makeup of phreatic groundwater is primarily dictated by rock–water interactions, such as silicate weathering and cation exchange reactions, with occasional influences from the dissolution of evaporites and carbonates, as well as reverse cation-exchange processes. While agricultural activities have not caused a notable rise in salinity, they are the main contributors to nitrogen pollution in the study area’s phreatic groundwater. Agricultural-derived nitrogen pollutants require vigilant monitoring to avert extensive deterioration of groundwater quality and to ensure the sustainable management of groundwater resources in alpine areas.

Iron redox shuttling and uptake by silicate minerals on the Namibian mud belt

Anoxic marine sediments represent an important source of bioavailable iron (Fe) to the ocean. The highest sedimentary Fe fluxes are observed in open-marine oxygen minimum zones where anoxic bottom waters are in contact with ferruginous surface sediments. Here, sedimentary Fe release, transport and re-deposition (i.e., Fe shuttling) may generate a lateral pattern of sedimentary Fe enrichment and depletion, which can be used to trace redox-related Fe mobility in the paleo-record. However, depending on the balance between terrigenous and authigenic (i.e., shuttle-related) Fe flux, the stability of bottom water redox conditions as well as post-depositional processes of mineral alteration, the sedimentary fingerprint of an Fe redox shuttle may be obscured and difficult to identify.We investigated sedimentary Fe cycling along two transects across the Namibian mud belt with variable terrigenous sedimentation (23°S < 25°S) and during two seasons with opposing bottom water redox conditions (oxic in austral winter versus anoxic to sulfidic in austral summer). On both transects, substantial benthic Fe fluxes up to −50 µmol m−2 d−1 were inferred based on pore water profiles. The magnitude of these fluxes is comparable to those reported for other open-marine oxygen minimum zones. On the transect at 23°S, Fe source areas with ferruginous surface sediments were clearly separated from Fe sink areas with highly sulfidic surface sediments. Therefore, Fe redox shuttling was reflected by a lateral pattern of reactive Fe depletion and enrichment relative to the terrigenous background sedimentation. By contrast, on the transect at 25°S, benthic Fe fluxes were temporally and spatially more variable and surface sediments were ferruginous or only weakly sulfidic. Therefore, sedimentary Fe depletion and enrichment was less pronounced at 25°S. In the Fe sink area at 23°S, hydrogen sulfide was present at the sediment surface during both sampling campaigns and solid phase data suggest that Fe sulfide minerals represented the main burial phase of reactive Fe. By contrast, at 25°S excess Fe was associated with potassium (K) rather than reduced sulfur. While a differing sediment provenance cannot be ruled out entirely, combined evidence from pore water silica profiles, K to Fe stoichiometric relationships and electron microprobe images suggest that laterally derived excess Fe was incorporated into pre-existing and/or authigenic clay minerals during early diagenesis. Iron uptake by clay minerals may be supported by frequent redox oscillations and sediment mixing preventing preservation of Fe sulfide minerals and promoting Fe and K fixation in clay minerals. The burial fluxes of excess Fe associated with sulfide minerals at 23°S and silicate minerals at 25°S were similar. Our findings thus underscore that neoformation or alteration of silicate minerals can be important processes within the low-temperature marine Fe cycle.