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Micronutrients play an important role in enhancing the immune system, therefore, proper nutritional support of micronutrients could have a positive impact on COVID-19 outcome.

Watersheds are the fundamental Earth surface functioning units that connect the land to aquatic systems. Many watershed-scale models represent hydrological processes but not biogeochemical reactive transport processes. This has limited our capability to understand and predict solute export, water chemistry and quality, and Earth system response to changing climate and anthropogenic conditions. Here we present a recently developed BioRT-Flux-PIHM (BioRT hereafter) v1.0, a watershed-scale biogeochemical reactive transport model. The model augments the previously developed RT-Flux-PIHM that integrates land-surface interactions, surface hydrology, and abiotic geochemical reactions. It enables the simulation of (1) shallow and deep-water partitioning to represent surface runoff, shallow soil water, and deeper groundwater and of (2) biotic processes including plant uptake, soil respiration, and nutrient transformation. The reactive transport part of the code has been verified against the widely used reactive transport code CrunchTope. BioRT-Flux-PIHM v1.0 has recently been applied in multiple watersheds under diverse climate, vegetation, and geological conditions. This paper briefly introduces the governing equations and model structure with a focus on new aspects of the model. It also showcases one hydrology example that simulates shallow and deep-water interactions and two biogeochemical examples relevant to nitrate and dissolved organic carbon (DOC). These examples are illustrated in two simulation modes of complexity. One is the spatially lumped mode (i.e., two land cells connected by one river segment) that focuses on processes and average behavior of a watershed. Another is the spatially distributed mode (i.e., hundreds of cells) that includes details of topography, land cover, and soil properties. Whereas the spatially lumped mode represents averaged properties and processes and temporal variations, the spatially distributed mode can be used to understand the impacts of spatial structure and identify hot spots of biogeochemical reactions. The model can be used to mechanistically understand coupled hydrological and biogeochemical processes under gradients of climate, vegetation, geology, and land use conditions.

Enclosed topographic depressions are characteristic of karst landscapes on Earth. The developmental relationship between depression types, such as sinkholes (dolines) and uvalas, has been the subject of debate, mainly because the long developmental timescales in classical limestone karst settings impede direct observation. Here we characterize the morphometric properties and spatio-temporal development of ∼1150 sinkholes and five uvalas formed from ∼1980 to 2017 in an evaporite karst setting along the eastern coast of the hypersaline Dead Sea (at Ghor Al-Haditha, Jordan). The development of sinkhole populations and individual uvalas is intertwined in terms of onset, evolution and cessation. The sinkholes commonly develop in clusters, within which they may coalesce to form compound or nested sinkholes. In general, however, the uvalas are not defined by coalescence of sinkholes. Although each uvala usually encloses several clusters of sinkholes, it develops as a larger-scale, gentler and structurally distinct depression. The location of new sinkholes and uvalas shows a marked shoreline-parallel migration with time, followed by a marked shoreline-perpendicular (i.e. seaward) growth with time. These observations are consistent with theoretical predictions of karstification controlled by a laterally migrating interface between saturated and undersaturated groundwater, as induced by the 35 m fall in the Dead Sea water level since 1967. More generally, our observations indicate that uvalas and the sinkhole populations within them, although morphometrically distinct, can develop near-synchronously by subsidence in response to subsurface erosion.

Climate models predict amplified warming at high elevations in low latitudes, making tropical glacierized regions some of the most vulnerable hydrological systems in the world. Observations reveal decreasing streamflow due to retreating glaciers in the Andes, which hold 99 % of all tropical glaciers. However, the timescales over which meltwater contributes to streamflow and the pathways it takes – surface and subsurface – remain uncertain, hindering our ability to predict how shrinking glaciers will impact water resources. Two major contributors to this uncertainty are the sparsity of hydrologic measurements in tropical glacierized watersheds and the complication of hydrograph separation where there is year-round glacier melt. We address these challenges using a multi-method approach that employs repeat hydrochemical mixing model analysis, hydroclimatic time series analysis, and integrated watershed modeling. Each of these approaches interrogates distinct timescale relationships among meltwater, groundwater, and stream discharge. Our results challenge the commonly held conceptual model that glaciers buffer discharge variability. Instead, in a subhumid watershed on Volcán Chimborazo, Ecuador, glacier melt drives nearly all the variability in discharge (Pearson correlation coefficient of 0.89 in simulations), with glaciers contributing a broad range of 20 %–60 % or wider of discharge, mostly (86 %) through surface runoff on hourly timescales, but also through infiltration that increases annual groundwater contributions by nearly 20 %. We further found that rainfall may enhance glacier melt contributions to discharge at timescales that complement glacier melt production, possibly explaining why minimum discharge occurred at the study site during warm but dry El Niño conditions, which typically heighten melt in the Andes. Our findings caution against extrapolations from isolated measurements: stream discharge and glacier melt contributions in tropical glacierized systems can change substantially at hourly to interannual timescales, due to climatic variability and surface to subsurface flow processes.

The importance of water moving between the atmosphere and aquifers has led to efforts to develop and maintain coupled models of surface water and groundwater. However, developing inputs to these models is usually time-consuming and requires extensive knowledge of software engineering, often prohibiting their use by many researchers and water managers, thus reducing these models' potential to promote science-driven decision-making in an era of global change and increasing water resource stress. In response to this need, we have developed GSFLOW–GRASS, a bundled set of open-source tools that develops inputs for, executes, and graphically displays the results of GSFLOW, the U.S. Geological Survey's coupled groundwater and surface-water flow model. In order to create a robust tool that can be widely implemented over diverse hydro(geo)logic settings, we built a series of GRASS GIS extensions that automatically discretizes a topological surface-water flow network that is linked with an underlying gridded groundwater domain. As inputs, GSFLOW–GRASS requires at a minimum a digital elevation model, a precipitation and temperature record, and estimates of channel parameters and hydraulic conductivity. We demonstrate the broad applicability of the toolbox by successfully testing it in environments with varying degrees of drainage integration, landscape relief, and grid resolution, as well as the presence of irregular coastal boundaries. These examples also show how GSFLOW–GRASS can be implemented to examine the role of groundwater–surface-water interactions in a diverse range of water resource and land management applications.

Introduction: Increasing demand for water, depletion of resources of acceptable quality, and excessive water pollution due to agricultural and industrial developments has caused intensive social and environmental problems all over the world. Given the environmental importance of rivers, complexity and extent of pollution factors and physical, chemical and biological processes in these systems, optimal waste-load allocation in river systems has been given considerable attention in the literature in the past decades. The overall objective of planning and quality management of river systems is to develop and implement a coordinated set of strategies and policies to reduce or allocate of pollution entering the rivers so that the water quality matches by proposing environmental standards with an acceptable reliability. In such matters, often there are several different decision makers with different utilities which lead to conflicts. Methods/Materials: In this research, a conflict resolution framework for optimal waste load allocation in river systems is proposed, considering the total treatment cost and the Biological Oxygen Demand (BOD) violation characteristics. There are two decision-makers inclusive waste load discharges coalition and environmentalists who have conflicting objectives. This framework consists of an embedded river water quality simulator, which simulates the transport process including reaction kinetics. The trade-off curve between objectives is obtained using the Multi-objective Particle Swarm Optimization Algorithm which these objectives are minimization of the total cost of treatment and penalties that must be paid by discharges and a violation of water quality standards considering BOD parameter which is controlled by environmentalists. Thus, the basic policy of river’s water quality management is formulated in such a way that the decision-makers are ensured their benefits will be provided as far as possible. By using MOPSO, five alternatives and their performances under criteria are found. Values that are calculated by MOPSO are applied to form the cardinal Multi-Criteria Decision Making (MCDM) matrix. Afterwards, the cardinal MCDM matrix is transformed into the ordinal form. For studying competitive behaviors in such situations, a mathematical tool called game theory is used. Hence the transition matrix is formed for solving the problem by game theory and qualitative data. Finally the best non-dominated solution is defined using the Nash conflict resolution theory. Results and Discussion: The interaction point of the Sefidrood River and Caspian Sea is considered as a checkpoint and the standard amount of BOD considering the Iranian Protection Agency’s standards is equivalent to 5 mg/l. In the studied area, none of waste load dischargers perform current wastewater treatment. Under this circumstance, the BOD has the value of 26.59 mg/l which violated its standard amount. By MOPSO algorithm and Nash theory five alternatives, which each of them includes both the amount of BOD in checkpoint and treatment and penalty total cost, are obtained for two decision makers. The best and final alternative, that is preferred by both of decision-makers, reduces the BOD amount and the total payable cost to 6.16 mg/l and 296,293 $/year respectively. Conclusion: The practical utility of the proposed model in decision-making is illustrated through a realistic example of the Sefidrood River in the northern part of Iran. As a final alternative, that suggests the most economical measurement by minimizing of treatment and penalty total cost, there are acceptable percentage of treatment per discharge and the violation of standard for BOD parameter is negligible.

The current study presents the development of a simple and direct spectrophotometric approach for Hg(II) ions determination. This method has the significant advantage of being a simple procedure where no further solvent purification or pre-concentration is needed. The concentration of Hg(II) ions was determined in the presence of the Schiff base ligand named 2-((5-(2-hydroxy-3-methoxybenzylideneamino)–2H-1,2,4-triazole-3-ylimino)methyl)-6-methoxyphenol (HMBT), at pH 10 using Briton Robinson Buffer. The method Obey Beer's law in concentration range 0.1–6 µg mL- 1 of Hg with (LOD) 0 0.016 µg L -1 and (LOQ) 0.051 µg/L. The molar ratio ensured the formation of a metal complex between HMBT and Hg ions was in the molar ratio 2:1 (HMBT: Hg2+). The method was used for the determination of mercury ions in tap water and Zamzam water samples. The applied method has many advantages, such as simplicity, low cost, ease of operation, rapid detection, low-ligand consumption, and high sensitivity. The analytical method sensitivity was confirmed via the suitable selection of experimental circumstances. More information about the structure and stoichiometry of the complex formed in solution between Hg(II) and HMBT ligand has been gained through the isolation and investigation of solid complex (HMBT-Hg). The structure of the solid complex, HMBT-Hg, has been elucidated by applying analytical routes such as elemental analysis and the spectral mass, UV–vis spectra, and thermal analysis.

This study involves the preparation and investigation of a novel and highly selective poly(vinyl chloride)-based membrane of 2-((5-(2-hydroxy-3-methoxybenzylideneamino)-2H-1,2,4-triazol-3-ylimino)methyl)-6-methoxyphenol Schiff base ligand (HMBT), which is a neutral ionophore with sodium tetraphenyl borate (STB) in the form of an excluder and o-nitrophenyloctyl ether (o-NPOE) in the form of solvent mediators (plasticizing) as a Ni(II)-selective electrode. The observation of optimal performance was done wherein the membrane was shown to have the HMBT–PVC–NPOE-STB composition of 4:32:63:1.It worked effectively across a broad range of concentration (1.0 × 10−8 to 1.0 × 10−2 mol L−1). Meanwhile, the Nernstian slope was recorded as 29.3 mV per decade of activity between pH 3.0 and 8.0. The response time of this electrode was fast at 11 s which was used for a span of 100 days with sound reproducibility. According to the selectivity coefficients for trivalent, divalent, and monovalent cations, excellent selectivity was indicated for Ni(II) ions across a large number of citations, whereas no interference was caused by anions like PO43−, SO42− and Cl−. The proposed method in this study was applied successfully to determine Ni(II) content in different samples of water, obtaining suitable recoveries. Additionally, the probed sensor is utilized as indicator electrode when considering Ni2+ ion potentiometric titration against EDTA. In addition, the chelate’s geometry and structure of the complex formed between Ni2+ ions and HMBT, abbreviated as HMBT-Ni2, was evaluated by separating the solid product. Complex structure was confirmed based on alternative analytical and spectral methods to be structured in the bimetallic form with the formula [Ni2(HMBT)(H2O)2 Cl2]. The diamagnetic nature of the complex, which was concluded from the room temperature magnetic moment measurement combined with the UV–Vis measurement, suggested the square planar geometry around the Ni centers.