High‑magnesium waters and soils: Emerging environmental and food security constraints

A two-step electrochemical method for separating Mg(OH)2 and CaCO3: Application to RO reject and polluted groundwater

The process of removing Ca2+ and Mg2+ ions typically results in the co-precipitation of Ca2+ and Mg2+ along with other salt waste. To improve water treatment efficiency towards a zero-waste goal, it is crucial to separate Ca2+ and Mg2+, and recover them in their purified form. This study proposes a two-step electrochemical approach that separately recovers Ca2+ as CaCO3 and Mg2+ as Mg(OH)2. The first step uses an undivided cell with 3D electrodes and controlled flow directions to selectively precipitate CaCO3 on the electrode, keeping the cell removal efficiency. The second step employs a two-compartment cell with a cationic exchange membrane to recover Mg(OH)2. This approach was evaluated on RO reject water with high Ca2+ to Mg2+ ratio and industrial effluent-polluted groundwater with a low ratio. Treatment of domestic RO reject water using undivided cell specifically recovered 64% of CaCO3, although the low conductivity of the RO reject water limited further Mg2+ recovery. Conversely, treating industrial effluent-polluted groundwater with this two-step process successfully recovered 80% of CaCO3 and 94% of Mg(OH)2. SEM, EDAX, and XRD analysis confirmed the quality of the recovered products.

Assessment of irrigation water quality for vegetable farming in peri-urban Kumasi

Polluted water contains a variety of toxic compounds that tend to affect human health. Farmers have recently looked at runoff wastewater as a source of irrigation water because it comes at no cost and is a more efficient alternative to potable water due to the high demand but limited supply. This present study assesses the quality and suitability of water sources used for irrigation at the Kwame Nkrumah University of Science and Technology vegetable farmlands. The study specifically investigated the quality of water used for irrigation with the following parameters: pH, turbidity, total dissolved solids, total suspended solids, chloride, chemical oxygen demand, biological oxygen demand, oil and grease, fluoride, nitrate, nitrite, sulphate, sodium, calcium, magnesium, sodium adsorption potential, alkalinity, conductivity, phosphate, Escherichia coli, fecal and total coliforms. The results revealed that the water contained moderate levels of chloride and could be good for plant growth. The total coliform counts range from 2.1 × 106 to 4.15 × 107 MPN/100 mL, suggesting a relatively high microbial load in the irrigation water. The results also suggested that the sodium absorption ratio was very low and may not affect the quality of water for irrigation purposes. Fe levels far exceed the 5 mg/L maximum acceptable limits recommended by the WHO and FAO for the irrigation of vegetables. The high Fe concentration could discolor the leaves of some plants, especially foliage leaves. However, the levels of Cd were within the WHO maximum permissible limit of 0.01 mg/L.

Natural Zeolite for The Purification of Saline Groundwater and Irrigation Potential Analysis

Groundwater is one of the main sources of water for irrigation used worldwide. However, the application of the resource is threatened by the possibility of high saline levels, especially in low-lying coastal regions. Furthermore, the lack of readily accessible materials for successful treatment procedures makes the purification of such water a constant challenge. Based on the fact that natural zeolite is one of the easily accessible and relatively cheap filter materials, this study examined the potential use of high-salinity groundwater filtered by natural zeolite for irrigation. Zeolite-filled filters at two different depths (0.5 m and 1 m) were studied. The samples were collected from the low-lying areas of Dar es Salaam City, Tanzania. The study observed that when the raw groundwater samples were exposed to the 0.5 m column depth, sodium (Na⁺) had the lowest removal efficiency at 40.2% and calcium (Ca²⁺) had the highest removal efficiency at 98.9%. On the other hand, magnesium (Mg²⁺) had the lowest removal efficiency, at about 61.2%, whereas potassium (K⁺) had up to about 99.7% removal efficiency from the 1 m column depth treatment system. Additionally, from the salinity hazard potential analysis, most of the samples fell within C4 (based on the electrical conductivity), which is a "very high salinity" class, and based on the quality it means the water cannot be directly applied for irrigation purposes. From the 0.5 m column depth, most of the samples fell within C3 (the "high salinity" class), and from the 1 m column depth most of the samples fell within C1 ("low salinity" class). The findings of this study offer some valuable insight into the prospective use of natural zeolite for the filtration of saline groundwater before its application for irrigation.

Magnesium Coprecipitation with Calcite at Low Supersaturation: Implications for Mg-Enriched Water in Calcareous Soils

The concentrations of magnesium (Mg) and calcium (Ca) in natural aqueous environments are controlled by sorption and dissolution–precipitation reactions. Ca binding in calcareous soils depends on the degree of solution saturation with respect to CaCO3. Mg may be bound in precipitating calcite. Here, we investigated Mg incorporation into calcite via the recrystallization of vaterite, which simulates a very low supersaturation in a wide range of Mg to Ca ratios and pH conditions. Increasing the Mg to Ca ratios (0.2 to 10) decreased the partition coefficient of Mg in calcite from 0.03 to 0.005. An approximate thermodynamic mixing parameter (Guggenheim a0 = 3.3 ± 0.2), that is valid for dilute systems was derived from the experiments at the lowest initial Mg to Ca ratio (i.e., 0.2). At elevated Mg to Ca ratios, aragonite was preferentially formed, indicating kinetic controls on Mg partitioning into Mg-calcite. Scanning electron microscopy (SEM-EDX) analyses indicated that Mg is not incorporated into aragonite. The thermodynamic mixing model suggests that at elevated Mg to Ca ratio (i.e., ≥1) Mg-calcite becomes unstable relative to pure aragonite. Finally, our results suggest that the abiotic incorporation of Mg into calcite is only effective for the removal of Mg from aqueous environments like calcareous soil solution, if the initial Mg to Ca ratio is already low.

An Evaluation of the Khubelu Wetland and Receiving Stream Water Quality for Community Use

Wetlands in Lesotho are at the headwaters of some shared river basins like the Orange-Senqu River basin. These wetlands are threatened by various anthropogenic activities which are compromising their water quality. This study assessed the water quality status of the Khubelu wetland and stream using various water quality parameters to determine its suitability for domestic use, irrigation, and livestock watering. This was a preliminary research study on the suitability of the stream water for various uses in the study area. Calcium was the most concentrated cation in the stream (8.20 mg/L to 16.8 mg/L), followed by magnesium (7.29 mg/L to 12.51 mg/L), with sodium and potassium showing minimum values. The chemical oxygen demand values were in the range of 48 to 160 mg/L. All parameters were within the EU and WHO ranges for drinking water, except EC, DO, BOD, COD, and PO4 levels. The Khubelu wetland water quality index (WQI) had a value of 93, whereas the stream WQI value was 107. The sodium Adsorption Ratio (SAR) values for the wetland and stream were 3.83 and 1.04, respectively, whereas the Soluble Sodium Percentage (SSP) ranged from 18.19 to 39.25%. The stream water quality was acceptable for animal watering and crop irrigation, whereas wetland water would be acceptable for animal watering and would present some challenges for crop irrigation purposes due to the magnesium hazard it poses. The implications for the management of the wetland are discussed.

The protein kinase SlCIPK23 boosts K+ and Na+ uptake in tomato plants

Regulation of root transport systems is essential under fluctuating nutrient supply. In the case of potassium (K⁺ ), HAK/KUP/KT K⁺ transporters and voltage-gated K⁺ channels ensure root K⁺ uptake in a wide range of K⁺ concentrations. In Arabidopsis, the CIPK23/CBL1-9 complex regulates both transporter- and channel-mediated root K⁺ uptake. However, research about K⁺ homeostasis in crops is in demand due to species-specific mechanisms. In the present manuscript, we studied the contribution of the voltage-gated K⁺ channel LKT1 and the protein kinase SlCIPK23 to K⁺ uptake in tomato plants by analysing gene-edited knockout tomato mutant lines, together with two-electrode voltage-clamp experiments in Xenopus oocytes and protein-protein interaction analyses. It is shown that LKT1 is a crucial player in tomato K⁺ nutrition by contributing approximately 50% to root K⁺ uptake under K⁺ -sufficient conditions. Moreover, SlCIPK23 was responsible for approximately 100% of LKT1 and approximately 40% of the SlHAK5 K⁺ transporter activity in planta. Mg⁺² and Na⁺ compensated for K⁺ deficit in tomato roots to a large extent, and the accumulation of Na⁺ was strongly dependent on SlCIPK23 function. The role of CIPK23 in Na⁺ accumulation in tomato roots was not conserved in Arabidopsis, which expands the current set of CIPK23-like protein functions in plants.

Phospholipase Dα1 Acts as a Negative Regulator of High Mg2+-Induced Leaf Senescence in Arabidopsis

Magnesium (Mg2+) is a macronutrient involved in essential cellular processes. Its deficiency or excess is a stress factor for plants, seriously affecting their growth and development and therefore, its accurate regulation is essential. Recently, we discovered that phospholipase Dα1 (PLDα1) activity is vital in the stress response to high-magnesium conditions in Arabidopsis roots. This study shows that PLDα1 acts as a negative regulator of high-Mg2+-induced leaf senescence in Arabidopsis. The level of phosphatidic acid produced by PLDα1 and the amount of PLDα1 in the leaves increase in plants treated with high Mg2+. A knockout mutant of PLDα1 (pldα1-1), exhibits premature leaf senescence under high-Mg2+ conditions. In pldα1-1 plants, higher accumulation of abscisic and jasmonic acid (JA) and impaired magnesium, potassium and phosphate homeostasis were observed under high-Mg2+ conditions. High Mg2+ also led to an increase of starch and proline content in Arabidopsis plants. While the starch content was higher in pldα1-1 plants, proline content was significantly lower in pldα1-1 compared with wild type plants. Our results show that PLDα1 is essential for Arabidopsis plants to cope with the pleiotropic effects of high-Mg2+ stress and delay the leaf senescence.

Freshwater availability status across countries for human and ecosystem needs

Water demand is expected to continue rising to support growing population, particularly in water-stressed countries and regions. Amid competitive water needs for agricultural, domestic, and industrial sectors, water allocations for environmental requirements are critical to ensure the sustainability of the ecosystems. This study takes stock of water availability trends per capita across countries and proposes a water scarcity indicator to quantify the amount of water available for agricultural, domestic, and industrial activities after the needs of freshwater ecosystems (environmental flow requirements, EFR) are ideally fulfilled. The study reveals that by 2050, 87 out of 180 countries will have annual renewable water resources (ARWR) per capita below 1700 m³/year. The number of countries with absolute water scarcity - ARWR per capita below 500 m³/year is projected to increase from 25 in 2015 to 45 by 2050. Population growth is projected to cause a sharp decline in water availability in many low-income and lower-middle-income countries, while economic development will push water use upwards, making the water supply gap more complicated and challenging to address. After the Middle East and North Africa region, Sub-Saharan Africa is expected to become the next hotspot of water scarcity along with several countries from Asia. In response, water-scarce countries need to promote water conservation, water recycling, and reuse; ensure sustainable water resources augmentation via harnessing the potential of unconventional water resources; support productivity enhancement of underperforming land and water resources; and address challenges beyond technical solutions. Pertinent political agenda and associated public policies, supportive institutions, institutional collaborations, and skilled professionals would be the key to ensure sufficient water supply for human use and ecosystems.

Nutritional quality and health risk of pepper fruit as affected by magnesium fertilization

BACKGROUND

Magnesium (Mg) fertilization is a promising practice to improve vegetable yield. However, its impacts on vegetable quality and human health have not been examined. Thus, a field experiment was conducted to investigate the effects of varying Mg fertilization rates on yield and quality of pepper (Capsicum annuum L.) fruit. Furthermore, result of the field experiment was linked to pepper consumption data from the China Health and Nutrition Survey (CHNS) in the disability-adjusted life years (DALYs) framework to evaluate the potential health impact of Mg fertilization for the first time.

RESULTS

Compared to control, Mg fertilization increased the 2-year average pepper yield by 25.6%, whereas there was no significant yield improvement when Mg rates exceeded 112.5 kg MgO ha^-1 . Magnesium application increased concentrations of Mg and capsaicinoids, decreased those of calcium (Ca), zinc (Zn) and vitamin C (Vc), and had no effect on potassium (K) and iron (Fe) in pepper fruit. As a result, Mg fertilization decreased the comprehensive nutrition level of pepper by 16.6%. Furthermore, the current health burden of the Chinese adult population associated with pepper consumption is estimated at 21.3 million DALYs per year, with the risk being increased by 5.40 DALYs for per megagram of Mg fertilizer application. Increasing health risk was mainly attributed to decreasing concentrations of Ca and Vc in pepper fruit, though the increased Mg intakes offset the impact of 1.74% to 14.4%.

CONCLUSION

Magnesium fertilization significantly improved the yield but reduced nutritional quality of pepper fruit, and increased human health risks associated with consumption of pepper fruit. © 2020 Society of Chemical Industry.

Optimizing water resources allocation and soil salinity control for supporting agricultural and environmental sustainable development in Central Asia

In this study, a stochastic-fuzzy-based fractional programming (SFFP) method is advanced for optimizing water-resources allocation and soil-salinity control under uncertainty. The developed method can address ratio objective optimization problems of complex system in association with stochastic and fuzzy uncertainties, which can help gain in-depth analysis of the interrelationships between marginal effectiveness and system reliability. Then, SFFP is applied to an irrigation region in the lower reach of Amu Darya River basin, where linear crop yield-salinity functions and salt-leaching functions are introduced into the modeling formulation for reflecting the complicated interactions among water resources, soil salinity, arable land, and electricity supply. Solutions under 96 scenarios related to different irrigation efficiencies, water availabilities, and electricity supplies have been obtained. Our findings are: i) increased water availability, electricity supply, and irrigation efficiency result in high marginal benefit; ii) irrigation efficiency is the key factor influencing water allocation patterns for crop irrigation and salt-leaching, promotion of which can facilitate mitigating economic and environmental losses in the water-deficit and soil-salinized region; iii) leaching water allocation patterns for soil-salinity washing is related to salinity characters of crops and regions, and boosting drought- and salt-tolerance crop can be effective in adaption to risks of water scarcity and land salinization. Compared to the conventional approaches, SFFP can generate more flexible alternatives and achieve higher marginal effectiveness. These findings can provide effective decision support to identify desired water management strategies under multiple uncertainties for supporting agricultural sustainability in arid regions.

Effect of elevated magnesium sulfate on two riparian tree species potentially impacted by mine site contamination

Globally, mining activities have been responsible for the contamination of soils, surface water and groundwater. Following mine closure, a key issue is the management of leachate from waste rock accumulated during the lifetime of the mine. At Ranger Uranium Mine in northern Australia, magnesium sulfate (MgSO₄) leaching from waste rock has been identified as a potentially significant surface and groundwater contaminant which may have adverse affects on catchment biota. The primary objective of this study was to determine the effect of elevated levels of MgSO₄ on two riparian trees; Melaleuca viridiflora and Alphitonia excelsa. We found that tolerance to MgSO₄ was species-specific. M. viridiflora was tolerant to high concentrations of MgSO₄ (15,300 mg l^-1), with foliar concentrations of ions suggesting plants regulate uptake. In contrast, A. excelsa was sensitive to elevated concentrations of MgSO₄ (960 mg l^-1), exhibiting reduced plant vigour and growth. This information improves our understanding of the toxicity of MgSO₄ as a mine contaminant and highlights the need for rehabililitation planning to mitigate impacts on some tree species of this region.

Impact of Integrated and Conventional Plant Production on Selected Soil Parameters in Carrot Production

Currently, the level of efficiency of an effective agricultural production process is determined by how it reduces natural environmental hazards caused by various types of technologies and means of agricultural production. Compared to conventional production, the aim of integrated agricultural cultivation on commercial farms is to maximize yields while minimizing costs resulting from the limited use of chemical and mineral means of production. As a result, the factor determining the level of obtained yield is the soil’s richness in nutrients. The purpose of this study was to conduct a comparative analysis of soil richness, depending on the production system appropriate for a given farm. The analysis was conducted for two comparative groups of farms with an integrated and conventional production system. The farms included in the research belonged to two groups of agricultural producers and specialized in carrot production.

Current states and challenges of salt-affected soil remediation by cyanobacteria

Natural and human activities lead to soil degradation and soil salinization. The decrease of farmlands threatens food security. There are approximately 1 billion ha salt-affected soils all over of world, which can be made available resources after chemical, physical and biological remediation. Nostoc, Anabaena and other cyanobacterial species have outstanding capabilities, such as the ability to fix nitrogen from the air, produce an extracellular matrix and produce compatible solutes. The remediation of salt-affected soil is a complex and difficult task. During the past years, much new research has been conducted that shows that cyanobacteria are effective for salt-affected soil remediation in laboratory studies and field trials. The related mechanisms for both salt tolerance and salt-affected soil remediation were also evaluated from the perspective of biochemistry, molecular biology and systems biology. The effect of cyanobacteria on salt-affected soil is related to nitrogen fixation and other mechanisms. There are complicated interactions among cyanobacteria, bacteria, fungi and the soil. The interaction between cyanobacteria and salt-tolerant plants should be considered if the cyanobacterium is utilized to improve the soil fertility in addition to performing soil remediation. It is critical to re-establish the micro-ecology in salt-affected soils and improve the salt affected soil remediation efficiency. The first challenge is the selection of suitable cyanobacterial strain. The co-culture of cyanobacteria and bacteria is also potential approach. The cultivation of cyanobacteria on a large scale should be optimized to improve productivity and decrease cost. The development of bio-remediating agents for salt-affected soil remediation also relies on other technical problems, such as harvesting and contamination control. The application of cyanobacteria in salt-affected soil remediation will reconstruct green agriculture and promote the sustainable development of human society.