Aqueous Calcium Research Articles

Examining the Hydration Behavior of Aqueous Calcium Chloride (CaCl2) Solution via Atomistic Simulations

Equilibrium molecular dynamics simulations are performed to examine the hydration behavior of Ca2+ and Cl− across a wide range of salt concentrations (from 1 wt.% to 60 wt.% CaCl2) in an aqueous solution. The predicted radial distribution functions (RDFs) and coordination numbers (CNs) of Ca2+–water, Cl−–water, and Ca2+–Cl− agree with the previous studies conducted at concentrations below the solubility limit at room temperature. The hydration limit of aqueous calcium chloride solution is identified at 10 wt.% CaCl2 as the CNs remain constant below it. Beyond the bulk solubility limit ~44.7 wt.% CaCl2, a noticeable decrease in the CN of Cl− and water is recorded, implying the saturation of the solution. The solvating water molecules decrease with increasing salt concentration, which can be attributed to the growth in the number of ion pairs.

Covalent Organic Framework with Multiple Redox Active Sites for High-Performance Aqueous Calcium Ion Batteries.

Organic materials are promising for cation storage in calcium ion batteries (CIBs). However, the high solubility of organic materials in an electrolyte and low electronic conductivity remain the key challenges for high-performance CIBs. Herein, a nitrogen-rich covalent organic framework with multiple carbonyls (TB-COF) is designed as an aqueous anode to address those obstacles. TB-COF demonstrates a high reversible capacity of 253 mAh g-1 at 1.0 A g-1 and long cycle life (0.01% capacity decay per cycle at 5 A g-1 after 3000 cycles). The redox mechanism of Ca2+/H+ co-intercalated in COF and chelating with C═O and C═N active sites is validated. In addition, a novel C═C active site was identified for Ca2+ ion storage. Both computational and empirical results reveal that per TB-COF repetitive unit, up to nine Ca2+ ions are stored after three staggered intercalation steps, involving three distinct Ca2+ ion storage sites. Finally, the evolution process of radical intermediates further elucidates the C═C reaction mechanism.

Enhanced injectability of aqueous β-tricalcium phosphate suspensions through PAA incorporation, gelling and preshearing

The major shortcoming of aqueous calcium phosphate suspensions used in biomedical applications is their unstable flow during delivery by mechanical means. In this study, microstructural changes and the resulting flow instabilities of aqueous β-TCP suspensions are demonstrated under both pressure-induced and drag-induced flow regimes and then remedied with the incorporation and subsequent gelling and preshearing of Carbopol 940, a biocompatible hydrogel. Mixing and dispersion of calcium phosphate particles into the hydrogel matrix was not efficient under simple agitation conditions. Swelling of the polymer chains was induced at approximately pH = 9.0 by water and particle intrusion within the opened-up coil structure due to deprotonation of the carboxylic acid groups by NaOH. As a result the composite material underwent a rapid viscoplastic transition into a doughy state which was not amenable to further processing without preshearing. Manual kneading converted the material into viscous state and enhanced the flow behavior significantly. Preshearing and probing the microstructure by mechanical spectrometer revealed multiple microstructural mechanisms responsible for the observed stable flow behavior, including improved dispersion of the particles, attrition of the polymeric network into microgel domains, enhanced adhesion and lubrication between the solid and liquid phase, crosslinking of the polymeric network. The net effect of these probable mechanisms was stiffening of the composite matrix, mobilization of solid particles and a marked enhancement in the stability of pressure-induced flow. The resistance of the material to liquid phase migration and its ability to undergo wall-slip and relax under stress were confirmed by simultaneous capillary rheometry and thermogravimetric analyses. The processing method enables improvements in the delivery of this composite material for injection and direct ink writing of scaffolds.

Freshwater fishes maintain multi-trait phenotypic stability across an environmental gradient in aqueous calcium.

Reductions in a limiting nutrient might be expected to necessitate compromises in the functional traits that depend on thatnutrient; yet populations existing in locations with low levels of such nutrients often do not show the expected degradation of functional traits. Indeed, logperch (Percina caprodes), pumpkinseed sunfish (Lepomis gibbosus) and yellow perch (Perca flavescens) residing in low-calcium water in the Upper St. Lawrence River were all previously found to maintain levels of scale calcium comparable to those of conspecific populations in high-calcium water. Yet it remains possible that the maintenance of one functional trait (i.e., scale calcium)under nutrient-limited (i.e., low calcium)conditions could come at the expense of maintaining other functional traits that depend on the same nutrient. The present study therefore examines other calcium-dependent traits, specifically skeletal element sizes and bone densities in the same fish species in the same area. Using radiographs of 101 fish from the three species across four locations (two in high-calcium water and two in low-calcium water), this new work documents multi-trait "homeostasis" along the gradient of water calcium. That is, no effect of calcium regime (low-calcium vs. high-calcium) was detected on any of the measured variables. Further, effect sizes for the skeletal traits were very low - lower even than effect sizes previously documented for scale calcium. These results thus show that native fishes maintain phenotypic stability across a suite of functional traits linked to calcium regulation, perhaps pointing to an "organismal-level homeostasis" scenario rather than a "trait-level homeostasis" scenario.

Microfluidic dual picoinjection based encapsulation of hemoglobin in alginate microcapsules reinforced by a poly(L-lysine)-g-poly(ethylene glycol).

Hemoglobin (Hb) encapsulation inside polysaccharide hydrogels has been considered a possible red blood cell (RBC) surrogate in transfusiology. Here we report on the microfluidic dual picoinjection assisted synthesis of Hb encapsulated alginate-poly(L-lysine)-g-poly(ethylene glycol) beads. This process is realized by the on-chip injections of blended Hb alginate solutions in emulsified aqueous calcium chloride (CaCl2) droplets followed by a subsequent injection of an aqueous PLL-g-PEG into each emulsified aqueous droplet. The proposed fabrication approach was realized using a flow-focusing and two picoinjection sites in a single PDMS device. Aqueous CaCl2 solution was emulsified and infused with Hb-alginate solution as the squeezed droplet passed through the first picoinjection site. The injection of PLL-g-PEG to reinforce the microgel and minimize the protein leaching was realized in the second picoinjection site located downstream from the first in the same microfluidic channel. In this process, monodisperse Hb-alginate-PLL-g-PEG particles with a diameter around the size of RBCs (9 μm) were obtained with around 80% of the 7.5 mg ml-1 Hb included in the injected aqueous alginate retaining in the obtained microparticles. Microparticles with Hb loading (32.8 pg per bead) and retention (28.8 pg per bead) over a week of storage at 4 °C are in accordance with the average amount of Hb per RBC. The Hb-alginate-PLL-g-PEG microbeads fabricated in the size range of RBCs are significant for further exploration.

Enhancing growth and production of carrot plant by spraying aqueous barley sprouts extract, trehalose, and calcium

This research was implemented at vegetable field of the College of Agricultural Engineering Sciences - University of Baghdad during fall seasons, 2018 and 2019. The experiment was conducted using factorial within Randomized Complete Block Design arrangement with three factors and replicates (3X3X2). The aqueous barley sprouts extract (B0, B1) (0, 100 g.L-1) represented the first factor. Trehalose (T0, T1, T2) (0, 50, 75 mmole. L-1) represented the second factor. Calcium (C0, C1, C2) (0, 1, 2 ml.L-1) represented the third factor. The research objectives are assessing the impact of the mentioned factors and their interaction on carrot growth and production. Results showed the superiority of three ways interaction treatment B1T2C1 in producing significant increases nitrogen percent in leaves (2.857, 2.9%), roots (1.273, 1.283%), and carrot production (161.6, 159 ton. ha-1) for both seasons respectively in compare with control treatment B0T0C0.

Substrate dependent structural variations of biomimetic carbonated hydroxyapatite deposited on glass, Ti and sputtered ZnO thin films

The formation of hydroxyapatite films on glass, titanium (Ti), and sputtered ZnO is attempted to understand the crystal growth and its manipulation by substrates of a different kind. The substrates used are commercially available glass and polished Ti (99.9% purity), as-deposited, and annealed nanostructured ZnO thin films developed by pulsed DC magnetron sputtering, which are immersed in the calcifying solution for the nucleation and growth of the hydroxyapatite. The calcifying solution is obtained by mixing equal volumes of aqueous calcium (5 mM) and carbonate-containing phosphate (3 mM) solutions prepared at 37 °C and with a pH of ~7.4. X-ray diffraction, Raman spectroscopy, and Field Emission Scanning & Transmission Electron Microscopy (FESEM & FETEM) analyses reveal that the structure and morphology of the hydroxyapatite films are dependent on the growth duration, substrate type, and even on the post-deposition annealing of the sputtered ZnO substrates. The Ti substrate induces greater crystallinity in hydroxyapatite, whereas sputtered ZnO thin films cause a significantly reduced crystallinity. Moreover, the thicknesses of HAp are exacerbated by increasing deposition time irrespective of the substrate. FETEM analyses reveal the formation of needle-shaped hydroxyapatite nanocrystals grown on Ti and ZnO thin films. Thicker needle-shaped hydroxyapatite nanocrystals are observed when grown on Ti (~6–12 nm) than ZnO thin films (~4–6 nm). Further, the amorphous calcium phosphate phase coexists with nanocrystalline hydroxyapatite when ZnO thin films deposited at 50 and 70 W sputtering powers are used as the substrates. Both charged surfaces and the supersaturation of the calcifying solution impact the nucleation of hydroxyapatite onto substrates.

Repeatability of B1 + inhomogeneity correction of volumetric (3D) glutamate CEST via High-permittivity dielectric padding at 7T.

Ultra-high field MR imaging lacks B1 + inhomogeneity due to shorter RF wavelengths used at higher field strengths compared to human anatomy. CEST techniques tend to be highly susceptible to B1 + inhomogeneities due to a high and uniform B1 + field being necessary to create the endogenous contrast. High-permittivity dielectric pads have seen increasing usage in MR imaging due to their ability to tailor the spatial distribution of the B1 + field produced. The purpose of this work is to demonstrate that dielectric materials can be used to improve glutamate weighted CEST (gluCEST) at 7T. GluCEST images were acquired on a 7T system on six healthy volunteers. Aqueous calcium titanate pads, with a permittivity of approximately 110, were placed on either side in the subject's head near the temporal lobes. A post-processing correction algorithm was implemented in combination with dielectric padding to compare contrast improvement. Tissue segmentation was performed to assess the effect of dielectric pads on gray and white matter separately. GluCEST images demonstrated contrast enhancement in the lateral temporal lobe regions with dielectric pad placement. Tissue segmentation analysis showed an increase in correction effectiveness within the gray matter tissue compared to white matter tissue. Statistical testing suggested a significant difference in gluCEST contrast when pads were used and showed a difference in the gray matter tissue segment. The use of dielectric pads improved the B1 + field homogeneity and enhanced gluCEST contrast for all subjects when compared to data that did not incorporate padding.

Reactive precipitation of vaterite calcium carbonate microspheres in supercritical carbon dioxide-water dispersion by microfluidics

Vaterite, a polymorphic form of precipitated calcium carbonate, is an interesting material for various applications such as formulation of drug delivery systems due to its nanoporous structure. One of the carbonation processes to obtain nanostructured microspheres of vaterite consists in mixing an aqueous calcium phase with a supercritical CO2 phase, resulting in a heterogeneous dispersion. In this study, a continuous microfluidic method has been evaluated to produce monodisperse porous vaterite microparticles. A high-pressure microfluidic set-up has been developed, revealing that the dimensions and the dispersity of the CaCO3 particles are not affected by pressure but can be decreased by increasing the flow rate of the scCO2 and aqueous phases or addition of polymers in the aqueous phase. These observations were shown not to be related to the degree of dispersion of each phase within the microfluidic channel but to the interaction of the polymer with the CaCO3 particles and to the depressurization step at the end of the channel.

The Effect of pH, Metal Ions, and Insoluble Solids on the Production of Fumarate and Malate by Rhizopus delemar in the Presence of CaCO3

Calcium carbonate has been extensively used as a neutralising agent in acid-forming microbial processes. The effect of increasing calcium carbonate concentrations on Rhizopus delemar has not been previously investigated. In this study, an evaluation of fumaric acid (FA) and malic acid (MA) production was conducted at three CaCO3 concentrations in shake flask cultivations. Increased CaCO3 concentrations resulted in the co-production of FA and MA in the first 55 h of the fermentation (regime 1), and the subsequent depletion of FA thereafter (regime 2). Three factors were highlighted as likely causes of this response: insoluble solids, metal ion concentrations, and pH. Further shake flask cultivations as well as a continuous fermentation with immobilised R. delemar were used to explore the effect of the three factors on regime 1 and 2. Insoluble solids were found to have no effect on the response in either regime 1 or 2. Increasing the aqueous calcium ion concentrations to 10 g L−1 resulted in a three-fold increase in MA titres (regime 1). Moreover, an increase in pH above 7 was associated with a drop in FA concentrations in regime 2. Further tests established that this was due to the hydration of FA to MA, influenced by high pH conditions (7 or higher), nitrogen starvation, and glucose depletion. Anaerobic conditions were also found to significantly improve the hydration process. This study presents the first investigation in which the production of FA followed by in situ hydration of FA to MA with R. delemar has been achieved.

Blood calcium dynamics in cows receiving an aqueous calcium suspension for voluntary consumption or a calcium bolus following parturition.

The form of oral calcium (Ca) supplement and the Ca source influence Ca absorption dynamics resulting in different postpartum calcemia. The objective of this study was to investigate whether an oral Ca supplement (mainly CaCO3) offered for voluntary consumption would maintain or increase postpartum blood Ca to the same degree as a Ca bolus (mainly CaCl2) providing an equivalent dose of a Ca. A total of 72 Holstein cows were blocked by expected parturition date and parity. Within each block of 3 animals, cows were randomly assigned to one of three treatments, including an oral Ca supplement offered for voluntary consumption (Ca-drink, n = 23), an oral Ca bolus (Ca-bolus, n = 24), or an untreated group (CON, n = 25). Treatments were administered once within 15 min postpartum. The Ca-drink provided 45 g of Ca (CaCO3 source) and was mixed in 20 L of lukewarm water and offered to cows for 30 min. The Ca-bolus provided 43 g of Ca (71% from CaCl2 and 29% from CaSO4) and was administered once. Both Ca-bolus and CON cows received 20-l of lukewarm water at parturition to standardize the volume of fluids (Ca-drink or 20-l lukewarm water) offered at parturition. Dairy cows offered Ca-drink had a 28% higher fluid consumption than Ca-bolus and CON cows. Milk yield and milk composition expressed in percentage protein, fat, lactose, and urea did not differ, whilst there was a small but significant increase in DMI in cows receiving the Ca-drink compared to CON, while Ca-bolus did not differ from other groups. This was consistent with reduced BW losses between week 1 and 3 in cows receiving the Ca-drink suspension. Treatment by time interactions were present for blood Ca, glucose, and urea concentrations. Blood Ca was relatively stable in Ca-drink cows, while higher fluctuations were observed in Ca-bolus cows. In Ca-bolus cows, blood Ca increased from 15 min to 6 h, decreased from 6 to 24 h, and finally increased again from 24 to 48 h. At 24 h post administration, blood Ca was greater in cows receiving the Ca-drink than cows receiving the Ca-bolus. Blood glucose was greater in Ca-bolus cows at 15 min after treatment administration compared with Ca-bolus and CON, while blood urea was higher in CON than Ca-drink and Ca-bolus throughout the sampling period. These results indicate that voluntary oral Ca resulted in a relatively stable calcemia, whereas higher fluctuations were observed in cows receiving the Ca-bolus. Due to a lack of differences between Ca-drink and Ca-bolus compared with CON, it is not possible to conclude regarding the efficacy in maintaining postpartum blood Ca.

Surface modification of Trema orientalis wood biochar using natural coconut vinegar and its potential to remove aqueous calcium ions: column and batch studies

Recent investigations have revealed the harmful health effects of elevated calcium levels in drinking water. Chemically activated biochar is the most popular option for low-cost cation adsorption. However, most of these chemicals are hardly available for rural communities, corrosive, and difficult to handle by unskilled personnel. This study aimed to determine the ability of natural coconut vinegar, a common mild acid, to activate Trema orientalis wood biochar pyrolyzed at 300˚C (BC) as a facile, safe, and low-cost approach for aqueous calcium ion (Ca2+) removal. Column tests showed a two-fold increase of Ca2+ adsorption capacity and a ten-fold increase of Ca2+ retaining capacity of BC after activation with vinegar. The isotherm results were well correlated with the Langmuir model. The maximum Langmuir adsorption of the activated biochar (BC-A) was 9.96 mg/g. Ca2+ amount was determined using flame photometry. EDX analysis showed that the O/C ratio of BC increased from 0.07 to 0.13 after activation. FTIR and wettability studies showed increased oxygenated functional groups on the BC-A surface. The authors suggest a possible acid-catalyzed hydration of the C-O-C bridges of the biochar, introducing new hydroxyl/carbonyl/ester/carboxylic/lactone groups to the biochar surface due to the vinegar activation, enhancing Ca2+ adsorption through chemisorption.

Reversible photodissipation of composite photochromic azobenzene-alginate supramolecular hydrogels.

Supramolecular smart materials can quickly elicit macroscopic changes upon external stimulation. Here we report that an azobenzene-containing cyclic dipeptide can form composite supramolecular hydrogels with alginate based on the charge complementarity, at lower loading than the critical gelation concentrations of either component. The gels can reversibly dissipate to fluids with UV light. They can also encapsulate and photorelease fluorescent cargo. Upon treatment of the gels with aqueous calcium salts, the alginate component is permanently cross-linked and the photochromic component is solubilized.

Amorphous and crystalline CaCO3 phase transformation at high solid/liquid ratio – Insight to a novel binder system

The transformation reactions in aqueous calcium carbonate systems are relevant for biomineralization processes, functionalised materials design and recently for the potential development of inorganic binders. The so-called ‘calcium carbonate cements’ are obtained by mixing amorphous (ACC) and crystalline CaCO3 (herein the anhydrous minerals calcite, aragonite and vaterite) with low amounts of water. The mechanisms behind the setting and hardening of these binders are still not clear. In the present study, the dissolution and precipitation reactions in low water ACC systems with and without crystalline CaCO3 have been investigated by in-situ techniques, Raman spectroscopy and optical pH measurements, coupled with reaction time resolved mineralogical and chemical analyses of solid and liquid samples. The results clearly indicate the presence of initial crystalline CaCO3 polymorphs to control the reactions kinetics and the resulting individual microstructure. Vaterite, with a considerably higher surface area than calcite and aragonite, produces more bonded and connected material. In the ACC-vaterite system the transformation of vaterite to calcite takes places in two dissolution-precipitation stages, accompanied by typical pH in- and decreases. Time-resolved analyses and hydrochemical modelling clearly reveal the solid transformation behaviour to be governed by the presence/absence of Mg2+ in the solution and the impurities, such as Na+, liberated from the educts to the reactive solution. The control and adjustment of the identified influencing parameters could allow for promising future development of CaCO3-based binders.

The effect of saturation Methods on natural gypsum rocks

When the gypsum rock is exposed to the relative humidity in a closed environment for a continuous period, the result is an increase in the weight of these rocks after the passage of the first 24 hours, and there is no effect on the percentage of gypsum that the rocks contain, as the weight increase occurred at the same time for the different gypsum ratios. For rocks submerged in potable water and located within a humid environment, most of these rocks witnessed weight gain, with some exhibiting dissolving behavior. As for the gypsum rocks submerged with water saturated with aqueous calcium sulfate salt, they witnessed weight gain without any solubility. It is worth noting the important effect that relative humidity plays in the atmosphere at high levels, as it stimulated the saturation property to cover and overcome the famous property of gypsum rocks, which is the melting at high humidity.

Enhancement of dissolution profile of poorly aqueous soluble atorvastatin calcium by binary and ternary solid dispersion techniques

Atorvastatin calcium (ATV) is an HMG-CoA (3-hydroxy-3-methylglutaryl coenzyme A) reductase inhibitor commonly known as a cholesterol-lowering agent. As a poorly water-soluble drug its absolute bioavailability is very low. To increase the water solubility as well as oral bioavailability, different hydrophilic carriers were used in different ratios (1:0.5, 1:1 and 1:2) to prepare reproducible binary and ternary solid dispersion formulations of ATV by simple physical mixing (PM) and fusion or melting technique. In vitro dissolution studies results revealed that in all cases, the cumulative percent drug release from ATV ternary SD formulations were greater than binary formulations, some marketed products and pure ATV powder. The order of the carriers in enhancing the drug release was found as kollidon 90F > pregelatinized starch > lutrol> kollidon 12F (99.1%, 98.8%, 96% and 95% respectively) for ternary SD formulations whereas pure ATV powder and marketed products showed cumulative percentage release 70.8%, 68.9% (B1) and 73.1% (B2), respectively. The best-out performed ternary SD formulation ATV:Kollidon 90 F (1:2) were further characterized using FT-IR and SEM. SEM analyses indicated conversion of crystal drug to amorphous form and FT-IR data suggested that little or no interaction between the drug and polymer. Bangladesh J. Sci. Ind. Res.56(3), 165-176, 2021

Study the antibacterial activity of hydroxyapatite- nano silver coating on titanium substrate

The most often encountered laborer as a consequence prosthetic titanium (Ti) implant, failure is infection. Implant surfaces that are antibacterial due to nanoscale titanium modifications appear as an appealing peri-implantitis prevention approach. In this study, composite coating preparation) and antimicrobial properties (hydroxyapatite, hydroxyapatite/nanosilver) on titanium substrate by Micro Arc Oxidation(MAO). Preparation the electrolyte in the electrolyte, cell was an aqueous calcium acetate monohydrate solution of 0.1.3 mol/L ((CH3-COO)2..Ca.H2O) and 0.0.6 mol/l sodium biphosphate dihydrate (NaH2PO4.2H2O) in distilled, water, pH of electrolyte was 2.3 after that, nano silver was added to the electrolyte in different proportions (0.5, 1, 1.5, 2) g/L, and the coating times were also different (30, 45, 60) sec at a constant voltage 200 V. To observe the morphology a AFM test was done and must be known if there are bacteria present or not on Ti substrate and composite coating (HA, HA/nAg) samples by the antibacterial test. In addition, the surface, roughness was measured to study the extent of bacterial adhesion. The result of the tests for coated samples better compared with the uncoated sample. As a result, in the antibacterial test, composite coatings (HA, HA/nAg) were found to be more effective than Ti samples in destroying bacteria that had formed on their surfaces.

Superior performance of calcium birnessite by electrochemical conversion as cathode for aqueous calcium ion battery

Aqueous Ca2+ ion battery (ACIB) is known as a promising candidate for large-scale grid storage due to its low cost, high performance and safety. However, the large ion size of Ca2+ (1.00 Å) limits the ability of Ca2+ to (de)intercalate in the host structure. In this report, hierarchical Ca-birnessite with ultrathin and intertwined nanosheets structure converted from Mn3O4 nanowall arrays (NWAs) was successfully fabricated via an electro-conversion method, showing a fast surface faraday reaction as well as favorable Ca2+ storage kinetics and properties. When tested in ACIB, the electro-converted Ca-birnessite (ECCB) electrode exhibits an excellent specific capacity of 175 mAh g − 1 at 0.1 A g − 1, high rate performance (89 mAh g − 1 at 2 A g − 1) and long cycling stability (83.2% retention after 2000 cycles at 1 A g − 1). A kinetic analysis indicates that the reaction mechanism is dominated by surface-limited capacitance. Moreover, we constructed a balanced 1.9 V full cell of ECCB//PI, which delivers a reversible capacity of 42.1 mAh g − 1 at 0.2 A g − 1 and an energy density of 30.56 Wh kg−1 at power density of 143.4 W kg−1. Furthermore, the full cell shows an excellent cycling stability with almost no capacity decay after 1500 cycles at 1 A g − 1. This work offers a new strategy for designing high performance cathodes for aqueous calcium ion battery.

Development and performance evaluation of a passive solar liquid desiccant regenerator

Vapour Compression Refrigeration (VCR) cycle that consumes electrical energy dominates airconditioning market today. Production of electrical energy is generally associated with fossil fuel consumption, emission of greenhouse gases and pollution. Air conditioning systems that use waste or renewable energy sources should be investigated as an alternative solution. Liquid desiccant-based air conditioning system (LDAC) is one such a potential candidate. The heat from a solar thermal collector can be supplied to the regeneration process of LDAC systems. A novel solar collector with the goal of no electrical power consumption, simplicity, low cost, and high efficiency was developed in this work for the regeneration of LD (aqueous calcium chloride solution). Condensate output in this device used for water desalination was 3.7 kg/m2, which is comparable with the best in the literature. An area of 7.5 m2 of such a device with no parasitic power would be needed per kW of latent cooling.

Phenotypic stability in scalar calcium of freshwater fish across a wide range of aqueous calcium availability in nature.

Spatial environmental gradients can promote adaptive differences among conspecific populations as a result of local adaptation or phenotypic plasticity. Such divergence can be opposed by various constraints, including gene flow, limited genetic variation, temporal fluctuations, or developmental constraints. We focus on the constraint that can be imposed when some populations are found in locations characterized by low levels of an essential nutrient. We use scales of wild fish to investigate phenotypic effects of spatial variation in a potentially limiting nutrient—calcium. If scale calcium (we use “scalar” calcium for consistency with the physiology literature) simply reflects environmental calcium availability, we expect higher levels of scalar calcium in fish from calcium‐rich water, compared to fish from calcium‐poor water. To consider this “passive response” scenario, we analyzed scalar calcium concentrations from three native fish species (Lepomis gibbosus, Percina caprodes, and Perca flavescens) collected at multiple sites across a dissolved calcium gradient in the Upper St. Lawrence River. Contradicting the “passive response" scenario, we did not detect strong or consistent relationships between scalar calcium and water calcium. Instead, for a given proportional increase in water calcium across the wide environmental gradient, the corresponding proportional change in scalar calcium was much smaller. We thus favor the alternative “active homeostasis” scenario, wherein fish from calcium‐poor water are better able to uptake, mobilize, and deposit calcium than are fish from calcium‐rich water. We further highlight the importance of studying functional traits, such as scales, in their natural setting as opposed to only laboratory studies.