Hydrological budget,carbon sources and biogeochemical processes in Lac Pavin (France): Constraints from δO of water and δC of dissolved inorganic carbon

Lac Pavin (French Massif Central) is a permanently stratified lake: the upper water layers (mixolimnion, from 0 to 60 m depth) are affected by seasonal overturns, whereas the bottom water layers (monimolimnion, from 60 to 90 m depth) remain isolated and are never mixed. Hence, they are capable of storing important quantities of dissolved gases, mainly CO₂. With the aim of better constraining the water balance and of gaining new insights into the carbon cycle of Lac Pavin, an isotopic approach is used. The δ¹⁸OH₂O$\delta {}^{18}{\text{O}}_{{\text{H}}_2\text{O}}$ profiles lead the authors to give a new evaluation of the evaporation flow rate (8 L s⁻¹), and to propose and characterize two sub-surface springs. The sub-surface spring located at the bottom of the lake can be deduced from the 1% isotopic difference between the upper water layers (mean δ¹⁸OH₂O$\delta {}^{18}{\text{O}}_{{\text{H}}_2\text{O}}$ value: −7.3‰) and the bottom water layers (δ¹⁸OH₂O=-8.4‰$\delta {}^{18}{\text{O}}_{{\text{H}}_2\text{O}}=-8.4‰$). It is argued that this sub-surface spring has isotopic and chemical characteristics similar to those of the magmatic CO₂-rich spring (i.e. Fontaine Goyon, δ¹⁸OH₂O=-9.4‰$\delta {}^{18}{\text{O}}_{{\text{H}}_2\text{O}}=-9.4‰$), and we calculate its flow rate of 1.6 L s⁻¹. The second sub-surface spring is located around 45 m depth, with a composition close to those of the water surface streams (δ¹⁸OH₂O<-7.6‰$\delta {}^{18}{\text{O}}_{{\text{H}}_2\text{O}}<-7.6‰$).     

The stable isotopic composition (Cl/Cl) of dissolved chloride in rainwater

The stable isotopic composition of dissolved Cl^-${\text{Cl}}^{-}$ in rainwater was measured from a coastal and an interior location in eastern Canada. At the interior Bonner Lake, Ontario, site the δ³⁷Cl values of dissolved Cl^-${\text{Cl}}^{-}$ in precipitation ranged from −3.5‰ to −1.2‰ (SMOC) with an amount-weighted annual average of −2.3‰. At the coastal site, Bay D’Espoir, Newfoundland, δ³⁷Cl values of dissolved Cl^-${\text{Cl}}^{-}$ values ranged from −3.1‰ to 0.0‰ with an amount-weighted annual average of −1.3‰. These negative δ³⁷Cl values provide evidence that atmospheric HCl is ³⁷Cl depleted, presumably from acidification of sea-salt aerosols. Accordingly, dissolved Cl^-${\text{Cl}}^{-}$ in the headwaters of two montane rivers in Western Canada had similarly depleted δ³⁷Cl values. These results have implications to the interpretation of the isotopic compositions of dissolved Cl^-${\text{Cl}}^{-}$ in surface waters, formation fluids, and groundwaters.     

Surface phase transformations,surface complexation and solubilities of hydroxyapatite in the absence/presence of Cd(II) and EDTA

The removal of Cd from aqueous solutions by hydroxyapatite (HAP) was investigated with and without EDTA being present. Batch experiments were carried out using synthetic hydroxyapatite with Ca/P 1.57 and a specific surface area of 37.5 m²/g in the pH range 4–9 (25 °C; 0.1 M KNO₃). The surface composition of the solid phases were analysed by X-ray Photoelectron Spectroscopy (XPS). The surface layer of HAP was found to undergo a phase transformation with a (Ca + Cd)/P atomic ratio of 1.4 and the involvement of an ion exchange process (Ca²⁺ ↔ Cd²⁺). The amount of Cd removed from the solution increased with increasing pH, reaching ≈100% at pH 9. In the presence of EDTA Cd removal was reduced due to the formation of [CdEDTA]²⁻ in solution. The solubility of HAP increases in the presence of EDTA at pH values above 5, mainly due to the formation of [CaEDTA]²⁻. In contrast to this, the solubility was found to decrease in the presence of Cd²⁺ and CdEDTA²⁻. Using XPS the formation of a Cd-enriched HAP surface was found, which was interpreted as the formation of a solid solution of the general composition: Ca_8.4-xCd_x(HPO_4)1.6(PO_4)4.4(OH_)0.4${\text{Ca}}_{8.4-x}{\text{Cd}}_x({\text{HPO}}_4{)}_{1.6}({\text{PO}}_4{)}_{4.4}(\text{OH}{)}_{0.4}$.     

Geochimie et teneurs isotopiques des systèmes saisonniers de dissolution de la calcite dans un sol sur craie

In a soil developed on the Cretaceous chalk of the Eastern Paris basin, calcite dissolution begins at the surface. The soil water is rapidly saturated in calcite. Calcite dissolution follows two different pathways according to seasonal pedoclimatic conditions.During winter: the soil is only partly saturated in water and the CO₂ partial pressure is low (Ca 10^?3 atm.). As a consequence total inorganic dissolved carbon (TIDC) is a hundred times the carbon content of the gaseous phase. Equilibrium is usually observed between the two phases. It is a closed system. The measured carbon 14 activity (87,5%) and ¹³C content ($\text{δ}{}_{\mathrm{tidc}}{}^{13}\text{C = ?12,2\%0}$) of the drainage water are very close to theoretical values calculated for an ideal mixing system between gaseous and mineral phases (respectively characterized by the following isotopic values: $\text{δ}{}_{\mathrm{G}}{}^{13}\text{C = ?21,5\%0}$; $\text{A}{}_{\mathrm{G}}{}^{14}\text{C = 118\%}$; $\text{δ}{}_{\mathrm{M}}{}^{13}\text{C = +2,9\%0}$; $\text{A}{}_{\mathrm{M}}{}^{14}\text{C = 28\%}$).During spring and summer: the soil moisture decreases, the input of biogenic CO₂ induces an increase of the soil CO₂ partial pressure (Ca from 3.10^?3 atm to 7.10^?3 atm). The carbon content of the gaseous phase is higher by an order of magnitude compared to winter conditions. Therefore the aqueous phase is undersaturated in CO₂ with respect to the latter. This disequilibrium occurs as a result of unbalanced rates of CO₂ dissolution and CO₂ effusion toward atmosphère. It is an open system. The carbon isotopic ratio of the aqueous phase is regulated by that of the gaseous phase, as demonstrated by the agreement between measured and calculated isotopic compositions (respectively δ_{L mes} = from ?9,4%0 to ?11,5%0, δ_{l calc} = from ?9,8%0 to ?13,9%0 A_{L mes} = 119%, A_{L calc} = from 119% to 125%).The solutions originating from both systems (open and closed) move downwards without significant mixing together. It has also been observed that no significant variation of the TIDC isotopic composition occurs during precipitation of secondary calcite.     

Settling velocities of particulate systems, 3. Power series expansion for the drag coefficient of a sphere and prediction of the settling velocity

The following equation has been previously developed for the drag coefficient of a sphere.

$\text{C}{}_{\mathrm{D}}\text{= C}{}_0\text{[1 + (σ}{}_0\text{/Re}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{)]}{}^2$

In this work the authors propose a power series expansion for C₀ in terms of the Reynolds number:

$\text{C}{}_0\text{= 0 284153}\text{Σ}\text{α=0}\text{n}\text{B}{}_{\mathrm{\alpha }}\text{Re}{}^{\mathrm{\alpha }}$

A fifth-order polynomial permits obtaining the drag coefficient and the settling velocity of a sphere, up to a Reynolds number of 3 × 10⁵, with an average relative error of about 2%.     

Dissociation constants for alkali earth and sodium borate ion pairs from 10 to 50°C

Potentiometric measurements in dilute sodium borate solutions with added alkali earth chlordie salts yield the following expressions for the dissociation constants of alkali earth borate ion pairs from 10 to 50°C:

$\text{p}\text{K(}\text{MgH}{}_2\text{BO}{}_3{}^{\mathrm{+}}\text{=1.266+0.001204 T}$

$\text{p}\text{K(}\text{CaH}{}_2\text{BO}{}_3{}^{\mathrm{+}}\text{=1.154+0.002170 T}$

$\text{p}\text{K(}\text{SrH}{}_2\text{BO}{}_3{}^{\mathrm{+}}\text{=1.033+0.001738 T}$

$\text{p}\text{K(}\text{BaH}{}_2\text{BO}{}_3{}^{\mathrm{+}}\text{=1.942+0.001850 T}$

where T is in °K. Enthalpies for the dissociation reactions at 25°C are less than 1 kcal./mole for all the alkali earth borate ion pairs.Values for pK(NaH₂BO₃°) from 5 to 55°C computed from the experimental data of Owen and King are in good agreement with those determined potentiometrically. The average value from both methods is 0.22 ± 0.1 at 25°C.Application to seawater of computed pK's for MgH₂BO₃⁺, CaH₂BO₃⁺ and NaH₂BO₃⁰ yields an apparent dissociation constant for boric acid of 8.73 vs. 8.70 measured by Lyman, 8.68 by Buch and 8.73 by Byrne and Kester.     

The effect of pressure on the solubility of minerals in water and seawater

The effect of presure on the solubility of minerals in water and seawater can be estimated from In

$\text{(}\text{K}{}^{\mathrm{P}}{}_{\mathrm{sp}}\text{K}{}^0{}_{\mathrm{sp}}\text{) +}\text{(?ΔVP + 0.5ΔKP}{}^2\text{)}\text{RT}$

where the volume (ΔV) and compressibility (ΔK) changes at atmospheric pressure (P = 0) are given by

$\text{ΔV =}\text{V}\text{?}\text{(M}{}^{\mathrm{+}}\text{, X}{}^{\mathrm{?}}\text{) ?}\text{V}\text{?}\text{[MX(s)]ΔK =}\text{K}\text{?}\text{(M}{}^{\mathrm{+}}\text{, X}{}^{\mathrm{?}}\text{) ?}\text{K}\text{?}\text{[MX(s)]}$

Values of the partial molal volume ($\text{V}\text{?}$) and compressibilty ($\text{K}\text{?}$) in water and seawater have been tabulated for some ions from 0 to 50°C. The compressibility change is quite large (~10 × 10^?3 cm³ bar^?1 mol^?1) for the solubility of most minerals. This large compressibility change accounts for the large differences observed between values of ΔV obtained from linear plots of In K_sp versus P and molal volume data (Macdonald and North, 1974; North, 1974). Calculated values of $\text{K}{}^{\mathrm{P}}{}_{\mathrm{sp}}\text{K}{}^{\mathrm{o}}{}_{\mathrm{sp}}$ for the solubility of CaCO₃, SrSO₄ and CaF₂ in water were found to be in good agreement with direct measurements (Macdonald and North, 1974). Similar calculations for the solubility of minerals in seawater are also in good agreement with direct measurements (Ingle, 1975) providing that the surface of the solid phase is not appreciably altered.