The hydrous magnesium carbonates, nesquehonite (MgCO3 3H2O) and dypingite (Mg5(CO3)4(OH)2 5(H2O)), were precipitated at 25 C in batch reactors from aqueous solutions containing 0.05 M NaHCO3 and 0.025 M MgCl2 and in the presence and absence of live photosynthesizing Gloeocapsa sp. cyanobacteria. Experiments were performed under a variety of conditions; the reactive fluid/bacteria/mineral suspen...

This study sought to characterize hydrogen isotopic fractionation during biosynthesis of leaf wax nalkanes in succulent plants capable of crassulacean acid metabolism (CAM). The metabolic and physiological features of CAM represent crucial strategies for survival in hot and dry climates and have been hypothesized to impact hydrogen isotope fractionation. We measured the stable carbon and hydrog...

Chiral pesticides are important contaminants affecting the health and functioning of aquatic systems. The combination of stable isotope and enantiomer analysis techniques has been recently proposed to better characterize the fate of these contaminants in natural and engineered settings. We introduce a modeling approach with the aim of unifying and integrating the interpretation of isotopic and ...

Whether photosynthetic pathway differences exist in the amplitude of nighttime variations in the carbon isotope composition of leaf dark-respired CO2 (δ13Cl) and respiratory apparent isotope fractionation relative to biomass (ΔR,biomass) in response to drought stress is unclear. These differences, if present, would be important for the partitioning of C3-C4 mixed ecosystem C fluxes. We measured...

Variation in the natural abundance stable carbon isotope composition of respired CO2 and biomass has been measured for two types of aerobic bacteria found in contaminated land sites. Pseudomonas putida strain NCIMB 10015 was cultured on phenol and benzoate and Rhodococcus sp. I1 was cultured on phenol. Results indicate that aerobic isotope fractionations of di€ering magnitudes occur during aero...

Various isotope studies require accurate fractionation factors (a’s) between different chemical compounds in thermodynamic equilibrium. Although numerous isotope systems involve aqueous solutions, the conventional theory is formulated for the gas-phase and predicts incorrect a’s for many compounds dissolved in water. Here I show that quantum-chemistry calculations, which take into account solut...

Amino acids (AAs) are critical biochemical compounds for living organisms. Because of the limited capacity for their de novo synthesis in many animals, the nutritional value of food largely depends on its AA composition relative to the animal’s requirements. To improve present knowledge on AA variability in freshwater crustaceans, we studied the interand intraspecific variability in three contr...