Three Mn dioxides—birnessite, cryptomelane, and pyrolusite—were examined for their ability to deplete the concentration of As(III), a highly toxic pollutant, in solution. The depletion [oxidation of As(III) to As(V) and sorption of As(III)] of As(III) by all three Mn dioxides follows first‐order kinetics. The rate constants for the depletion of As(III) by birnessite and cryptomelane at 298 K are 0.267 and 0.189 h−1, respectively. On the other hand, the depletion rate of As(III) by pyrolusite is much slower: the rate constant at 298 K is 0.44 × 10−3 h−1. This difference in the rate of depletion is largely attributed to the crystallinity and specific surfaces of the Mn dioxides. Pyrolusite is highly ordered and has a low specific surface of 0.8 hm2/kg (7.9 m2/g); conversely, birnessite and cryptomelane are poorly crystalline and have relatively high specific surfaces of 27.7 and 34.6 hm2/kg (277 and 346 m2/g), respectively. The energies of activation for the depletion of As(III) by the Mn dioxides range from 26.0 to 32.3 kJ/mol. The reaction appears to be predominantly diffusion‐controlled. The ability of the Mn dioxides to sorb As(III) and As(V) appears to be related to the specific surface and the point‐of‐zero charge of the oxides. The data indicate that, after the systems have reached equilibrium with respect to the sorption of total As, the depletion of As(III) by the oxides is still progressing. This is apparently because of the one‐to‐one relationship between the amount of As(III) depleted and the amount of As(V) appearing in solution.
Collections of algae, mainly planktonic, were made from 41 saline lakes in southern Saskatchewan ranging in salinity from 3.2 to 428 g 1-I. Algae in 7 phyla, 8 classes, 42 families, 91 genera and 212 species and varieties were identified. Fourteen species were restricted to hypersaline (50 g 1-I) waters and eleven of these were diatoms. In general, species diversity was inversely related to lake salinity.Algae that were important community constituents over a broad spectrum of salinities were the green algae Ctenocladus circinnatus, Dunaliella salina and Rhizoclonium hieroglyphicum, the blue-green Lyngbya Birgei, Microcystis aeruginosa, Oscillatoria tenuis, 0. Utermoehli and Nodularia spumigena and the diatoms Melosira granulata, Stephanodiscus niagarae and Chaetoceros Elmorei. In general green algae were dominant when lake salinity exceeded 100 g 1-I although diatoms played important roles in most of these highly saline lakes except for Patience Lake.
The salinity of Saskatchewan saline lakes varies up t o 342yw. Highly saline lakes are widely distributed. Some reach saturation a t high summer temperatures b u t salt precipitation occurs on cooling. Saline lakes tend t o increase in salinity with time but t h e greatest changes occur in the shallow more saline lakes.The lakes are dominated by sodium, magnesium and sulphate. The cation sequences are dominated by sodium or magnesium while calcium and potassium are proportionally much smaller. Chloride or bicarbonate-carbonate are secondary to sulphate among the anions. Ion sequences tend to be characteristic of certain physiographic regions. Lake types were magnesium (sodium) sulphate, sodium sulphate and sodium (magnesium) sulphate in order of abundance of lakes.Phosphorus and ammonia were high in concentration but nitrate and silica were scarce. The lakes were all alkaline between p H 7.8 and 9.8.The evolution of closed saline lakes is briefly discussed.
The spring benthos of 22 lakes ranging from 1-88 gl-1 salinity contained 58 species of macroinvertebrates, but only 23 species occurred in waters >3 gl-i. The amphipod Hyalella azteca and the chironomids Procladius freerani, Chironomus nr. muratensis and Cryptochkronomus spp. were important a t loner salinities (1-12 gl-f) whereas the chironomids Tunypus nubifer, Cricotopna ornatus and Chironomus nr. annularis dominated at moderate salinities (5-30 gl-1) and dolichopodid and ephyrid dipterans were the only species in hypersaline lakes ( >50 gl-i). Diversity decreased significantly with increased salinity.Mean dry biomass ranged from 0-9.12 gm-1, showing little correlation with salinity, though hyposaline lakes often had elevated values and hypersaline lakes very low values. Shallow lakes ( -=5 m) had significantly lower standing crops. There were long term changes in biomass (over 45 years) in mme lakes due to cultural eutrophication or secular changes in salinity. Chironomids irere by far the dominant contributors t o biomass a t salinities to 50 gl-1, above which dolichopodid and ephyrid dipterans dominated.The lakes were classified into four groups-subsaline, hyposaline, shallow hypo-mesosaline and hypersaline, reflecting the importance of salinity and also relative depth as major controlling factors.
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