Dynamics of Tree and Shrub Vegetation in the Eastern Sayan Mountain Tundra

Russian Journal of Ecology - Climate change entails shifts in the ranges of woody plants along both latitudinal and altitudinal gradients in the boreal forest biome. In this study,...     

Larch forests of Middle Siberia: long-term trends in fire return intervals

Fire history within the northern larch forests of Central Siberia was studied (65 + °N). Fires within this area are predominantly caused by lightning strikes rather than human activity. Mean fire return intervals (FRIs) were found to be 112 ± 49 years (based on firescars) and 106 ± 36 years (based on firescars and tree natality dates). FRIs were increased with latitude increase and observed to be about 80 years at 64°N, about 200 years near the Arctic Circle and about 300 years nearby the northern range limit of larch stands (~71° + N). Northward FRIs increase correlated with incoming solar radiation (r = ?0.95). Post-Little Ice Age (LIA) warming (after 1850) caused approximately a doubling of fire events (in comparison with a similar period during LIA). The data obtained support a hypothesis of climate-induced fire frequency increase.     

Ethoxylated Soybean Polyols for Polyurethanes

Soybean polyols prepared by ring opening reactions of epoxidized soybean oil with hydrogen active compounds (water, alcohols, organic or inorganic acids, thiols, hydrogen etc.) have a low reactivity in the reaction with isocyanates because the hydroxyl groups are secondary. This paper presents a simple and convenient method to increase the reactivity of soybean polyols with secondary hydroxyl groups by ethoxylation reactions with the preservation of triglyceride ester bonds. The method uses mild reaction conditions: low alkoxylation temperature of 35–45 °C, low pressure of 0.1–0.2 MPa (15–30 p.s.i.) and a superacid as catalyst (HBF₄). The new soybean polyols have a higher reactivity toward isocyanates in polyurethane formation due to the high percentage of primary hydroxyl groups. The primary hydroxyl content was determined by the second order kinetics of polyol reaction with phenyl isocyanate.     

Fir decline and mortality in the southern Siberian Mountains

Regional Environmental Change - Increased dieback and mortality of “dark needle conifer” (DNC) stands (composed of fir (Abies sibirica), Siberian pine (Pinus sibirica) and spruce (Picea...     

The total content of toxic elements in horsehair given the level of essential elements

Environmental Science and Pollution Research - Elemental status of 214 mares aged 3–7 years from 11 breeds was studied: Arabian purebred (n = 20), Bashkir (n = 20), Kabarda (n = 20), Vyatka...     

Chemical speciation in mining affected waters: the case study of Asarel-Medet mine

The inorganic chemical species in Maresh and Luda Yana rivers affected by the Cu– Mo Asarel-Medet mine, Bulgaria were determined during a low-flow and a high-flow period. The mining activities, the weathering and the oxidation processes strongly influenced the physicochemical processes in the whole water system. The main pollution source was a small lake receiving the acid effluents of the mining activities. High levels of SO₄ ^2???, Cu, Mg, Al, Mn and Fe were determined at the mining polluted and affected stations. Cu^2?+? and CuCO₃ ⁰ species (1:1) were present in the reference waters and Cu^2?+? and CuSO₄ ⁰ species (1:1) in the polluted and affected waters; Cu^2?+? species was dominating downstream. Me^2?+? followed by $\rm{MeSO}_{4}^{\kern3pt{0}}$ (Me = Mn, Zn, Cd and Pb), $\rm{PbCO}_{3}^{\kern3pt{0}}$ and $\rm{PbHCO}_{3}^{\kern3pt{+}}$ species as well as $\rm{Fe(OH)}_{2}^{\kern3pt{+}}$ , $\rm{Al(OH)}_{4}^{\kern3pt{-}}$ , $\rm{Al(OH)}_{2}^{\kern3pt{+}}$ , $\rm{Al(OH)}_{3}^{\kern3pt{0}}$ were prevailing in the system. $\rm{MeSO}_{4}^{\kern3pt{+}}$ and $\rm{Me(SO}_{4})_{2}^{\kern3pt{-}}$ (Me = Fe, Al), $\rm{Me(SO}_{4})_{2}^{\kern3pt{2-}}$ (Me = Zn, Cd and Pb), $\rm{Me(SO}_{4})_{3}^{\kern3pt{4-}}$ (Me = Zn, Cd) and $\rm{Cd(SO}_{4})_{4}^{\kern3pt{6-}}$ species polluted and affected waters. The major elements K and Na were mainly Me^?+? species, whereas Ca and Mg were Me^2?+? and $\rm{MeSO}_{4}^{\kern3pt{0}}$ species in different ratios. The concentration of concentration of $\rm{NO}_{2}^{\kern3pt{-}}$ , $\rm{NO}_{3}^{\kern3pt{-}}$ and $\rm{NH}_{4}^{\kern3pt{+}}$ species as well as complex phosphorous species such as H₂ $\rm{PO}_{4}^{\kern3pt{-}}$ , $\rm{FeHPO}_{4}^{\kern3pt{+}}$ , $\rm{HPO}_{4}^{\kern4pt{2-}}$ , $\rm{CaPO}_{4}^{\kern3pt{-}}$ , $\rm{CaHPO}_{4}^{\kern3pt{0}}$ and $\rm{MgHPO}_{4}^{\kern3pt{0}}$ were also calculated. The trace element concentrations decreased downstream due to dilution, sorption processes and precipitation, but the percentage of free metal species, which are more toxic, increased. An exception was iron and aluminum of which the dominant hydroxy colloidal and sulphate species were easily incorporated into the suspended phase.     

Uranium uptake by hydroponically cultivated crop plants

Hydroponicaly cultivated plants were grown on medium containing uranium. The appropriate concentrations of uranium for the experiments were selected on the basis of a standard ecotoxicity test. The most sensitive plant species was determined to be Lactuca sativa with an EC₅₀ value about 0.1 mM. Cucumis sativa represented the most resistant plant to uranium (EC₅₀ = 0.71 mM). Therefore, we used the uranium in a concentration range from 0.1 to 1 mM.Twenty different plant species were tested in hydroponic solution supplemented by 0.1 mM or 0.5 mM uranium concentration. The uranium accumulation of these plants varied from 0.16 mg/g DW to 0.011 mg/g DW. The highest uranium uptake was determined for Zea mays and the lowest for Arabidopsis thaliana. The amount of accumulated uranium was strongly influenced by uranium concentration in the cultivation medium. Autoradiography showed that uranium is mainly localized in the root system of the plants tested. Additional experiments demonstrated the possibility of influencing the uranium uptake from the cultivation medium by amendments. Tartaric acid was able to increase uranium uptake by Brassica oleracea and Sinapis alba up to 2.8 times or 1.9 times, respectively. Phosphate deficiency increased uranium uptake up to 4.5 times or 3.9 times, respectively, by Brassica oleracea and S. alba. In the case of deficiency of iron or presence of cadmium ions we did not find any increase in uranium accumulation.