Chemosphere - Global Change Science最新文献

In a greenhouse study, CH₄ flux from alluvial and laterite soils planted to rice (cv. CR 749-20-2) was monitored under non-flooded and flooded conditions. CH₄ flux from continuously non-flooded pots was always lower than from pots maintained under flooded conditions. The cumulative CH₄ flux was 150 and 880 mg pot⁻¹ in laterite and 105 and 405 mg pot⁻¹ in alluvial soils under non-flooded and flooded conditions, respectively. While non-flooded conditions exhibited a single CH₄ peak at vegetative stage, flooded conditions showed additional peak at reproductive stage. CH₄ flux maxima was more intense under flooded conditions and persisted for a longer period during the reproductive stage than at the vegetative stage. Soil contents of Fe²⁺, readily mineralizable carbon (RMC) and ninhydrin reactive nitrogen (NRN) exhibited significant positive relationship with CH₄ flux. Among the plant characters, a significant negative relationship existed between CH₄ flux and α-naphthylamine oxidase activity of the root base under flooded condition and root tip under non-flooded conditions.

The production rates of a range of low molecular weight halogenated organics have been determined in cultures of five temperate species of macroalgae collected from the north coast of Norfolk, England. Compounds studied included CH₃Br, the chlorinated organics CH₃Cl, CH₂Cl₂ and CHCl₃, and the iodinated organics CH₃I, C₂H₅I, and CH₂ClI. Measurements of a wider range of halocarbon concentrations in an isolated rockpool and in air over the seaweed bed were also conducted to evaluate the local impact of the seaweeds on halocarbon concentrations in the natural environment. Estimates for the global emissions of some of the key halogenated compounds from macroalgae have been derived. In general macrophytes appear not to be globally significant producers of the particular halocarbons studied. In coastal regions, however, the impact on local atmospheric composition and chemistry could be greater.

Open burning was carried out for rice straw samples with moisture contents of 0%, 5%, 10%, 15%, 20%, 25%, and 30%, respectively. The 10 EPA priority polycyclic aromatic hydrocarbons (PAHs) compounds plus naphthacene and perylene were analyzed by means of GC/MS. Total particulate PAHs emission varied between 1 and 38 mg/kg for12 species-specific PAHs. Experimental results showed that water has a depression effect on PAHs emission during rice straw burning. The lowest emission of total particulate PAHs was obtained when rice straw with 15% moisture content was burned. 11 species-specific PAHs showed the lowest emissions within 10–20% moisture content exclusive of naphthacene. In addition, higher emission was observed for intermediate molecular weight compounds such as fluoranthene, pyrene, benz[a]anthracene and chrysene, and relatively lower emission for heavier molecular weight compounds such as perylene, benzo[a]pyrene and dibenz[ah]anthracene.

Measurement of ammonia in vapour phase, particulate and rain was made at a suburban site of India. Vapour phase concentrations varied between 0.97 and 25.5 μg m⁻³ (57.1–1500.0 nmol m⁻³) and diurnal variation study showed high concentration of NH₃ during night time and minimum at 0600 h (early morning). Particulate phase NH₄ values ranged between 1.2 and 5.3 μg m⁻³ (66.7–294.4 nmol m⁻³). Dry deposition flux was determined from model calculations. Day time NH₃ flux was found to be 8.4±4.0 mg m⁻² d⁻¹ and that of night 2.2±1.2 mg m⁻² d⁻¹. With respect to particulate deposition flux was found 0.2±0.1 mg m⁻² d⁻¹ while in precipitation values of NH₄ ranged between 0.7 and 74.4 μeq l⁻¹. Regression analysis of ammonium concentration with rain volume and deposition indicates that NH₃ concentration is being controlled by both gas and particulate ammonium. Annual inputs for wet and dry deposition were found to be 0.34±0.3 and 3.9±1.9 g m⁻² y⁻¹.