A method for removal of CO from exhaust gas using pulsed corona discharge

An experimental study of the oxidation of CO in exhaust gas from a motorcycle has been carried out using plasma chemical reactions in a pulsed corona discharge. In the process, some main parameters, such as the initial CO concentration, amplitude and frequency of pulses, residence time, reactor volume, and relative humidity (RH), as well as their effects on CO removal characteristics, were investigated. O3, which is beneficial to reducing CO, was produced during CO removal. When the exhaust gas was at ambient temperature, more than 80% CO removal efficiency was realized at an initial concentration of 288 ppm in a suitable range of the parameters.     

Uncertainty analysis of parameters for modeling the transfer and fate of benzo(a)pyrene in Tianjin wastewater irrigated areas

A Monte Carlo simulation for uncertainty analysis of three key parameters (local coal consumption rate Q(1L), dry deposition velocity of aerosol particulate Kp and biodegradation rate of benzo(a)pyrene in soil and sediment K(R3)) was conducted in this study. Results of the simulation indicate that the three parameters were influenced by uncertainty and that all equilibrium concentrations in the four bulk compartments and various sub-compartments were log-normally distributed. However, the results also indicated that among the six primary transfer fluxes, erosion associated with solids in soil and deposition associated with solids in water, along with output from sewers were also log-normally distributed, while deposition from air to soil and biodegradation in soil and sediment followed normal distributions. The effect of uncertainty on the model results of the three key parameters was derived using a comparison of upper and lower of confidence interval boundaries at the 95% level of confidence. The results reveal that uncertainty in the key parameters had a more significant influence on equilibrium concentrations of the chemical in the bulk compartments of soil and sediment than on concentrations in the other two bulk compartments, various sub-compartments and the six predominant transfer fluxes.     

Photodegradation of 17alpha-ethynylestradiol in aqueous solution exposed to a high-pressure mercury lamp (250 W)

The photodegradation of 17alpha-ethynylestradiol (EE(2)) induced by high-pressure mercury lamp (lambda> or =313, 250 W) in aqueous solution of EE(2) was investigated initially. The affecting factors on the photodegradation were studied and described in details, such as EE(2) initial concentration, Fe(3+), algae, exposure time, and so on. The concentration of EE(2) in distilled water was mainly determined using fluorescence spectrophotometer. The photodegradation of EE(2) in aqueous solution exposed to high-pressure mercury lamp was evident and could be accelerated by Fe(3+) or algae (e.g. Anabaena cylindrica) in general. With the algae concentration increasing, photodegradation rate increased. In this paper, the mechanism of photocatalytic degradation of EE(2) by Fe(3+) or algae is discussed primarily.     

Evidence of in situ diel vertical migration of a red-tide microplankton species in Ría de Vigo (NW Spain)

The migration capacity of red-tide species in the natural environment was studied at a station in the Ría de Vigo (Rías Bajas, NW Spain) over a 24 h period in September 1991. The Ría de Vigo, where red tides are frequent, normally shows a positive estuarine circulation and is subjected to seasonal upwelling and downwelling phenomena. A marked diel pattern was observed for five species that are capable of causing red tides (Ceratium furca, Scrippsiella trochoidea, Dinophysis acuminata, Mesodinium rubrum, and Eutreptiella sp.). Such diel behaviour could be clearly advantageous in a stratified environment where light and nutrients are often in two separate layers. Active movement enables species such as dinoflagellates and some ciliates to exploit high levels of irradiance at the surface during the day and to take up nutrients in deeper layers at night. Patchy distribution of phytoplankton, shear-induced horizontal dispersion and density variations were considered, but none of them accounted for the vertical changes observed. Vertical migration is thought to be one of the mechanisms that could promote blooms in nutrient-depleted surface layers.     

Inorganic mercury and methylmercury in surface sediments and mussel tissues from a microtidal lagoon (Bizerte, Tunisia)

The aim of this study was to investigate the distribution of mercury compounds in marine sediments and mussel tissues collected in the lagoon of Bizerte, Tunisia, during two seasons (summer and winter). Inorganic mercury (Hg²⁺) concentrations in sediments were found to be highly variable, ranging from 0.04 nmol.g¹ to 3.22 nmol.g⁻¹ (dry weight) with a mean value of 0.52 nmol.g⁻¹. Anthropogenic sources of Hg²⁺, most probably metallurgy or tire production industries, have been evidenced. The mean concentration of monomethylmercury (MeHg⁺) in the surface sediments is 2.32 pmol g⁻¹ ranging from below the detection limit (0.45 pmol.g⁻¹) to 14.6 pmol.g⁻¹. No significant variation was observed between winter and summer seasons for both mercury species concentration in the sediments. The Hg²⁺ concentrations in mussel tissues are also variable, ranging from 0.007 to 1.347 nmol.g⁻¹ (dry weight). The mean concentration is 0.70 nmol.g⁻¹. In these tisssues, Hg²⁺ is generally the major compound, making up ca. 88% of total mercury concentrations. However, methylmercury concentrations are significant and homogeneous, ranging from 62 to 121 pmol.g⁻¹ (mean 96 pmol.g⁻¹). The results suggest that a fraction of the inorganic mercury load in the sediments of the lagoon undergoes methylation pathways. MeHg⁺ produced is assimilated in the mussels more readily than Hg²⁺.     

Response of Savanna Fire Regimes to Changing Fire-Management Policies in a Large African National Park

Abstract:  Approaches to fire management in the savanna ecosystems of the 2-million ha Kruger National Park, South Africa, have changed several times over the past six decades. These approaches have included regular and flexible prescribed burning on fixed areas and a policy that sought to establish a lightning-dominated fire regime. We sought to establish whether changes in management induced the desired variability in fire regimes over a large area. We used a spatial database of information on all fires in the park between 1957 and 2002 to determine elements of the fire regime associated with each management policy. The area that burned in any given year was independent of the management approach and was strongly related to rainfall (and therefore grass fuels) in the preceding 2 years. On the other hand, management did affect the spatial heterogeneity of fires and their seasonal distribution. Heterogeneity was higher at all scales during the era of prescribed burning, compared with the lightning-fire interval. The lightning-fire interval also resulted in a greater proportion (72% vs. 38%) of the area burning in the dry season. Mean fire-return intervals varied between 5.6 and 7.3 years, and variability in fire-return intervals was strongly influenced by the sequencing of annual rainfall rather than by management. The attempt at creating a lightning-dominated fire regime failed because most fires were ignited by humans, and the policy has been replaced by a more pragmatic approach that combines flexible prescribed burning with lightning-ignited fires.     

Fractionation of heavy metals in surface sediments of Taihu Lake, East China

The BCR (European Communities Bureau of Reference) three-step sequential extraction procedure was applied to fractionate heavy metals in the sediment of Taihu Lake. For the determination of total metal concentration of the sediments, sample digestion was achieved by using HF/H2O2/HNO3 (2/1/1) acid mixture in a microwave-irradiated closed vessel system. The concentrations of Cd, Ni, Cr, Zn, Cu and Pb in various extracts solutions were analyzed by Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES). The results obtained from the BCR three-step sequential extraction indicated relatively high mobility of Zn, Cu, Pb and Ni in the sediments while Cd and Cr were poorly mobile. Enrichment of heavy metals was found in the sediments collected in the northern parts of Taihu Lake. In the sediments collected in the southern and western sides of the Lake, heavy metal concentrations were relatively low. The relationship between total organic carbon (TOC) and heavy metals concentrations in the sediments is discussed.     

Residues of Organochlorinated Pesticides in Eggs of Water Birds from Tai Lake in China

The levels of organochlorine compounds in eggs of water birds from the colony on Tai Lake in China were studied. The eggs were collected in 2000 and belonged to the following species: 65 samples of black-crowned night heron (Nycticorax nycticorax), 36 samples of little egret (Egretta garzetta), 26 samples of cattle egret (Bubulcus ibis) from 13 clutches and 43 samples of Chinese pond heron (Ardeola bacchus) from 17 clutches. Dichlorodiphenyltrichloroethane (DDT) and its derivates (DDE and DDD), hexachlorocyclohexane (HCH) and its isomers (-HCH, -HCH, -HCH, -HCH), heptachlor, heptachlor epoxide, aldrin, dieldrin, endrin, endrin aldehyde, -endosulfan, -endosulfan, and endosulfan sulfate were determined in the laboratory by gas chromatography. The data showed that DDE had the highest levels in all the samples, followed by -HCH. The mean levels of DDE among the water bird species were in the order as follows: black-crowned night heron (5464.26ng/g, dry weight) > Chinese pond heron (2791.12ng/g, dry weight) > little egret (1979.97ng/g, dry weight) > cattle egret (660.11ng/g, dry weight). DDT and its metabolites accounted for 90% of the total organochlorines, except that it was only 73% for cattle egret. The differences of the residue among the bird species were statistically significant and could be attributed to their variations in prey and habitat. Although the DDE burdens in Tai Lake were much lower than 8 g/g (wet weight) which are thought to have significant adverse effects on black-crowned night herons, they would be expected to increase the risk of adverse effects on survival of chicks of herons and egrets, particularly black-crowned night heron, based on the critical value of 1 g/g (wet weight) DDE. The burdens of HCHs in this study were higher and the cyclodienes were lower than those found elsewhere.     

Fitness consequences of body-size-dependent host species selection in a generalist ectoparasitoid

In insect parasitoids, offspring fitness is strongly influenced by the adult females choice of host, particularly in ectoparasitoids that attack non-growing host stages. We quantified the fitness consequences of size-dependent host species selection in Dirhinus giffardii, a solitary ectoparasitoid of tephritid fruit fly pupae. We first showed a positive correlation between the size of emerged D. giffardii wasps and the size of their host fruit fly species (in order of decreasing size): Bactrocera latifrons, B. cucurbitae, B. dorsalis or Ceratitis capitata. We then manipulated individual wasps to show that the parasitoid preferred to attack the largest (B. latifrons) to the smallest (C. capitata) host species when provided with a choice, and laid a greater proportion of female eggs in B. latifrons than in C. capitata. There were no differences in developmental time or offspring survival between individuals reared from these two host species. Finally, we compared the foraging efficiency of large versus small wasps (reared from B. latifrons vs C. capitata) under two different laboratory conditions: high versus low host habitat quality, given that realized fecundity in parasitoids may be influenced by either egg-limited or time-limited factors. Under both conditions, large wasps parasitized more hosts than did small ones as a consequence of high searching efficiency in the host-poor habitat, and high capacity for adjusting egg maturation in response to host availability in the host-rich habitat. Considering the flexibility of body growth, the apparent lack of cost of achieving large body size in either development or survival, and the strong dependence of realized reproductive success on a females size, we argue that body size may be a key to understanding evolution of host species selection in ectoparasitoids. We also discuss constraints upon the evolution of size-dependent host species selection in parasitoids.Communicated by D. Gwynne     

Model calculating annual mean atmospheric dispersion factor for coastal site of nuclear power plant

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