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331.
Effects of 11 years (1978-1988) of nutrient enrichment (fertilizer or sludge) on microbial metabolic activity in soil samples collected from contrasting types of old-field communities were studied during September 1989. During the 1989 growing season, subplots were manipulated by tilling and/or liming to evaluate mechanisms of ecosystem recovery or were left undisturbed. Metabolic activities of soil microorganisms were determined by measuring dehydrogenase activity within soil samples collected from these subplots. The amounts of 2,3,5-triphenyltetrazolium formazan formed during incubation by the reduction of 2,3,5-triphenyltetrazolium chloride were used to evaluate dehydrogenase activity. Plots that had received long-term applications of sludge or fertilizer had significantly lower rates of microbial activity (P<0.05) than did control plots. Fertilizer and sludge plots treated with lime had significantly higher microbial metabolic activity (P<0.05) than those not receiving lime. Whereas liming stimulated microbial activity to near control levels, tilling had no significant treatment effect. 相似文献
332.
333.
334.
The response of forest understory vegetation to trampling applied at different temporal and spatial scales was determined
in a cliff-edge forest in Ontario, Canada. Three frequencies (0, 50, 500 passes per year) of short-term trampling (one year)
were applied to plots previously undisturbed. Existing trails that had received three frequencies (approx. 100, 500, 25,000
passes per year) of long-term trampling (18 years) were also studied. Community composition, species richness, and individual
species frequency were recorded in plots within 4 m and (or) 1 m of the patch centerline. The quantitative and qualitative
form of plant response to increased trampling was compared for short-term and long-term treatments, both within 4 m and within
1 m of the path centerline, to judge the consistency of trampling effects at different temporal and spatial scales.
As trampling frequency increased, community composition changed progressively, but consistently, in plots both within 4 m
and 1 m of the path centerline. Species richness was less affected by trampling and only decreased within 1 m of the path
centerline at the highest level of trampling (25,000 passes per season for 18 years). Effects of trampling on individual species
frequency were much less consistent at different temporal and spatial scales of trampling. The scale-dependence results suggest
that field workers and resource managers both should try explicitly to include and define multiple scale components when trying
to ascertain the response of vegetation to human disturbance factors. 相似文献
335.
Snow was used as a collection medium to examine 1,3,5-hexahydro-1,3,5-trinitrotriazine (RDX) and 2,4,6-trinitrotoluene (TNT) residues post-detonation of 60-, 81-, and 120-mm mortar rounds, 105- and 155-mm howitzer rounds, M67 hand grenades, 40-mm rifle grenades, and blocks of C4. Residue-covered snow samples were collected, processed, and analyzed for explosives without cross-contamination from previous detonations and other potential matrix interferences. Detonation trials were performed following standard military live-fire and blow-in-place techniques. When possible, replicate munitions were detonated under similar conditions to provide a more reliable estimation of the mass of unconsumed high explosive residues. Overall the amount of energetic residues deposited from live-fire detonations were considerably less than the energetic residues deposited by blow-in-place detonations. 相似文献
336.
Effects of ethanol addition on micellar solubilization and plume migration during surfactant enhanced recovery of tetrachloroethene 总被引:4,自引:0,他引:4
Alcohol addition has been suggested for use in combination with surfactant flushing to enhance solubilization kinetics and permit density control of dense non-aqueous phase liquid (DNAPL)-laden surfactant plumes. This study examined the effects of adding ethanol (EtOH) to a 4% Tween 80 (polyoxyethylene (20) sorbitan monooleate) solution used to flush tetrachloroethene (PCE)-contaminated porous media. The influence of EtOH concentration, subsurface layering and scale on flushing solution delivery and PCE recovery was investigated through a combination of experimental and mathematical modeling studies. Results of batch experiments demonstrated that the addition of 2.5%, 5% and 10% (wt.) EtOH incrementally increased the PCE solubilization capacity and viscosity of the surfactant solution, while reducing solution density from 1.002 to 0.986 g/cm3. Effluent concentration data obtained from one-dimensional (1-D) column experiments were used to characterize rate-limited micellar solubilization of residual PCE, which was strongly dependent upon flow velocity and weakly dependent upon EtOH concentration. Two-dimensional (2-D) box studies illustrated that minor differences (0.008 g/cm3) between flushing and resident solution density can strongly influence surfactant front propagation. A two-dimensional multiphase simulator, MISER, was used to model the influence of EtOH composition on the aqueous flow field and PCE mass recovery. The ability of the numerical simulator to predict effluent concentrations and front propagation was demonstrated for both 1-D columns and 2-D boxes flushed with EtOH-amended Tween 80 solutions. Results of this study quantify the potential influence of alcohol addition on surfactant solution properties and solubilization capacity, and demonstrate the importance of considering small density variations in remedial design. 相似文献
337.
This paper reveals a substantial capacity for herbivory of seaweeds in the gammarid amphipod Aora typica, adults eating seven of ten taxonomically and morphologically diverse seaweed species offered to them in a no-choice assay. The green algae Ulva spathulata and Enteromorpha intestinalis were consumed at the highest rates in both no-choice (2.3–2.5 mg blotted weight individual−1 day−1) and multiple-choice assays (0.5–1.3 mg blotted weight individual−1 day−1). Adult A. typica collected from two different species of brown seaweeds had very similar feeding preferences to each other. Juvenile A. typica grew to reproductive maturity on the green algae E. intestinalis and U. spathulata, and the brown algae Carpophyllum maschalocarpum and Ecklonia radiata. In common with previous studies on members of other amphipod families, survivorship of juvenile amphipods was positively correlated with feeding preferences of adults across seaweed species (r
2=0.43, P=0.04). However, densities of A. typica on seaweeds in the field (excluding the intertidal E. intestinalis and U. spathulata) were not significantly correlated with feeding preferences of adults (r
2=0.07, P=0.5) or survivorship of juveniles (r
2=0.17, P=0.31). This suggests that either host seaweeds are not a major dietary component of these amphipods in nature, or that the host’s value as a food source is overridden by other properties such as the degree of shelter it affords from larger consumers. This study provides the first demonstration that a member of the cosmopolitan amphipod family Aoridae is capable of consuming a diverse range of seaweeds. 相似文献
338.
Male velvet swimming crabs [Necora puber (L.)] were observed to engage in long and vigorous agonistic interactions to gain possession of a sexually receptive female. The role of agonistic behaviour in male mate competition in this species was examined by investigating the effect of the perceived presence of sexually receptive females on interactions between males. Exposing male crabs to water conditioned by sexually receptive females resulted in prolonged interactions, with a greater incidence of potentially injurious behaviour than interactions between control crabs, exposed only to sea water. Maleconditioned water also resulted in more offensive behaviour, but these interactions were of shorter duration and not significantly different from sea water controls. Agonistic superiority was strongly correlated with contestant relative size when males were exposed to male-conditioned water or sea water, but not when exposed to female-conditioned water. Overall, the results conformed with the general predictions of game theoretic models in relation to the influence of resource value on agonistic behaviour. Crabs were more persistent and probably incurred greater fitness costs in the perceived presence of a sexually receptive female, when interactions may have been resolved on the basis of factors more closely related to actual fighting ability than the relative body sizes of contestants. 相似文献
339.
Freer-Smith PH Beckett KP Taylor G 《Environmental pollution (Barking, Essex : 1987)》2005,133(1):157-167
Trees are effective in the capture of particles from urban air to the extent that they can significantly improve urban air quality. As a result of their aerodynamic properties conifers, with their smaller leaves and more complex shoot structures, have been shown to capture larger amounts of particle matter than broadleaved trees. This study focuses on the effects of particle size on the deposition velocity of particles (Vg) to five urban tree species (coniferous and broadleaved) measured at two field sites, one urban and polluted and a second more rural. The larger uptake to conifers is confirmed, and for broadleaves and conifers Vg values are shown to be greater for ultra-fine particles (Dp < 1.0 microm) than for fine and coarse particles. This is important since finer particles are more likely to be deposited deep in the alveoli of the human lung causing adverse health effects. The finer particle fraction is also shown to be transported further from the emission source; in this study a busy urban road. In further sets of data the aqueous soluble and insoluble fractions of the ultra-fines were separated, indicating that aqueous insoluble particles made up only a small proportion of the ultra-fines. Much of the ultra-fine fraction is present as aerosol. Chemical analysis of the aqueous soluble fractions of coarse, fine and ultra-fine particles showed the importance of nitrates, chloride and phosphates in all three size categories at the polluted and more rural location. 相似文献
340.
Mousumi Mani Biswas Keith E Taylor Jatinder K Bewtra Nihar Biswas 《Water environment research》2007,79(4):351-356
Anaerobic degradation, an effective treatment process of textile industry effluent, generates sulfonated aromatic amines, which are carcinogenic, mutagenic, and resistant to microbial degradation. These aromatic amines can be effectively removed by oxidative polymerization catalyzed by peroxidase enzyme. The amines, generated in this study from the anaerobic reduction by zero-valent iron of two reactive azo dyes (Reactive Red 2 [RR2] and Reactive Black 5 [RB5]), were successfully removed (90%) by Arthromyces ramosus peroxidase (ARP). For better understanding of the process, enzymatic treatment of two model compounds, diphenylamine (DPA) and 2-amino-8-naphthol-3,6-disulfonic acid (ANDSA), were also studied. Diphenylamine has a similar diarylamine bond as RR2. The ANDSA has a similar structure as the dye reduction products. The secondary amine bond in DPA and RR2 were oxidized by ARP. Enzymatic reaction of sulfonated aromatic amines generated soluble colored compounds, which were removed by coagulant. Optimum reaction parameters were also determined. 相似文献