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301.
Edgar F. Lowe Lawrence E. Battoe David L. Stites Michael F. Coveney 《Environmental management》1992,16(1):67-74
Lake Apopka in Florida, USA, is a large (area=124 km2), hypertrophic (mean total phosphorus=0.220 g/m3; mean chlorophylla=60 mg/m3) lake, with a large sedimentary store of available P (1635 × 106 g P). Phosphorus loading from floodplain farms (132 × 106 g P/yr) has been the primary cause of eutrophication. Assuming elimination of farm P loading, the Vollenweider model predicts
a decline in equilibrium P concentration from 0.270 to 0.024 g/m3, if the P sedimentation coefficient (σ) remains constant. It is likely, however, that the value for σ will fall with the
elimination of farm loading due to unabated internal P loading from the sediments. Under a worst-case scenario (σ=0), the
model predicts that exportation of P from the lake via wetland filtration will greatly accelerate the lake's recovery. Recirculation
of lake water through a 21-km2, created wetland and elimination of farm P loading is projected to result in a negative P balance for the lake (−23 × 106 g P/yr) leading to depletion of P stores in the lake in about 60 yr. The estimated cost of the project, $20 million, is less
than 3% of the estimated cost of dredging. A 3.65-km2 demonstration project is underway to test and refine the wetland filtration technique. We believe the technique could be
cost-effective for other hypertrophic lakes. 相似文献
302.
A quasi-experiment was used to compare employee behaviors before and after stress management training. Organizational records on employee absenteeism, performance ratings, equipment accidents, and work injuries were obtained for highway maintenance workers who received biofeedback (BIO=21) or muscle relaxation (MR=16) training. Similar data were gathered for a comparison group of employees who did not volunteer for training (n = 80). The pre-training period (time 1) consisted of 2 1/2 years. The post-training period was divided into the year immediately after training (time 2) and the following 1/2 year (time 3). Multiple regression analyses indicated that the MR (but not BIO) group variable explained unique variance in time 2 absenteeism (p < 0.05) but not in performance ratings, equipment accidents, nor work injuries (p > 0.05). Neither group entered predictive models for any measure at time 3 (p > 0.05). The results provide limited support for relaxation training offered as a prevention activity in work settings. 相似文献
303.
Henricus F M Vester Deborah Lawrence J Ronald Eastman B L Turner Sophie Calmé Rebecca Dickson Carmen Pozo Florencia Sangermano 《Ecological applications》2007,17(4):989-1003
The southern Yucatán contains the largest expanse of seasonal tropical forests remaining in Mexico, forming an ecocline between the drier north of the peninsula and the humid Petén, Guatemala. The Calakmul Biosphere Reserve resides in the center of this region as part of the Mesoamerican Biological Corridor. The reserve's functions are examined in regard to land changes throughout the region, generated over the last 40 years by increasing settlement and the expansion and intensification of agriculture. These changes are documented from 1987/1988 to 2000, and their implications regarding the capacity of the reserve to protect the ecocline, forest habitats, and butterfly diversity are addressed. The results indicate that the current landscape matrix serves the biotic diversity of the reserve, with several looming caveats involving the loss of humid forests and the interruption of biota flow across the ecocline, and the amount and proximity of older forest patches beyond the reserve. The highly dynamic land cover changes underway in this economic frontier warrant an adaptive management approach that monitors the major changes underway in mature forest types, while the paucity of systematic ecological and environment-development studies is rectified in order to inform policy and practice. 相似文献
304.
Summary. Male locust borers, Megacyllene robiniae
(Förster), responded to females only after contacting them
with their antennae, indicating that mate recognition was
mediated by a contact sex pheromone. GC-MS analyses of
whole-body extracts of males and females determined that the
profiles of compounds in the extracts were qualitatively similar,
but differed considerably in the ratios of compounds
between sexes. Biological activities of reconstructed blends
of the most abundant straight-chain (nC23, nC24, nC25, nC26),
methyl-branched (3me-C23, 3me-C25), and unsaturated
(Z9:C23, Z9:C25, Z9:C27 compounds in extracts from females
were assessed in arena bioassays, assessing four distinct steps
in the mating behavior sequence of males (orientation, arrestment,
body alignment, mounting and attempting to couple the
genitalia). Males were unresponsive to freeze-killed, solventwashed
females treated with blends of straight-chain and
methyl-branched alkanes, but responded strongly to females
treated with the blend of alkenes. Further trials determined
that the complete sequence of mating behaviors, up to and
including coupling the genitalia, was elicited by Z9:C25 alone.
Z9:C25 comprised 16.4 ± 1.3% of the total hydrocarbons in
whole-body hexane extracts of females and was co-dominant
with two other hydrocarbons that were not active. In contrast,
in solid phase microextraction (SPME) wipe samples from
several areas of the cuticle, Z9:C25 appeared as the single
dominant peak, comprising 34.6 – 37.8% of the sampled
hydrocarbons. Our data indicate that Z9:C25 is a contact sex
pheromone of M. robiniae, being the most abundant hydrocarbon
on the surface of the cuticular wax layer of females
where it is readily accessible to the antennae of males. 相似文献
305.
306.
Postelsia palmaeformis were collected from the lower intertidal at Pigeon Point, California, USA, in May 1987, and the proximate composition and allocation of energy to the various body components were determined. The holdfast and stipe have a proximate composition (% dry weight) of ca. 40% ash, 5.3% protein, 1% lipid, 2% soluble carbohydrate, and 55% insoluble carbohydrate. The fronds have a proximate composition of ca. 25% ash, 6.5% protein, 2% lipid, 3% soluble carbohydrate, and 65% insoluble carbohydrate. The energetic level was ca. 12 kJ g-1 dry wt and ca. 19 kJ g-1 ash-free dry wt. The relative proportion of three plant components varied, comprising 26, 39, and 35% wet wt and 20, 42, and 38% kJ for the holdfast, stipe, and fronds, respectively. A plant with a basal stipe diameter of 33 mm contains 114 g wet wt and 266 kJ. The maximal density found in May 1987 was 826 plants, 49 301 g wet wt, and 106 157 kJ m-2.P. palmaeformis differs in these characteristics from another intertidal pheophyte,Durvillaea antarctica, that is found in a high-energy intertidal zone. 相似文献
307.
Summary. The purpose of this study was to identify plant volatiles that provide host location cues for adult females of the gall wasp Antistrophus rufus Gillette (Hymenoptera: Cynipidae). Larvae of this species inhabit flowering stems of the prairie perennial Silphium laciniatum L. (Asteraceae). Adult females responded to volatile compounds emitted by stems of S. laciniatum in field olfactometer bioassays. Plant volatiles were monoterpenes, including, in descending order of abundance, racemic - and -pinene (~50% + enantiomer for both), (+)-limonene, (–)-camphene, and -myrcene. In laboratory bioassays, females responded to aeration extracts of plant stems, the full blend of synthetic monoterpenes, and the four-component blend of -pinene, -pinene, (+)-limonene, and (–)-camphene. This monoterpene blend apparently serves as an olfactory cue for host plant location for female A. rufus and is the first such cue to be reported for a cynipid gall wasp. Species-specific ratios of plant monoterpenes may provide cues for gall wasp females to distinguish between plant species and choose appropriate hosts for oviposition. The olfactometer and bioassay techniques developed for this research may be useful for field bioassays of other types of minute arthropods. 相似文献
308.
A. Mansingh D. E. Robinson C. Henry V. Lawrence 《Environmental monitoring and assessment》2000,63(3):459-480
Only organochlorine (OC) residues were monitored by gas chromatographyin water, sediment and shrimp samples collected everymonth between July 1982 and August 1983 from therivers of Rio Cobre basin. In samples collected everyfour months during 1989–1990, and seven times duringJuly 1995–March 1996, OC and OP (organophosphates)residues were monitored. Carbamate and pyrethroidresidues were not monitored. The detection ofresidues in 1982–1983 was 54 to 100% in water andsediment, and 83 to 100% in shrimp samples fromvarious sampling stations in the four rivers. In otheryears, it ranged from about 40 to 100% in the threetypes of samples.In 1982–1983, DDE and dieldrin residues were found tobe much higher than those of lindane and - and-endosulfan in Black River, Rio Pedro, ThomasRiver and Rio Cobre in the watershed. The ranges ofmeans of each residue in water (g L-1), sediment(ng g-1) and shrimp (ng g-1) samples, respectively, were:DDE, 0.059–102.0, 3.44–13.97, 0.344–14.57;dieldrin, 0.026–173.6, 1.21–2.75, 0.427–5.59;-endosulfan, bdl, 1.75–4.00, bdl;-endosulfan, bdl (below detectable limits), 2.51–9.48, bdl;and lindane, (bdl), 0.110–0.319, 2.90.In 1989–1990 and 1995–1996, residues of six OCs and two OPs were detected quite regularly. DDE, dieldrinand Chlorpyrifos residues were much higher than thoseof the other insecticides. The range of their meansin water (g L-1), sediment and shrimp (ng g-1),respectively, were: DDE, 1.66–19.76, 0.941–5.84,1.11–8.32; dieldrin, 0.077–7.22, 0.425–3.31,0.385–1.59; -endosulfan, 0.034–1.25, 0.021–1.22, 0.032–3.62; -endosulfan, 0.665–1.23,0.008–3.60, 0.005–3.97; endosulfan sulphate, 0.959–1.34, 0.035–3.08, 0.012–1.80; lindane, bdl,0.005–0.82, 1.19–1.56; chlorpyrifos, 0.702–4.06,0.005–1.51, 0.156–7.04; and diazinon, bdl, 0–0.150, 0.001–0.006. At the mouth of the river, whereit discharges into the sea, the levels of almost allthe residues were higher than upstream. 相似文献
309.
A strategic framework to eco-regionalize Ontario 总被引:1,自引:0,他引:1
310.
Hwan-Man Park Amar K. Mohanty Lawrence T. Drzal Ellen Lee Deborah F. Mielewski Manjusri Misra 《Journal of Polymers and the Environment》2006,14(1):27-35
Injection molded nanocomposites have been successfully fabricated from cellulose acetate (CA), eco-friendly triethyl citrate
(TEC) plasticizer, and organically modified clay with and without maleic anhydride grafted cellulose acetate butyrate (CAB-g-MA)
as a compatibilizer. The effects of processing conditions such as mixing methods, pre-plasticizing times, extruder retention
times (RT) and addition of compatibilizer on the performance of these nanocomposites have been evaluated. The cellulosic plastic
with CA/TEC (80/20 wt%) was used as the polymer matrix for nanocomposite fabrication. The morphologies of these nanocomposites
were evaluated through X-ray diffraction (XRD) and transmission electron microscopy (TEM) studies. The mechanical properties
of the nanocomposites were measured and have been correlated with the XRD and TEM observations. From all of the sequential
mixing methods used, powder–powder mixing leads to the most transparent nanocomposites. Cellulosic plastic-based nanocomposites
obtained using increased pre-plasticizing times and RT showed better exfoliated structures. In the system containing compatibilizer,
the minimum retention time required for obtaining almost completely exfoliated hybrid nanocomposites was shorter than in the
system without compatibilizer. 相似文献