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41.
Despite numerous reviews suggesting that microbial biosensors could be used in many environmental applications, in reality they have failed to be used for which they were designed. In part this is because most of these sensors perform in an aqueous phase and a buffered medium, which is in contrast to the nature of genuine environmental systems. In this study, a range of non-exhaustive extraction techniques (NEETs) were assessed for (i) compatibility with a naphthalene responsive biosensor and (ii) correlation with naphthalene biodegradation. The NEETs removed a portion of the total soil naphthalene in the order of methanol > HPCD > βCD > water. To place the biosensor performance to NEETs in context, a biodegradation experiment was carried out using historically contaminated soils. By coupling the HPCD extraction with the biosensor, it was possible to assess the fraction of the naphthalene capable of undergoing microbial degradation in soil. 相似文献
42.
Riprap, consisting of large boulders or concrete blocks, is extensively used to stabilize streambanks and to inhibit lateral erosion of rivers, yet its effect on river morphology and its ecological consequences have been relatively little studied. In this paper, we review the available information, most of it culled from the “grey” literature. We use a simple one‐dimensional morphodynamic model as a conceptual tool to illustrate potential morphological effects of riprap placement in a gravel‐bed river, which include inhibition of local sediment supply to the channel and consequent channel bed scour and substrate coarsening, and downstream erosion. Riprap placement also tends to sever organic material input from the riparian zone, with loss of shade, wood input, and input of finer organic material. Available information on the consequences for the aquatic ecosystem mainly concerns effects on commercially and recreationally important fishes. The preponderance of studies report unfavorable effects on local numbers, but habitat niches created by openings in riprap can favorably affect invertebrates and some small fishes. There is a need for much more research on both morphological and ecosystem effects of riprap placement. 相似文献
43.
44.
Plants offer metabolically rich floral nectar to attract visiting pollinators. The composition of nectar includes not only
sugars, but also amino acids. We have examined the amino acid content of the nectar of ornamental tobacco and found that it
is extremely rich (2 mM) in proline. Because insect pollinators preferentially utilize proline during the initial phases of
insect flight and can reportedly taste proline, we determined whether honeybees showed a preference for synthetic nectars
rich in proline. We therefore established an insect preference test and found that honeybees indeed prefer nectars rich in
the amino acid proline. To determine whether this was a general phenomenon, we also examined the nectars of two insect-pollinated
wild perennial species of soybean. These species also showed high levels of proline in their nectars demonstrating that plants
often produce proline-rich floral nectar. Because insects such as honeybees prefer proline-rich nectars, we hypothesize that
some plants offer proline-rich nectars as a mechanism to attract visiting pollinators. 相似文献
45.
In Part I, the concepts of inherent, local and distant residence times (DRTs) were reviewed as metrics of the extent to which chemical discharges or emissions in one region or box are transported to distant regions. In this second part, the concepts are applied to geographically relevant systems to illustrate their applicability to the assessment of chemicals for long-range transport potential (LRTP). It is shown that the relative ranking of chemicals as characterized by the DRT method is similar to that of the characteristic travel distance concept. A DRT source-receptor matrix is developed that can express the chemical-specific potential of source regions to contaminate a specific receptor region of concern such as the Arctic. The matrix can be modified to identify for a specific source region the likely destinations of emissions as well as to assess the relative vulnerability of regions in the global environment to contaminants of concern. 相似文献
46.
47.
Water level management in Mississippi River Pool 25 differentially influences off-channel habitats in the mid-pool and lower
pool. Hydrologic models indicate lower pool off-channel habitats dry with greater frequency and duration compared to similar
habitats at mid-pool. We examined the influence of this contrasting hydrology on substrate characteristics, organic matter,
macroinvertebrate, and fish communities in off-channel habitats during 2001–2003. Benthic organic matter standing stocks were
stable in mid-pool habitats but lower pool values were variable because of annual differences in moist-soil vegetation production.
Generally, small-bodied and multivoltine invertebrate taxa had high community biomass and dominated lower pool habitats, whereas
longer-lived and large-bodied taxa were more abundant and had higher community biomass in mid-pool habitats having longer
hydroperiods. Fish communities were dominated by cyprinids in both habitats, and mid-pool habitats tended to be higher in
overall species richness. Unique fish taxa were collected in each pool, with primarily rheophilic forms in mid-pool habitats
and limnophilic forms in lower pool habitats. Results indicate that contrasting hydrology associated with a mid-pool control
point directly and indirectly influences biological communities in off-channel habitats. Further, management regimes that
promote hydrologic diversity in off-channel habitats may enhance biological diversity at larger spatial and temporal scales. 相似文献
48.
Reid VanBenthysen Ethan Thibaudeau Brad L. Kinsey 《Journal of Manufacturing Processes》2013,15(2):194-200
The specimen parameter that is often mentioned with respect to the ability to achieve electromagnetic forming (EMF) is the specimen thickness. If the skin depth is small compared to this parameter, efficient forming will be achieved. However, another parameter that may affect the ability to achieve efficient forming is the specimen's planar area, i.e., the length and width of the specimen. This would particularly become an important factor if EMF is used to fabricate meso/microscale components. In this research, a flat spiral coil was used to flange 0.508 mm thickness, CuZn30 specimens of varying widths (i.e., 10, 14, 18, 22, 35, and 47 mm). These widths were varied in order to modify the projected area of the coil over the specimen. Results showed that a decrease in the specimen width was generally associated with a decrease in forming (i.e., lower flanging angle) due to edge effects in induced eddy currents. Since the magnetic field distribution from the flat spiral coil is asymmetric, material was overhung on both sides of the die. This yielded an extra half turn on the left side of the specimen, and increased forming. The die was also translated to assess differences in flanging generated. In order to achieve meso/microforming with EMF, attention to the interaction between coil design and specimen dimensions is required. 相似文献
49.
In this, Part I of a two-part series, a review is presented of some generally appreciated residence time properties of multimedia models. The novel concept of “distant residence time” (DRT) is developed to provide additional insights into the characterization of environmental transport. DRT is the proportionality constant between the rate of emission of a contaminant into one compartment or region and the mass that results at steady-state in a distant compartment. The concept, which can be viewed as an expression of environmental mobility, is illustrated for various configurations of compartments and is shown to be consistent with the concepts of global fractionation and cold condensation. The dynamic responses of chemical quantities at distant locations to changing emission rates are also discussed. It is shown that approximate solutions for DRTs and their time dependence are useful for characterizing the long-range transport of chemicals and for interpreting monitoring data. 相似文献
50.