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2.
Michela Marchi Sven Erik JørgensenEloy Bécares Ilaria CorsiNadia Marchettini Simone Bastianoni 《Ecological modelling》2011,222(16):2992-3001
Using a dynamic model of Lake Chozas developed by Marchi et al. (2011), we tested three hypotheses about recovery of the indigenous community and water quality after radical changes caused by introduction of an invasive allochthonous crayfish, Procambarus clarkii:
- 1.
- Can the lake resist the pressure of an invasive species, like P. clarkii, by adaptation?
- 2.
- Can the ecosystem recover when all the crayfish are removed and low phosphorus concentrations persist in inflow water?
- 3.
- Does the simulated recovery of submerged vegetation occur at a total phosphorus concentration below 100 mg TP m−3, as estimated by Scheffer et al. (1993), Scheffer (1997), Jeppesen et al. (1998) and Zhang et al. (2003)?
- 1.
- Lake Chozas can at least partly resist by adaptation. A combination of possible parameter changes could lead to a significant increase in eco-exergy.
- 2.
- Removal of the phosphorus represented by crayfish (by harvesting) implies complete recovery of the lake and its eco-exergy, albeit not necessarily with the same organisms having the same properties.
- 3.
- The expected hysteresis created by introduction and harvesting of crayfish is observed under the following conditions: phytoplankton dominance at total phosphorus ≥ about 200-250 mg TP m−3 and submerged vegetation returns at total phosphorus < 100 mg TP m−3.
3.
Increasing antibacterial resistance and pathogenicity in the environment is of growing concern due to its potential human risk. In the present study, 236 Escherichia coli isolates were collected from Wenyu River in China on drugless (48 isolates) and quinolone-containing plates (189 isolates). Their minimum inhibitory concentrations (MICs) were determined ranging from 0.125 μg mL−1 to 128 μg mL−1. Mutation points related to fluoroquinolone resistance were observed at S83 to L and D87 to N or Y in the GyrA subunit and S80 to R or I and E84 to G in the ParC subunit. Generally, MICs of LEV and GAT are dependent on the patterns of these mutation points. The profile with three mutation points was related to LEV-resistant E. coli isolates, and the (S83L, D87N + S80I) mutation profile was most prevalent (65.7%) in LEV-resistant isolates, while a large proportion of isolates, even those with three mutation points, were susceptive to GAT. The incidence of virulence factors in LEV-resistant isolates (44.7%, 59/132) was much higher than in nonresistant isolates (23.1%, 24/104) (χ2 = 11.925, 1° of freedom, p < 0.001) indicating that fluoroquinolone-resistant E. coli would pose a potential risk. A similar distribution was also found in isolates resistant to GAT (χ2 = 7.843, 1° of freedom, p = 0.0079). 相似文献
4.
《Journal of environmental science and health. Part. B》2013,48(4):665-673
Abstract Monosodium methanearsonate (MSMA)-resistant and -susceptible common cocklebur (Xanthium strumarium L.) and cotton (Gossypium hirsutum L.) were treated with MSMA. Plant parameters analyzed were: glutathione synthetase activity, selected amino acid (arginine, glutamic acid, alanine, citrulline, glutamine, and glutathione) content and arsenic content (MSMA, total arsenic, and arsonate). No reduction of arsenic from the parent pentavalent form present in MSMA to the trivalent form was detected. Arginine, glutamic acid, and glutamine content increased in tissue three days after MSMA treatment. Glutathione content decreased during the first three days after treatment; however, five days after treatment the resistant biotype of cocklebur and cotton had elevated glutathione levels (8–20 times greater, respectively). Glutathione Synthetase activity was higher in cotton than in either of the cocklebur biotypes; MSMA did not affect its activity in cotton or either cocklebur biotype. Resistant biotypes have a slightly higher activity than the susceptible biotype. Tolerance of cotton to MSMA may be related to glutathione synthetase activity and possibly to the presence of phytochelatins. Also, increased glutathione levels in the resistant biotype may implicate phytochelatin involvement in the resistance mechanism. 相似文献
5.
Disturbance of natural vegetation by camping: Experimental applications of low-level stress 总被引:3,自引:0,他引:3
David N. Cole 《Environmental management》1995,19(3):405-416
Previously undisturbed sites in four different vegetation types were camped on for one night and for four nights. Changes
in vegetation cover and vegetation height were measured after camping and one year later. Results are presented separately
for different campsite zones—parts of the site where campers slept, cooked meals, and stored their packs. Just one night of
camping was sufficient to cause evident impact in all four vegetation types, although the amount of impact varied significantly
between zones and between vegetation types. Vegetation impact on campsites used four nights was generally less than twice
as severe as impact on the sites used one night. The effects of camping on vegetation were also predicted for 12 other vegetation
types on the basis of vegetational responses to experimental trampling. These results suggest that impact can almost always
be minimized by confining camping to a small number of campsites instead of dispersing use across many campsites. 相似文献
6.
D. L. DeAngelis P. J. Mulholland J. W. Elwood A. V. Palumbo A. D. Steinman 《Environmental management》1990,14(5):685-697
In systems where production is limited by the availability of a nutrient, nutrient input to and recycling within the system
is related to the resilience, or speed of recovery, of a system to its steady state following a disturbance. In particular,
it is shown that the return timeT
s
of the system to steady state, or the inverse of the resilience, is approximately equal to the mean turnover time of the
limiting nutrient in the system. From this relationship, it is possible to understand and predict how various properties of
food webs and their environments affect resilience. These properties include nutrient input rate, loss rate, size of the detritus
compartment, and trophic structure. The effects of these properties on resilience are described by using simple mathematical
models.
To test model predictions, experimental studies of the response of periphyton-dominated stream ecosystems to disturbance are
being conducted on a set of laboratory streams in which nutrient inputs and grazing intensity are regulated at different levels.
In streams without snail grazers (low-grazed streams), 90% recirculation of stream water to reduce nutrient inputs resulted
in longer turnover times (T
r
) of phosphorus within the stream compared with once-through flow. However, in streams with snail grazers (high-grazed streams),
there were no differences in phosphorus turnover time between once-through and partially recirculated treatments. Results
on the rate of recovery of periphyton from a flood/scour disturbance to each stream partially support the model prediction
of a positive relationship between ecosystem return time (T
s
) and nutrient turnover time (T
r
) within the streams. 相似文献
7.
Kimiran-Erdem A Arslan EO Sanli Yurudu NO Zeybek Z Dogruoz N Cotuk A 《Environmental monitoring and assessment》2007,125(1-3):219-228
A hundred Enterococcus strains were isolated from seawater samples collected from coastal areas of Istanbul. Isolates were identified to the species
level using standard biochemical tests specified by Facklam and Collins. The species distribution was as follows Enterococcus
faecalis (96%), Enterococcus gallinarum (3%) and Enterococcus solitarius (1%). The resistance of bacteria to both heavy metals (zinc [Zn], iron [Fe], cadmium [Cd], chrome [Cr], cobalt [Co]) and
antibiotics (ampicillin 10 μg [AP], penicillin G 10 Units [PG], gentamycin 10 μg [GM], streptomycin 10 μg [S], chloramphenicol
10 μg [C], erythromycin 15 μg [E], kanamycin 30 μg [K], amikacin 30 μg [AK], nalidixic acid 30 μg [NA], and vancomycin 30 μg
[VA]) was evaluated. None of the strains was resistant to VA. It was found that among the 100 isolates, those that exhibit
resistance to antibiotics, particularly NA, S and K, were also resistant all the heavy metals tested. To our knowledge this
is the first report focusing on determination of resistance of environmental enterococci found in Istanbul against heavy metals
and antibiotics. Thus, combined expressions of antibiotic and heavy metal resistance may help to reinforce ecological and
epidemiological studies and to determine the role of these strains in antibiotic and heavy metal resistance dissemination. 相似文献
8.
The automotive industry is developing designs and manufacturing processes for a new generation of electric motors intended for use in hybrid and electric vehicles. This paper is focused on using solid-state welding to join rectangular wires in the fabrication of motor stators. Resistance welding has not typically been applied to copper due to its very high electrical conductivity; however through optimization of the current and pressure profiles, excellent quality copper-to-copper joints have been demonstrated with a technique known as resistance mash welding. A better understanding of resistance mash welding characteristics will help advancements in its application for stators. The limitations of this application will be discussed. 相似文献
9.
10.
Kelsey RH Scott GI Porter DE Thompson B Webster L 《Environmental monitoring and assessment》2003,81(1-3):337-348
Multiple Antibiotic Resistance (MAR) analysis and regression modeling techniques were used to identify surface water areas impacted by fecal pollution from human sources, and to determine the effects of land use on fecal pollution in Murrells Inlet, a small, urbanized, high-salinity estuary located between Myrtle Beach and Georgetown, South Carolina. MAR analysis was performed to identify areas in the estuary that are impacted by human-source fecal pollution. Additionally, regression analysis was performed to determine if an association exists between land use and fecal coliform densities over the ten-year period from 1989 to 1998. Land-use variables were derived using Geographic Information System (GIS) techniques and were used in the regression analysis.MAR analyses were conducted by comparing the frequency and patterns of antibiotic resistance found in Escherichia coli isolates derived from surface water samples and from sewage sources in the Murrells Inlet sewage collection system. The MAR results suggest that the majority of the fecal pollution detected in the Murrells Inlet estuary may be from non-human sources, including fecal coliforms isolated from areas in close proximity to high densities of active septic tanks.A MAR Index, which measures the frequency of antibiotic resistance, was calculated for each of twenty-three water samples and nine sewage samples. The antibiotic resistance pattern comparisons were performed using cluster analysis. Although the MAR indices indicated that several surface water sites had potential human-source contamination, the cluster analysis suggests that only one sampling site had MAR patterns that were similar to those found in the sewage samples. This site was in close proximity to several large pleasure boats as well as a sewage collection system lift station, but was not near areas with active septic tanks. The results of the regression analysis also suggest that sewage sources and rainfall runoff from urbanized areas may contribute to fecal pollution in the estuary. 相似文献