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排序方式: 共有149条查询结果,搜索用时 265 毫秒
61.
Angela M. Wallace Melanie V. Croft-White Jan Moryk 《Environmental monitoring and assessment》2013,185(9):7857-7875
Impacts of urbanization on aquatic ecosystems are intensifying as urban sprawl spreads across the global land base. The urban stream syndrome (USS) identifies “symptoms” associated with urban development including changes in biotic communities, hydrology, water chemistry, and channel morphology. Direct relationships between road density (as surrogate of urbanization) and indicators of the USS were identified for streams in the Toronto region. Significant negative relationships were revealed between road density and biological (fish and benthic macroinvertebrate) richness, diversity, and fish Index of Biotic Integrity scores. Significant positive relationships were found between road density and tolerant fish/benthic macroinvertbrates, benthos Family Biotic Index scores, mean summer stream temperature, stream flashiness, and several water quality variables. Analysis of biological data showed that only four fish species and a reduced number of benthic macroinvertebrate families remained at the most urbanized sites. Road density was found to be a major determinant in both the fish and benthic macroinvertebrate community structure. 相似文献
62.
Hunt J Anderson B Phillips B Tjeerdema R Largay B Beretti M Bern A 《Environmental pollution (Barking, Essex : 1987)》2008,156(2):348-358
Evidence of ecological impacts from pesticide runoff has prompted installation of vegetated treatment systems (VTS) along the central coast of California, USA. During five surveys of two on-farm VTS ponds, 88% of inlet and outlet water samples were toxic to Ceriodaphnia dubia. Toxicity identification evaluations (TIEs) indicated water toxicity was caused by diazinon at VTS-1, and chlorpyrifos at VTS-2. Diazinon levels in VTS-1 were variable, but high pulse inflow concentrations were reduced through dilution. At VTS-2, chlorpyrifos concentrations averaged 52% lower at the VTS outlet than at the inlet. Water concentrations of most other pesticides averaged 20-90% lower at VTS outlets. All VTS sediment samples were toxic to amphipods (Hyalella azteca). Sediment TIEs indicated toxicity was caused by cypermethrin and lambda-cyhalothrin at VTS-1, and chlorpyrifos and permethrin at VTS-2. As with water, sediment concentrations were lower at VTS outlets, indicating substantial reductions in farm runoff pesticide concentrations. 相似文献
63.
Gas-phase photolytic production of hydroxyl radicals in an ultraviolet purifier for air and surfaces
David R. Crosley Melanie Doyle-Eisele Jacob D. McDonald 《Journal of the Air & Waste Management Association (1995)》2017,67(2):231-240
We have measured the concentration of hydroxyl radicals (OH) produced in the gas phase by a commercially available purifier for air and surfaces, using the time rate of decay of n-heptane added to an environmental chamber. The hydroxyl generator, an Odorox® BOSS? model, produces the OH through 185-nm photolysis of ambient water vapor. The steady-state concentration of OH produced in the 120 m3 chamber is, with 2σ error bars, (3.25 ± 0.80) × 106 cm?3. The properties of the hydroxyl generator, in particular the output of the ultraviolet lamps and the air throughput, together with an estimation of the water concentration, were used to predict the amount of OH produced by the device, with no fitted parameters. To relate this calculation to a steady-state concentration, we must estimate the OH loss rate within the chamber owing to reaction with the n-heptane and the 7 ppb of background hydrocarbons that are present. The result is a predicted steady-state concentration in excellent agreement with the measured value. This shows we understand well the processes occurring in the gas phase during operation of this hydroxyl radical purifier.Implications: Hydroxyl radical air purifiers are used for cleaning both gaseous contaminants, such as volatile organic compounds (VOCs) or hazardous gases, and biological pathogens, both airborne and on surfaces. This is the first chemical kinetic study of such a purifier that creates gas-phase OH by ultraviolet light photolysis of H2O. It shows that the amount of hydroxyls produced agrees well with nonparameterized calculations using the purifier lamp output and device airflow. These results can be used for designing appropriate remediation strategies. 相似文献
64.
A discrepancy is reported between the karyotype of both direct and cultured chorionic villus cells (46,XX) and a fetal skin biopsy (47,XX,+18). The significance of this result is discussed and compared with similar discordant findings reported in the literature. 相似文献
65.
Melanie von der Wiesche und Dietrich Werner 《Umweltwissenschaften und Schadstoff-Forschung》1998,10(3):179-187
Zusammenfassung Nach wie vor findet der Faktor Zeit in den Umweltwissenschaften zu wenig Beachtung. Langfristige Beobachtungen und Me?reihen
in der ?kologischen Forschung, wie sie für die Bewertung und Prognosen von Umweltzust?nden und-entwicklunger, unabdingbar
w?ren, scheinen die Ausnahme zu sein. Besonders komplexe ?kosysteme, wie terrestrische oder marine Systeme, kennzeichnen sich
auch durch l?ngere natürliche Eigenzeiten, die deshalb bei ihrer Erforschung berücksichtigt werden mü?ten. In diesem Zusammenhang
soll verdeutlicht werden, welche Rolle zeitliche Parameter speziell in der terrestrischen ?kosystemforschung spielen. Zu diesem
Zweck wurde eine Datenbank konzipiert, die Hauptcharakteristika von ?kosystemaren Analysen aufnehmen kann. Forschungsberichte
verschiedener ?kosystemforschungszentren wurden zur Aufnahme in die Datenbank bearbeitet. Gezielte Abfragen auf den Datenpool
erm?glichen dann eine Auswertung hinsichtlich der zeitlichen Ausrichtung bestimmter Untersuchungen. Dabei stellte sich — neben
einer teilweisen Ungleichheit der Zeitskalen von Experiment und Realit?t — u.a. heraus, da? l?ngerfristige Untersuchungen
?u?erst selten durchgeführt werden. So vielf?ltig die Gründe für dieses Defizit auch sein m?gen, sie k?nnen nicht von der
Forderung nach st?rkerer Berücksichtigung von langzeitlichen Beobachtungen ablenken, will die ?kosystemforschung die an sie
gestellten Aufgaben erfüllen.
相似文献
66.
Connectivity of Streams and Wetlands to Downstream Waters: An Integrated Systems Framework 总被引:1,自引:0,他引:1
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Scott G. Leibowitz Parker J. Wigington Jr. Kate A. Schofield Laurie C. Alexander Melanie K. Vanderhoof Heather E. Golden 《Journal of the American Water Resources Association》2018,54(2):298-322
Interest in connectivity has increased in the aquatic sciences, partly because of its relevance to the Clean Water Act. This paper has two objectives: (1) provide a framework to understand hydrological, chemical, and biological connectivity, focusing on how headwater streams and wetlands connect to and contribute to rivers; and (2) briefly review methods to quantify hydrological and chemical connectivity. Streams and wetlands affect river structure and function by altering material and biological fluxes to the river; this depends on two factors: (1) functions within streams and wetlands that affect material fluxes; and (2) connectivity (or isolation) from streams and wetlands to rivers that allows (or prevents) material transport between systems. Connectivity can be described in terms of frequency, magnitude, duration, timing, and rate of change. It results from physical characteristics of a system, e.g., climate, soils, geology, topography, and the spatial distribution of aquatic components. Biological connectivity is also affected by traits and behavior of the biota. Connectivity can be altered by human impacts, often in complex ways. Because of variability in these factors, connectivity is not constant but varies over time and space. Connectivity can be quantified with field‐based methods, modeling, and remote sensing. Further studies using these methods are needed to classify and quantify connectivity of aquatic ecosystems and to understand how impacts affect connectivity. 相似文献
67.
68.
Traditionally, evolutionary ecology and conservation biology have primarily been concerned with how environmental changes
affect population size and genetic diversity. Recently, however, there has been a growing realization that phenotypic plasticity
can have important consequences for the probability of population persistence, population growth, and evolution during rapid
environmental change. Habitat fragmentation due to human activities is dramatically changing the ecological conditions of
life for many organisms. In this review, we use examples from the literature to demonstrate that habitat fragmentation has
important consequences on oviposition site selection in insects, with carryover effects on offspring survival and, therefore,
population dynamics. We argue that plasticity in oviposition site selection and maternal effects on offspring phenotypes may
be an important, yet underexplored, mechanism by which environmental conditions have consequences across generations. Without
considering the impact of habitat fragmentation on oviposition site selection, it will be difficult to assess the effect of
fragmentation on offspring fitness, and ultimately to understand the impact of anthropogenic-induced environmental change
on population viability. 相似文献
69.
70.
Denitrification in alluvial wetlands in an urban landscape 总被引:1,自引:0,他引:1
Harrison MD Groffman PM Mayer PM Kaushal SS Newcomer TA 《Journal of environmental quality》2011,40(2):634-646
Riparian wetlands have been shown to be effective "sinks" for nitrate N (NO3-), minimizing the downstream export of N to streams and coastal water bodies. However, the vast majority of riparian denitrification research has been in agricultural and forested watersheds, with relatively little work on riparian wetland function in urban watersheds. We investigated the variation and magnitude of denitrification in three constructed and two relict oxbow urban wetlands, and in two forested reference wetlands in the Baltimore metropolitan area. Denitrification rates in wetland sediments were measured with a 15N-enriched NO3- "push-pull" groundwater tracer method during the summer and winter of 2008. Mean denitrification rates did not differ among the wetland types and ranged from 147 +/- 29 microg N kg soil(-1) d(-1) in constructed stormwater wetlands to 100 +/- 11 microg N kg soil(-1) d(-1) in relict oxbows to 106 +/- 32 microg N kg soil(-1) d(-1) in forested reference wetlands. High denitrification rates were observed in both summer and winter, suggesting that these wetlands are sinks for NO3- year round. Comparison of denitrification rates with NO3- standing stocks in the wetland water column and stream NO3- loads indicated that mass removal of NO3- in urban wetland sediments by denitrification could be substantial. Our results suggest that urban wetlands have the potential to reduce NO3- in urban landscapes and should be considered as a means to manage N in urban watersheds. 相似文献