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791.
Thomas F. Cuffney Michael R. Meador Stephen D. Porter Martin E. Gurtz 《Environmental monitoring and assessment》2000,64(1):259-270
The condition of 25 stream sites in the Yakima River Basin, Washington, were assessed by the U.S. Geological Survey's National Water-Quality Assessment Program. Multimetric condition indices were developed and used to rank sites on the basis of physical, chemical, and biological characteristics. These indices showed that sites in the Cascades and Eastern Cascades ecoregions were largely unimpaired. In contrast, all but two sites in the Columbia Basin ecoregion were impaired, some severely. Agriculture (nutrients and pesticides) was the primary factor associated with impairment and all impaired sites were characterized by multiple indicators of impairment. All indices of biological condition (fish, invertebrates, and algae) declined as agricultural intensity increased. The response exhibited by invertebrates and algae suggested a threshold response with conditions declining precipitously at relatively low levels of agricultural intensity and little response at moderate to high levels of agricultural intensity. This pattern of response suggests that the success of mitigation will vary depending upon where on the response curve the mitigation is undertaken. Because the form of the community condition response is critical to effective water-quality management, the National Water-Quality Assessment Program is conducting studies to examine the response of biota to gradients of land-use intensity and the relevance of these responses to water-quality management. These land-use gradient pilot studies will be conducted in several urban areas starting in 1999. 相似文献
792.
793.
The dispersion of pollutants from naturally ventilated underground parking garages has been studied in a boundary layer wind tunnel. Two idealized model setups have been analysed, one was simulating pollutant dispersion around an isolated rectangular building and one was representing dispersion in a finite array of idealized building blocks. Flow and dispersion close to modelled ground level emission sources was measured. The results illustrate the complexity of the flow around buildings and provide insight in pollutant transport from ground level sources located directly on building surfaces. As a result, areas critical with respect to high pollutant concentrations could be visualized. Particularly, the results show high concentration gradients on the surface of the buildings equipped with modelled emission sources. Inside the boundary layers on the building walls, a significant amount of pollutants is transported to upwind locations on the surface of the building. The paper documents the potential of physical modelling to be used for the simulation and measurement of dispersion close to emission sources and within complex building arrangements. 相似文献
794.
The in vivo toxic impact of chromium in its two forms(trivalent and hexavalent) on glycogen metabolism in the tissuesof freshwater field crab Barytelphusa guerini was studied.In a sublethal long-term exposure of 30, 60 and 90 days, thedepletion of glycogen and glucose levels reflected in theactivity of glycogenphosphorylases `a' and `ab'. A tissuespecific and time-dependent variation in tissue glucose reservesparelleled the progressive accumulation of haemolymph sugars.Trivalent and hexavalent chromium induced alterations in metabolite levels and in enzyme activities in the tissues. Themagnitude of responses were found more in the hexavalent formthan in trivalent form. 相似文献
795.
Affum HA Oduro-Afriyie K Nartey VK Adomako D Nyarko BJ 《Environmental monitoring and assessment》2008,137(1-3):15-24
Lichens collected in an unpolluted forest (background) in November 2004, transplanted at 41 sampling sites along the Madina-Tetteh
Quarshie road, retrieved in February 2005 and analysed were found to contain higher concentrations of Manganese (Mn), Vanadium
(V), lead, Cadmium (Cd), Chromium (Cr) and Nickel (Ni) than in the background area. Observations showed that of all the heavy
metals studied, Manganese concentrations were highest at all sampling points with maximum values around a traffic light, an
intersection and car fitting/mechanic workshops. Significant correlations were found between Ni and Mn, Mn and Cr and Mn and
V. Statistical analysis also revealed a relatively even dispersion of the studied elements on the eastern side of the road
than on the western side. 相似文献
796.
797.
May TW Fairchild JF Petty JD Walther MJ Lucero J Delvaux M Manring J Armbruster M 《Environmental monitoring and assessment》2008,137(1-3):213-232
The Solomon River Basin is located in north-central Kansas in an area underlain by marine geologic shales. Selenium is an
indigenous constituent of these shales and is readily leached into the surrounding groundwater. Portions of the Basin are
irrigated primarily through the pumping of selenium-contaminated groundwater from wells onto fields in agricultural production.
Water, sediment, macroinvertebrates, and fish were collected from various sites in the Basin in 1998 and analyzed for selenium.
Selenium concentrations were analyzed spatially and temporally and compared to reported selenium toxic effect thresholds for
specific ecosystem components: water, sediments, food-chain organisms, and wholebody fish. A selenium aquatic hazard assessment
for the Basin was determined based on protocol established by Lemly. Throughout the Basin, water, macroinvertebrate, and whole
fish samples exceeded levels suspected of causing reproductive impairment in fish. Population structures of several fish species
implied that successful reproduction was occurring; however, the influence of immigration of fish from low-selenium habitats
could not be discounted. Site-specific fish reproduction studies are needed to determine the true impact of selenium on fishery
resources in the Basin.
The U.S. Government’s right to retain a non-exclusive, royalty free license in and to any copyright is acknowledged. 相似文献
798.
Turias IJ González FJ Martin ML Galindo PL 《Environmental monitoring and assessment》2008,143(1-3):131-146
The 'Campo de Gibraltar' region is a very industrialized area where very few air pollution studies have been carried out. Up to date, no model has been developed in order to predict air pollutant levels in the different towns spread in the region. Carbon monoxide (CO), Sulphur dioxide (SO(2)) and suspended particulate matter (SPM) series have been investigated (years 1999-2000-2001). Multilayer perceptron models (MLPs) with backpropagation learning rule have been used. A resampling strategy with two-fold crossvalidation allowed the statistical comparison of the different models considered in this study. Artificial neural networks (ANN) models were compared with Persistence and ARIMA models and also with models based on standard Multiple Linear Regression (MLR) over test sets with data that had not been used in the training stage. The models based on ANNs showed better capability of generalization than those based on MLR. The designed procedure of random resampling permits an adequate and robust multiple comparison of the tested models. Principal component analysis (PCA) is used to reduce the dimensionality of data and to transform exogenous variables into significant and independent components. Short-term predictions were better than medium-term predictions in the case of CO and SO(2) series. Conversely, medium-term predictions were better in the case of SPM concentrations. The predictions are significantly promising (e.g., d (SPM 24-ahead) = 0.906, d (CO 1-ahead) = 0.891, d (SO2 1-ahead) = 0.851). 相似文献
799.
Yu Y Wen S Lü H Feng Y Wang X Sheng G Fu J 《Environmental monitoring and assessment》2008,137(1-3):275-285
The diurnal variation of atmospheric carbonyls and VOCs in a forest in south China were studied in summer 2004. Twenty kinds
of carbonyls and eight kinds of VOCs were identified and quantified. Formaldehyde and acetaldehyde were the two most abundant
carbonyls, while the most abundant VOCs were isoprene, followed by o-xylene. Most C3-C10 carbonyls had higher concentrations from 09:00 to 15:00, and their levels were lower during night-time and often reached
the lowest in early morning. Formaldehyde and acetaldehyde, however, showed two high levels in their diurnal patterns partly
due to their different sources and sinks. The VOCs had different diurnal patterns compared to most carbonyls. The highest
concentrations were observed from 03:00 to 06:00 for 1-butene, from 06:00 to 12:00 for isoprene, and from 12:00 to 15:00 for
α-pinene. The highest levels for aromatic hydrocarbons occurred during midnight and the lowest in late afternoon. According
to the study, emissions from vegetation and photo-oxidation of gas-phase hydrocarbons were the main sources for some carbonyls
and VOCs in this region. Other compounds, such as formaldehyde, acetaldehyde and BTEX, showed anthropogenic sources. 相似文献
800.