RELATIONSHIP OF NITRATE CONCENTRATIONS TO DISTANCE OF WELL SCREEN OPENINGS BELOW CASING WATER LEVELS1

ABSTRACT: Data from 54 well in central and eastern Kansas developed in unconsolidated deposits of Quaternary age indicate that nitrate concentrations are inversely related to the depth of the well screen opening below the water level in the well casing because this relationship was found to exist in an area of Nebraska and in a large area of Kansas, the relationship is generally valid over a wide geo- graphical area. In addition, the data indicate that the incidence of nitrate concentrations exceeding 45 milligrams per liter and nitrate concentrations, in general, are significantly lower in water from wells with screens deeper than 25 feet below the water table in unconfined aquifers or where screens are placed in deep confined aquifers. No concentrations of nitrate greater than 45 milligrams per liter were in obseved wells where screens were deeper than 60 feet below the casing water level. These findings suggest that general placement of well screens as far below the water table as possible in unconfined unconsolidated aquifers in Kansas. and possibly other areas of the Midwest, may be an effective measure in preventing undesirable nitrate concentrations in ground water supplies. particularly in areas where nitrate is a problem.     

气候变化对淡水珍珠蚌种群的威胁

引言 在过去的100年中,淡水珍珠蚌Margaritfera margaritifera(L.)的数量在地球北区范围内已经下降到被IUCN列为濒危品种[1].人们认为主要原因是严重的工业污染和农业(有机)污染,采珠渔民的过度开采,寄主鲑科鱼类的减少,以及由于水力发电和河流管理计划的实施所造成的自然河床栖息环境的退化[2].     

Comparative Toxicities of Polar and Non-Polar Organic Fractions From Sediments Affected By the Exxon Valdez Oil Spill in Prince William Sound, Alaska

Standardized tests were applied to aromatic and polar fractions of sediment extracts to determine whether polar constituents or oxidative degradation products contributed significantly to the toxicity of sediments oiled by the Exxon Valdez spill. Intertidal sediment and pore-water samples were collected in September 1990 from two heavily oiled sites and an unoiled site in Prince William Sound (PWS). Methylene chloride extracts from these samples were fractionated by liquid chromatography into aliphatic, aromatic and polar fractions, and the aromatic and polar fractions were tested for toxicity using the Microtox^R test, bivalve larval mortality and development (Mytilus); several measures of genotoxicity in Mytilus, including SOS Chromotest^R, anaphase aberrations and sister chromatid exchange; and survival, anaphase aberrations and teratogenicity in coho salmon (Onchorhynchus kisutch). Microtox^R and SOS Chromotest^R protocols were applied in a screening mode to all samples, whereas other tests were applied only to selected fractions from two sites. Samples from Bay of Isles (oiled) were consistently more toxic (usually only 2 to 5-fold) than the Mooselips Bay (unoiled) samples, which gave very low responses in all tests. for both sites, however, responses to polar and aromatic fractions were about the same in most tests, suggesting that while the overall toxicity of the oil was low in these samples, at least part of that toxicity was derived from polar constituents. Compared to the parent hydrocarbons, polar oxidation products partition preferentially into pore-water and are more rapidly diluted and dispersed in the water column. These results suggest that polar oxidation products of petroleum hydrocarbons pose little risk to marine organisms, except possibly for infauna continuously exposed to pore-water in heavily oiled sediments. Independent surveys showed that sediment toxicity in PWS declined during 1989-1991 to near background levels, in accord with previous understanding of oil weathering and toxicity.     

The Seventh Kew Environmental Lecture: Our global future: climate change

The Kew lecture provides a major contribution to contemporary environmental views. The Hon. Timothy E. Wirth is US Under Secretary of State for Global Affairs and he is responsible within the US State Department for overseeing environment, population, human rights, refugee, narcotics and related programmes. He was elected to the US Senate from Colorado in 1986 and served until 1993 when he chose not to run for re-election. He was, previously, a Congressman for 12 years and was voted one of the 25 most effective Members of Congress. In 1992, he served as national co-chair of the Clinton – Gore presidential campaign. The lecture was delivered at the Royal Botanic Gardens, Kew, London, on 15 September 1997.     

The mental health of expatriate and Kosovar Albanian humanitarian aid workers

The mental health consequences of exposure to traumatic events and the risk factors for psychological morbidity among expatriate and Kosovar Albanian humanitarian aid workers have not been well studied. In June 2000, we used standardised screening tools to survey 285 (69.5%) of 410 expatriate aid workers and 325 (75.8%) of 429 Kosovar Albanian aid workers from 22 humanitarian organizations that were implementing health programmes in Kosovo. The mean number of trauma events experienced by expatriates was 2.8 (standard deviation: 2.7) and by Kosovar staff 3.2 (standard deviation: 2.8). Although only 1.1% of expatriate and 6.2% of Kosovar aid workers reported symptoms consistent with the diagnosis for post-traumatic stress disorder, 17.2% and 16.9%, respectively, reported symptoms satisfying the definition of depression. Regression analysis demonstrated that the number of trauma events experienced was significantly associated with depression for the two sets of workers. Organisational support services may be an important mediating factor and should be targeted at both groups.     

The implosion of the Calgary General Hospital: ambient air quality issues

This paper discusses the implosion of a large inner-city hospital in Calgary, Alberta, Canada, on October 4, 1998. Stationary and mobile air monitoring conducted after the implosion indicated there were several short-term air quality issues, including significant temporal increases in total suspended particles, particulate matter (PM) with aerodynamic diameter less than or equal to 10 microm (PM10), PM with aerodynamic diameter less than or equal to 2.5 microm (PM2.5), asbestos, and airborne and settled lead. In addition, the implosion created a dust cloud that traveled much further than expected, out to 20 km. The ability of an implosion to effectively aerosolize building materials requires the removal of all friable and nonfriable forms of asbestos and all Pb-containing painted surfaces during pre-implosion preparatory work. Public advisories to mitigate personal exposure and indoor migration of the implosion dust cloud constituents should extend to 10 or 20 km around an implosion site. These findings point to a number of complex and problematic issues regarding implosions and safeguarding human health and suggest that implosions in metropolitan areas should be prohibited. Further work to characterize the public health risks of conventional versus implosion demolition is recommended.     

Detection of scale-specific community dynamics using wavelets

The response of ecological communities to anthropogenic disturbance is of both scientific and practical interest. Communities where all species respond to disturbance in a similar fashion (synchrony) will exhibit large fluctuations in total biomass and dramatic changes in ecosystem function. Communities where some species increase in abundance while others decrease after disturbance (compensation) can maintain total biomass and ecosystem function in the face of anthropogenic change. We examined dynamics of the Little Rock Lake (Wisconsin, USA) zooplankton community in the context of an experimental pH manipulation conducted in one basin of the lake. A novel application of wavelets was used to partition patterns of synchrony and compensation by time scale. We find interestingly that some time series show both patterns of synchrony and compensation depending on the scale of analysis. Within the unmanipulated basin, we found subtle patterns of synchrony and compensation within the community, largely at a one-year time scale corresponding to seasonal variation. Within the acidified lake basin, dynamics shifted to longer time scales corresponding to the pattern of pH manipulation. Comparisons between pairs of species in different functional groups showed both strong compensatory and synchronous responses to disturbance. The strongest compensatory signal was observed for two species of Daphnia whose life history traits lead to synchrony at annual time scales, but whose differential sensitivity to acidification led to compensation at multiannual time scales. The separation of time scales inherent in the wavelet method greatly facilitated interpretation as patterns resulting from seasonal drivers could be separated from patterns driven by pH manipulation.     

Evaluating the long-term metacommunity dynamics of tree hole mosquitoes

Four different conceptual models of metacommunities have been proposed, termed "patch dynamics," "species sorting", "mass effect", and "neutral". These models simplify thinking about metacommunities and improve our understanding of the role of spatial dynamics both in structuring communities and in determining local and regional diversity. We tested whether mosquito communities inhabiting water-filled tree holes in southeastern Florida, U.S.A., displayed any of the characteristics and dynamics predicted by the four models. The densities of the five most common species in 3-8 tree holes were monitored every two weeks during 1978-2003. We tested relationships between habitat variables and species densities, spatial synchrony, the presence of life history trade-offs, and species turnover. Dynamics showed strong elements of species sorting, but with considerable turnover, as predicted by the patch dynamics model. Consistent with patch dynamics, there was substantial asynchrony in dynamics for different tree holes, substantial species turnover in space and time, and an occupancy/colonization trade-off. Substantial correlations of density and occupancy with tree hole volume were consistent with the species-sorting model, but unlike this model, species did not have permanent refuges. No evidence of mass effects was found, and correlations between habitat variables and dynamics were inconsistent with neutral models. Our results did not match a single model and therefore caution against overly simplifying metacommunity dynamics by using one dynamical characteristic to select a particular metacommunity perspective.     

Real-world vehicle emissions: A summary of the 15th coordinating research council on-road vehicle emissions workshop

The Coordinating Research Council held its 15th workshop in April 2005, with nearly 90 presentations describing the most recent mobile source-related emissions research. In this paper, the authors summarize the presentations from researchers who are engaged in improving our understanding of the contribution of mobile sources to air quality. Participants in the workshop discussed emission models and emission inventories, results from gas- and particle-phase emissions studies from spark-ignition and diesel-powered vehicles (with an emphasis in this workshop on particle emissions), effects of fuels on emissions, evaluation of in-use emissions control programs, and efforts to improve our capabilities in performing on-board emissions measurements, as well as topics for future research.