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231.
232.
Charles R. Fellows Patrick L. Brezonik 《Journal of the American Water Resources Association》1980,16(4):635-641
ABSTRACT: Direct measurements indicate that subsurface seepage in the littoral zone contributed 17.5 and 2.0 percent of the total hydraulic inputs, respectively, to Lakes Conway and Apopka, Florida. Two variations of seepage measuring devices were evaluated and gave relative standard deviations of 7 and 24 percent. Measurement inaccuracies were minimized by using large diameter (0.9 cm ID) plastic tubing. For a given transect perpendicular to shore, flow patterns were reproducible over time. Seepage flows ranged from 0 to 112 1/m2-day and most were between 4 and 30 1/m2-day. The detection limit was about 0.2 1/m2-day for a one-hour collection period. Seepage occured primarily within 30 m of shore and generally decreased exponentially with distance from shore. The shape of the bottom profile influenced flow patterns; lake bottoms with steeper slopes had higher flows that were compressed within a narrower zone. After a short-term rain event at Lake Conway, seepage flows increased rapidly to 2.4 times the prerain flow for 1 h and decreased to near background within about 6 h. 相似文献
233.
234.
Patrick Schleppi Frank Hagedorn Isabelle Providoli 《Water, Air, & Soil Pollution: Focus》2004,4(2-3):453-467
Nitrate leaching was measured over seven years of nitrogen (N) addition in a paired-catchment experiment in Alptal, central Switzerland (altitude: 1200 m, bulk N deposition: 12 kg ha-1 a-1). Two forested catchments (1500 m2 each) dominated by Picea abies) were delimited by trenches in the Gleysols. NH4NO3 was added to one of the catchments using sprinklers. During the first year, the N addition was labelled with 15N. Additionally, soil N transformationswere studied in replicated plots. Pre-treatment NO3 --N leaching was 4 kg ha-1 a-1 from both catchments, and remained between 2.5 and 4.8 kg ha-1 a-1 in the control catchment. The first year of treatment induced an additional leaching of 3.1 kg ha-1, almost 90% of which was labelled with 15N, indicating that it did not cycle through the large N pools of the ecosystem (soil organic matter and plants). These losses partly correspond to NO3 - from precipitation bypassing the soil due to preferential flow. During rain or snowmelt events, NO3 - concentration peaks as the water table is rising, indicating flushing from the soil. Nitrification occurs temporarily along the water flow paths in the soil and can be the source of NO3 - flushing. Its isotopic signature however, shows that this release mainly affects recently applied N, stored only between runoff events or up to a few weeks. At first, the ecosystem retained 90% of the added N (2/3 in the soil), but NO3 - losses increased from 10 to 30% within 7 yr, indicating that the ecosystem became progressively N saturated. 相似文献
235.
A survey-based system for safety measurement and improvement 总被引:4,自引:0,他引:4
PROBLEM:A task force sought to develop a method for safety measurement that is reliable and valid and provides a framework for improvement efforts. METHOD: Over a 10-year period, through working in a chemical company with about 6,000 employees and over 50 plants, the authors researched the use of employee surveys to measure safety and as a diagnostic tool for improvement efforts. RESULTS: The statistical studies indicate that this survey, which evolved from the Minnesota Safety Perception Survey, is both reliable and valid as a measurement tool. The survey measures important components of the management system including (a) management's demonstration of commitment to safety, (b) education and knowledge of the workforce, (c) effectiveness of the supervisory process, and (d) employee involvement and commitment. This study also describes anecdotal evidence that the diagnostic element of the survey enables the development of effective action plans to improve safety performance. This evidence includes ratings of the process by plant managers who have used it. IMPACT ON INDUSTRY: The survey and related methods have helped to improve safety performance in several companies. 相似文献
236.
Arbaugh M Bytnerowicz A Grulke N Fenn M Poth M Temple P Miller P 《Environment international》2003,29(2-3):401-406
Toxic effects of photochemical smog on ponderosa and Jeffrey pines in the San Bernardino Mountains were discovered in the 1950s. It was revealed that ozone is the main cause of foliar injury manifested as chlorotic mottle and premature needle senescence. Various morphological, physiological and biochemical alterations in the affected plants have been reported over a period of about 40 years of multidisciplinary research. Recently, the focus of research has shifted from studying the effects of ozone to multiple pollutant effects. Recent studies have indicated that the combination of ozone and nitrogen may alter biomass allocation in pines towards that of deciduous trees, accelerate litter accumulation, and increase carbon sequestration rates in heavily polluted forests. Further study of the effects of multiple pollutants, and their long-term consequences on the mixed conifer ecosystem, cannot be adequately done using the original San Bernardino Mountains Air Pollution Gradient network. To correct deficiencies in the design, the new site network is being configured for long-term studies on multiple air pollutant concentrations and deposition, physiological and biochemical changes in trees, growth and composition of over-story species, biogeochemical cycling including carbon cycling and sequestration, water quality, and biodiversity of forest ecosystems. Eleven sites have been re-established. A comparison of 1974 stand composition with data from 2000 stand composition indicate that significant changes in species composition have occurred at some sites with less change at other sites. Moist, high-pollution sites have experienced the greatest amount of forest change, while dryer low-pollution sites have experienced the least amount of stand change. In general, ponderosa pine had the lowest basal area increases and the highest mortality across the San Bernardino Mountains. 相似文献
237.
The economic inputs and outputs for the Possum Point Biological Station in Belize during 1990–1992 are described to illustrate
some aspects of an ecotourism operation. Eight hundred fifty-four people in 59 groups visited Possum Point during the study
period to tour rain forests, estuaries, and coral reefs. The economic input to Possum Point from these groups increased from
$74,552 in 1990 to $166,268 in 1992. Outputs were for license fees, capital improvements, goods and services, labor, fossil
fuels, and development of a historic sugar mill site. An annual donation was also made to a scholarship fund for local Belizean
students. The net cash balance of income and outputs changed from negative (−$6678) in 1990 to positive (+$4811) in 1992,
suggesting development of the economic operation. Possum Point meets the economic criteria for ecotourism by feeding back
some tourist monies for community and environmental support, particularly donations for the sugar mill site and the scholarship
fund. Most of the outputs from Possum Point (about 80%) were retained in the local economy through employment and purchases,
which have a positive influence on the local community. We conclude that ecotourism operations, such as Possum Point, offer
important sustainable development opportunities for Belize. 相似文献
238.
James L. Oliver Patrick L. Hudson 《Journal of the American Water Resources Association》1987,23(2):257-269
ABSTRACT: Temperature and dissolved oxygen concentrations were measured monthly from January 1971 to December 1982 at 1-m depth intervals at 13 stations in Keowee Reservoir in order to characterize spatial and temporal changes associated with operation of the Oconee Nuclear Station. The reservoir water column was i to 4°C warmer in operational than in non-operational years. The thermo-dine was at depths of 5 to 15 m before the operation of Oconee Nuclear Station, but was always below the upper level of the intake (20 m) after the station was in full operation; this suggests that pumping by the Oconee Nuclear Station had depleted all available cool hypolimnetic water to this depth. As a result summer water temperatures at depths greater than 10 m were usually 10°C higher after plant operation began than before. By fall the reservoir was nearly homothemious to a depth of 27 m, where a thermocine developed. Seasonal temperature profiles varied with distance from the plant; a cool water plume was evident in spring and a warm water plume was present in the summer, fall, and winter. A cold water plume also developed in the northern section of the reservoir due to the operation of Jocassee Pumped Storage Station. Increases in the mean water temperature of the reservoir during operational periods were correlated with the generating output of the power plant. The annual heat load to the reservoir increased by one-third after plant operations began. The alteration of the thermal stratification of the receiving water during the summer also caused the dissolved oxygen to mix to greater depths. 相似文献
239.
Effects of stream channelization on exports of nitrogen and phosphorus from north Carolina coastal plain watersheds 总被引:1,自引:0,他引:1
Laura A. Yarbro Edward J. Kuenzler Patrick J. Mulholland Robert P. Sniffen 《Environmental management》1984,8(2):151-160
Nitrogen and phosphorus exports from channelizedstream watersheds were elevated over those from nearby natural swamp-stream watersheds. Nitrate exports were significantly greater from channelized-stream watersheds, and higher exports were attributed to faster groundwater drawdown, continual streamflow, and transformation of former floodplain to croplands following channelization. Exports of total organic nitrogen and total nitrogen were also significantly greater from channelized-stream watersheds. Differences in the exports of ammonium, filterable reactive phosphorus, and filterable unreactive phosphorus between the two watershed types were not detectable. Particulate phosphorus exports were significantly higher from channelized-stream watersheds, presumably because of greater erosion potential of nearby croplands and steep channel banks in the altered watersheds. The presence of nonpoint sources of pollution increased watershed exports of nutrients regardless of stream morphology. Examination of nutrient budgets for a portion of swamp floodplain at the base of one natural-stream watershed revealed that changes in local groundwater hydrology and stream morphology associated with channelization appeared to have greater effect on nutrient exports than simply the loss of bordering forested floodplain. 相似文献
240.
Stefaniak AB Hoover MD Day GA Dickerson RM Peterson EJ Kent MS Schuler CR Breysse PN Scripsick RC 《Journal of environmental monitoring : JEM》2004,6(6):523-532
Little is known about the physicochemical properties of beryllium aerosols associated with increased risk of beryllium sensitization and chronic beryllium disease (CBD). Such information is needed to evaluate whether airborne mass of beryllium is the appropriate metric of exposure or alternatively to provide a scientific basis for using information on particle size, surface area, and chemistry to support an improved exposure limit based on bioavailability through the inhalation and dermal routes of exposure. Thus, we used a suite of analytical techniques to characterize aerodynamically size-fractionated beryllium particles and powders that have been associated in epidemiological studies with higher prevalence of CBD. Aerosol particles were sampled from the ventilation systems of production lines for powders of beryllium metal and beryllium oxide and for ingots of copper-beryllium alloy. End product powders from the metal and oxide production lines were also collected.Particles released during production of beryllium metal were found to be complex, having heterogeneous composition, including reactive species such as fluorine. Powders from beryllium metal production were of high purity with only a minor component of beryllium oxide. Both particles and powders from oxide production were high-purity oxide. Particles released during production of copper-beryllium alloy were heterogeneous, being predominantly copper oxides. Thus, all particles and powders contain at least some beryllium in the form of beryllium oxide.These data justify efforts to thoroughly characterize beryllium aerosol properties when performing exposure assessments. The data also suggest that differences in particle chemical composition, size, number, and surface area may influence bioavailability of beryllium and contribute to risk of CBD. However, a scientific basis does not yet exist to replace mass as the current metric of exposure. 相似文献