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701.
Philippe G. Vidon Alan R. Hill 《Journal of the American Water Resources Association》2006,42(4):1099-1112
ABSTRACT: This study evaluates a conceptual model developed for riparian zones in Ontario, Canada, that links landscape hydrogeological characteristics to riparian ground water hydrology and nitrate removal efficiency. Data from a range of riparian sites in the United States and Europe suggest that the riparian zone types identified in the model are consistent with patterns of riparian hydrology and nitrate flux and removal in many humid temperate landscapes. These data also support the view that a riparian width of less than 20 m is often sufficient for effective nitrate removal unless riparian sediments are coarse grained or nitrate transport occurs mainly in surface‐fed ground water seeps. This study assesses the possibility of using topographic, soil, surficial geology, and vegetation maps to determine landscape attributes linked by the model to riparian zone hydrological functioning and nitrate removal efficiency. Although mappable data can help in determining broad classes of riparian zones, field visits are necessary to determine non‐mappable riparian attributes such as seeps, organic horizons, and permeable sediment depth in the riparian zone. This research suggests that the conceptual model could be used for landscape management purposes in most temperate landscapes with minor modifications and that the hydrological component of the model could be adapted for contaminants other than nitrate. 相似文献
702.
Kester GB Brobst RB Carpenter A Chaney RL Rubin AB Schoof RA Taylor DS 《Journal of environmental quality》2005,34(1):80-90
A wide array of organic chemicals occur in biosolids and other residuals recycled to land. The extent of our knowledge about the chemicals and the impact on recycling programs varies from high to very low. Two significant challenges in regulating these materials are to accurately determine the concentrations of the organic compounds in residuals and to appropriately estimate the risk that the chemicals present from land application or public distribution. This paper examines both challenges and offers strategies for assessing the risks related to the occurrence of organic compounds in residuals used as soil amendments. Important attributes that must be understood to appropriately characterize and manage the potential risks for organic chemicals in biosolids include toxicity and dose response, transport potential, chemical structure and environmental stability, analytical capability in the matrix of interest, concentrations and persistence in waste streams, plant uptake, availability from surface application versus incorporation, solubility factors, and environmental fate. This information is complete for only a few chemicals. Questions persist about the far greater number of chemicals for which toxicity and environmental behavior are less well understood. This paper provides a synopsis of analytical issues, risk assessment methodologies, and risk management screening alternatives for organic constituents in biosolids. Examples from experience in Wisconsin are emphasized but can be extrapolated for broader application. 相似文献
703.
Alan J. Potok Frank H. Quinn 《Journal of the American Water Resources Association》1979,15(6):1538-1555
ABSTRACT: A one-dimensional hydraulic transient model has been designed for water resource studies of Lake Ontario and the Upper St. Lawrence River. The model simulates water surface profiles and flows in the St. Lawrence River between Lake Ontario and the Moses-Saunders Power Dam under both open water and ice-covered conditions. Errors in water surface elevations were found to be less than 0.2 feet during quasi-steady conditions on the river. Comparable errors occurred during the ice-covered conditions. A sensitivity analysis found the model to be most sensitive to the roughness coefficients and the flow through the power dam. 相似文献
704.
Bruce P. Hayden Robert Dolan Scott Hoffman Alan Robinson 《Environmental management》1978,2(3):209-218
Beach erosion on Cinnamon Bay in the U.S. Virgin Islands results from storm waves in the North Atlantic. The net trend of erosion, however, is due to local environmental degradation. Reef die-back, initiated during the period of high sedimentation associated with 18th and 19th century sugar cane cropping, has reduced the rate of generation of new coral sands. Sand losses to deep water during periods of storm waves are not replenished. Engineering measures designed to check erosion at Cinnamon Bay have had little effect in this environment of low wave energies, but sand deficiency. The appropriate environmental focus for management of reef-beach systems is reef health and thus, water quality. 相似文献
705.
Alan R. Johnson 《Environmental management》1988,12(4):515-523
The state of an ecosystem may be represented by a multidemensional state vector,x. The goal of ecosystem management is to insure that the ecosystem remains within some setX of acceptable states, such thatx X. Since ecosystem management decisions must be based on limited knowledge, a small number of diagnostic variables must be found which accurately reflect ecosystem state. If the vector of diagnostic variables, , is found to be within a specified set , the state vectorx is predicted to be withinX. The selection and use of such diagnostic variables is examined in the context of an aquatic ecosystem simulation model. Techniques used in searching for diagnostic criteria include multiple linear regression, discriminant analysis, and visual inspection of graphical data displays. The adequacy of a diagnostic criterion as a predictor of ecological risk is demonstrated to be a function of the associated rates of type I and type II statistical errors. A simple cost-benefit analysis is undertaken to illustrate one approach for choosing an optimal balance between these error rates. 相似文献
706.
Employee's job destination choices, as part of the turnover process, reflect options for internal organizational or external labor market moves. A sample of 477 employees in 15 firms was used to decipher how bio‐demographic, job, plant, and labor market characteristics are related to five alternative job destinations. Multivariate logistic regression and odds–ratio analyses compared the five models confirming that different sets of variables influence each of the destination choices. Coworkers' intentions have a major significant impact on all destination options. The findings have implications for present turnover models, career paths, and promotion progression in the firm. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
707.
A Comparison of Urban-Proximate and Urban-Distant Wilderness Users on Selected Variables 总被引:1,自引:1,他引:0
Alan W. Ewert 《Environmental management》1998,22(6):927-935
/ The underlying premise of this study is that wilderness areas attract visitors desiring or expecting different wilderness experiences. In this study, wilderness areas were dichotomized according to distance from a large urban center (urban-proximate vs urban-distant). Four wilderness areas in southern California were used as the study sites. Comparisons were made on selected attributes commonly associated with the wilderness experience. Differences were observed on a number of variables such as acceptable number and type of encounters with other visitors, management preferences, and preferred group sizes. The findings of this study are congruent with those from previous studies and suggest that distance to large urban centers may be a functional variable in explaining differences among selected wilderness attributes.KEY WORDS: Expectancy theory; Normative standards; Wilderness; Wilderness experience; Urbanization 相似文献
708.
Batch adsorption experiment with four sulfide minerals - Chalcocite galena, pyrite and sphalerite - were used to study for the adsorption and desorp-tion behavior of La (III) in the presence of EDTA, a model humic matter. Linear adsorption was found in all cases.The presence of soluble organic complexing ligand should reduce the mobility of La (III) in porous media and its transport to groundwater in the percolating soil solution. Binding mechanism is proposed to account for this preferential binding behavior. 相似文献
709.
The rapid rate of development in the South Carolina (SC) coastal zone has heightened public concern for the condition of the state's estuaries, and alerted scientists to the potential that novel and adverse effects on estuarine ecosystems may result. Although well-developed databases from long-term monitoring programs exist for many variables valuable in predicting and following system responses, information on phytoplankton distributions in SC estuaries has lagged. Knowledge of the dynamical relationship between environmental (e.g., nutrient quantity and quality) and biological (e.g., grazing) regulation, and phytoplankton biomass and composition is critical to understanding estuarine susceptibility to eutrophication or harmful algal blooms (HABs). Recently, SC scientists from federal, state, and academic institutions established a collaborative monitoring program to assess HAB distribution and ecology statewide. The South Carolina Harmful Algal Bloom Program includes: a) intensive temporal monitoring at areas of known HAB occurrence or those exhibiting symptoms potentially related to HABs (e.g., prevalent fish lesions), b) extensive spatial monitoring in coordination with existing statewide efforts, c) a citizen volunteer monitoring network, d) nutrient response bioassays, and e) laboratory-based physiological experiments on HAB isolates. By combining trip-wire surveillance and rapid response systems, routine monitoring of environmental parameters and HAB distribution, and process-oriented studies examining the physiological functioning of HAB species, an enhanced understanding of the impact and environmental control of HABs in SC estuaries will be achieved. The application of this approach to studies on the distribution and physiological ecology of a new widespread SC red tide, and to the discovery of several potentially toxic blooms (including Pfiesteria) in SC holding ponds, are described. 相似文献
710.
Alan J. Domaracki Gopal Sistla Sury N. Putta 《Journal of the Air & Waste Management Association (1995)》2013,63(11):1068-1072
Air parcel trajectories originating from three locations in New York State are calculated for a three year period using the ARL-ATAD long-range transport model. Model output consisting of a trajectory segment's end point longitude and latitude position are analyzed to describe the long-range transport climatology by computing the frequency of occurrence of segment end points terminating over 33 receptor areas comprising east-central North America and a portion of the Atlantic Ocean. Results of the frequency of occurrence data show how often air pollutants emitted at or near the origin may be expected to drift over a specific downwind region. For the New York City airshed, it was found that 26.2% of the trajectories remain over New York State for transport times of 3 h and the frequency decreases to 5.2% after 24 h of transport. Approximately 40% of all trajectories are found to be over the Atlantic Ocean after 3 h of transport. When allowances are made for losses of data over the Atlantic Ocean, up to 64% of all trajectories are over the Atlantic Ocean after 24 h of transport. This frequency of trajectories over the Atlantic Ocean was found to be in agreement with wet and dry deposition modeling results conducted for power plants in New York City. 相似文献