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751.
752.
Zhi-Jun Liu George R. Hallberg George P. Malanson 《Journal of the American Water Resources Association》1997,33(6):1219-1235
ABSTRACT: Most research on the temporal aspect of nitrate pollution in water resources has focused on surface water. Comprehensive studies on the dynamics of nitrate in ground water are lacking, especially on a drainage basin scale and for relatively long periods of time. In this study, structural equation modeling is applied in investigating the influences of climate, hydrology, and nitrogen management in agricultural production on nitrate concentration in the Big Spring Basin, Iowa, over a 10-year period. The study shows that for given hydrogeological settings, nitrogen management practices and climate are the two most important factors that affect nitrate dynamics. The long-term trend of nitrate is closely related to the nitrogen input primarily determined by management practices. The potential effects of nitrogen management, however, are contingent on the variations of climate. The improvements in water quality (reduced nitrate concentration and loads) in relation to improved nitrogen management are often overshadowed by the impact of climate, especially in extremely dry or wet years. The variations of climate and hydrology have much greater impacts on the nitrate dynamics than the changes in nitrogen input. This study reveals significant seasonal variation in the relations between nitrate concentration and influencing factors, which is also closely related to the seasonal variation in climate. Assessment of management practices and resultant water quality should consider the impact of short- and long-term climate dynamics. 相似文献
753.
754.
William A. Battaglin Lauren E. Hay Randolph S. Parker George H. Leauesley 《Journal of the American Water Resources Association》1993,29(6):1021-1028
ABSTRACT: The Gunnison River drains a mountainous basin in western Colorado, and is a large contributor of water to the Colorado River. As part of a study to assess water resource sensitivity to alterations in climate in the Gunnison River basin, climatic and hydrologic processes are being modeled. A geographic information system (GIS) is being used in this study as a link between data and modelers - serving as a common data base for project personnel with differing specialties, providing a means to investigate the effects of scale on model results, and providing a framework for the transfer of parameter values among models. Specific applications presented include: (1) developing elevation grids for a precipitation model from digital elevation model (DEM) point-elevation values, and visualizing the effects of grid resolution on model results; (2) using a GIS to facilitate the definition and parameterization of a distributed-parameters, watershed model in multiple basins; and (3) nesting atmospheric and hydrologic models to produce possible scenarios of climate change. 相似文献
755.
756.
George William Sherk 《Journal of the American Water Resources Association》1994,30(3):397-400
ABSTRACT: As population growth occurs in regions of the eastern United States that do not have abundant water supplies, new transbasin diversions may be required. Such diversions are exceptionally politically divisive and are at the core of most of the interstate water conflicts that presently exist in the eastern states. This study examines alternative means by which these conflicts might be resolved. The strengths and weaknesses of these alternatives are examined. The study concludes that the federal-interstate compact should be the preferred alternative by which interstate water conflicts in the eastern United States are resolved. 相似文献
757.
Zhenquan Chen Daniel E. Storm Michael D. Smolen C. T. Haan Mark S. Gregory George J. Sabbagh 《Journal of the American Water Resources Association》1994,30(4):589-594
ABSTRACT: A UNIX-based windows application was developed to integrate a phosphorus transport model with the Geographic Resources Analysis Support System (GRASS). The system prioritizes potential phosphorus loading from fields or cells in a watershed and can evaluate the effects of alternate management practices on phosphorus yield. The model simulates phosphorus loading by using a daily mass balance on a unit-area basis and incorporates the effects from rainfall, topography, soil properties, fertilizer and animal waste application, and management. Model predictions include dissolved and sediment-bound phosphorus yield, runoff volume, and sediment yield. Within the integrated GRASS-modeling system, the user can obtain model input data, execute the model using various options, rank model input and out. put data, and display them as GRASS-based maps or data tables. All functions are menu driven, developed using C language and X-window tools to run on a SUN workstation platform. The system provides a powerful and efficient tool for prioritizing phosphorus loading from nonpoint sources. 相似文献
758.
This study examines several different kinds of correlates of career-oriented mentoring experiences among early career managers and professionals. Survey data were collected from 416 respondents employed in a wide variety of jobs, organizations, and industries. The respondents averaged 30 years of age, and 28 per cent were women. Results indicated that younger, more work-involved respondents from higher socioeconomic origins received more career-oriented mentoring. In addition, managers received more mentoring than professionals, as did those who were higher in the organization hierarchy. While gender of the protégé was unrelated to the amount of career mentoring received, reasons are offered for this result. Various boundary conditions likely to affect mentoring processes are discussed and several directions are recommended for future research on mentoring. 相似文献
759.
760.
Patricia M. Dooris George M. Dooris Dean F. Martin 《Journal of the American Water Resources Association》1982,18(2):335-337
ABSTRACT: Phytoplankton were studied in lakes augmented with water from the Floridan aquifer and in control lakes. Augmented lakes exhibited enhanced phytoplankton diversity which was believed to be related to chemical changes in the lakes brought about as a result of ground water addition. In particular, elevated concentrations of inorganic carbon appeared to influence phytoplankton populations. 相似文献