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排序方式: 共有1365条查询结果,搜索用时 312 毫秒
911.
Sharon C. Long Jeanine D. Plummer 《Journal of the American Water Resources Association》2004,40(6):1433-1448
ABSTRACT: A renewed emphasis on source water protection and watershed management has resulted from recent amendments and initiatives under the Safe Drinking Water Act and the Clean Water Act. Knowledge of the impact of land use choices on source water quality is critical for efforts to properly manage activities within a watershed. This study evaluated qualitative relationships between land use and source water quality and the quantitative impact of season and rainfall events on water quality parameters. High levels of specific conductance tended to be associated with dense residential development, while organic carbon was elevated at several forested sites. Turbidity was generally higher in more urbanized areas. Source tracking indicators were detected in samples where land use types would predict their presence. Coliform levels were statistically different at the 95 percent confidence levels for winter versus summer conditions and dry versus wet weather conditions. Other water quality parameters that varied with season were organic carbon, turbidity, dissolved oxygen, and specific conductance. These results indicate that land use management can be effective for mitigating impacts to a water body; however, year‐ round, comprehensive data are necessary to thoroughly evaluate the water quality at a particular site. 相似文献
912.
Brian A. Joyce Wesley W. Wallender Till Angermann Barry W. Wilson Ingeborg Werner Michael N. Oliver Frank G. Zalom John D. Henderson 《Journal of the American Water Resources Association》2004,40(4):1063-1070
ABSTRACT: Pesticide runoff from dormant sprayed orchards is a major water quality problem in California's Central Valley. During the past several years, diazinon levels in the Sacramento and San Joaquin Rivers have exceeded water quality criteria for aquatic organisms. Orchard water management, via post‐application irrigation, and infiltration enhancement, through the use of a vegetative ground cover, are management practices that are believed to reduce pesticide loading to surface waters. Field experiments were conducted in Davis, California, to measure the effectiveness of these management practices in reducing the toxicity of storm water runoff. Treatments using a vegetative ground cover significantly reduced peak concentrations and cumulative pesticide mass in runoff for first flush experiments compared with bare soil treatments. Post‐application irrigation was found to be an effective means of reducing peak concentrations and cumulative mass in runoff from bare soil treatments, but showed no significant effect on vegetated treatments. 相似文献
913.
L. Donald Duke Paul G. Beswick 《Journal of the American Water Resources Association》1997,33(4):825-838
ABSTRACT: Pollutants in urban storm water runoff, a significant and increasing fraction of pollutants in some waters of the U.S., originate from multiple activities. The industrial sector, one source category, is subject to federal and state-level storm water pollution prevention regulations, primarily General NPDES Permits that rely heavily on facility operators to identify themselves and develop appropriate site-specific pollutant controls. Degree of compliance is not readily determined and enforcement is inhibited because no publicly-available inventories contain data necessary to comprehensively identify facilities required to comply. This research evaluates the first stage of compliance, facility self-identification, concentrating on the motor-vehicle, transportation industry category using data at three scales: statewide, regional, and local or watershed. Data for California statewide and for the Los Angeles region show about 8 percent to 15 percent of motor-vehicle transportation facilities have complied with first-stage requirements. However, facility-specific evaluation in one Los Angeles County watershed suggests less than 50 percent of facilities in the industry conduct industrial activities of the kind covered by regulations; others need not comply. Results show strong variation by industry category. Second-stage compliance, follow-up reporting, is also evaluated for the Los Angeles region. About 17 percent to 34 percent of facilities completing first-stage requirements have also completed second-stage requirements. 相似文献
914.
Runoff and soil loss from steep slopes treated with low cost bioengineering measures 总被引:1,自引:0,他引:1
Soil loss and surface runoff patterns were studied in erosion plots developed on manmade steep slopes (60 percent) over three years (1997–2000) in which rainfall ranged from 1338.4 to 1429.2 mm/year. Surface runoff and soil loss was examined under three different rainfall intensity classes. Runoff was mainly controlled by the rainfall distribution pattern on the seasonal scale. The soil loss was influenced by runoff during the first year. Both soil loss and runoff were reduced due to bioengineering measures in the first year irrespective of species planted. In the third year, combined effects of growth of grasses on protected plots, soil compaction and sediment exhaustion was noticed on runoff and soil loss. This was reflected by reduction in the runoff and soil loss from untreated and treated plots. In the high intensity class, reduction in runoff in treated plots was about 50 percent in three years and reduction in soil loss ranged between 94–95 percent in all plots. Physical treatment with brushwood structures was more efficient in erosion control in the low intensity class. 相似文献
915.
916.
华北农牧交错带夏季降水变率及其与前期下垫面热力状况的关系 总被引:18,自引:3,他引:18
华北农牧交错带夏季降水有很大的变率 ,频繁的干旱对农牧业生产有严重影响。论文分析了1880年以来的夏季降水变化特征 ,近百年来农牧交错带夏季降水有明显的阶段性。功率谱分析显示有35年左右的周期。年代际尺度的波动是干湿变化的重要背景。以250mm等雨量线表示的农牧交错带南北位置也有明显的年际和年代际的变化 ,在1978年以前和以后的两段时期 ,平均位置有显著的差别 ,前后平均有大约1.5个纬度的变化。农牧交错带夏季降水与前期春季亚欧地区大范围的温度异常有较好的关系。印度和巴基斯坦及相邻印度洋地区是显著的正相关区 ;亚洲西部的内陆地区是显著的负相关区。这两个地区春季的温度能解释农牧交错带夏季降水方差的15 %左右。 相似文献
917.
Li Xiuzhen Wu Kunjun Gong PeiyuInstitute of Zoology Chinese Academy of Sciences Beijing China 《环境科学学报(英文版)》1993,(2)
Effects of cycling and constant temperature on development and reproduction of the armyworm, Mythimna separata (Walker) were investigated by rearing the insects on the artificial diet under temperatures covering low(16-24℃ vs. 20 ℃ ), medial(20-28℃ vs. 24℃ ) and high(24-32 ℃ vs. 28 ℃) regions. In the low region, all the immature stages of the insect developed significantly faster under alternating temperatures than at corresponding constant temperatures. For the medial region, their development was little affected by variable temperatures. For the high region, developmental durations tended to be longer under cycling temperatures except egg stage.Mean fecundities of the adult moths markedly increased under cycling temperatures as compared with those at respective constant temperature in all regions.Possible reasons for effect of alternating temperatures on insect development are discussed in some details. 相似文献
918.
919.
硒对烤烟的生态毒理效应及临界指标研究 总被引:4,自引:0,他引:4
通过营养液水培试验,研究了不同浓度Se对烤烟生物量、叶绿素a、叶绿素b、叶绿素a+b、类胡萝卜、SOD、POD和MDA活性的影响。Se胁迫下的烟株生长受到抑制,浓度越高,抑制效应越明显;低浓度Se对烤烟叶片中叶绿素a、叶绿素b、叶绿素a+b和类胡萝卜含量有促进作用,并提高烟株体内活性氧防御体系,使MDA酶含量下降;高浓度Se则对其有抑制作用,对活性氧防御体系产生胁迫效应,MDA上升,SOD、POD酶活性下降;相关分析表明,除MDA呈极显著正相关外,其余均呈极显著负相关。MDA含量变化为Se胁迫烤烟生长的最敏感生理指标。 相似文献
920.