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91.
92.
Larry C. Tennyson Peter F. Ffolliott David B. Thorud 《Journal of the American Water Resources Association》1974,10(6):1246-1254
ABSTRACT: The behavior of intercepted snow on a stand of uneven-aged ponderosa pine in east-central Arizona was evaluated with the use of a super 8-mm time lapse movie camera to determine the relative significance of snowfall interception in the water yield of this type forest. A snow load index was developed to estimate interception storage for two trees in the field of view for discrete time periods. The snow load index. photographs, and climatic data were combined to describe accumulation and to identify and rank according to relative magnitudes the basic processes of canopy snow removal. The rate of snow accumulation was nonlinear with initial storage being rapid. then slowing with time. Most of the intercepted snow eventually reached the snowpack on the ground by snowslide and wind erosion or by snowmelt and subsequent stemflow and drippmg of meltwater, and was therefore not considered a significant loss to the water budget on site. Some water apparently was disposed of by the evaporation of meltwater and sublimation of canopy snow, but these losses appeared to be comparatively minor. 相似文献
93.
Ambient air quality standards and control strategies are implemented to protect humans and vegetation from adverse effects. We used a process-based tree-growth model (TREGRO) to show that over the past 37 years, changes in O3 exposure, with accompanying variation in climate, are reflected in changes in the growth of Pinus ponderosa Dougl. ex Laws. in the San Bernardino Mountains near Los Angeles, California, USA. Despite variation in temperature and precipitation over the study period (1963–1999), O3 exposure consistently reduced simulated tree growth. Simulated growth reductions increased concurrent with increasing O3 exposure. The maximum growth reduction occurred in 1979. As O3 exposures decreased during the 1980s and 1990s, effects on growth also decreased. This implies that emission control strategies taken to reduce exposures to attain O3 standards benefited P. ponderosa growth in the San Bernardino Mountains. This modeling approach provides a powerful tool for solving the difficult problem of evaluating regulatory effectiveness by simulating plant response using long-term climate and air pollution exposure records for a given region.Phone 541 754-4621 Fax 541 754-4799 相似文献
94.
Mark H. Eisenbies James A. Burger W. Michael Aust Steve C. Patterson 《Water, Air, & Soil Pollution: Focus》2004,4(1):217-233
The timing of forestry operations relative to weather conditions is a consideration in applying Forestry Best Management Practices (BMPs). Harvesting during different seasons can result in degrees of soil disturbance, the distribution of logging debris, and potentially future stand productivity. The purpose of this study is to examine the response of loblolly pine (Pinus taeda L.) stands after wet- and dry-weather harvesting combined with three site preparation treatments. A 20 × 20 meter grid was established in fifteen 20-year-old, 3.3-ha loblolly pine plantations in South Carolina. A census of soil physical disturbance and slash distribution was made after harvesting. Growth was measured on 1/125th-ha plots at ages two and five. Dry-weather harvested (DWH) sites were 91% undisturbed, and 9% compressed. Wet-weather harvested (WWH) sites were 41% undisturbed, and 59% disturbed. WWH sites averaged 9% bare soil, while DWH sites averaged 16% with 1 kg m-2 less logging residue; primarily in the form of heavy and light slash. At age five, the green-weight biomass of flat-planted DWH and WWH sites were 13.3 and 12.6 kg tree-1 respectively, and on the bedded DWH and WWH sites were 18.6 and 22.8 kg tree-1. Wet weather harvesting did not seem to adversely affect stand growth, and may have improved it. Due to a prolonged drought, bedding had a larger effect on WWH sites than DWH harvested sites. The effects of droughty conditions may be influencing treatment response on these highly productive sites; however, the long-term effects of harvesting on stand growth remain to be seen. 相似文献
95.
Monitoring and dispersion modelling of emissions from the fluidised bed combustion of poultry litter
Henihan AM Kelleher BP Leahy MJ Cummins E Leahy JJ 《Environmental monitoring and assessment》2003,85(3):239-255
Gaseous emissions from the fluidised bed combustion of chickenlitter were monitored and recorded. Emission data was used tocreate a dispersion model for a proposed site on a poultry farmin Limerick, Ireland. Variables within the combustion unit notonly influenced combustion but also emission levels ofpollutants such as SO2 and NOx. CO emissions decreased withuse of the correct ratio between fluidising and secondary air,the staging of secondary air and the degree of turbulence withwhich the secondary air is introduced. Dispersion modelling ofactual combustion at a proposed poultry unit predicted thatground level concentrations for the set of emissions data wouldbe below the limits and guidelines set by air quality standards.This was true for both and line source. Line sourceconcentration levels were less than those for point source. 相似文献
96.
利用静态箱-气相色谱法对鼎湖山3 种处于演替不同阶段的森林类型(季风常绿阔叶林、针阔叶混交林和马尾松林)的地表N2O 通量进行了 1 年的原位观测和研究.结果表明,3 种林型地表 N2O 通量按从大到小的顺序为:季风林>混交林>松林;不同林型间的 N2O 通量差异与森林土壤的性质有密切关系,C/N 比值较低的季风林凋落叶对土壤中产生N2O 的微生物过程有较为明显的促进作用;从全年来看,松林地表N2O 通量的季节变化不明显,而季风林和混交林的地表 N2O 通量在雨季存在明显的降雨驱动效应,统计分析显示在该地区影响森林地表N2O 通量的主要因子是土壤湿度. 相似文献
97.
Dandan Wang Jianjun Zhang Guodong Jia Haibo Zhang Ziqiang Liu 《Chemistry and Ecology》2017,33(6):528-542
The impacts of vegetation on soil erosion are closely associated with the combined effects of above- and below-ground components. In this study, we explore the effects and contributions of Robinia pseudoacacia litter cover and roots on soil erosion. Experiment sites under natural conditions with vegetation cover, plant roots and bare ground plots were investigated for overland flow discharges of 0.5, 1.0 and 2.0?L?s?1 and slope gradients of 8.7%, 17.6%, 26.8%, 36.4% and 46.6%. Results indicate that litter cover and roots have a significant impact on sediment reduction; soil loss was reduced by about 57% and plant roots had a greater impact on the reduction of soil erosion than litter cover. The combination of litter cover and plant roots had a significant effect on decreasing Kr, increasing τc and consequently strengthening soil resistance capacity to erosion. When plants and roots existed on the slopes, Kr decreased by 81% and 66%, and τc increased by 319% and 246%, respectively, in comparison with bare slopes. These results illustrate the importance of high-forest in controlling soil erosion by quantifying the specific contributions of litter cover and plant roots in erosion reduction in the Loess Plateau. 相似文献
98.
99.
溶解有机物(DOM)是决定水环境中铅(Pb)的形态、环境行为和生态风险的重要因子.然而,落叶DOM与Pb(II)络合作用的调控机制尚不清楚.光和微生物降解是调控DOM含量、组成与活性的两个关键过程.本研究运用降解培养实验、光谱学表征和荧光猝灭滴定,考察光和微生物降解单独作用和共同作用对芦苇落叶DOM的改造及其对DOM与Pb(II)相互作用的影响.激发-发射三维荧光光谱-平行因子分析共识别出4个类腐殖质组分(C1~C4)和1个类蛋白质组分(C5).类腐殖质组分更容易被光降解,类蛋白质组分则被微生物优先利用,光降解在短期的光-微生物降解过程中起主导作用.对于原始落叶DOM,Pb(II)主要与类腐殖质组分C1、C2和C4络合,C3组分只在光-微生物降解后的样品呈现显著荧光猝灭,类蛋白质组分C5在光和光-微生物降解后开始参与络合.类腐殖质C1与Pb(II)络合的条件稳定常数logKM在光降解后升高而在光-微生物降解后下降,C2和C4的logKM值经过各降解过程后均升高.降解后这3个组分参与络合的比例f和络合容量Fmax·f均显著降低,且光降解的影响显著高于微生物降解.这些结果表明,光降解和微生物降解对DOM丰度、组成和结构的改造将显著影响其与金属离子的络合稳定性和络合容量. 相似文献
100.
Coşkun M 《Environmental monitoring and assessment》2006,121(1-3):173-178
Austrian pine (Pinus nigra) bark was collected in thirty-seven localities in the Thrace region, Turkey, for the determination of airborne toxic metal distribution. Five toxic metals, As, Cd, Cu, Pb, and Zn, were monitored using atomic absorption spectrometry. Distribution maps of toxic elements in the region were plotted according to Geographic Information System technology. In general, the concentrations of all investigated elements were not high in the region apart from the vicinity of big cities, Tekirdag, Istanbul and, close to Bulgarian border. However, the highest concentrations were not at pollution level. They have a similar distribution pattern throughout the region. 相似文献