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971.
Madhusudan MD 《Environmental management》2003,32(4):466-475
Dissolved copper was toxic to wild rice (Zizania palustris) seedlings when exposed in water from the seed collection site of Swamp Creek, Crandon, Wisconsin, USA, and in laboratory-prepared artificial or reconstituted water. Seeds for the study were harvested, then held through a portion of dormancy, in Swamp Creek. After 60 days they were shipped to a laboratory, chilled, and tested with copper after germination. The end point of the tests was net gain in wet weight of the seedlings; additionally, a pronounced reduction in root development was observed. Using measured concentrations, the lowest no-observable-effect concentration (NOEC) in our study was 37 g/liter in Swamp Creek water and the lowest-observable-effect concentration (LOEC) was 59 g/liter. However, it appeared that there was a point at which concentrations of copper above 400 g/liter did not result in any measurable effect or exhibit a definitive dose–response. Because the results in Swamp Creek water were more relevant to the possibility of local metals additions and the association of reduced seedling growth by copper was more powerful in this water, we derived an equation to express the relationship between copper concentration and toxicity for Swamp Creek water. As an example, we would expect a 3.0% reduction in seedling growth at 5.0 g/liter copper. Seedling roots were particularly affected and the resultant plants may be less well anchored and more susceptible to dislodging than plants not exposed to copper. Further refinement of the methodology may be used to address effects of other contaminants impacting rice beds in North America.
This study was conducted while the first author was employed by the U.S. Geological Survey, Mid-continent Ecological Science Center, Fort Collins, Colorado 相似文献
972.
Extending livestock grazing to the steep slopes has led to unstable grazing systems in the East African Highlands, and new
solutions and approaches are needed to ameliorate the current situation. This work was aimed at studying the effect of livestock
grazing on plant attributes and hydrological properties. The study was conducted from 1996 to 2000 at the International Livestock
Research Institute at Debre Ziet Research Station. Two sites were selected: one at 0–4% slope, and the other at 4–8% slope.
The treatments were: (1) no grazing (control); (2) light grazing, 0.6 animal unit months per hectare (aum/ha); (3) moderate
grazing, 1.8 aum/ha; (4) heavy grazing, 3.0 aum/ha; (5) very heavy grazing, 4.2 aum/ha; (6) initially plowed and continuously
very heavily grazed, 4.2 aum/ha. The result showed that species richness, infiltration rate, bare ground, and soil loss significantly
varied with grazing pressure. Species richness was higher in grazed plots compared to nongrazed plots. Biomass yield improved
on heavily grazed plots as cow dung accumulated over years. Cynodon dactylon plant species persisted with livestock grazing pressure in both sites. Infiltration rate improved and soil erosion declined
in all treatments after the first year. 相似文献
973.
R. M. Khanbilvardi A. S. Rogowski 《Journal of the American Water Resources Association》1984,20(6):865-874
Ability to adequately estimate sediment yield is an important step in dealing effectively with soil erosion problems. Predictions of sediment yield made using the Universal Soil Loss Equation (USLE) with different forms of sediment delivery ratio (SDR) are compared with those made by Modified USLE (MUSLE) and a fundamentally derived Erosion-Deposition Model (EDM). The USLE and USLE with SDR are poor predictors of sediment yield for individual storms compared to the MUSLE and EDM. Although MUSLE gave better results than USLE it showed somewhat more scatter of data points than the recently developed EDM. 相似文献
974.
975.
本文根据中国光温生态试验资料及四川水稻品比试验与气象观测的历史资料,讨论了早、中稻感温性和对温度的适应性,分析了播期、纬度、海拔等因素与稻种需求积温量的关系,以水稻品种类型对热量的适应性指标为依据,考虑四川水稻气候生态的差异性,划分出水稻综合气候生态类型区。 相似文献
976.
ABSTRACI:. Slash burning is a common site preparation technique used after timber harvest throughout the Southeastern United States. Little quantitative information exists on the hydrologic response to burn severity. This study compared the effects of low-severity and high-severity burns on runoff and sediment yields during rainfall simulation and during natural rainfall in the Southern Appalachian Mountains. Fire severity was largely determined by moisture conditions of the forest floor prior to ignition. Runoff and sediment yield variability was high between plots within the same treatment area due to differences in forest floor characteristics and infiltration rates. Conditions of high-severity resulted when burning was conducted with relatively dry fuels. Sediment yields were 40-times greater for the high-severity treatment areas than the low-severity treatment areas. 相似文献
977.
200 years of sustainability in forestry: Lessons from history 总被引:4,自引:0,他引:4
K. Freerk Wiersum 《Environmental management》1995,19(3):321-329
Since the end of the 1980s the concept of sustainable development has gained general acceptance, but much uncertainty still
exists on how to operationalize this concept. In forestry the concept of sustainability has been an accepted principle since
the 18th century. The experiences with its application in forestry may contribute towards obtaining a better insight into
the implications and operational significance of the concept of sustainability. This article describes the history of sustainability
in forestry, including the various social values on which its interpretation has been based. The original principle of sustained
yield has gradually been broadened to a more inclusive principle of sustainable forest management. The dynamics in social
valuation of forest resources resulted in various attempts at practical operationalization of the principle. Notwithstanding
200 years of efforts to operationalize the concept of sustainability, its exact application in forestry remains troublesome.
Three lessons are drawn: (1) the need to recognize the different nature of ecological limits and social dynamics, (2) the
role of dynamic social values with respect to forest resources, and (3) the significance of operational experiences in trying
to attain sustainability within a concrete context. 相似文献
978.
G. R. Sands I. D. Moore C. R. Roberts 《Journal of the American Water Resources Association》1982,18(5):831-839
ABSTRACT: A computer model was developed in order to establish a yield predictive relationship and to estimate the water requirements for supplemental irrigation of horticultural crops in the humid region. Alternative distribution systems were developed and designed using the results from the computer model and Wood's (1980) pipe network algorithm. The capital, operational, and maintenance costs of the distribution and recommended on-farm irrigation systems were determined and used to evaluate the economic feasibility of the alternative designs. Results show that the concentration of irrigated area along the distribution system, the length of the distribution system, and cropping system all have an important effect on the economic feasibility of supplemental irrigation in Wayne County, Kentucky. 相似文献
979.
R. J. Brozka G. L. Rolfe L. E. Arnold 《Journal of the American Water Resources Association》1982,18(1):139-145
ABSTRACT: Two intermittent streams on oak-hickory watersheds in southern Illinois were gaged with a V-notch weir and sampled with an automatic water sampler. Baseline data was collected for a period of three years. Flow volume showed large variations between years and watersheds. Water samples were analyzed for Na, K, Ca, Mg, ortho-P, and NO3-N. Water quality was consistently high, but there were significant differences between the watersheds during the calibration period. One watershed was clearcut in November 1979. One year of postharvest data has been analyzed. Flow volume increased 95 percent, but there was no evidence of increased sedimentation. There were significant increases in the stream water concentrations of K, Mg, and NO3-N of 18 percent, 8 percent, and 274 percent, respectively. Nutrient budgets for the site were not adversely affected by the harvest. The clearcutting operation appears to have had a small impact on the watershed due to minimal disturbance during the logging and below normal precipitation the first year following the harvest. 相似文献
980.
User-oriented criteria for the evaluation of physically based management models are presented. These criteria emphasize the utility rather than the elegance of the model. The standards are then applied to efforts at predicting non-point pollutant loadings. In particular a critical review of sediment pollution is used as the basis for the evaluation of sediment yield models as management tools. A wide range of sediment yield models are rated and recommendations for their use are made. 相似文献