排序方式： 共有50条查询结果，搜索用时 31 毫秒
21.
D. E. Gaskin 《新西兰海洋与淡水研究杂志》2013,47(3):387-389
Sightings of 85 icebergs south‐east of New Zealand in February and March 1967 are reported, with associated sea surface temperatures. 相似文献
22.
提高北方农牧交错带农业生态系统生产力的对策与建议 总被引：1，自引：0，他引：1
北方农牧交错带是中、东部平原农区的重要生态屏障,在我国具有重要的地位,并由于其系统生产力水平低下,生态和经济问题比较严重而倍受关注。如何协调农牧业生产及农牧民收入稳定增长,提高农业系统生产力是该区域的核心研究问题。围绕提高其系统生产力实现可持续发展的目标,提出了一些具体的对策和建议。 相似文献
23.
Quantifying the effects of Eucalyptus plantations and management on water resources at plot and catchment scales 
下载免费PDF全文
下载免费PDF全文 Auro C. Almeida Philip J. Smethurst Anders Siggins Rosane B. L. Cavalcante Norton Borges Jr 《水文研究》2016,30(25):4687-4703
Our aim was to quantify the effects of forest plantation and management (clear cut or 30% partial harvest) in relation to pasture, on catchment discharge in southeast Rio Grande do Sul state, Brazil. A paired‐catchment approach was implemented in two regions (Eldorado do Sul and São Gabriel municipalities) where discharge was measured for 4 years at three catchments in each region, two of which were predominantly eucalypt plantation (mainly Eucalyptus saligna, rotation of approximately 7–9 years) with native forest and grass in streamside zones. The third catchment was covered with grazed pasture. Weather, soils, canopy interception, groundwater level, tree growth, and leaf area index were also measured. The 3‐PG process‐based forest productivity model was adapted to predict spatial daily plantation and pasture water balance including precipitation interception, soil evaporation, transpiration, soil moisture, drainage, discharge, and monthly plantation growth. The TOPMODEL framework was used to simulate water pools and fluxes in the catchments. Discharge was higher under pasture than pre‐harvesting plantation and increased for 1–2 years after complete plantation harvest; this change was less pronounced in the catchments under partial harvest. The ratio of discharge to precipitation before harvesting varied from 7% to 13% in the eucalypt catchments and 28% to 29% under pasture. The ratio increases to 23–24% after total harvest, and to 17% after partial harvesting. The ratio under pasture also increases during this period (to 32–44%) owing to increased precipitation. The baseflow, in relation to total discharge, varied from 28% to 62% under Eucalyptus and from 38% to 43% in the pasture catchments. Hence, eucalypt plantations in these regions can be expected to influence discharge regimes when compared with pasture land use, and modelling suggests that partial harvesting would moderate the magnitude of discharge variation compared with a full catchment plantation harvesting. The model efficiency coefficient (Nash–Sutcliffe model efficiency coefficient) varied from 0.665 to 0.799 for the total period of the study. Simulation of alternative harvesting scenarios suggested that at least 20% of the catchment planted area must be harvested to increase discharge. This model could be a useful practical tool in various plantation forestry contexts around the world. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
24.
Two adjacent subcatchments on soils with very strong texture contrast between the A soil horizons (sandy loam texture) and B soil horizons (clay texture) in the Adelaide Hills, South Australia were instrumented to collect overland and subsurface flow from dairy pasture. Subcatchments were defined by exclusion drains in the upper reaches and stainless steel barriers at the lower boundary. Water samples were analysed for 20 different chemical fractions. Chemical loads were examined in order to determine relationships among simple empirical event and site characteristics, and between chemical fractions. All but five of the chemical fractions could be separated into one of two clear groups using a statistical technique based on the magnitude of simple correlation coefficients. The two groups consisted of either dissolved or particulate fractions. The clear separation into these groups is consistent with the majority of chemical fractions moving from pasture by one of only two processes. Simple empirical variables in a multiple regression explained a high proportion of variation in chemical loads in runoff water. These findings may have major implications in the modelling and prediction of chemical loads in runoff from agricultural catchments and the setting of environmental limits, in simplifying chemical loss predictions by adding a nutrient loss module to runoff volume predictions. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
25.
北方农牧交错带的地理界定及其生态问题 总被引：121，自引：1，他引：121
我国北方农牧交错带主要分布于降水量300～450 mm，干燥度 1～2的内蒙古高原南缘和长城沿线，其东界和南界为黑龙江的龙江、安达，吉林的乾安和长岭，辽宁的康平、阜新，河北的丰宁、淮安，山西的浑源、五寨，陕西神木、榆林，甘肃环县，宁夏同心；其西界和北界为内蒙古的陈巴尔虎旗、乌兰浩特、林西、多伦、托克托、鄂托克和宁夏盐池。行政区划涉及 9省106个旗（县市），总面积654564km2。全区耕地总面积804.69万hm2，人均占有耕地 0.32hm2，农、林、牧用地比例为 1.0∶1.17∶3.67。主要生态问题为：沙漠化急剧发展、可利用土地资源锐减；草地退化、沙化、盐渍化严重，承载力急剧下降；生态环境恶化，自然灾害频繁。其原因除了受自然不利因素影响和现代人为强烈干扰外，还有沙漠化的历史烙印、现代农牧交错带的北移错位和经济地理三大原因。该区的退化生态治理应注意：大部分地区要逐步用榆、柳、松、杏等乡土树种取代高耗水肥的杨树树种，采取以灌木为主的乔灌草结合的带状造林方式，建立类似原生植被的人工疏林草原植被，充分发挥其生态屏障作用。农业应以发展灌溉农业和保护型农业为主攻方向，改变生产经营方式，大力提高生产水平、防止土地沙漠化。 相似文献
26.
采用参与式农村评估法(PRA),在青藏高原腹地那曲县3个典型乡镇的实地调查基础上,分析了定居牧民对草地退化的适应策略.结果表明:研究区草地均有不同程度的退化,夏秋草场较冬春草场退化更明显.草地退化对牧民生计最明显的影响是牲畜大量死亡,牧民依靠省吃俭用及借贷勉强维持生计.在应对草地退化方面,政府采取集约化的思路,主导“四配套建设”.但定居并未从根本上改变牧民生计的脆弱性.牧民采取了多种适应策略,然而,集约化的适应策略极大地增加了牧民的负担,定居牧民难以通过迁移来实现草料补给及应对极端灾害天气的胁迫.因此,政府的应对策略应该有所调整,不能仅仅局限于集约化,应当采取措施,扶持牧民的生计多样化,大力扶持牧业合作社的发展,同时,尊重牧民联户放牧的意愿. 相似文献
27.
基于灾损评估的青海省牧草干旱风险区划研究 总被引：3，自引：1，他引：2
在全球气候变暖的大背景下, 表现出温度升高、 降水变率加大的区域响应, 造成极端天气气候事件、 气象灾害加剧. 基于青海省1961-2010年47个气象站和20个农气站的气象资料、 牧草的实际产量以及牧草的理论产量等资料, 采用相关分析、 线性回归等方法, 在分析致灾因子危险性、 牧草相对产量的基础上, 确定了青海省牧区牧草干旱风险评估的实际阈值.通过海拔、 经度、 纬度、 牧草旱灾发生频次的拟合方程, 结合GIS平台对青海省牧草干旱进行风险区划.结果表明: 青南牧区西部、 环青海湖地区、 柴达木盆地东部边缘地区、 祁连山地区为易受旱灾影响的特高风险或高风险区域;青南牧区西南部为中风险区域;低风险区域主要在青南牧区东南部, 区划结果基本上于历史旱灾的实际情况相吻合, 区划结果旨在为青海省牧区牧业良性发展提供科学依据. 相似文献
28.
Faecal contamination of rural streams is of increasing concern in New Zealand. This study assessed hill‐country streams in the Whatawhata district that were impacted by pastoral farming, indigenous forest, or Pinus radiata forest; by measuring Escherichia coli bacteria at 14 sampling sites fortnightly for 2 years. E. coli concentrations were highest in streams flowing through grazed pasture. In both years there was a noticeable seasonal pattern in all streams irrespective of land use, with highest bacterial concentrations in summer and autumn and lowest in winter and early spring. There was no obvious correlation between E. coli concentration and rainfall or stream flow. In those streams impacted by a change in land use from pastoral to pines during the study, E. coli concentration fell rapidly and remained at levels lower than those in streams impacted by either indigenous or 7‐year pine forests. As E. coli was detected in all but two samples, the water in these streams is not suitable for human consumption. The pastoral streams consistently failed to meet stock drinking‐water guidelines (median concentration not greater than 100 E. coli 100 ml–1) and the forest streams failed to do so in summer. Twenty‐eight percent of pastoral samples, 25% of indigenous forest samples, 14% of 7‐year pine forest samples, and 5% in New Pines stream samples (after planting) had E. coli concentrations associated with a high level of risk for contact recreation (>500 E. coli 100 ml‐1) and the high concentrations usually occurred in summer. 相似文献
29.
30.
甘南高寒牧区牧民参与合作经济组织的意愿及影响因素 总被引：2，自引：0，他引：2
在广大牧区发展牧民合作经济组织,对于提升畜牧业竞争力、增加牧民收入、培养新型牧民具有至关重要的作用。利用入户调查资料分析了甘南牧区牧民参与合作经济组织的意愿,通过实地调研总结了影响农户参与专业合作经济组织行为的主要因素,建立了牧民参与合作经济组织的行为模型,并运用Logistic模型进行了实证研究。研究结果表明:牧民参与合作经济组织的意愿受户主的受教育程度、畜牧业生产的专业化程度、畜产品的商品化程度等因素的影响。基于这些实证研究结果,提出了相关的政策建议。 相似文献