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排序方式: 共有162条查询结果,搜索用时 125 毫秒
81.
江苏北部城镇绿化策略研究   总被引:4,自引:0,他引:4  
在对江苏北部气候,植物区系,森林植被研究的基础上,从生态学角度提出该地区城镇绿化策略,包括:立足于落叶阔叶树种,积极引种耐寒发阔叶树种,根据生境特点合理布局树种。  相似文献   
82.
This review focuses on the occurrence and treatment of arsenic (As) in the arid region of northern Mexico (states of Chihuahua and Coahuila) and bordering states of the southwestern US (New Mexico, Arizona, and Texas), an area known for having high As concentrations. Information assembled and assessed includes the content and probable source of As in water, soil, and sediments and treatment methods that have been applied in the area. High As concentrations were found mainly in groundwater, their source being mostly from natural origin related to volcanic processes with significant anthropogenic contributions near mining and smelting of ores containing arsenic. The affinity of As for solid phases in alkaline conditions common to arid areas precludes it from being present in surface waters, accumulating instead in sediments and shifting its threat to its potential remobilization in reservoir sediments and irrigation waterways. Factors such as oxidation and pH that affect the mobility of As in the subsurface environment are mentioned. Independent of socio-demographic variables, nutritional status, and levels of blood lead, cognitive development in children is being affected when exposed to As. Treatments known to effectively reduce As content to safe drinking water levels as well as those that are capable of reducing As content in soils are discussed. Besides conventional methods, emergent technologies, such as phytoremediation, offer a viable solution to As contamination in drinking water.  相似文献   
83.
Accurately determining methane emission factors of dairy herd in China is imperative because of China’s large population of dairy cattle. An inverse dispersion technique in conjunction with open-path lasers was used to quantify methane emissions from a dairy feedlot during the fall and winter seasons in 2009-2010. The methane emissions had a significant diurnal pattern during both periods with three emission peaks corresponding to the feeding schedule. A 10% greater emission rate in the fall season was obtained most likely by the higher methane emission from manure during that period. An annual methane emission rate of 109 ± 6.7 kg CH4 yr−1 characterized with a methane emission intensity of 32.3 ± 1.59 L CH4 L−1 of milk and a methane conversion factor (Ym) of 7.3 ± 0.38% for mature cattle was obtained, indicating the high methane emission intensity and low milk productivity in Northern China.  相似文献   
84.
Sonja Kivinen  Sirpa Rasmus 《Ambio》2015,44(3):214-225
We studied trends and variability in snow and climate characteristics in 1978–2012 in the Värriötunturit fell area, northern Finland. Cold season changes were examined using long-term observational data on snow depths, meteorological data, large-scale climate indices, and reindeer herders’ experiences with difficult snow conditions. Snow depths declined, and temperatures increased significantly over the study period, with the largest changes observed in October–December and in April. Snow depths decreased particularly in forests at lower altitudes but not in treeless areas at higher altitudes. Interannual variability (but not the trends) in snow depths could be partially linked to large-scale climate indices. A majority of difficult reindeer grazing conditions were related to deep snow in the winter or spring. Our observations suggest that shortened duration of snow cover may facilitate reindeer grazing, whereas potentially more frequent formation of ice layers and mold growth on pastures in the future is disadvantageous for reindeer husbandry.  相似文献   
85.
Rebuilding collapsed fisheries is a multifaceted problem, requiring a holistic governance approach rather than technical management fixes. Using the Northern Gulf cod case study in eastern Canada, we illustrate how a “fish chain” framework, drawn from the interactive governance perspective, is particularly helpful in analyzing rebuilding challenges. The analysis demonstrates that factors limiting rebuilding exist along the entire fish chain, i.e., the pre-harvest, harvest, and post-harvest stages. These challenges are embedded in both the ecological and social systems associated with the Northern Gulf cod fisheries, as well as in the governing systems. A comparative analysis of the pre- and post-collapse of the cod fisheries also reveals governance opportunities in rebuilding, which lie in policy interventions such as integrated and ecosystem-based management, livelihood transitional programs, and cross-scale institutional arrangements. Lessons from the Northern Gulf cod case study, especially the missed opportunities to explore alternative governing options during the transition, are valuable for rebuilding other collapsed fisheries.  相似文献   
86.
依据2011年8月24日—9月5日对南海北部海域的现场调查,分析了涡旋这一典型中尺度物理过程对营养盐(NO-3-N,PO3-4-P,SiO2-3-Si)及溶解氧分布特征的影响.结果表明,夏季南海北部营养盐及溶解氧的分布受中尺度海洋过程的影响显著.在水平分布上,各项营养盐基本呈现近海高远海低的分布特征.东沙群岛附近海域由于受反气旋型涡旋的影响,反气旋型涡旋将珠江口水推至外海,使得东沙群岛附近海域呈现明显的高N、Si,低P的珠江口水特征.在断面分布上,位于珠江口附近海域的B、C断面营养盐浓度水平较低,表层低浓度营养盐向下扩张明显,营养盐浓度等深线也明显下移,其可能受到反气旋型涡旋中心区域的影响;而位于海南岛附近海域的D、F断面,底层低温高盐海水不断向上涌升,可能受到反气旋型涡旋边缘的影响,使得表层海水受到富含高浓度营养盐的底层海水的补充,为表层浮游植物的生长提供了丰富的物质基础.位于广东沿岸附近海域的A断面及东沙群岛附近海域的E断面则受季节性上升流的影响大于反气旋型涡旋的影响,表现出明显的低温、高盐、高P、低溶解氧的上升流特征.  相似文献   
87.
中国北方沙漠化发展趋势及对策   总被引:5,自引:0,他引:5  
80年代中期,中国北方已经沙漠化的土地有20.12万平方公里,比十年前增加了2.48万平方公里,平均每年增加2103.2平方公里,发展速率1.47%,沙漠化主要发展在河北坝上、察哈尔草原和乌盟后山地区等农牧交错区.同时约有4.53万平方公里沙漠化土地得到控制,2250平方公里沙漠化土地治理逆转.只要各级重视、采取措施、恢复生态平衡,使农牧交错地区土地沙漠化得以逆转.这里还是一个很有前途的地方.  相似文献   
88.
1960-2016年中国北方地区极端干湿事件演变特征   总被引:2,自引:0,他引:2  
贾艳青  张勃 《自然资源学报》2019,34(7):1543-1554
基于中国北方地区424个气象站点1960-2016年的日气象数据础,应用FAO Penman-Monteith模型计算潜在蒸散(ET0),基于降水量和潜在蒸散计算湿润指数,对湿润指数进行标准化后统计极端干湿事件频率,分析极端干湿事件频率的空间变化趋势、多时间尺度演变特征以及ENSO事件对极端干湿事件变化趋势的影响。结果表明:北方极端干旱和极端湿润事件频率分别呈显著下降和显著上升趋势,年际倾向率分别为-0.10次/10年和0.13次/10年。空间上,极端干旱频率整体呈减少趋势,包括青藏高原、西北和东北地区。西北极端干旱频率减少速率较大,青藏高原中部、新疆北部和东北北部部分站点极端湿润频率增加幅度较大。各年代中,华北极端干旱多发,东北和青藏高原极端湿润多发。季节上,分区极端干旱发生概率均大于极端湿润发生概率,华北极端干旱发生概率最高,青藏高原极端湿润发生概率最高。ENSO与湿润指数存在滞后性的关系。El Niño翌年,气候偏湿润的年份较多;La Nina翌年,气候偏干旱的年份较多。SSTA与翌年湿润指数在年际和夏季两个时间尺度上存在显著的正相关关系。  相似文献   
89.
冬小麦产量高低及稳定性对于保障我国粮食安全同等重要。鉴于北方冬小麦主产区受气候变化的负面影响显著,有必要从高产—稳产关联特征入手,探究全面提升冬小麦产量及稳定性的途径。基于598个县1985—2014年的单产数据,分析了冬小麦高产与稳产关联性时空分异特征,并结合气象、物候观测、农业生产要素等数据,应用无序多分类Logistic模型揭示了冬小麦高产—稳产关联特征的影响因素。主要结论为:(1)冬小麦产量随时间不断提高的同时稳定性也增强,高产性和稳产性均呈东北向西南降低的特征。(2)冬小麦高产与稳产、低产与不稳产密切关联,在研究区占据主导地位,且这两种关联类型的分布区域相对稳定,空间聚集性强。(3)灌溉条件是促进冬小麦高产—稳产的关键因素,影响随时间逐渐增强;具备灌溉条件的情况下,研究区的光温水等气象条件均比较适合冬小麦生产,但不同物候期气象要素的波动对高产和稳产均有负向影响。研究结果可为划定冬小麦优质产区和制定气候变化应对策略提供依据。  相似文献   
90.
研究了陕北主要石油勘探开发地区地表水的水质状况,分析了pH、矿化度(全盐量)、硬度、六价铬、砷、镉、铅、氨氮、挥发酚、石油类、化学需氧量(COD)、氯化物、硫酸盐、硝酸盐氮、总磷、氰化物、氟化物等17个指标,结果显示砷、镉、铅、氟化物、硝酸盐、氰化物、氟化物的Pi值均小于1;挥发酚、总磷、石油类、氨氮、COD、六价铬、硫酸盐、矿化度、氯化物、硬度均超标。研究区东部和西部地表水呈现出不同的污染特征,通过分析不同区域污染物来源,提出了污染防治对策与建议。  相似文献   
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