后嘴山市北沙湖湿地综合整治规划中水资源循环问题的探讨

本文探讨了石嘴山市北沙湖湿地综合整治中的水资源循环问题。笔者认为,在我国西北地区,维持湿地水资源循环是保障湿地生态功能可持续发挥的关键,也是进行湿地综合整治规划时应优先考虑的问题。区域水资源平衡是确保湿地水资源有效循环的基础,在规划中应充分分析湿地的来水水源和水资源消耗,由此确定湿地水资源循环的方式和线路。北沙湖湿地水循环确定了4条外循环线路和2条内循环线路。在水资源循环体系建设中,应充分利用现有水利设施和地势条件,尽量采用自流循环,减少设施设备投资和能源消耗。     

Influences of mean advection and simple behavior on the distribution of cod and haddock early life stages on Georges Bank

Results of a modeling study designed to explore the influences of physical advection and certain biological mechanisms on the distribution of cod (Gadus morhua) and haddock (Melarwgrammus aeglefinus) early life stages on Georges Bank are described. Using a late-winter/early-spring 3-D circulation field driven by the M₂ tidal current, mean wind stress and Scotian Shelf inflow, we examine the distribution of cod and haddock larvae spawned on the Northeast Peak of the Bank. The sensitivity to a March-April baroclinic field is also explored. Results indicate that larvae remaining in the surface Ekman layer are generally advected off-bank. However, downwelling associated with Ekman layer convergence near the shelf break provides a mechanism for larvae to exit from the off-bank surface drift. Larvae below the surface layer are transported south-westward along the southern flank of Georges Bank and are retained on the Bank if their position immediately upstream of the Great South Channel is shoalward of (roughly) the 70 m isobath. Within the Great South Channel region and between the 50 and 70 m isobaths, retention can depend on the phase of the tide. Spawning shoalward of the 50 m isobath on the Northeast Peak greatly increases the chances of retention. These results apply to passive larvae and to those with specified vertical distributions and migration based on observations. Directional on-bank swimming at rates of 0.5 to 1 body length per second would substantially enhance shoalward displacement, resulting in larval distributions during the first 2 months that are consistent with field observations.     

Site of acid-base relevant ion transfer in the gills of rainbow trout (Oncorhynchus mykiss) exposed to environmental hypercapnia

In order to delineate the contribution of primary vs. secondary circulatory circuits in the gill for acid-base and ionic regulation, the flow and composition of the fluids in the central venous sinus (CVS) and the systemic circuit of rainbow trout were studied by application of a previously developed microcannulation technique during normocapnic and hypercapnic conditions. The average haematocrit (Hct) of blood from dorsal aorta (DA) and sinus venosus (SV) ranged from 20.1 to 26.7%, whereas average Hct in the fluid from the branchial vein (BV), representing drainage from the central venous sinus (CVS), was in the range of 4.2 to 7.0%. Under normocapnic conditions, the largest fraction of cardiac output, 92.9%, was directed through the systemic vascular circuit, whereas the CVS circuit was perfused with 7.1 % of cardiac output. Hypercapnia did not significantly affect the blood flow distribution between the two circuits. The pattern of acid-base regulation in dorsal aortic blood reflected the characteristic response of fish exposed to environmental hypercapnia. Upon initiation of environmental hypercapnia (2% CO₂), plasma P_{CO 2} was elevated in all three flow compartments (CVS, DA, SV), inducing an extracellular respiratory acidosis of about 0.4 pH units. pH and [HCO₃ ^-] values in the DA were consistently lower, than those for both CVS and SV sites throughout the hypercapnic period. During the 8h of exposure plasma bicarbonate concentration was elevated by about 12 mM, complemented by a fall in extracellular [Cl^-] of about 10 mM in all three compartments. The amount of HCO₃ ^- gained at the CVS site during 8h of hypercapnia (3.3 mmol · kg^-1) exceeds the amount accumulated in the extracellular space (2.1 mmol·kg^-1), suggesting the CVS as the main site of ionic acid-base regulation in trout.     

应用高效草坪产业推动土地流转

一项新科技在示范、推广过程中,凭借龙头企业的经济实力,发挥其对草坪产业开发的拉动与扩张能力。采用先示范、获效益、再利用农民专业合作社等多种形式,把农民自愿地组织在一起,从事某一项草坪产业,实现土地的流转和产业专业化,促进农村经济发展、农民增收、农村面貌改善。     

2012年7月我国中东部持续性强降水形成机制分析

利用NCEP/NCAR再分析资料,通过对2012年7月中旬我国中东部地区持续性强降水过程中东亚夏季风系统中主要成员的时空变化特征进行分析.结果表明,此次持续性强降水期间,副高北界、南亚高压脊线及中纬度锋区位置相对稳定,长江中下游地区一直处于南亚高压反气旋环流东侧偏北风与西风槽前偏南风之间的风向开口辐散区中;副高南撤时,强降水主要位于584 dagpm线北侧,副高北抬时,强降水主要位于584 dagpm线南侧;此次持续性强降水发生前期,大气为上干下湿不稳定层结,当西风带低槽频频携带冷空气南下影响,同时低空西南急流反复加强,其出口区左侧较强的风速梯度为暴雨的发生发展提供了动力条件;低层干空气的不断侵入,低槽和低涡间的垂直正反环流促使垂直上升运动维持或发展,进而造成持续性强降水;高空西风急流加强(减弱)超前低空西南急流加强(减弱)2～5 d,对持续性强降水有超前指示意义.     

西北地区中东部秋季连阴雨天气过程与环流背景诊断分析

利用1956～2003年的NCEP资料(2.5°×2.5°)和西北地区5个气象站的逐日降水资料,对出现在我国西北地区中东部(甘肃河东和宁夏南部)的秋季连阴雨天气过程进行了统计分析。结果表明,连阴雨次数在20世纪总体上呈下降趋势;连阴雨的环流形势,在高纬为一槽一脊或二槽一脊,中纬度短波活动较多,青藏高原为一槽区,西北地区中东部受西南暖湿气流的控制且为高能区,短波活动带来的冷空气与西南暖湿气流在西北地区中东部不断交馁,造成降水过程;对流层中部500 hPa欧亚环流形势相对稳定,乌拉尔山的长波脊和中亚低槽维持,该区域的偏南气流为该区输送了大量的水汽,从而形成了西北地区中东部持续的连阴雨天气;当西风带中纬度新疆高压脊建立,副热带高压东移南退时,西北地区中东部的连阴雨天气过程结束。     

低循环风速下木材表层水分蒸发的试验研究

木材干燥过程中,介质循环速度是一个影响木材干燥的重要工艺参数.在木材各含水率阶段,通过试验分析研究不同介质循环速度对木材干燥速度的影响.结果表明,介质循环速度对干燥速度的影响显著,但其影响随木材含水率（MC）的降低而减弱.在低介质循环速度条件下,试件MC大于45％时,表现为木材干燥速度和木材含水率偏差（△MC）随循环风速的增加而增加,呈显著正相关关系;试件MC介于35％ ～ 45％之间时,正相关关系存在但不显著;试件MC小于35％时,干燥室内循环风速的大小不影响木材的干燥速度和木材含水率偏差（△MC）.对试件表层含水率分析,试件表层含水率大于25％时,试件表面循环风速对试件表层含水率的影响显著;试件表层含水率小于25％时,试件表面循环风速对试件表层含水率的影响很小,不同循环风速下试件表层含水率基本一样.     

湖北省农村土地流转存在的问题及对策

结合近2年湖北省农村土地流转数据,从实证的角度分析了湖北省农村土地流转现状,指出了农村土地流转中存在的问题,并提出了相应的对策,以期为湖北省农村土地流转提供参考。     

农业现代化进程中农户对土地流转意愿的影响因素研究

完善土地流转是推进农业现代化的一项重要举措,基于农户家庭视角,依据采集的1 036份全国农户样本数据,运用二元Logit选择模型分析了农户进行土地流转意愿的影响因素.研究发现,受教育程度、家庭非农收入、耕地流转价格、流转区域经济水平与农户进行土地流转的意愿有显著正相关影响,农户年龄、家庭农业劳动力数量、耕地质量与农户进行土地流转意愿有显著负相关影响.建议政府加快农村土地流转法治建设,强化土地流转规范化管理;建立城乡发展一体化体制,完善农村社会保障机制;积极推进新型城镇化建设,创造更多非农就业机会;改善农村教育培训条件,提高农民素质与技能.     

水果流通模式与竞争力评价研究——以广东省为例

当前国内水果流通逐渐形成了以批发商、龙头企业、连锁超市和电商为核心的4种模式。对4种模式的特点与结构进行分析,从销售能力、成本与费用、安全性、公平性以及损耗等5个方面建立水果流通模式的竞争力评价体系。通过专家调查,对广东省水果流通情况进行具体评价,评价结果显示,广州应该大力发展水果电子商务,促进水果的网络销售,推动水果产业的发展。