Windbreaks as a pesticide drift mitigation strategy: a review

The use of natural and artificial barriers to mitigate pesticide drift from agricultural and forest applications is discussed. This technique has been considered as an alternative to current methods at a time when environmental concerns are under great public scrutiny. There has been a variety of research experiments on this subject from New Zealand to The Netherlands which have documented reductions in spray drift of up to 80-90%. However, there are still enormous data gaps to utilize this method accurately. The aerodynamic factors of wind barriers and shelter effects on crop growth and yield have been well investigated. In contrast, some of the important aspects of drift mitigation, e.g. porosity and turbulence, have been difficult to obtain and no standard methodologies are currently available to evaluate and classify windbreaks and shelterbelts or to determine their efficiency in reducing drift. Thus there is a significant opportunity to incorporate windbreaks into the tool set of drift mitigation tactics. Government policies, initiatives, legislation, etc, which currently address water quality, BMP, stewardship, buffers, etc, are issues which so far have not included windbreaks as a valuable drift mitigation strategy.     

Cell Loss Analysis Based ATM Networks of On-Off Traffic Source

Cell loss, which occurs when buffers overflow in ATM switches, is a key measure for the performance of an ATM network .An ATM network must be designed for very low and predictable cell loss probabilities to provide adequate quality of service for all users. Many methods have been proposed for allocating bandwidth and determining buffer size requirements to provide quality of service guarantees. These methods are subject to overly optimistic allocations or overly pessimistic allocations. The authors present an exact analysis of cell for on off traffic source which can be used in concert with probabilistic methods to ensure that buffer and bandwidth allocation are mode between the best case and worst case requirements.     

凡河流域河流植被评价及保护对策

为加强河流植被修复及保护,通过对河流植被的现状调查,采用河岸带植被缓冲区宽度、河岸带植被缓冲区纵向连续性及植被覆盖丰富度3个指标对凡河流域河流植被进行评价。结果表明:凡河流域植被健康综合指数为0.21~0.76;黄河子断面的植被健康等级很健康;夹河厂、老边台及树芽屯断面的植被健康等级为健康;岱海寨、榛子岭、小屯及凡河站断面植被健康等级为亚健康;仅杨坟沟断面植被状况为不健康。     

基于GIS的城市公交换乘查询系统的设计与开发

为提高城市居民出行的信息化和智能化水平,设计并开发了基于GIS的城市公交换乘查询系统。分析了该系统中公交与街道网络数据的组织方式,即动态分段以及线性参考方法;利用地理信息系统(GIS)中的缓冲区分析获得用于换乘的临近点,提出基于动态分段与缓冲区分析的公交出行线路查询算法;并以Geodatabase存储淄博市张店区公交数据基础数据;在微软的Visual Studio 2005平台中C#语言环境下利用ArcEngine组件开发了淄博市张店区的公交换乘查询系统。     

川西3种茶园土壤的酸度和酸碱缓冲能力 及石灰需要量比较

以川西名山县处于同一地形序列上的漂洗水稻土、黄壤和酸性紫色土3种主要茶园土壤0~20 cm土层为研究对象,于春、夏、秋3个季节采样,对土壤pH、交换性酸含量、水解性酸含量、酸碱缓冲能力及石灰需要量等进行分析。结果表明:1 3种茶园土壤pH均低于4.5,不适于无公害茶叶生产。交换性酸均以交换性铝为主,交换性铝含量和交换性酸含量均以漂洗水稻土的最低。水解性总酸度表现为酸性紫色土显著高于漂洗水稻土,酸性紫色土和漂洗水稻土的水解性总酸度与黄壤的差异均无统计学意义。漂洗水稻土以非交换性酸为主,黄壤和酸性紫色土以交换性酸为主。2 3种茶园土壤交换性氢含量、交换性铝含量、交换性酸含量和水解性总酸度等指标由于地形条件、气候特征、茶树生物学特性和人类活动等影响而总体上呈夏季低于春(秋)季的趋势变化。3 3种茶园土壤的酸碱缓冲曲线均呈"S"型,但土壤缓冲容量有差异,表现为酸性紫色土、黄壤、漂洗水稻土的缓冲能力依次减小。4 3种茶园土壤必须进行改良,但用不同方法计算出的石灰需要量有较大差异,建议将氯化钙交换–氢氧化钙滴定法得出的石灰需要量结合田间试验进行校正;若调节至同一pH,漂洗水稻土的石灰需要量相对较少。     

湿地缓冲带对氮磷营养元素的去除研究

湿地缓冲带是介于水-陆之间特殊的生态交错带,具有独特的水体净化功能。基于国内较少开展自然湿地水体净化功能的研究,选取扎龙湿地湖滨湿地缓冲带剖面作为研究对象,利用电导率的剖面变化判断水流的方向,同时利用氯离子作为示踪剂验证剖面水体来自同一水源。在此基础上,发现其对水体中营养元素具有明显的去除效应,TN、TP的去除率分别达74.1%、84.6%。缓冲带内的湿地植物量较小,决定了植物吸收并非氮磷去除的主要机制。根据溶解有机碳和重碳酸酸根的变化,认为反硝化作用是湿地缓冲带去除氮的主要途径,剖面末段处的浅水位和相对茂盛的植物,使其具有相对较强的脱氮能力;土壤吸附与沉淀作用是湿地缓冲带去除磷的主要途径,剖面起始处较高的磷浓度使其具有较高的磷去除能力。因此,利用并强化湿地缓冲带的自然净化能力有助于控制湿地水体富营养化的发展。     

河岸水稻缓冲带宽度对排水中氮磷流失的影响

研究表明，在正常条件下，可溶态P、NH4-N和NO3-N在稻田水平方向的扩散距离较短，一般小于10m；扩散距离：可溶态P〈NH4-N〈NO3-N。缓冲带宽度（0～90m）对排水中可溶态P、NH4-N和NO3-N的浓度有很大的影响，但这种影响随施肥后时间的延长而减小。宽度大于15m的水稻缓冲带可显著地降低排水中氮磷的流失，因此在沿河用不施肥的水稻带也可有效地控制氮、磷的流失，替代一般的缓冲带，其机理与湿地相似。     

玉米秸秆覆盖缓冲带对细沟侵蚀及其水动力学特征的影响

玉米秸秆覆盖缓冲带是一项有效的坡面水土保持措施,为探究其减少细沟侵蚀的效果及水动力学机理,在室内人工模拟连续降雨条件下,选取黄土高原高强度侵蚀性降雨标准和细沟发育活跃的典型坡度,根据细沟发育的不同阶段,研究了不同布设部位(坡面中部5 m和坡面下部7 m)的秸秆覆盖缓冲带对细沟侵蚀及其水动力学特征的影响。结果表明:与裸露处理相比,玉米秸秆覆盖缓冲带可以减少坡面侵蚀量27.2%~54.8%,减少细沟侵蚀量40.8%~59.2%,减小细沟侵蚀量对坡面总侵蚀量的贡献率。对于细沟形态,缓冲带可减少细沟割裂度23.0%~32.0%,减少细沟平均深度6.7%~10.5%。比较2种布设部位,在坡面细沟发育后期,坡面下部7 m处布设的秸秆缓冲带可以取得更好地减少侵蚀和约束细沟形态变化的效果。对于单条细沟,裸露坡面上的细沟宽度沿坡长方向呈现约1.2 m长的周期性变化规律,而秸秆缓冲带改变了细沟宽度沿坡长方向的周期性变化趋势,此外还通过拦截淤积上方来沙减小了布设位置细沟侵蚀深度,通过拦截径流保护下方有限长度内的细沟。分析其水动力学原因可知,玉米秸秆覆盖缓冲带可使细沟水流向缓层流流态方向延伸,与缓冲带上方相比,秸秆缓冲带下方的细沟水流流速显著减小19.6%~21.9%,雷诺数和佛汝德数分别减少了29.6%~37.9%和8.3%~18.5%,而通过秸秆缓冲带后,细沟水流Darcy-weisbach阻力系数增加了22.4%~43.3%,水流剪切力、单位水流功率和断面单位能量分别减小13.6%~21.5%、20.0~21.0%和9.5%~21.0%,径流能量和侵蚀能力的降低最终导致了坡面总侵蚀量的减小。因此,在坡面上每隔5~7 m布设缓冲带可以有效的削弱坡面径流侵蚀能力,减少坡面细沟侵蚀量和总侵蚀量。该研究结果可为类似地形条件下的坡面水土保持措施合理配置提供理论基础。     

The effects of clearcuts and forest buffer size on post-breeding emigration of adult wood frogs (Lithobates sylvaticus)

The establishment of terrestrial buffer zones around vernal pools has been recommended to provide upland habitat for pool-breeding amphibians in areas where forestry practices occur adjacent to breeding sites. However, few studies have empirically tested the effectiveness of buffers. We assessed post-breeding emigration behavior (net emigration distance, rate of movement, proportionate use of available habitats) of radio-tagged adult wood frogs (Lithobates sylvaticus) at nine vernal pools with experimental forest buffer treatments in central Maine, USA. Buffer treatments were either 30-m (N = 3) or 100-m (N = 3) forest buffers surrounded by a 100-m wide clearcut; pools surrounded by uncut forest served as reference sites (N = 3). We tracked 33 individuals in 2004 and 2005, for an average of 41 days, as they emigrated from breeding pools. Recently clearcut habitat was permeable to emigrating adult wood frogs, particularly females. A higher proportion of frogs at 30-m buffer sites than at 100-m buffer sites traveled through the clearcuts to reach intact forest beyond, suggesting that 30-m buffers may not provide sufficient upland habitat to support adult wood frog populations. There was high variability in emigration behavior among frogs, regardless of buffer treatment, and males and females tended to exhibit differential responses to different buffer sizes and to clearcut habitat. Although wood frogs in this study utilized both 30-m and 100-m forest buffers, variability between sexes and density-dependent effects could render small buffers (e.g., 30 m or less) inadequate to support these populations.