滴灌条件下水的硬度对滴头堵塞的影响

为探明滴灌条件下水的硬度对滴头堵塞的影响规律及堵塞机理,该文选取不同硬度水源和2种滴头(内镶圆柱式、内镶贴片式)进行滴灌试验,研究滴头的流量变化和堵塞规律,并用场发射扫描电镜技术观测了滴头内堵塞物的结构及成分。结果显示:硬水滴灌条件下,2种滴头的平均相对流量随着滴灌运行时间的增加呈均匀下降趋势,且水质越硬下降越明显;硬水滴灌会造成滴头堵塞,且水质越硬堵塞程度越严重。但同一硬度水源处理下,2种滴头的平均相对流量和堵塞程度基本一致。堵塞的滴头在毛管的前1/3段、中1/3段、后1/3段都有分布。堵塞物质分析显示,Ca CO3沉淀导致的化学堵塞是滴头堵塞的主要原因。研究结果为滴灌技术在灌溉水质较硬地区的推广使用提供参考。     

滴灌湿润体交汇情况下土壤水分运移特征的研究

以室内试验为基础，测定了重壤土、中壤土、砂壤土在不同滴头流量、不同灌水量下的滴灌交汇土壤水分入渗运动过程。研究结果显示了滴头流量、灌水量和土壤质地对交汇入渗湿润体形状的影响规律。滴灌入渗交汇界面的湿润锋水平和垂直距离与入渗时间之间符合良好的线性关系，湿润锋水平和垂直速度随着交汇时间的延长而增大。随着距滴头距离的增加，滴灌交汇入渗湿润体内的土壤含水率降低，湿润锋交汇界面处的土壤含水率一般均大于同等土壤深度的含水率。研究结果对滴灌系统设计理论具有一定的指导作用。     

地下水人工回灌物理堵塞特征及机理试验分析

通过砂柱试验模拟了填砾石滤料雨洪水地下水人工回灌过程,通过3组对比试验分析了砾石滤料的厚度和砾石的粒径对物理堵塞控制效果的影响。试验结果表明,砾石反滤层能够在很大程度上去除回灌水中的悬浮物,进而起到控制堵塞,提高补给效率的作用。砾石反滤层的厚度和粒径选择对堵塞的控制效果起到关键作用,反滤层厚度越大,对堵塞的控制效果越好。反滤层对回灌水悬浮物的去除作用是有限的,而且随着时间的延长,到达反滤层和砂样界面的悬浮物浓度变大,因此反滤层并不能完全避免堵塞的发生,必须定期对反滤层底部的淤泥层进行处理。     

不同工作压力下穿孔形灌水器内的旋涡作用分析

为探究穿孔形流道内的旋涡对灌水器的抗堵塞与消能性能的影响,基于试验验证的数值模拟方法,对4种工作压力下流道中的流场分布、旋涡区的几何特征、涡旋强度及压力分布进行了分析,同时分析了该灌水器内不同粒径泥沙颗粒的运动情况.结果表明:旋涡区可对流道边壁进行持续冲刷清洗并减缓颗粒在流道内部的聚积,旋涡区可发挥抗堵塞作用;旋涡区内不同流速的流层间、旋涡区与主流区间、旋涡区与流道边壁间的摩擦作用都会消耗能量,旋涡区可发挥消能作用;旋涡区可在不同压力下形态稳定.以上分析表明,旋涡区在不同压力下稳定存在,并可提高滴灌灌水器的抗堵塞与消能性能,为灌水器的抗堵塞及水力性能优化提供参考.     

迷宫流道灌水器抗堵塞设计与PIV试验

为提高迷宫流道灌水器的抗堵塞性能,通过数值模拟的方法对梯形流道内含沙量分布以及水沙流速进行了分析,并采用PIV测试优化前后流道内颗粒运动轨迹和速度来进行验证。结果表明:梯形迷宫流道灌水器流道内高含沙量区域主要在迎水面且流速较低的位置,在优化流道时可适当增加迎水面的修改,结合流道整体和加工需求可适当、甚至不修改流道背水面尺寸;以某一含沙量分布线作为流道边界,通过多次数值模拟获得较低含沙量的流道后,进行标准化再选取流道较宽的流道。该方法基本消除了沙粒大量集中的现象,获得抗堵塞性能较好的流道模型。经水沙速度分析和PIV测试验证了该方法不仅保持了灌水器优化前的水力性能,而且抗堵塞能力得到了提高。     

Diel drift behaviour of fish eggs and larvae, in particular barbel, Barbus barbus (L.), in an English chalk stream

To estimate the potential loss of fish larvae to downstream stretches, the downstream drift behaviour of fish eggs and larvae, in particular barbel, Barbus barbus (L.), was examined in the River Lee, a small, nutrient-rich chalk stream in England, using drift nets over nine consecutive 24-h periods in June 1993 at one location and over ten 24-h periods, once a week for 10 weeks from May to July 1995 at a location slightly more upstream. The density of drifting fish larvae was not correlated with river discharge in 1993 or 1995. A clear diel pattern was found in the drift of fish eggs and larvae, with barbel being a predominant species. Almost all fish larvae drifted at night both in 1993 and 1995, but the drift of eggs in 1995 occurred regardless of luminosity, although most eggs drifted during the day and at dawn. The highest densities of drifting fish larvae (in particular barbel) were found in the nets set in the highest water velocities, with the opposite pattern observed for fish eggs, suggesting either active response to the water current or shape-related differences in the drift behaviour of passive particles.     

边缝式迷宫滴灌带灌水器流道内泥沙沉积影响因素分析

为研究灌水器流道内泥沙颗粒淤积特性的影响因素，进一步降低物理堵塞发生的风险，该研究配置不同浓度（1.8、2.8、3.8 g/L）和不同粒径（0 $\leqslant $ d < 0.054 mm、0.054 mm $\leqslant $ d < 0.075 mm、0.075 mm $\leqslant $ d < 0.1 mm）的含沙水，进行全组合间歇滴灌堵塞试验，对含沙水灌溉下灌水器泥沙沉积特性进行分析并对灌水器内流态进行数值模拟研究。结果表明：灌溉结束后，经由边缝式迷宫灌水器输出的泥沙中，黏粒与砂粒比例下降，粉粒比例上升，即灌水器弯曲流道对小于0.002 mm和大于0.05 mm粒径的泥沙具有明显阻滞作用，流道内堵塞的泥沙集中在0.054～0.1 mm的中大粒径范围内。灌水器流道内部流线在主流区呈波浪状前进，主流区水流流速大于近壁区，中部转角处流速均偏大。沙粒易受上转角和下转角处产生的漩涡影响而沉降集中在漩涡中心及背水面。滞留在漩涡区内的泥沙颗粒是引起灌水器堵塞的主要因素。为减少灌水器堵塞风险，在设计优化时宜考虑减少直角、锐角区域以减少漩涡区的形成。     

间接地下滴灌水盐运移影响因素研究

为研究不同灌溉要素对间接地下滴灌土壤水盐运移的影响规律,通过小区试验,分析流量、灌水量及导水装置直径对间接地下滴灌条件下枣树根区水盐分布的影响。结果表明：增大流量或减小导水装置直径会使土壤表层的含水率提高;大灌水量、小流量会加大水分向下运移的深度;灌水量的增加显著增大主要根区含水率;流量、导水装置直径对水分的横向运移影响比灌水量更显著。     

Clarification of water movement properties in a multi-soil-layering system

Maize (Zea mays L.) cv. T42 was grown in refined sand at low (0.1 μM) and normal (30 μu) concentrations of boron each under low (1 mM), normal (4 mM), and excess (8 mM) supply of calcium. Visible symptoms of boron deficiency which appeared first, were accentuated by calcium deficiency and were least evident when calcium was added in excess. The yield was maximum at normal levels of boron and calcium and was the lowest under boron and calcium deficiency.

In maize leaves when both calcium and boron were deficient together the activity of starch phosphorylase increased markedly and that of ribonuclease and polyphenol oxidase also increased. The increase in the calcium content inhibited the starch phosphorylase activity when boron was deficient. The activity of peroxidase was stimulated under boron deficiency at all levels of calcium and that of ATPase was depressed significantly when calcium was deficient alone.

A decrease in the tissue boron (except in old leaves) and tissue calcium content as well as sugar and starch contents was observed under the combined deficiency of calcium and boron.

Excess calcium at both levels of boron increased the tissue boron and calcium contents and decreased the concentration of starch, sugars, nucleic acids, total and inorganic phosphorus, and the activities of starch phosphorylase and ATPase.

The activity of ATPase increased upon the addition of calcium to plants deficient in calcium and boron respectively. The tissue concentration of the element added increased when the element was applied to calcium or boron deficient maize plants.     

Pollen transfer from invasive Carpobrotus spp. to natives - A study of pollinator behaviour and reproduction success

The influence of invasive plant species on native community composition is well-documented, but less is known about underlying mechanisms. Especially scarce is knowledge about effects on biotic interactions such as relationships between native plants and their pollinators. In this study we investigate if pollen transfer from the invasive and highly pollen productive Carpobrotus spp. affects seed production and/or seed quality in three native species. We monitored pollinator movements and pollen loads on pollinators and native stigmas, and in a field pollination experiment we investigated the effect of invasive pollen on reproduction. Invasive pollen adhered to pollinators, pollinators switched from Carpobrotus spp. to natives, invasive pollen was transferred to native stigmas, and it affected seed production in one species. Although all possible steps for interference with seed production were found to be qualitatively taken, invasive pollen has probably little impact on the native community because the frequency of invasive pollen transfer to natives was low. However, pollination interactions may change with plant abundance and our study provides evidence that pollen transfer from Carpobrotus spp. to natives does occur and have the potential to affect seed production. We found the species identity of shared pollinators to be of importance, higher flower constancy and lower capacity of pollen adherence are likely to result in less invasive pollen transfer.