Desiccation of a Clay by Grass,Bushes and Trees

After reviewing the past 60 years of research into the desiccation of clay soils by grass, bushes and trees as it affects shallow building foundations and roads pavements, it was concluded that most past research has been opportunistic and unplanned. Also, no attempt has been made to relate changes of soil water content to rainfall and rates of evapotranspiration. The paper reports the second stage of a sustained programme to observe and understand seasonal and annual changes of soil water content under grass and adjacent to bushes and trees. A 12 months set of two-monthly soil water content contours is presented together with the associated soil water balance, and a method is described for assessing evapotranspiration by bushes and trees by means of a solar energy balance.     

The performance of grass filter strips in controlling high‐concentration suspended sediment from overland flow under rainfall/non‐rainfall conditions

There is little information on the performance of vegetative filter strips (VFS) in filtering high‐concentration sediment from subcritical overland flow. Flume experiments on simulated grass strips were conducted using combinations of three slope gradients (3°, 9° and 15°), five 1‐m‐wide slope positions (from upslope to downslope), two flow rates (60 and 20 L min^‐1 m^‐1) and sediment concentrations of 100–300 kg m^‐3 under simulated rainfall and non‐rainfall conditions. The results showed that sediment deposition efficiency increased with VFS width as a power function. Rainfall significantly reduced sediment deposited within VFS. Higher sediment concentration corresponded to a larger sediment deposition load but reduced deposition efficiency. Flow rate had a negative effect on deposition efficiency but no effect on deposition load. Sediments were more easily deposited at the upper slope position than downslope, and the upper slope position had a higher percentage of coarse sediments. The deposited sediment had significantly greater median diameters (D₅₀) than the inflow sediment. A greater proportion of coarse sediments larger than 25 µm in diameter were deposited, and particles smaller than 1 µm and of 10–25 µm had a better deposition performance than particles of 1–10 µm. Rainfall reduced the deposited sediment D₅₀ at a slope gradient of 3° and had no significant influence on it at 9° or 15°. A higher sediment concentration led to a smaller D₅₀ of the deposited sediment. Rainfall had no significant effect on overland flow velocity. Both the deposited sediment load and D₅₀ decreased with increasing flow velocity, and flow velocity was the most sensitive factor impacting sediment deposition. The results from this study should be useful to control sediment flowing into rivers in areas with serious soil erosion. Copyright © 2013 John Wiley & Sons, Ltd.     

Coupled influence of flow velocity and water temperature on grass carp swimming behaviour and gonad development

Reproductive migration is an essential phase in the life of many fish. During this process, swimming behaviour and gonad development are key factors related to the migration quality, and both factors are strongly influenced by water temperature and flow velocity. Many studies have explored the separate effects of these variables on fish swimming ability or gonad development, but researchers have seldom investigated the simultaneous effects of low flow velocity and water temperature on the fish swimming behaviour and gonad development. To provide that knowledge, we conducted laboratory experiments that explored the coupled effects of low water temperature and flow on warm water fish swimming behaviour and gonad development. At five temperatures (16, 18, 20, 22, and 24°C), we observed the movement of migratory warmwater grass carp (Ctenopharyngodon idellus) at seven flow velocities (0.15, 0.2, 0.25, 0.3, 0.35, 0.40, and 0.45 m/s), then explored their gonad development by comparing the level of plasma 17β-estradiol and testosterone in fish travelling through a simulated fish way (flow stimulation) and in a fish tank (no flow stimulation). We used Bayesian networks to explore the acceptable hydrological condition for fish migration. We found that the minimum flow velocity for acceptable migration quality is a function of the water temperature, and that increasing water temperature improves fish movement success and increases the movement distance, especially at a low flow velocity. In addition, increasing water temperature (between 16 and 24°C in this experiment design) can enhance the effect of flow stimulation on gonad development. Overall, our results can broaden the understanding of reducing water temperature and flow velocity in fish swimming behaviour and gonad development, provide basic data to support hydrological process controls and the development of measures to protect fish migration.     

Meiobenthic communities of seagrass beds (Zostera capricorni) and unvegetated sediments along the coast of New South Wales,Australia

Seagrass beds have higher biomass, abundance, diversity and productivity of benthic organisms than unvegetated sediments. However, to date most studies have analysed only the macrofaunal component and ignored the abundant meiofauna present in seagrass meadows. This study was designed to test if meiobenthic communities, especially the free-living nematodes, differed between seagrass beds and unvegetated sediments. Sediment samples from beds of the eelgrass Zostera capricorni and nearby unvegetated sediments were collected in three estuaries along the coast of New South Wales, Australia. Results showed that sediments below the seagrass were finer, with a higher content of organic material and were less oxygenated than sediments without seagrass. Univariate measures of the fauna (i.e. abundance, diversity and taxa richness of total meiofauna and nematode assemblages) did not differ between vegetated and unvegetated sediments. However multivariate analysis of meiofaunal higher taxa showed significant differences between the two habitats, largely due to the presence and absence of certain taxa. Amphipods, tanaidacea, ostracods, hydrozoans and isopods occurred mainly in unvegetated sediments, while kinorhyncs, polychaetes, gastrotrichs and turbellarians were more abundant in vegetated sediments. Regarding the nematode assemblages, 32.4% of the species were restricted to Z. capricorni and 25% only occurred in unvegetated sediments, this suggests that each habitat is characterized by a particular suite of species. Epistrate feeding nematodes were more abundant in seagrass beds, and it is suggested that they graze on the microphytobenthos which accumulates underneath the seagrass. Most of the genera that characterized these estuarine unvegetated sediments are also commonly found on exposed sandy beaches. This may be explained by the fact that Australian estuaries have very little input of freshwater and experience marine conditions for most of the year. This study demonstrates that the seagrass and unvegetated sediments have discrete meiofaunal communities, with little overlap in species composition.     

退耕还林(草)背景下中国北方农牧交错带土地利用及碳储量变化

为明析退耕还林(草)背景下生态环境较为脆弱的北方农牧交错带土地利用及碳储量变化,基于该区2000、2010、2018年土地利用数据,通过动态度、土地转移矩阵,景观指数等指标从土地利用变化的数量、速率以及空间格局特征加以分析,同时基于In VEST模型定量估算了该区近20年来的碳储量变化.结果表明:(1)北方农牧交错带土...     

Negative effects of blue mussel (Mytilus edulis) presence in eelgrass (Zostera marina) beds in Flensborg fjord,Denmark

The effect of blue mussel (Mytilus edulis) presence in eelgrass (Zostera marina) beds was studied from June 2004 to July 2005 in Flensborg fjord, Denmark. The field experiments were conducted at two stations, one with only Z. marina (Eelgrass station) present and one where M. edulis were present in the Z. marina beds (Mixed station). Zostera marina parameters were measured (growth of leaves, shoot density, leaf length, and nutrient content) in combination with epiphyte cover and sediment parameters (sulphate reduction rates, sediment nutrient fluxes, organic content, C, N and P content) to examine possible positive and negative effects of the mussels on eelgrass performance. The fluxes of ammonium from the sediments were stimulated at all sampling dates at the Mixed station, and possibly stimulated epiphyte growth at this station. Further ¹⁵N signals in epiphytes from the Mixed station suggested that excretion products from the mussels were important nitrogen sources at this station. Sulphate reduction rates were enhanced at the Mixed station and also sediment sulphide concentrations increased under mussel influence, which may have resulted in sulphide toxicity and decreased growth of Z. marina at this station. The study indicates that for Z. marina beds in Flensborg Fjord the effects of M. edulis in seagrass beds are primarily negative, and raises the question whether this leads to negative effects on the stability and expansion of Z. marina beds.     

几种禾本科植物淀粉粒形态比较及其考古学意义

对5种禾本科植物种子中的淀粉粒（包括粟、黍、青狗尾草、高粱及薏苡等）进行了形态学观察和描述,结合颗粒长度的测量和统计学分析,建立了区分这些作物淀粉粒的一般方法。结果显示,粟和黍的淀粉粒以多边形居多,比例分别为75％和96％;青狗尾草中的淀粉粒以圆形为主;高粱和薏苡的淀粉粒形态具有较高的多样性。表现在消光臂上,高粱淀粉粒的消光臂呈现弯曲特征,而其他4种作物淀粉粒的消光臂则较为平直。在颗粒的长度分布上,粟淀粉粒为2.77～18.40μm,黍淀粉粒为3.93～12.85μm,青狗尾草淀粉粒为 2.19～11.90μm,高粱淀粉粒为4.11～30.30μm,薏苡淀粉粒为 5.48～25.44μm。研究表明,粟、黍、青狗尾草、高粱及薏苡等5种禾本科植物的淀粉粒形态特征存在相似性,但是也有差异。综合运用二维形状、脐点位置、表面特征、消光臂特征及长度等多种指标,可以对这几种作物的淀粉粒进行一定程度的区分。这一研究结果可用于辅助对古代淀粉粒的种属鉴定。     

草鱼、鲢鱼和凡纳滨对虾多元化养殖系统结构优化的研究

采用陆基围隔实验法,开展了草鱼(Ctenopharyngodon idellus)、鲢鱼(Hypophthalmichthys molitrix)和凡纳滨对虾(Litopenaeus vannamei)三元混养结构优化的初步研究。实验于2009年5～10月进行,每月定期采样,分别测定了各混养系统水质和底质的变化、养殖生物的成活率和养殖产量,分析了各混养系统的饲料转化效率、氮磷利用率及产出投入比。实验结果初步表明,草鱼放养密度为0.77尾/m2时,既可以保证出池规格(>1 100 g/尾)又不影响收获产量(>8 400 kg/hm2),同时饲料转化效率(>52%)及氮磷利用率(N>30%,P>14%)也较高;鲢鱼放养密度为0.23尾/m2或0.45尾/m2,可以起到调节水质的作用;对虾放养密度越大(48.9尾/m2),底质被污染程度越小。在本实验条件下,最佳的混养模式:草鱼与鲢鱼混养比例为草鱼0.77尾/m2鲢鱼0.45尾/m2;草鱼、鲢鱼和对虾混养比例为草鱼0.77尾/m2鲢鱼0.23尾/m2凡纳滨对虾16.3尾/m2。     

地表面物理过程与生物地球化学过程耦合反馈机理的模拟研究

利用大气—植被相互作用模式（AVIM）研究地表面物理过程与生物地球化学过程耦合的机理和实现方法,其基础是植物与非生物环境之间物质和能量交换等物理过程影响植物的生理生长过程,使得植被宏观形态和相应的地表的动力学参数上发生显著变化,又反过来作用于植被与大气、土壤之间的物理交换过程。这种气候与生物圈双向反馈过程是在季节和年际时间尺度上的主要相互作用机理。应用AVIM于内蒙古半干旱草原,模拟了在大气状况强迫下,草原生态系统初级生产力,植被与大气之间CO2、潜热和感热的交换,揭示了地表物理和生物学过程耦合反馈机理。     

甘肃省林草研究和业务进展综述

从历史时期森林变迁,林业与气候、经济林果适宜种植区、草场与气候、卫星遥感技术应用和森林防火服务方面综合了甘肃省关于林草科学研究和业务的进展,可供西北大开发参考。