淤地坝减轻坡沟系统滑坡侵蚀的数值模拟

基于边坡分析软件及有限元软件,通过建立陕北绥德县关地沟4号坝上游典型坡沟系统的概化模型,应用概率统计和数值仿真分析方法,从坡沟系统的力学稳定和受力破环的角度,得到了随淤地坝坝地的逐渐淤高坡沟系统的稳定性、滑塌概率和滑塌量分别增强、减弱和减少,其随坝地淤高的变化分别满足二项式、二项式和直线规律.应用有限元强度折减法原理,对坡沟系统的应力场和位移场进行了仿真分析,指出了稳定系数最小,滑坡概率最大时坡沟系统濒临滑坡侵蚀时的最大应力和位移分布区域:(1)X方向的最大位移是沟坡中下部位垂直向坡体内约15 m的范围;(2)y方向的最大位移是从峁顶向两侧各延伸10 m左右的扇形区域;(3)拉应力最大值区域是从峁顶经峁坡向沟坡坡缘线向坡体内延伸9m左右的带形区域.研究结果可为坡沟系统水土保持工程措施的配置及生物措施的实施提供有益的参考,并为评价坡沟系统的稳定性提供一定可靠度的依据.     

黄土丘Ⅴ区典型小流域坝控区重力侵蚀分析与预测

黄土丘Ⅴ区因其独特的土壤及地形和水文地质条件,使淤地坝坝控区的重力侵蚀严重,以至于毁坏耕地、道路和桥梁等,严重影响淤地坝效益的发挥。针对黄土丘Ⅴ区典型小流域坝控区在运行期间因沟岸崩塌和岸坡滑塌等产生的重力侵蚀导致淤地坝泥沙淤积量计算失真的问题,采用实测库容与3S技术生成库容资料和原设计库容曲线复核率定的三重复核分析方法,对运行期淤地坝坝控区域的重力侵蚀来源、诱发因素及预测进行分析。结果表明:(1)反映淤地坝淤积形态的形态判别系数α'为0.711~208.517,均值48.238,说明除阳山上小型坝小于临界数2.2为椎体淤积外,其他淤地坝为三角洲淤积;(2)坝控区形态参数如淤积面面积、周长、淤积体积及淤积形态判别系数等对重力侵蚀影响较大,给出了重力侵蚀量及侵蚀模数的计算关系;(3)重力侵蚀模数的范围184.79~812.80t/(km~2·a),均值360.68t/(km~2·a),坝控区淤积产沙模数的范围225~2 719t/(km~2·a),均值1 382t/(km~2·a)。重力侵蚀模数约占淤积产沙模数的26.1%,说明在黄土丘陵沟壑区第Ⅴ副区淤地坝的库区拦沙既有上游因水力侵蚀产沙又有库区自身重力侵蚀所致,淤地坝的运行管理既要防止重力侵蚀破坏现有耕地,又要防止淤地坝淤积出的土地被沟道基流苦咸水破坏,从而导致淤地坝淤地无法高效利用。     

黄土高原坡沟系统重力侵蚀数值模拟研究

采用有限差分软件FLAC3D对黄土高原坡沟系统重力侵蚀机理进行探索,对坡沟系统应力场和位移场进行数值模拟,分析了不同侵蚀基准面抬升高度对坡沟稳定性及重力侵蚀的影响。结果表明,随侵蚀基准面逐渐抬升,坡沟系统逐渐稳定,最大位移、安全系数及滑塌概率的变化符合指数函数分布规律。拟合方程精度较高,可应用于坡沟重力侵蚀的定性分析与定量计算。凹形边坡整体几何形态能够有效降低应力集中,减缓重力侵蚀的发生程度;坡沟系统上部位移是以"沉降"模式为主,梁峁顶和梁峁坡是重力侵蚀最为强烈的部位。随侵蚀基准面逐渐抬升,各方向位移均有不同程度降低。     

黄河流域第三副区坝系拦沙输沙监测成果分析

黄河流域第三副区聂家河小流域坝系工程布局以现有骨干工程为骨架,各级沟道自上而下逐段布设小型淤地坝、中型淤地坝和骨干工程,分级拦蓄径流泥沙;在其示范坝系的典型淤地坝上布设了降雨、拦沙及输沙监测点.监测结果表明:坝系工程抬高了侵蚀基准,稳定了沟坡,控制了沟床下切和沟岸扩张,增强保土保水能力,尤其骨干坝在坝系拦沙中起关键作用,能够快速有效地拦蓄径流泥沙,控制水土流失,是水土保持生态建设的重要措施,为保护下游河流安全起到了重要作用.     

淤地坝“淤满”后的水沙效应及防控对策

黄土高原大规模的淤地坝建设在减少黄河泥沙以及改善区域生态环境方面发挥了巨大作用.但是,在淤地坝“淤满”的极端条件下,关于其水沙效应变化及防治对策的研究还较少涉及.经分析,淤地坝“淤满”后:1)坝控范围内坡度降低,径流长度减少,沟道比降降低,而横断面由原来的“V”型沟道,演变为“U”型沟道;2)以关地沟4号坝为例,使用RUSLE计算,修建淤地坝前,坝控范围内平均每年土壤侵蚀模数为4 472 t/(km2 ·a),淤满后,土壤侵蚀模数下降至4 019 t/(km2·a),降幅约10％,“原地”减蚀作用显著,从修建至淤满阶段,拦沙作用巨大;3)淤地坝淤满后,坝地流速显著降低,从修建淤地坝前的0.83 m/s降至0.27 m/s,但坝体外坡的流速显著增加,特别是坡底,最大流速可达3.76 m/s;4)淤地坝淤满后,淤地坝“异地”减蚀作用会降低.基于上述变化,针对淤地坝淤满后的极端条件,本文提出如下防治对策:1)以小流域为单元,以溢洪道为主体,完善沟道排洪设施布设,提高支沟内以及支沟与主沟的连通度,提升排洪能力;2)遵循“因地制宜”原则,科学合理植树种草、修建梯田,加强坡面治理,减少坡面来水来沙,消耗和分散坡面来水侵蚀能量,降低坝地淤满后被损毁的风险;3)采取“截水沟和排水沟相结合,工程措施和植物措施相结合”的方法,做好坝体陡坡防治,提高坝体外边坡植被覆盖度.研究结果以期为黄土高原淤地坝建设提供理论支撑.     

小流域坡沟侵蚀关系的模拟试验研究

由于研究方法和研究流域的不同，关于小流域的坡沟侵蚀关系仍有不同的观点，通过室内模拟试验，研究了小流域的坡沟侵蚀关系，结果表明，小流域的坡沟侵蚀关系随小流域的沟道发育而变人,现出沟道侵蚀量逐渐减少，坡面侵蚀量逐渐增大总趋势，在次降雨中，也表现出类似的变化过程。     

淤地坝坝体体积的计算

对于已确定的淤地坝坝址,坝体的纵断面（即沟道横断面）是一定的。根据实测的沟造横断面,以沟底最低点为坐标原点,沟道一侧的岸壁曲线可用幂函数形式表示之。利用这种幂函数关系,对于坝坡均一的坝体．在设定坝顶宽、坝高和上下游边坡之后,作者推导出沟道一侧坝体体积的计算公式;沟道两侧的坝体体积即为坝体总体积。对于非均一坝坡、设有马道的坝和坝体加高的体积,可将坝体横断面分割为由几个均一坝坡组成的坝体断面,分别计算其体积。这种计算方法的精度,取决于坝址横断面岸壁曲线回归方程与实际岸壁的符合程度。     

不同土地利用对黄土区小流域坡沟系统土壤水分变化及水盐的响应

采用野外分峁坡和沟坡调查、采样和测量,研究了不同土地利用类型下小流域坡沟系统土壤水分变化的规律及与土壤含盐置的相关关系.结果表明:(1)峁坡和沟坡降雨前与降雨后土体的体积含水量随土层垂直深度呈二项式变化规律.(2)峁坡和沟坡电导率随含水量的变化分别呈幂函数和二项式变化规律.     

黄土沟道重力侵蚀地貌因素分析

地貌是黄土沟道中重力侵蚀发生的重要条件。基于对黄土沟壑区桥沟小流域的实地观测和DEM数据,从沟道侵蚀的垂直分带性、沟道地貌发育的阶段性、坡面坡度分布等方面分析了流域地貌因素对重力侵蚀的影响。研究表明,桥沟流域存在<20°、20°～32°、32°～42°、>42°四个类型的坡面,其中30°左右是梁峁坡的临界坡面,40°左右是坡积物堆积坡的临界坡面,42°以上可以作为沟坡的判定界限。对不同坡度坡面水流输沙能力进行对比,可以估算出桥沟流域典型坡面重力侵蚀产沙量占总产沙量的42%左右。     

黄土丘陵第三副区典型淤地坝系结构特征分析

为科学认识黄土丘陵区淤地坝系结构特征,对黄土丘陵区第三副区车路沟坝系沟道特征、库容分布特征、泥沙淤积及蓄水量分布特征进行了总结,并对坝系的级联方式进行了解析,对把口站的水沙变化趋势进行了分析。结果表明:(1)车路沟流域随着沟道级别的提高,沟道平均面积增大,平均沟长增加,平均比降减小;Ⅰ级沟道小型坝的数量最多,Ⅱ级沟道中型坝数量最多,Ⅲ级和Ⅳ级沟道则以骨干坝建设为主。(2)随着沟道级别的提高,骨干坝的总库容、设计防洪库容和设计淤积库容表现为逐渐增大,中型坝、小型坝的总库容和设计防洪库容表现为逐渐减小,设计淤积库容先增大后减小。(3)车路沟坝系中型坝和小型坝的设计淤积库容已经几乎淤满,而骨干坝还剩余较大的淤积库容。(4)车路上游坝系单元通过拦蓄洪水泥沙为下游主沟的淤地坝减轻防洪压力,坝系单元内部各中小型坝尽快淤积成地,车路沟坝系仍有较大的淤地潜力;随着车路沟淤地坝系的建设,流域把口站的水沙趋势发生了明显变化。研究成果以期为黄土高原淤地坝系建设管理提供参考。     

低氮和干旱胁迫对富士和秦冠生长及氮素利用的影响

【目的】以富士（Fuji）、 秦冠（Qinguan）嫁接在平邑甜茶（Malus hupehensis Rehd.）上的当年生盆栽苗为试验材料,采用砂培方法,研究了缺氮胁迫和干旱对富士和秦冠生长情况、 光合参数、 植株各部位氮磷钾含量及氮素利用效率的影响,分析比较了低氮干旱条件下富士和秦冠生长及氮素利用的差异,以期为果树生产高效肥水利用提供理论指导。【方法】试验共设四个处理: 正常氮正常水（ZZ）、 低氮正常水（DZ）、 正常氮干旱（ZG）、 低氮干旱（DG）。氮素和水分均设置两个水平,分别为正常氮（6 mmol/L NO-3-N）、 低氮（0.3 mmol/LNO-3-N）、 正常供水（保持盆中砂子相对含水量为饱和含水量的80%~85%）、 干旱处理（保持盆中砂子相对含水量为饱和含水量的60%~65%）。【结果】富士和秦冠的生物量（茎和叶）、 株高茎粗等生长指标以及光合速率、 气孔导度、 蒸腾速率均为正常氮正常水（ZZ）＞低氮正常水（DZ）＞正常氮干旱（ZG）＞低氮干旱（DG）,并且相对应处理下秦冠的以上指标均高于富士;正常供水下,缺氮处理使富士、 秦冠的根冠比比正常氮处理均有所增加,富士提高了2.05%,秦冠提高了22.40%。富士和秦冠的氮、 磷、 钾含量均表现出正常氮正常水（ZZ）＞低氮正常水（DZ）＞正常氮干旱（ZG）＞低氮干旱（DG）; 氮、 钾元素含量在植株各部位的分布顺序依次是叶＞根＞茎,磷元素则是根＞叶＞茎;光合氮素利用效率（PNUE）和氮素利用效率表现为秦冠处理之间差异极显著,富士处理之间差异不显著;秦冠的PNUE和NUE明显高于富士,在低氮正常水（DZ）处理下,秦冠氮肥利用率比富士高42.07%,在低氮干旱（DG）处理下高64.14%;低氮胁迫下富士和秦冠的NUE显著提高,并且秦冠提高的幅度高于富士。【结论】施用氮肥能够显著提高富士与秦冠的干物质量,同等水肥条件下,秦冠生长优于富士;水分亏缺会减少叶片对氮的吸收,干旱条件下适度增施氮肥,可提高果树的抗旱能力;低氮干旱胁迫下秦冠的生长指标、 光合指标及氮素利用效率指标均优于富士,表现出较强的抗低氮干旱胁迫的能力。     

Pasture Vegetation Elemental Analysis by Laser-Induced Breakdown Spectroscopy

Laser-induced breakdown spectroscopy (LIBS) is a new technique for the analysis of plant material. This study investigates the application of LIBS to pasture-based plant samples. The LIBS measurements were obtained from pelletized pasture samples (100 samples) that had been also analyzed by inductively coupled plasma–optical emission spectroscopy (ICP-OES) following microwave digestion for calibration and comparison purposes. Comparisons for elements sodium (Na), potassium (K), magnesium (Mg), calcium (Ca), manganese (Mn), iron (Fe), copper (Cu), zinc (Zn), boron (B), phosphorus (P), and sulfur (S) showed that LIBS could be used for almost all the standard profile total elements with concentrations down to low mg/kg levels (observed error of Na: 0.024 percent, K: 0.18 percent, Mg: 0.016 percent, Ca: 0.073 percent, P: 0.017 percent, Mn: 31 mg/kg, Fe: 150 mg/kg, Zn: 6.6 mg/kg, and B: 1.1 mg/kg). Elemental analysis at less than mg/kg levels was not possible using LIBS. The elements S and Cu were particularly difficult to analyze with reliability using LIBS at the concentration levels found in the plant samples. Replacing microwave digestion and subsequent ICP analysis with a direct analysis of dried plant samples using LIBS has the potential to improve the productivity and reduce the cost of testing.     

Assessing the effectiveness of conservation measures: Resolving the “wicked” problem of the Steller sea lion

“Wicked” problems are those that are complex and that change when solutions are applied. Many conflicts in conservation fall into this category. The study approached the problem of how to constrain the apparent wickedness of a problem in the conservation management of a species by using simple empirical indicators to carry out iterative assessment of the risk to a population and to document how this risk evolves in relation to the addition of new data and the implementation of management actions. Effects of high levels of uncertainty within data and also concerning population structure were examined through stochastic simulation and by exploration of scenarios. Historical trends in the example used, the Steller sea lion, showed rapid declines in abundance in some regions during the 1980s. The current total population is 130,000-150,000 Steller sea lions through Alaska and British Columbia and this number has been stable since about 1990 in spite of regional differences in population dynamics. Regional differences in the sequence of changes in the number of pups and non-pups, suggested that an internal re-distribution of juveniles could have happened between 1980 and 1990. Current productivity also appears close to the long-term mean. Stochastic population projection using various scenarios showed that, based upon this history, the risk of extinction for the population has declined and is below reasonable thresholds for considering the population to be endangered. The trends in risk suggest that management actions taken since 1990 have probably been effective. Consequently, the conservation management objectives for the Steller sea lion are probably being met. The approach provides a mechanism, based upon experience and scenario analysis, for exploring future policy options and may help to constrain the debate amongst stakeholders about the cost-benefit trade-offs associated with different options.     

Soil-profile distribution of primary and secondary plant-available nutrients under conventional and no tillage

Nutrient distributions under no tillage (NT) compared with conventional disk-and-bed tillage (CT) management in the warm, humid region of the southeastern USA need to be assessed so that future placement, quantity, and type of fertilizers can be altered, if necessary, to efficiently match crop demands. We determined soil-profile distributions of pH, N, P, S, K, Ca, Mg, Na, Zn, Fe, Mn, and Cu to a depth of 0.9 m at the end of 8.5 years of continuous CT and NT management on a Weswood silty clay loam (fine, mixed, thermic Fluventic Ustochrept) in southcentral Texas. Most dramatic changes occurred within the 0–0.05 m depth, where soil under NT had lower pH, Fe, and Cu than under CT, but greater P, K, Zn, and Mn. Greater P and K under NT than under CT also occurred below the till-zone (0.15–0.3 m). At a depth of 0–0.3 m, soil under NT contained greater amounts of extractable P, K, Zn, Fe, Mn, and Cu than under CT. Nitrogen fertilization had little effect on nutrient distributions, except resulting in greater extractable K at 0–0.05 m and greater nitrate at 0–0.15 m. Few changes in soil-profile distributions were observed for extractable S, Ca, Mg, and Na. Long-term continuous use of NT on this fine-textured, high-fertility (except for N) soil had no apparent adverse effects on nutrient distributions relative to CT, but enhanced conservation and availability of P, K, Zn, Fe, Mn, and Cu near the soil surface where crop roots proliferate.     

Faculty positions:Center for Agricultural Resources Research,Chinese Academy of Sciences

正The Center for Agricultural Resources Research(CARR),the Institute of Genetics and Developmental Biology(IGDB),Chinese Academy of Sciences,invites applicants for several research group leader positions.CARR is one of the research organizations in Chinese Academy of Sciences(CAS).We seek nominations and applications from individuals who have expertise and a record of accomplishment in research areas related to ecology,agro-hydrology,     

Macroinvertebrates in North American tallgrass prairie soils: effects of fire, mowing, and fertilization on density and biomass

The responses of tallgrass prairie plant communities and ecosystem processes to fire and grazing are well characterized. However, responses of invertebrate consumer groups, and particularly soil-dwelling organisms, to these disturbances are not well known. At Konza Prairie Biological Station, we sampled soil macroinvertebrates in 1994 and 1999 as part of a long-term experiment designed to examine the effects and interactions of annual fire, mowing, and fertilization (N and P) on prairie soil communities and processes. For nearly all taxa, in both years, responses were characterized by significant treatment interactions, but some general patterns were evident. Introduced European earthworms (Aporrectodea spp. and Octolasion spp.) were most abundant in plots where fire was excluded, and the proportion of the total earthworm community consisting of introduced earthworms was greater in unburned, unmowed, and fertilized plots. Nymphs of two Cicada genera were collected (Cicadetta spp. and Tibicen spp.). Cicadetta nymphs were more abundant in burned plots, but mowing reduced their abundance. Tibicen nymphs were collected almost exclusively from unburned plots. Treatment effects on herbivorous beetle larvae (Scarabaeidae, Elateridae, and Curculionidae) were variable, but nutrient additions (N or P) usually resulted in greater densities, whereas mowing usually resulted in lower densities. Our results suggest that departures from historical disturbance regimes (i.e. frequent fire and grazing) may render soils more susceptible to increased numbers of European earthworms, and that interactions between fire, aboveground biomass removal, and vegetation responses affect the structure and composition of invertebrate communities in tallgrass prairie soils.     

Enhanced establishment and growth of giant cardon cactus in an eroded field in the Sonoran Desert using native legume trees as nurse plants aided by plant growth-promoting microorganisms and compost

To evaluate the feasibility of long-term desert reforestation technology of mixed vegetation, cardon cactus (Pachycereus pringlei) seedlings from indoor and outdoor nurseries were planted in the field adjacent to one seedling of potential legume nurse trees: mesquite amargo (Prosopis articulata), yellow palo verde (Parkinsonia microphylla), and blue palo verde (Parkinsonia florida). Some of the planting holes were also supplemented with common dairy compost. Additionally, the combinations of legume tree–cactus were inoculated with either a consortium of desert arbuscular mycorrhizal (AM) fungi, plant growth promoting bacteria (PGPB; the diazotroph Azospirillum brasilense Cd, and the phosphate solubilizer Paenibacillus sp.), or a mixture of all. The field experiments were evaluated periodically during 30 months for survival and growth. Cardons reared in an outdoor screen house survived better in the field than those reared in a controlled growth chamber and hardened later outdoors. Association with any legume nurse tree increased survival and enhanced growth of untreated cardons. For cardons growing alone, application of either compost, AM fungi, and all the treatments combined increased survival. For these plants, no treatment affected plant growth during the first 3 months after transplanting. Later, all treatments, except for AM fungi, enhanced plant growth. However, only 2 years after transplanting the enhanced growth effect of AM fungi was also significant. In the presence of the legume nurse trees, transient positive effects on cardon growth were recorded. General evaluation after 30 months of cultivation showed that the treatments positively affected cardon growth when growing alone or in combination only with mesquite amargo but not with the other two legume trees. This study proposes that young legume trees have the capacity to enhance survival and growth of cardon cactus, depending on the legume cactus combination. Additional treatments such as compost or PGPB can either amplify the effect or else attenuate it.     

Variation in quality parameters between and within 14 Nordic tree fruit and berry species

Abstract

A 3-year study was carried out to investigate quality parameters in 14 tree fruit and berry species grown in southern Norway. The species were blueberry, apple, aronia, sour cherry, sweet cherry, red raspberry, strawberry, blackcurrant, gooseberry, red currant and elderberry, harvested along with wild bilberry, cloudberry and lingonberry. Significant differences between species were identified for all quality parameters. The coefficient of variation between species was lowest for pH (12.5%), dry matter (18.9%) and soluble solids (25.3%), followed by titratable acids (59.3%), total phenolics (83.8%), antioxidant capacity FRAP (85.7%) and antiradical power by the DPPH-assay (97.8%), total monomeric anthocyanins (132%) and ascorbic acid (137%). Average coefficient of variation within species were lower and ranged from 4 (pH) to 62% (ascorbic acid). Only the FRAP values were significantly affected by harvesting year with lower levels in 2004 than in 2005 and 2006. There were significant interactions between species and harvesting year for dry matter, soluble solids, pH, ascorbic acid and FRAP. The results indicate generic ranges in composition within species independent upon growing location and climate, and the composition of the tree fruits and berries is not likely to deviate from these ranges. It is concluded that desirable composition of tree fruits and berries and their products should primarily be achieved by selection among species rather than searching fors broadened variation within individual species.     

Karyotypic and genome size variation in Cajanus cajan (L.) Millsp. (pigeonpea) and some wild relatives

Detailed karyotypes and 4C DNA amounts have been studied in five cultivars of Cajanus cajan and 20 species belonging to Cajanus, Rhynchosia, Dunbaria, Flemingia and Paracalyx. C. cajan shows intraspecific variability and its karyotype is most similar to that of C. cajanifolius (sect. Cajanus) in the morphology and number of satellite chromosomes and the lack of any correlation between chromosome size within the complement and asymmetry. Karyotypes of C. lineatus and C. sericeus belonging to sect. Atylia are similar with respect to maximum r-index and the ratio of longest and shortest chromosomes in their respective complements. C. acutifolius (sect. Frutocosa) is distinct in having a very low ratio (1.44) between the longest and the shortest chromosomes, while in C. albicans, C. goensis, C. scarabaeoides (sect. Cantharospermum) there is no chromosome pair with r-index >2.0. C. mollis and C. volubilis (sect. Volubilis) show similarity with regard to ratio between the longest and the shortest chromosomes and a distinct chromosome pair with an arm ratio of 2.7 and C. platycarpus is distinct (sect. Rhynchosoides) in having the smallest ratio (1.36) between the longest and the shortest chromosomes. 4C DNA amounts in Cajanus and Rhynchosia vary between 3.28 pg to 11.69 pg and 4.92 pg to 11.13 pg respectively, while in Dunbaria, Flemingia and Paracalyx these vary between 4.70 and 7:06 pg. In the genus Cajanus karyotypic features and 4C DNA amounts agree with the sectional classification and bring out a close relationship between C. cajan and C. cajanifolius. This is supported by studies based on seed protein patterns, isozyme analysis, trypsin and chymotrypsin inhibitor patterns, RFLP and RAPD data and crossability relationships. A clear relation between DNA amount and abnormalities effecting the extent of pairing and recombination in interspecific hybrids shows the importance of this study in developing future breeding programme involving C. cajan and its wild relatives that are of potential value.     

Effect of some fungicide seed treatments on the survival of Bradyrhizobium japonicum and on the nodulation and yield of soybean [Glycine max. (L) Merr.]

Several commercial fungicide seed treatments were evaluated for their possible effect on the survival of Bradyrhizobium japonicum on seeds and on the nodulation and yield of soybeans in a greenhouse and a field experiment. quinolate Pro (carbendazim and oxine copper), Vitavax 200FF (carboxin and thiram), and Monceren (pencycuron) had a small effect or no effect on the survival of B. japonicum and on the nodulation and yield of soybeans. They can thus be considered compatible with soybean seed inoculation. Germipro UFB (carbendazim and iprodione), Apron 35J (metalaxyl), and Tachigaren (hymexazol) decreased B. japonicum survival and the nodulation and yield of soybeans and thus cannot be considered compatible with soybean seed inoculation.