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1.
群落物种组成及种群分布格局特征是揭示种群发展趋势及与环境相互关系的基础.以滇西北剑湖湿地海菜花群落为对象,采用样方法与扩散系数法对其物种组成与种群分布格局进行研究.结果表明:群落共有物种18种,分属12科、14属,包括沉水、漂浮、浮叶及湿生4类生活型;海菜花(Ottelia acuminata)、豆瓣菜(Nasturtium officinale)、马来眼子菜(Potamogeton malaianus)和草茨藻(Najas graminea)呈集群分布,其余种群呈随机分布;海菜花种群个体间拥挤效应最大,种内竞争最为激烈.保育海菜花种源、开展流域和生境治理以减缓湖泊沼泽化进程,是目前剑湖海菜花群落保护的当务之急. 相似文献
2.
Latitudinal changes in larger benthic foraminiferal assemblages in shallow-water reef sediments along the Ryukyu Islands, Japan 总被引：1，自引：0，他引：1
Abstract The taxonomic diversity of hermatypic corals decreases with increasing latitude, which correlates with sea‐surface temperatures. However, little is known about latitudinal changes in the taxonomic diversity and biogeographic patterns of larger benthic foraminifera, although their physiological requirements are similar to those of hermatypic corals because of their symbiotic relationships with microalgae. The present study examined how the abundance and taxonomic composition of larger foraminiferal assemblages in shallow‐water reef sediments change with latitude along the Ryukyu Islands (Ryukyus), which are located near the northern limit of coral‐reef distributions in the western Pacific Ocean. Three islands from different latitudes in the Ryukyus were selected to investigate latitudinal changes in larger foraminiferal assemblages: Ishigaki Island (24°20′N, 124°10′E), Kudaka Island (26°09′N, 127°54′E) and Tane‐ga‐shima Island (30°20′N, 131°E). Four sediment samples were taken at each of three topographic sites (beach, shallow lagoon and reef crest) on the reef flat of each island. Foraminiferal tests of a 2.0‐ to 0.5‐mm size fraction were selected, identified and counted. The variations in foraminiferal abundance in reef sediments from three latitudinally different islands exhibit two contrasting trends along reef flats: a shoreward decrease on Ishigaki and Tane‐ga‐shima Islands and a shoreward increase on Kudaka Island. A total of 25, 24 and 13 foraminiferal taxa were identified in Ishigaki, Kudaka and Tane‐ga‐shima Islands, respectively. Baculogypsina sphaerulata, Neorotalia calcar and Amphistegina spp. were dominant (i.e. >3% of foraminiferal assemblages) in the three islands. Calcarina gaudichaudii and Calcarina hispida were common on Ishigaki and Kudaka Islands but were absent on Tane‐ga‐shima Island. Larger foraminiferal assemblages from three different reef‐flat environments on Ishigaki Island can be distinguished, whereas those from the three environments on Kudaka and Tane‐ga‐shima Islands are similar in composition. These latitudinal changes in larger foraminiferal assemblages in reef sediments may possibly be caused by variations in the topography of reef flats, distributions and standing crops of living foraminifers on reef flats, and the northern limit of some calcarinid species in the northern Ryukyus. 相似文献
3.
现代分子生物学技术为蓝藻的生物多样性研究提供了更多信息和证据.单细胞蓝藻——双囊藻属（Geminocystis）是2009年从集胞藻（Synechocystis）分离出来的新属.2017年5月从青海湖的封闭子湖——月牙湖采集分离到一株单细胞蓝藻藻株,16S rRNA基因序列显示此藻株和双囊藻的藻种显示出最高的相似性,都在97%以上,并且在分子系统树聚为一束.此株的细胞结构以及超微结构显示,细胞纵轴具有窝式结构以及类囊体不规则的排列等双囊藻属所具有的特征.双囊藻是我国蓝藻的新报道纪录属,本研究还对双囊藻的分类和生态进行了讨论. 相似文献
4.
Catherine Quiblier Gilles Bourdier Christian Amblard Denise Pepin 《Aquatic Sciences - Research Across Boundaries》1994,56(1):29-39
Phyto-zooplankton trophic relationships were studied using phytoplanktonic pigments (chlorophylls and carotenoids) as organic natural markers. Pigments were separated by high-pressure liquid chromatography (HPLC).Comparison of pigment profiles from monospecific cultures of various taxonomic groups (Chlorophyceae, Bacillariophyceae and Cyanobacteria) and from Cladocera crustaceans (Daphnia magna) fed with these cultures, showed that the characteristic pigment associations of the different taxa are conserved during their transfer from primary producers to secondary consumers.Chromatographic profiles of the Bacillariophyceae and Chlorophyceae type were obtained fromDaphnia respectively fed with mixtures of a Chlorophyceae and a diatom species and mixture of a Chlorophyceae and a Cyanobacterium. This showed the importance of this method in demonstrating a possible selective feeding by the herbivorous zooplankton.The observation of pigment profiles of the Dinophyceae type following feeding of a zooplankton assemblage from Lake Pavin within this natural medium (phytoplankton dominated by a Dinophyceae) and of a Chlorophyceae type profile as the same assemblage was fed in the laboratory on phytoplankton from Lake Villerest (composed of about 80% Cyanobacteria and 20% Chlorophyceae), suggested that this method could be applied to the natural environment. 相似文献
5.
水位洪枯变化对菜子湖江湖过渡带鱼类物种和功能多样性的影响 总被引：1，自引：1，他引：0
水位的洪枯变化通过江湖连通影响泛滥平原湖泊鱼类的组成和分布,因而江湖过渡带是反映泛滥平原生态系统鱼类交流和多样性变动的关键区域.尽管如此,针对江湖过渡带鱼类群落随水位洪枯变化的研究十分匮乏.本研究以菜子湖江湖过渡带为例,分别在洪水和枯水期选取包括静水和流水生境的样点对鱼类群落进行系统的调查采样,探讨水位洪枯变化对菜子湖江湖过渡带鱼类物种和功能多样性的影响.共采集到鱼类6目12科37属52种,其中,洪水期和枯水期物种数差异显著,分别采集到鱼类50和42种,而静水生境和流水生境物种数差异不明显,分别采集到鱼类47和48种.与洪水期相比,枯水期山溪河流性鱼类的物种数、重量、尾数和优势度百分比分别减少了7.3%、6.3%、14.4%和12.0%;与静水生境相比,流水生境山溪河流性鱼类的物种数、重量、尾数和优势度百分比分别增加了5.3%、14.6%、18.0%和22.3%.SIMPER分析结果显示,麦穗鱼（Pseudorasbora parva）、蛇鮈（Saurogobio dabryi）、（Hemiculter leucisculus）、鲤（Cyprinus carpio）、鲫（Carassius auratus）、短颌鲚（Coilia brachygnathus）、似鳊（Pseudobrama simoni）、翘嘴鲌（Culter ilishaeformis）、达氏鲌（Culter dabryi）、光唇蛇鮈（Saurogobio gymnocheilus）和无须鱊（Acheilognathus gracilis）是引起水位洪枯变化以及不同生境类型鱼类群落结构差异的主要物种.优势度分析结果表明枯水期和静水生境的优势种鱼类相似,重要值较高的优势种鱼类为鲤、鲫、和似鳊;而洪水期和流水生境的优势种鱼类同样相似,重要值较高的优势种鱼类为麦穗鱼、蛇鮈、光唇蛇鮈和短颌鲚.通过双因素方差分析解析了水位洪枯变化和不同生境类型对鱼类物种和功能多样性的影响.发现洪枯水位变化仅对物种多样性指数中的物种数（Richness）产生显著差异,而对功能多样性的3个指数（功能丰富度指数（FRic）、功能离散指数（FDiv）和功能分散指数（FDis））均有显著影响.洪水期鱼类的Richness、FRic、FDiv和FDis指数均显著高于枯水期.同时,静水生境条件下的FRic指数要显著高于流水生境.本研究发现,与传统的物种多样性相比,基于功能性状的功能多样性对水位的洪枯变动更为敏感,河流周期性洪泛是泛滥平原生态系统中鱼类功能补充的重要方式. 相似文献
6.
为了解向家坝水电工程对金沙江下游鱼类多样性的影响,基于2016—2018年邵女坪(库首)、绥江(库中)和桧溪(库尾)3个江段的鱼类群落调查数据,分析了向家坝库区鱼类物种、分类和功能多样性空间格局,结合蓄水前(2011年)和蓄水初期(2015年)的资料,探讨了蓄水后向家坝库区不同维度鱼类多样性的变化趋势。向家坝库区各江段以广适性的瓦氏黄颡鱼(Pelteobagrus vachelli)和静水性的(Hemiculter leucisculus)占优势,两者的数量百分比分别为30.15%±14.82%和13.91%±11.16%。非度量多维尺度分析显示,蓄水后向家坝库区库首邵女坪和库中绥江鱼类群落差异最小,库首邵女坪和库尾桧溪鱼类群落差异最大;库中绥江在蓄水前、蓄水初期和2016—2018年3个时期的鱼类群落差异均较大,表明蓄水后绥江江段鱼类群落经历了剧烈变化。库区不同江段鱼类Margalef丰富度指数、Shannon-Wiener多样性指数和Pielou均匀度指数均表现为:桧溪>邵女坪>绥江,鱼类分类多样性指数和分类差异指数均表现为:桧溪>绥江>邵女坪。库区鱼类摄食、运动和繁殖等不同维度的功能多样性(功能丰富度、功能均匀度、功能离散度)空间格局不同,但总体上库中绥江鱼类功能丰富度最高,功能均匀度最低。与蓄水前相比,绥江江段鱼类物种、分类多样性呈下降趋势,鱼类功能丰富度和均匀度也有下降趋势。蓄水后绥江江段鱼类群落主要功能性状发生了明显变化,如蓄水前以下位口、纺锤形体型鱼类占优势,蓄水后以端位口、侧扁形体型鱼类占优势。不同维度多样性指数侧重于鱼类多样性的不同方面,结合多种指数分析有利于更全面地了解鱼类群落对环境变化和外界干扰的响应。研究结果有助于深入了解水电工程建设对金沙江下游鱼类多样性的影响,为鱼类多样性保护提供依据,也可为长江“十年禁渔”效果评估提供本底资料。 相似文献
7.
Macrophyte community diversity and composition respond to ecosystem conservation and local environmental factors. In this study, we developed a multidimensional diversity framework for macrophyte communities, including the taxonomic and functional alpha and beta diversity. We used the framework to explore the relationships among water level regimes and these diversity parameters in a case study of China's Baiyangdian Lake. Analysis of indicators of hydrologic alteration divided the water level from 1959 to 2019 into four regimes (dry, <6.42 m; low, 6.42–7.23 m; medium, 7.23–8.19 m; high, >8.19 m). Alpha and beta diversity were significantly higher in the medium regime than in the low and high regimes. Redundancy analysis indicated that the maximum water depth significantly affected taxonomic alpha diversity, and total nitrogen (TN) and chemical oxygen demand (COD) concentration significantly affected functional alpha diversity, respectively. Mantel tests showed that TN, Secchi depth (SD), and water depth in the high water level regime significantly increased the total beta diversity and turnover components. TN was the main factor that increased total taxonomic beta diversity. Water level regime mainly influenced interspecific relationships by changing the TN and COD concentration. The water level should be maintained between the medium and high water level regimes to promote restoration of the macrophyte community and improve ecosystem stability. The biodiversity evaluation framework would provide a deeper insight into the hydrological process management for restoration of aquatic macrophyte communities in shallow lakes. 相似文献
8.
Dr. E. Fjerdingstad 《Aquatic Sciences - Research Across Boundaries》1968,30(2):385-396
Summary Bacteriological studies of bottom deposits from Ens? indicate that the bacterial activity is on the whole slight and that
the lake is oligotrophic.
In the sediments endophytic blue-green algae were found in colonies ofAphanothece microscopica N?g. As regardsPhormidium ambiguum andP. bigranulatum taxonomic problems are discussed, and it is mentioned that the denotation f.brevicellulata Claus (P. bigranulatum) is scarcely tenable.
Phormidium Franqueti has been examined in greater detail with regard to cell dimensions and taxonomic relationships. Reasons are given why the
material from Ens? is considered to be identical withPhormidium Franqueti Bourr. and why the species should more correctly be described as an endophytic form ofMicrocoleus chthonoplastes (Mertenes) Thuret f.Franqueti (Bourr.) nov. comb.
Zusammenfassung Bakteriologische Studien von Bodenablagerungen im See Ens? zeigen, dass die bakteriologische T?tigkeit im ganzen gesehen nur schwach ist und dass es sich um einen oligotrophen See handelt. In den Sedimenten wurden endophytische Blaualgen gefunden, und zwar in Kolonien vonAphanothece microscopica N?g. BezüglichPhormidium ambiguum undP. bigranulatum werden taxonomische Probleme diskutiert, und es wird erw?hnt, dass die Bezeichnung f.brevicellulata Claus (P. bigranulatum) kaum haltbar ist. Phormidium Franqueti ist auf die Beziehung zwischen Zelldimensionen und Taxonomie eingehender untersucht worden. Weiter werden Gründe geneannt, weshalb das Material des Sees Ens? als mitPhormidium Franqueti Bourr. identisch betrachtet wird und weshalb die letztere Art korrekter als eine endophytische Form vonMicrocoleus chthonoplastes (Mertens) Thuret f.Franqueti (Bourr.) nov. comb. bezeichnet werden sollte.相似文献
9.
In the present study, we used mitochondrial cytochrome oxidase subunit I (COI) and nuclear D2 region of 28S rDNA sequence
data to examine the taxonomic status of the water mite species Hygrobates nigromaculatus from two types of freshwater habitats: lentic (lakes) and lotic (streams). Previous hypotheses about (sub)species status
of populations inhabiting lakes and streams based on differences in morphometric data and life-cycle strategy (parasitic vs.
non-parasitic larvae) were strongly supported by molecular data. Levels of COI and D2 28S rDNA differentiation between lake
and stream populations were much higher (ca. 18 and 7.5%, respectively) than those typically observed for populations of a
single species. Both lake and stream populations showed similar high levels of gene diversity (Hd = 0.894 and 0.836, respectively).
However, nucleotide within-population polymorphism was more than twice as high in lake populations as that in stream populations
(π = 1.33 and 0.60%, respectively). We hypothesize that the ancestral lake-dwelling population originated from a stream form
with parasitic larvae (here: H. setosus nov. stat.). For the observed populations, H. nigromaculatus individuals could be separated from H. setosus by distinct morphometric characters. The loss of phoretic parasitic larvae greatly decreased dispersal ability of lake-dwelling
mites and consequently also the gene flow between lake populations. Thus, relatively more differentiated genetic structure
in lake populations probably results from a stronger isolation between particular lake habitats, but this hypothesis needs
further extensive studies. 相似文献
10.
区域增温和大气氮沉降作用已成为高山湖泊面临的重要环境胁迫,已有高山湖泊生物群落响应的长期模式研究主要集中于藻类而缺乏更高营养级生物(如浮游动物)的系统调查。本研究选择滇西北地区深水型的高山湖泊沃迪错开展沉积物调查,通过多指标分析(总氮、总磷、叶绿素a、氮稳定同位素等)并结合区域气候重建记录,识别近两百年来该湖泊及流域环境的变化历史,进一步利用枝角类群落指标(物种组成、生物量等)定量评价了湖泊生物群落的响应模式与驱动因子。结果表明,湖泊营养水平(如总氮浓度)和初级生产力(叶绿素a浓度等)在过去近两百年总体呈上升趋势。相关分析显示,大气氮沉降和流域外源输入是影响总氮上升的主要因素,同时区域增温和营养盐富集促进了湖泊初级生产力的不断上升。自1960s以来区域升温明显,湖泊营养水平和叶绿素a浓度呈现加速上升的趋势。钻孔中枝角类群落以浮游属种(Daphnia longispina等)为优势种,在1900AD以前D.longispina相对丰度较为稳定(40.83%±8.02%),之后出现下降趋势且在1948—1965年间明显下降,之后再次明显上升并成为主要优势种。排序分析显示,气温、叶绿素a和总... 相似文献
11.
Calanco (plural, calanchi) is a term widely used in the northern Apennines, Italy, to define a type of badland formed in clayey bedrock. However, no precise geomorphological definition of calanco has been established and a variety of map symbols are used to indicate the presence of calanco landforms. With the aim of developing an improved approach to identifying calanchi, a group of experienced surveyors identified 24 catchments with calanco characteristics among 67 catchments located between Bologna and Faenza in the northern Apennines. The morphology of each catchment was classified using traditional quantitative geomorphic approaches including fieldwork, map interpretation, hypsometric curve construction and computation of the annual sediment yield. Consideration of the parameters produced by these approaches indicated that none was capable of representing the presence of calanchi unequivocally and the basins were grouped into five classes on the basis of number and type of calanco criteria that they met. A characteristic of calanchi that is evident on topographic maps is crenulation of the contour lines and in this study a new topographic parameter was developed to represent the degree of contour crenulation. This parameter, LO/LF, is defined as the ratio of the actual length of a contour line (LO) to the length of the same line smoothed by an algorithm based on a moving average (LF). Calculated values of LO/LF ranged from 1·05 to 1·38. To test whether high values of the contour crenulation parameter were associated with calanchi, LO/LF values were added to other criteria for the five classes of catchment. Class 1 catchments, consisting of 14 of the 24 calanchi catchments identified in the field, displayed all of the criteria defining calanchi, and were characterized by the highest values of LO/LF (mean value 1·27 ± 0·15). It is proposed, therefore, that the contour crenulation ratio (LO/LF) may be useful in identifying the calanco landform. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
12.
In Carrara marble basins, the long and intensive quarrying activities (which began in the first century BC ) have produced extensive dump deposits, locally known as ravaneti. Ravaneti are of such large dimensions and diffusion as to make them a widespread landform of the Apuane Alps (Tuscany). In recent years these quarry dump deposits have been affected by frequent debris flows, more than 50 in 1996/97. This phenomenon is the most significant currently active geomorphological process in this landscape. The evolution of quarrying techniques produced a variety of sedimentological compositions of ravaneti. The debris flows analysed involve only the surface layers where debris is mixed with fine material with a lower permeability (active ravaneti) than the coarser underlying debris (older ravaneti). The presence of different permeability layers causes a wetting front to move downwards. Source area observations indicate a soil slip movement in the initial phases of the failure. The transformation of landslides into debris flow occurs by means of both soil contractive failure and an increase of granular temperature. The morphological and sedimentological analyses of depositional lobes resulted in a classification of three types of lobe, based on fabric–morphometry relationships allowing the identification of different flow dynamics: (1) type A lobe (platy form), matrix‐supported and well developed fabric with general tendency of ab clast plane strikes to lie generally parallel to flow direction as a consequence of laminar flow; (2) type B lobe (elongated form), clast‐supported and random fabric as a consequence of both turbulent flow and coarser composition of starting material; (3) type C lobe, intermediate type A–B morphometry, tendency for ab clast plane to lie in a semi‐circle around the main flow direction determined by the presence of secondary flow lines divergent from it in the stopping phase. In Carrara marble basins, the anomalous frequency with which debris flows tend to be triggered by medium‐intensity rainstorms (about 30 mm h−1 rainfall) is due to the recent increases in silt dump produced by modern quarrying techniques. This represents a significant example of debris flows as an environmental problem in major anthromorphized landscapes. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
13.
The numerical and proportional distributions of zoobenthos in lake Uluabat, which is located in the Northwestern part of Turkey and having international importance according to the Ramsar Convention, were determined from August 2004 to July 2005 at monthly intervals (except for December 2004, January and February 2005) at 12 different stations. Thirty‐three taxonomic groups were recorded. It was found that the zoobenthos consisted of 35.6 % Oligochaeta, 27.7 % Nematoda, 12.3 % Chironomidae larvae, 10.7 % Gastropoda, 3.6 % Ostracoda, and 10.1 % Varia by numbers (Bivalvia, Ceratopogonidae, Hirudinea, Odonata, Ephemeroptera, Asilidae, Hydraacarina, Hemiptera, Argulidae, and Gammaridae). The average number of invertebrates was 160 individuals for 33 taxa at the 12 different stations. Also some environmental parameters of the lakewater were analyzed (temperature, pH, dissolved oxygen, biochemical oxygen demand, chemical oxygen demand, NO2–N, NO3–N, NH3–N, PO4–3, fecal coliform, and total coliform). The relationships between the dynamics of the Oligochaeta and the physicochemical variables were supported by the Pearson correlation index and the canonical correspondence analysis (CANOCO). It was found that the relation between the average number of P. hammoniensis and P. albicola (p < 0.05, r = 0.590 and 0.593, respectively) and L. hoffmeisteri (p < 0.01, r = 0.777) was directly proportional while the relation between the average number of some taxa Trichodrillus sp., Rhyacodrilus coccineus, Nais communis, N. variabilis, and N. barbata and NO3–N (p < 0.05, r = –0.685) was inversely proportional. 相似文献
14.
Fission track and U–Pb zircon ages of psammitic rocks from the Harushinai unit,Kamuikotan metamorphic rocks,central Hokkaido,Japan: constraints on metamorphic histories 
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下载免费PDF全文 Ayumi S. Okamoto Toru Takeshita Hideki Iwano Tohru Danhara Takafumi Hirata Hirotsugu Nishido Shuhei Sakata 《Island Arc》2015,24(4):379-403
Accurate pressure–temperature–time (P–T–t) paths of rocks from sedimentation through maximum burial to exhumation are needed to determine the processes and mechanisms that form high‐pressure and low‐temperature type metamorphic rocks. Here, we present a new method combining laser ablation–inductively coupled plasma–mass spectrometry (LA–ICP–MS) U–Pb with fission track (FT) dates for detrital zircons from two psammitic rock samples collected from the Harushinai unit of the Kamuikotan metamorphic rocks. The concordant zircon U–Pb ages for these samples vary markedly, from 1980 to 95 Ma, with the youngest age clusters in both samples yielding Albian‐Cenomanian weighted mean ages of 100.8 ± 1.1 and 99.3 ± 1.0 Ma (2σ uncertainties). The zircon U–Pb ages were not reset by high‐P/T type metamorphism, because there is no indication of overgrowth within the zircons with igneous oscillatory zoning. Therefore, these weighted mean ages are indicative of the maximum age of deposition of protolithic material. By comparison, the zircon FT data yield a pooled age of ca. 90 Ma, which is almost the same as the weighted mean age of the youngest U–Pb age cluster. This indicates that the zircon FT ages were reset at ca. 90 Ma while still at their source, but have not been reset since. This conclusion is supported by recorded temperature conditions of less than about 300 °C (the closure temperature of zircon FTs), as estimated from microstructures in the deformed detrital quartz grains in psammitic rocks, and no shortening of fission track lengths in the zircon. Combining these new data with previously reported white mica K–Ar ages indicates that the Harushinai unit was deposited after ca. 100 Ma, and underwent burial to its maximum depth before being subjected to a localized thermal overprint during exhumation at ca. 58 Ma. 相似文献
15.
Relationships between riverbed morphology, concavity, rock type and rock uplift rate are examined to independently unravel the contribution of along-strike variations in lithology and rates of vertical deformation to the topographic relief of the Oregon coastal mountains. Lithologic control on river profile form is reflected by convexities and knickpoints in a number of longitudinal profiles and by general trends of concavity as a function of lithology. Volcanic and sedimentary rocks are the principal rock types underlying the northern Oregon Coast Ranges (between 46°30′ and 45°N) where mixed bedrock–alluvial channels dominate. Average concavity, θ, is 0·57 in this region. In the alluviated central Oregon Coast Ranges (between 45° and 44°N) values of concavity are, on average, the highest (θ = 0·82). South of 44°N, however, bedrock channels are common and θ = 0·73. Mixed bedrock–alluvial channels characterize rivers in the Klamath Mountains (from 43°N south; θ = 0·64). Rock uplift rates of ≥0·5 mm a−1, mixed bedrock–alluvial channels, and concavities of 0·53–0·70 occur within the northernmost Coast Ranges and Klamath Mountains. For rivers flowing over volcanic rocks θ = 0·53, and θ = 0·72 for reaches crossing sedimentary rocks. Whereas channel type and concavity generally co-vary with lithology along much of the range, rivers between 44·5° and 43°N do not follow these trends. Concavities are generally greater than 0·70, alluvial channels are common, and river profiles lack knickpoints between 44·5° and 44°N, despite the fact that lithology is arguably invariant. Moreover, rock uplift rates in this region vary from low, ≤0·5 mm a−1, to subsidence (<0 mm a−1). These observations are consistent with models of transient river response to a decrease in uplift rate. Conversely, the rivers between 44° and 43°N have similar concavities and flow on the same mapped bedrock unit as the central region, but have bedrock channels and irregular longitudinal profiles, suggesting the river profiles reflect a transient response to an increase in uplift rate. If changes in rock uplift rate explain the differences in river profile form and morphology, it is unlikely that rock uplift and erosion are in steady state in the Oregon coastal mountains. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
16.
2012-2016年,每年的春、夏、秋季对汾河太原河段进行浮游植物样品采集.通过对样品的形态观察和描述,共鉴定出5种水华优势种,5月发生的裸藻水华优势种为裸藻属的膝曲裸藻(Euglena geniculata)和血红裸藻(E.sanguinea).而7-9月发生的微囊藻水华优势种为微囊藻属的铜绿微囊藻(Microcystis aeruginosa)、挪氏微囊藻(M.novacekii)和惠氏微囊藻(M.wesenbergii).分离纯化共得到11株单克隆水华藻,其中铜绿微囊藻8株,挪氏微囊藻2株,血红裸藻1株.运用cpcBA-IGS、gyrB和cpSSU基因序列构建分子系统发育树,进一步确定水华藻的系统分类地位,结果表明cpcBA-IGS是研究汾河太原河段铜绿微囊藻分类很好的分子标记,而cpSSU基因可很好地区分血红裸藻和其他裸藻种. 相似文献
17.
Predicting unit plot soil loss in Sicily,south Italy 总被引：2，自引：0，他引：2
Predicting soil loss is necessary to establish soil conservation measures. Variability of soil and hydrological parameters complicates mathematical simulation of soil erosion processes. Methods for predicting unit plot soil loss in Sicily were developed by using 5 years of data from replicated plots. At first, the variability of the soil water content, runoff, and unit plot soil loss values collected at fixed dates or after an erosive event was investigated. The applicability of the Universal Soil Loss Equation (USLE) was then tested. Finally, a method to predict event soil loss was developed. Measurement variability decreased as the mean increased above a threshold value but it was low also for low values of the measured variable. The mean soil loss predicted by the USLE was lower than the measured value by 48%. The annual values of the soil erodibility factor varied by seven times whereas the mean monthly values varied between 1% and 244% of the mean annual value. The event unit plot soil loss was directly proportional to an erosivity index equal to , being QRRe the runoff ratio times the single storm erosion index. It was concluded that a relatively low number of replicates of the variable of interest may be collected to estimate the mean for both high and particularly low values of the variable. The USLE with the mean annual soil erodibility factor may be applied to estimate the order of magnitude of the mean soil loss but it is not usable to estimate soil loss at shorter temporal scales. The relationship for estimating the event soil loss is a modified version of the USLE‐M, given that it includes an exponent for the QRRe term. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
18.
长孢藻是具有产多种蓝藻毒素及异味物质潜在能力的丝状异形胞蓝藻.为了探究长孢藻的生物学特性,我们从江西柘林湖分离24株长孢藻,经形态鉴定分成4个种类,分别为浮游长孢藻(Dolichospermum planctonicum)、近亲长孢藻(D. affine)、卷曲长孢藻(D. circinale)、螺旋长孢藻(D. spiroides). 16S rRNA基因序列表明柘林湖长孢藻与日本等地区的长孢藻高度相似,但只有近亲长孢藻与日本近亲长孢藻在分子系统进化树上聚为一支.基于16S-23S rRNA之间高变异性的ITS序列分析,4种长孢藻的D1-D1'螺旋结构相同,藻丝为直型的浮游长孢藻、近亲长孢藻与藻丝为弯型的卷曲长孢藻、螺旋长孢藻的Box-B、V3螺旋结构差异较大.通过对毒素和异味的分子生物学检测显示24株长孢藻均不产毒,但是4株浮游长孢藻及1株卷曲长孢藻含有土腥素合成基因.本研究不仅对柘林湖水华蓝藻的多样性以及潜在生态风险提供科学的基础资料,也在流域层面上为鄱阳湖的水生态系统研究和保护提供了一定的科学基础. 相似文献
19.
J. Manninen N. G. Kleimenova O. V. Kozyreva P. A. Bespalov T. Raita 《Geomagnetism and Aeronomy》2012,52(1):77-87
The results of an analysis of ground-based observations of very low frequency (VLF) emissions in Scandinavia (L ∼ 5) in April 2011 are discussed. A detailed study is conducted of an non-typical event (April 3, 2011) of simultaneous generation
of VLF chorus at frequencies below 3 kHz and quasi-periodic VLF emissions (QP) in the band of 4–6 kHz, which were not discrete emissions but consisted of separate short (about 20 s) bursts of hiss. It
is shown that these emissions were mainly characterized by right-hand polarization, which indicates the location of the exit
point of waves from the ionosphere near the point of ground observations. Based on an analysis of the spectral characteristics
of emissions, it is concluded that the generation regions of chorus and QP emissions were located at different L shells. The appearance of QP emissions coincided with the excitation of resonance geomagnetic pulsations of the Pc4 range in the magnetosphere with a period that was close to the quasi-period of repetition of spectral forms in QP emissions. However, based on the available data, it is not possible to conclude that these geomagnetic pulsations caused
the quasi-periodic generation of bursts of VLF hiss. The time shift between the peaks of QP and geomagnetic pulsations was inconsistent and varied from one burst of hiss to another. It is suggested that the discussed
QP emissions were a result of the development of self-oscillations in the Earth’s radiation belts. 相似文献
20.
Ashok Sinha 《Annales Geophysicae》1996,14(3):329-335
Recent studies have provided new evidence that models may systematically underestimate cloud solar absorption compared to observations. This study extends previous work on this “absorption anomaly” by using observational data together with solar radiative transfer parameterisations to calculate fs (the ratio of surface and top of the atmosphere net cloud forcings) and its latitudinal variation for a range of cloud types. Principally, it is found that (a) the zonal mean behaviour of fs varies substantially with cloud type, with the highest values obtained for low clouds; (b) gaseous absorption and scattering can radically alter the pattern of the variation of fs with latitude, but gaseous effects cannot in general raise fs to the level of around 1.5 as recently determined; (c) the importance of the gaseous contribution to the atmospheric ASR is such that whilst fs rises with surface albedo, the net cloud contribution to the atmospheric ASR falls; (d) the assumed form of the degree of cloud overlap in the model can substantially affect the cloud contribution to the atmospheric ASR whilst leaving the parameter fs largely unaffected; (e) even large uncertainties in the observed optical depths alone cannot account for discrepancies apparent between modelled and newly observed cloud solar absorption. It is concluded that the main source of the anomaly may derive from the considerable uncertainties regarding impure droplet microphysics rather than, or together with, uncertainties in macroscopic quantities. Further, variable surface albedos and gaseous effects may limit the use of contemporaneous satellite and ground-based measurements to infer the cloud solar absorption from the parameter fs. 相似文献