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1.
Rebi Nijboer   《Limnologica》2004,34(3):213-223
Agapetus fuscipes is a caddisfly that only seems to occur in unimpacted streams and therefore can be a suitable indicator species for natural conditions. The species has decreased in the Netherlands because of human activities which caused organic pollution and hydromorphological degradation. Literature was reviewed to study the autecology and life cycle of A. fuscipes in order to reveal the ecological requirements of this species. By taking Agapetus fuscipes as an example, it is shown that the autecology and life cycle of an indicator species can give important clues for its presence in unimpacted and absence in impacted streams. A. fuscipes is very susceptible to organic pollution and to a lesser degree to discharge dynamics (dropping water level and discharge peaks). The species copes with dynamic discharge events by maintaining a high population density and recolonisation of disturbed habitats from refuges. However, the vulnerability of the species strongly depends on the life stage of the animals (e.g., the ability to migrate, the oxygen demand and the habitat requirements differ between instars). Although several adaptations to dynamic conditions, a high frequency of discharge peaks or a long period of drought can cause the population to decline. Once a population has totally disappeared from a stream it will take the species a long time to recolonise the stream because of its low dispersion capacity. To protect this species stream restoration should focus on water quality (avoid organic pollution and agricultural run off) and on stabilising the discharge by taking care of natural infiltration in the catchment area instead of fast removal of rain water by drainage systems.  相似文献   

2.
Nitrogen and carbohydrate utilization in Phragmites australis rhizomes was investigated under natural conditions at 10 sites in 5 lakes in Upper Bavaria over a period of two years. Nitrate and ammonium of surface and interstitial water was determined. The results indicate that conditions of habitat and environment, such as climate and fluctuation of water level, lead to different adaptations of reed. These parameters had an effect on the storage of nitrogen and carbohydrate. The reed stands exposed to high water level during spring and summer have a high carbohydrate content in the rhizomes. A positive correlation was shown between the aboveground biomass and the content of storaged carbohydrates during the vegetation period. No relationship could be demonstrated between the nitrogen availability of the habitats and the type of storage of carbohydrates and nitrogen. The nitrogen content in the rhizomes can be used as an indicator of the ability of reed stands to produce new secondary shoots after shoot loss. The differently established reed genotypes are not able to compensate short-term environmental changes, such as growing leisure problems and higher shoot loss by the increasing appearance of waterfowl, from their reserve storage.  相似文献   

3.
The aphid Hyalopterus pruni migrates to its secondary host Common Reed in late spring and early summer. Reed fields are known to be more heavily infested at the edges compared to the centre, as the migrants are attracted to the colour of the reed. There is also evidence that reeds growing at wet sites are more heavily infested than at dry sites. This paper shows that both proceses interact in determining the distribution of aphids in different habitats.The observations were carried out in the vast reed field of the Zuidelijk Flevoland polder (The Netherlands) during a number of years after its reclamation in 1968. In the period of migration flying aphids were caught with sticky traps situated in and around the reed field. The distribution of aphids on the reed was determined at different times during the season along transects through the centre of the polder. The existence early in the season (June) of a higher infestation at the edges than in the centre of the field was confirmed. The density of winged aphids in this early period was higher in wet than in dry habitats, which may have been a result of a preference of the settling migrants for reed standing in water. Later in the season (August) the dry habitat still had a relatively low infestation in the centre, but at the wet sites the infestation was high everywhere. This could be attributed to the much quicker population growth that was found in the wet habitat and subsequent short range movement of newly born winged aphids.  相似文献   

4.
Distribution, abundance and life history characteristics of Mysis relicta were studied in the Feldberg Lake District (Lake Breiter Luzin, Lake Schmaler Luzin, Lake Zansen) located in northeastern Germany. Between July 2001 and November 2002 mysids were collected by vertical net hauls. In order to determine the impact of the current trophic conditions on the distribution of mysids in these lakes, oxygen concentration, total phosphorus, chlorophyll a and water transparency were also measured. All investigated lakes are mesotrophic at present. Lake Breiter Luzin exhibited great seasonal and spatial variations in mysid abundance. Density of adults and juveniles had a mean of 44.9 ± 57.1 and 68.7 ± 99.6 m−2, respectively. Highest abundance of adults was 110.4 ± 76.5 m−2 in summer, lowest abundances of 2.0 ± 4.0 m−2 occurred in spring. For juveniles, highest density of 218.4 ± 174.6 m−2 was detected in summer and lowest of 0.8 ± 1.8 m−2 in winter. No mysids were caught in any of the daytime hauls, but they were widely distributed throughout the water column at night. Size frequency distribution of mysids suggested that reproduction occurred year-round, the most consistent influx of juveniles occurred in early summer and a smaller second cohort in autumn. Highest mysid abundance was 189.2 ± 318.6 adults and 127.0 ± 66.3 juveniles m−2 in Lake Schmaler Luzin, and 59.6 ± 5.6 adults and 79.4 ± 11.2 juveniles m−2 in Lake Zansen. There were great spatial differences in abundance in both lakes.  相似文献   

5.
himu, em i andem ii are three of the main geochemical mantle components that give rise to oceanic island basalts [1]. They represent the end members that produce the extreme isotopic compositions measured on intraplate volcanics. In French Polynesia, all three mantle components are represented in volcanic rocks. The characteristichimu signature is found in Tubuai, Mangaia and Rurutu,em i is present in the source of Rarotonga and Pitcairn volcanics andem ii dominates the composition of most Society Islands. Intermediate values between the three end members are found on most islands.We suggest that the three components are not independent but are physically related in the mantle. Thehimu component is thought to be recycled oceanic crust that lost part of its Pb through hydrothermal processes prior to and during subduction.em i andem ii are believed to acquire their isotopic and trace element characteristics through entrainment of sediments that were subducted together with the oceanic crust.The trace element pattern and the isotopic composition ofhimu lavas can be quantitatively modelled using a mixture of 25% old recycledmorb crust and 75% mantle peridotite. The extreme Pb composition is modelled assuming that Pb was lost from oceanic crust when hydrothermal alteration at the ridge leached Pb from the basalt to redeposit it as sulphides on top of and throughout the crust, followed by preferential dissolution of sulphides during dehydration in the subduction zone. These processes led to a drastic increase of theU/Pb ratio of the subducted material which evolved over 2 Ga to very radiogenic Pb isotopic compositions. Pb isotopic compositions similar to those ofem i andem ii are modelled assuming that sediments with average crustal Pb isotopic compositions were subducted and recycled into the mantle together with the underlyingmorb oceanic crust. Pelagic sediments (μ 5 andκ 6) account for the Pb isotopic composition ofem i whereas terrigenous sediments (μ 10 andκ 4.5) evolve towards theem ii end member. A few percent of sediment in the recycled crust-sediment mixture will destroy the characteristic Pb isotopic signature of thehimu component. This, together with the low probability of isolating oceanic crust in the mantle for 2 Ga, explains why the extremehimu composition, as seen on Tubuai and St Helena, is sampled so rarely by oceanic volcanism.  相似文献   

6.
The structure, function and dynamics of reed-belts from three ‘Bornhoeved-Lakes’ was investigated by using methods from vegetation science and molecular biology. Between 1992 and 1994 the morphometry and production of Phragmites was measured at twelve locations, differing in sedimentology and hydrochemistry. The development and production of the plants, as well as the nutrient uptake and relocation, were similar throughout the years within each of the twelve plots. Differences in stand-structure and amounts of nutrients occurred between the habitats. Nitrogen content in the plant material varied between 5 and 30 g N m−2 and phosphorus between 0.3 and 1.2 g PO4-P m−2.80 natural reed habitats were measured for Restriction Fragment Length Polymorphisms (RFLPs) in order to identify the genetic diversity of Phragmites within the lakes. A cluster analysis exhibited groups with high, as well as groups with low genetic similarity. Even if genetically similar, the habitats were not necessarily directly neighboured at the shoreline. A discriminance analysis showed 40% correspondence of the genetic groups with their phenotype and habitat parameters.  相似文献   

7.
The French Ecors program was launched in 1983 by a cooperation agreement between universities and petroleum companies. Crustal surveys have tried to find explanations for the formation of geological features, such as rifts, mountains ranges or subsidence in sedimentary basins. Several seismic surveys were carried out, some across areas with complex geological structures. The seismic techniques and equipment used were those developed by petroleum geophysicists, adapted to the depth aimed at (30–50 km) and to various physical constraints encountered in the field. In France, Ecors has recorded 850 km of deep seismic lines onshore across plains and mountains, on various kinds of geological formations. Different variations of the seismic method (reflection, refraction, long-offset seismic) were used, often simultaneously. Multiple coverage profiling constitutes the essential part of this data acquisition. Vibrators and dynamite shots were employed with a spread generally 15 km long, but sometimes 100 km long.Some typical seismic examples show that obtaining crustal reflections essentialy depends on two factors: (1) the type and structure of shallow formations, and (2) the sources used. Thus, when seismic energy is strongly absorbed across the first kilometers in shallow formations, or when these formations are highly structured, standard multiple-coverage profiling is not able to provide results beyond a few seconds. In this case, it is recommended to simultaneously carry out long-offset seismic in low multiple coverage.Other more methodological examples show: how the impact on the crust of a surface fault may be evaluated according to the seismic method implemented (vibroseis 96-fold coverage or single dynamite shot); that vibrators make it possible to implement wide-angle seismic surveying with an offset 80 km long; how to implement the seismic reflection method on complex formations in high mountains.All data were processed using industrial seismic software, which was not always appropriate for records at least 20 s long. Therefore, a specific procedure adapted to deep seismic surveys was developed for several processing steps. The long duration of the vibroseis sweeps often makes it impossible to perform correlation and stack in the recording truck in the field. Such field records were first preprocessed, in order to be later correlated and stacked in the processing center. Because of the long duration of the recordings and the great length of the spread, several types of final sections were replayed, such as: (1) detailed surface sections (0–5 s), (2) entire sections (0–20 s) after data compression, (3) near-trace sections and far-trace sections, which often yield complementary information.Standard methods of reflection migration gave unsatisfactory results. Velocities in depth are inaccurate, the many diffractions do not all come from the vertical plane of the line, and the migration software is poorly adapted to deep crustal reflections. Therefore, migration is often performed graphically from arrivals picked in the time section. Some line-drawings of various onshore lines, especially those across the Alps and the Pyrenees, enable to judge the results obtained by Ecors.  相似文献   

8.
Azolla filiculoides Lam. is a tiny aquatic fern growing as free floating mats covering the stagnant water of the irrigation and drainage canals of Damietta district, Egypt. Ecological characteristics and distribution of the fern were investigated and results were discussed.Vegetation analysis of Azolla indicate that the most common associated species with Azolla are: Phragmites australis [presence (P) = 93.3%], Echinochloa stagnina (P = 70%), Eichhornia crassipes (P = 57%), Pluchea dioscoridis (P = 56.7%), Persicaria salicifolia (P = 26.7%), Phylla nodiflora (P = 13.3%) and Ludwigia stolonifera (P = 10%). Submerged species, e.g. Ceratophyllum spp. and Potamogeton spp. are completely absent in the stands dominated with solid mats of Azolla. This could be explained by that these mats prevent light penetration and oxygen which are required to submerged plants which in turn are decayed.The pH of the water where Azolla was recorded ranged from 7.1 to 9.0 (mean = 7.8), total dissolved salts ranged from 280 to 2600 mg/l (mean = 880 mg/l). The total phosphorus showed the range from 0.01 to 0.82 mg/l (mean = 0.22 mg/l). The ammonia-N is relatively high, varying from 2 to 18 mg/l (mean = 7.0 mg/l), however, the nitrate-N varied from 2.1 to 54.1 mg/l with a mean value of 20.5 mg/l.The fresh biomass of Azolla ranged from 114 to 4280 g/m2 in irrigation canals and from 506 to 2760 g/m2 in drainage canals. The dry biomass varied from 16 to 23 g/m2 in irrigation canals. The range from 26 to 320 g/m2 was obtained for drainage canals.  相似文献   

9.
青海湖最近25年变化的遥感调查与研究   总被引:23,自引:6,他引:23  
沈芳  匡定波 《湖泊科学》2003,15(4):289-296
青海湖是我国最大的内陆水体,它及其流域的生态环境近来一直倍受广泛关注.其水位下降、湖水面积缩小、湖体分离等更是研究的热点问题.本文针对这些问题展开遥感调查与研究,收集了多时相、多种信息源的影像数据;分析了1975年至2000年25年以来湖泊的变迁及成因,湖岸变化及湖体分离状况;用遥感方法反推25年以来湖水位的变化;计算了1975、2000年两个年份的湖水面积,并遥感分析了湖水面积萎缩的原因.此外,对青海湖进行了实地调查与水深测量,建立了该湖泊水深反演模型.  相似文献   

10.
Bimodal volcanism, normal faulting, rapid sedimentation, and hydrothermal circulation characterize the rifting of the Izu-Bonin arc at 31°N. Analysis of the zigzag pattern, in plan view, of the normal faults that bound Sumisu Rift indicates that the extension direction (080° ± 10°) is orthogonal to the regional trend of the volcanic front. Normal faults divide the rift into an inner rift on the arc side, which is the locus for maximum subsidence and sedimentation, and an outer rift further west. Transfer zones that link opposing master faults and/or rift flank uplifts further subdivide the rift into three segments along strike. Volcanism is concentrated along the ENE-trending transfer zone which separates the northern and central rift segments. The differential motion across the zone is accommodated by interdigitating north-trending normal faults rather than by ENE-trending oblique-slip faults. Volcanism in the outer rift has built 50–700 m high edifices without summit craters whereas in the inner rift it has formed two multi-vent en echelon ridges (the largest is 600 m high and 16 km long). The volcanism is dominantly basaltic, with compositions reflecting mantle sources little influenced by arc components. An elongate rhyolite dome and low-temperature hydrothermal deposits occur at the en echelon step in the larger ridge, which is located at the intersection of the transfer zone with the inner rift. The chimneys, veins, and crusts are composed of silica, barite and iron oxide, and are of similar composition to the ferruginous chert that mantles the Kuroko deposits. A 1.2-km transect of seven alvin heat flow measurements at 30°48.5′N showed that the inner-rift-bounding faults may serve as water recharge zones, but that they are not necessarily areas of focussed hydrothermal outflow, which instead occurs through the thick basin sediments. The rift basin and arc margin sediments are probably dominated by permeable rhyolitic pumice and ash erupted from submarine arc calderas such as Sumisu and South Sumisu volcanoes.  相似文献   

11.
人类活动强度的空间异质性是理解区域人地关系和生态环境效应的基础。基于云南九大高原湖泊流域2020年土地利用数据,构建不同景观类型的人类影响强度系数,运用GIS空间分析量化流域人类活动强度与空间分异,探讨人类活动强度对水质的影响。结果表明:人类活动强度总体特征由高到低依次是杞麓湖(4.83)、星云湖(4.71)、滇池(4.19)、阳宗海(4.11)、抚仙湖(4.03)、异龙湖(4.01)、程海(3.93)、洱海(3.88)和泸沽湖(2.96)。人类活动强度指数(HAI)在流域尺度、坝区尺度、湖岸尺度的空间分异特征明显,每个流域都受到高强度人类活动影响,最大值出现在坝区,滇池、杞麓湖岸线存在完全开发的区域。人类活动强度随海拔和坡度增高而下降,高强度区集中在地势低平的湖泊周围。湖泊营养状态指数与流域尺度和坝区尺度高强度区呈显著正相关,这些区域应作为景观优化和管理的重点;与岸线尺度低强度区呈显著负相关,有必要减少湖滨带人类活动。综合考虑流域地形地貌-人类活动强度-水质的级联效应,应从不同空间尺度对各景观要素与过程管控。鉴于人类活动强度对水质的影响,可把湖泊管理分为预防型、保护型、治理型。  相似文献   

12.
土地利用/覆被变化对明晰气候变化和人类活动对湖泊水环境的影响有重要作用.以北方典型农牧交错的岱海流域为研究对象,基于遥感解译技术、马尔可夫转移矩阵、综合污染指数法等方法,对2000-2018年岱海流域土地利用/覆被和湖泊水质的变化进行分析,并结合冗余分析法和计量分析模型探究长时间序列尺度下土地利用/覆被变化对湖泊水质的...  相似文献   

13.
14.
From April 1997 to June 1998 Nemurella pictetii populations were regularly sampled in two springstreams at 220 and 850 m a.s.l., respectively, in Hesse (Germany), at approximately 51°N. Random samples of larvae were taken at three week intervals during the vegetation period, and once a month during winter. Sex, instar, body length, head capsule width and wing pad length of all larvae were recorded. Temperatures were recorded every hour, temporal patterns of temperature agreed closely between sites. Mean winter lows were 3.9 °C at both sites, the mean summer high was 11.9 °C at the lower site, as opposed to 9.6 °C at the mountain site.At both sites, adult emergence started in May. At the mountain site, recruitment started in late July and continued into autumn. There was cohort splitting in the young generation. Some individuals grew rapidly until October–November, but last instar larvae first appeared in March the next year. 1600 degree-days above 0 °C were accumulated during complete development. At the lower site, recruitment began in early July, and cohort splitting also occurred. Fast growing summer recruits emerged as adults in late August, having accumulated only 700 degree-days (above 0 °C). Their offspring hatched in November-December and emerged the next spring, having accumulated also only 700 degree-days. However, only part of the population was bivoltine. Many of the summer recruits grew more slowly and accumulated close to 1900 degree days until they emerged the next spring, together with the offspring of their own fast-growing siblings. Dependence of growth rate on temperature could not be estimated and appears to vary with daylength. For example, 3–6 °C support growth and development provided daylength exceeds 10 hrs of light, or is rising.At both sites and in all cohorts individuals emerging earliest were larger than later emerging ones. The size decline is significantly correlated with number of days after the winter solstice. For the first time it is shown that the decline does not occur shortly before adult emergence but actually takes place several instars before the last. Size differences are then carried on, and amplified, during subsequent molts, until adulthood. The literature presently relates seasonal size declines of insects to high or rising temperatures experienced by larvae approaching adulthood. Our data show that, at least in Nemurella, this explanation fails. On average, females were distinctly larger than males. Differences in mean last instar size were noticed also between sites and years. They remain presently unexplained. The mean sex ratio in both populations was close to 1:1.  相似文献   

15.
Marina P. Vega   《Limnologica》1999,29(2):186
The diet of P. sarsi in different life-stages from copepodid I to adult was investigated. Gut contents of copepodid I to II consisted mainly of algae such as diatoms and dinoflagellates. From copepodid III to adult stages the composition of the diet changed towards the inclusion of nauplii, cladocerans and copepods. The importance of the algae on the diet decreased with the inclusion of the prey items. Copepods were the most important components of the diet from C V to adult. Differences in the capture and ingestion of cladocerans and copepods were found. Diet of P. sarsi can be characterized as diverse consisting of diatoms, phagotrophic algae, protozoans, rotifers and nauplii from C I to C III and consisting mainly of carnivorous items from C IV to adult. The ability to eat a variety of food allows the copepods to modify their diet with varying conditions in the food environment. The effect of these diversity in the diet seems to be advantageous, specially in stressed environments imposed by episodes of drying.  相似文献   

16.
Abstract

A water balance model of the Nile is described, working in terms of dry season flows. The main use of the modelling studies was to extend flows back to the start of observations at Aswan in 1869, and hence to estimate the levels of Lake Victoria during the high flow event of the 1870s. New estimates of Lake Victoria levels and outflows for the period 1870–1895 are deduced, extending the length of the observed data for Lake Victoria by some 25%. Crucially, the analysis includes the major flood event of 1878, which historical evidence suggests was the highest since 1860 or earlier. The modelling results are compared with previous estimates and a detailed examination of historical evidence. Some prospects for future levels are considered, taking into account the reconstructed levels of the late nineteenth century.  相似文献   

17.
关于湖泊沉积物磷释放及其测定方法的雏议   总被引:16,自引:5,他引:16  
湖水位下降是近期我国西北地区湖泊一种普遍现象,由于该地区湖泊多属闭合流域,湖泊水位下降往往导致湖水浓缩咸化,进而给湖体及湖周带来一系列的生态环境问题,本文根据近几十年来岱海的湖区气候,湖泊集水域的入湖径流特征分析,以及湖泊水量平衡计算,分辨出1955-1995年3.85m,的水位降幅中,人为影响的贡献为3.17m,占82%,自然因素的贡献为0.68m,占18%,说明岱海湖水位下降主要是集水域内人类  相似文献   

18.
A theoretical solution framework to the nonlinear stochastic partial differential equations (SPDE) of the kinematic wave and diffusion wave models of overland flows under stochastic inflows/outflows, stochastic surface roughness field and stochastic state of flows was obtained. This development was realized by means of an eigenfunction representation of the time-space overland flow depths, and by transforming the problem into the phase space. By using Van Kampen's lemma and the cumulant expansion theory of Kubo-Van Kampen-Fox, the deterministic partial differential equation (PDE) for the evolutionary probability density function (pdf) of overland flow depths was finally obtained. Once this deterministic PDE is solved for the time-varying pdf of overland flow depths, then the time-space varying pdf of overland flow depths can be obtained by a transformation given in the text. In this solution framework it is possible to incorporate the stochastic dynamic behavior of the parameters and of the forcing functions of the overland flow process. For example, not only the individual rainfall duration and fluctuating rain intensity characteristics but also the sequential behavior of rainfall patterns is incorporated into the evolutionary probability density function of overland flow depths.  相似文献   

19.
淡水湿地水文过程控制着湿地植被景观的形成与演变.基于Landsat TM/ETM+遥感影像数据,利用决策树分类法提取鄱阳湖湿地1992、1999、2006、2012年4期景观信息,通过景观格局指数、转移矩阵和质心迁移法对苔草景观的空间变化及其与水文过程关系进行分析.结果表明:研究期间,鄱阳湖湿地秋、冬季苔草景观分布面积受到水位和退水过程的影响,低水位年的中滩位缓慢退水与低滩位快速出露更有利于苔草景观的扩张;苔草景观的空间格局与水位关系密切,在低水位年份,低位洲滩提前出露,苔草景观分布高程较低,部分低位光滩被苔草所侵占,原苔草分布的部分洲滩转变为芦荻景观,景观的破碎化程度较重,在高水位年份,低位洲滩长期被水体淹没,苔草景观分布高程相对较高,部分芦荻分布区被苔草所侵占,而原苔草景观的部分区域转变为水体和光滩,由于该期间苔草主要集中分布在湖周和入湖河口地带的高位洲滩上,其景观破碎化程度较轻;水位年际间的升降变化会影响苔草景观质心位置,年均水位上升引起景观质心发生向湖岸方向推进,而年均水位下降则会导致苔草景观质心向湖心方向转移.  相似文献   

20.
Four araphid diatom taxa were collected from Florida streams and studied with both light microscopy (LM) and scanning electron microscopy (SEM). Three taxa, formerly in the genus Fragilaria Lyngbye, are here placed in the genus Pseudostaurosira Williams et Round. On the basis of ultrastructure observed by SEM, the remaining taxon is placed in a new genus, Sarcophagodes. At least two of the species referred to Pseudostaurosira may have been confused with species of the genus Opephora Petit, which may have led to misinterpretation of the ecological characteristics of the latter genus.All the taxa treated here belong to the Family Fragilariaceae Greville as delimited in current classification schemes. Two new combinations Pseudostaurosiropsis geocollegarum (=Fragilaria geocollegarum Witkowski et Lange-Bertalot), Pseudostaurosira neoelliptica (=Fragilaria neoelliptica Witkowski) and the new species Pseudostaurosira clavatum are presented herein. Additionally, a new genus, Sarcophagodes, is erected to accommodate the new species S. delicatula. LM and SEM details, as well as criteria delimiting these taxa are discussed. More collections and further analyses are needed to assess the distribution of both Opephora and Sarcophagodes.  相似文献   

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