A marine calanoid copepod (Temora longicornis) in a semi-stagnant coastal lagoon (Lake Grevelingen,S.W.-Netherlands)

The marine calanoid copepodTemora longicornis was introduced in saline Lake Grevelingen (S.W.-Netherlands), when the lake was continuously flushed with North Sea water in 1979, to enhance the reduced salinity. Development of the copepod proceeded suboptimally as a consequence of an unfavourable environment in the lake: 1. The phytoplankton assemblage, mainly consisting of crytomonad flagellates, less suitable for growth and reproduction of the adult stages. 2. An acute food shortage occurring at a crucial moment in the development. 3. A. pronounced salinity-and oxygen stratification in June, preventing further development ofTemora.Communication nr. 474 of the Delta Institute for Hydrobiological Research, Yerseke.     

Production and ecology of eelgrass (Zostera marinal L.) in the Grevelingen estuary,the Netherlands,before and after the closure

The Grevelingen estuary was cut off from the North Sea and from the influences of the river Rhine by a dam in 1971, and became a stagnant salt-water lake. Production and ecology ofZostera marina L. were studied in 1968 and in 1973–1975, both through standing stock estimations, biomass increases in permanent quadrats, and correlation of distribution patterns with ecological factors. After the closure of the estuary the intertidal eelgrass population extended downwards to 5 m below lake level, probably owing to the increased transparency of the water; the area occupied, and the density of the eelgrass beds increased strongly. Eelgrass annual overground production, based on doubled maximum standing crop values in July–August, was estimated at 50 g C/m² in 1968, 121 g C/m² in 1973 and 91 g C/m² in 1975 inZostera beds, and 4 g C/m² in 1968, 18 g C/m² in 1973 and 23 g C/m² in 1975 for the entire Grevelingen area. A minimum estimate of net production inZostera beds at a depth of 0.50–0.75 m, based on short term changes in biomass in 2 permanent quadrats in 1974 and 1975, was 40.5 g C/m²/yr for overground parts and 12.7 g C/m²/yr for underground parts. Horizontal distribution of celgrass is not primarily limited by grainsize distribution, but more by exposure to wave action and currents. On account of irradiance reduction light is a limiting factor in the vertical distribution of the eelgrass population in Lake Grevelingen. Communication no. 146 of the Delta Institute for Hydrobiological Research, Yerseke, The Netherlands.     

Phytoplankton primary production in Lake Grevelingen (II)

Summary During the period 1976–1978 particulate phytoplankton production and phytoplankton excretion were estimated at weekly intervals at anchor station G11 in Lake Grevellingen. Additional data were gathered in a monthly measuring programme at four localities spread over the lake.     

不同管理主体对泸沽湖流域生态系统影响的比较分析

行政边界将自然生态系统从主观上切割为可供管理的空间单元,而人类介入一个相对完整的生态系统,会从根本上影响生态系统的格局和生态学过程,这种影响对流域生态系统更为显著。以我国西南川滇两省交界处的泸沽湖流域生态系统为例,运用对比分析法,先从不同行政尺度定性比较了流域两侧生态系统管理主体在自然、社会、经济子系统方面的差异性。再采用遥感与地理信息系统变化监测技术,定量分析流域省界两侧土地利用类型、林分结构、归一化植被指数、生态系统服务功能等关键要素上的差异,形成对流域省界两侧生态系统功能的差异性的全面认识,从而对产生生态系统功能差异的驱动力进行了分析。最后,以此为基础,有针对性的提出了泸沽湖流域综合管理的对策,以实现泸沽湖流域生态系统的可持续发展。     

The impact of zooplankton status on the management of Lake Kinneret (Israel)

Monthly averages of standing stock wet biomass of zooplankton in Lake Kinneret (Israel) varied between 11 and 76 g m^–2 during 1969–1981, with the exception of two months. Averaged contributions of different groups were: Cladocera 58%, Copepoda 35% and Rotifera 7%. Total standing crop wet biomass is highest during January–June, averages varied between 35 and 50 g m^–2, and decreases during summer–fall (23–36 g m^–2). The winter biomass of Cladocera fluctuated between 22 and 35 g m^–2 and dropped to a range of 9–23 g m^–2 in summer, whereas copepod biomass varied very little around an average of 18 g (ww) m^–2 with the exception of low values from April to June. The stock biomass of Rotifera is relatively high during winter floods season (December-March) whilst in summer it is very low.Young stages of fish in Lake Kinneret feed mostly on zooplankton and zoobenthic forms. The most abundant fish in the Kinneret ecosystem, Mirogrex terraesanctae terraesanctae, also feed on zooplankton at the adult stage throughout the year, and herbivorous fish consume zooplankton during the summer when lake plankton resources are limited.The summer ecosystem of Lake Kinneret is characterised as a steady state type, in which the impact of the zooplankton-chain is of great importance. Increase of predation pressure on zooplankton by fish can disequilibrate the balanced trophic relations existing between nannoplankton production and zooplankton grazing capacity. Such a situation can lead to organics accumulation as nannoplankton blooms, resulting in water quality deterioration. Management options aimed at preventing collapse of zooplankton populations are discussed.     

Temperature dependence of sediment-water exchange in Lake Grevelingen,SW Netherlands

Extended abstract Lake Grevelingen is a brackish water lake in the SW Netherlands. The lake has an area of 108 km², a mean depth of 5.3 m (maximum 48 m), a mean chlorinity of 13 to 16%0 Cl⁻, and a hydraulic residence time of about 8 years. Mass budget studies have shown a consistent seasonal pattern in the phosphorus sediment-water exchange in Lake Grevelingen (Kelderman 1980). From May to August a P mobilization from the sediment takes place, estimated atca. 12.5 mg P · m⁻² · day⁻¹. The sediment accumulatesca. 5.5 mg P · m⁻² · day⁻¹ during the rest of the year. Temperature may be an important factor in establishing this pattern. Sediment-water exchange was studied by means of laboratory experiments under specified conditions. Sediment cores (30 cm depth, 11 cm diameter) were taken at four stations in the lake, with sediment types varying from medium- to muddy sand (Fig. 1). The cores with overlying water (ca. 21) were placed in the dark at 5 °C in thermostatically controlled water baths. After a week's incubation time the temperature was slowly raised, such that after three weeks eight cores (four sediment types, duplicates) were at 5 °C, eight were at 10 °C, eight at 15 °C and eight at 20 °C. The same procedure was applied to the four control cores, containing lake water.     

生境管理——保护性生物防治的发展方向

生境管理是近年来保护性生物防治的重要研究方向,也是利用农业景观格局进行生物防治的重要策略。生境管理是指从农田景观的角度,在大时空尺度范围内进行多种作物与非作物生境的设计与布局,创造有利于天敌的环境条件,抑制害虫种群发生,达到减小环境污染、增强农业生态系统的控害保益功能,最终实现害虫种群控制的可持续性。景观尺度下的生境管理不仅强调单一农田生物控害作用,而是以多生境农业景观整体布局为指导,探索各种生境功能的整合利用,以发挥各种生境最大的生物控害潜能,为实现多目标生态服务价值管理提供重要的理论基础和现实依据。本文系统地总结了生境管理的研究内容与实现途径,论述了农业景观格局与过程对害虫种群控制的机理,并对作为保护性生物防治发展方向的生境管理研究趋势进行了展望。     

武汉东湖主要养殖水域的浮游甲壳动物群落分析

报道了1994－1996年武汉东湖水果湖、郭郑湖、汤林湖和后湖4个主要鱼类养殖水域甲壳动物群落结构变化的调查结果,其目的旨在比较4个湖区甲壳动物群落结构的差异,探讨甲壳动物群落变化与鱼类养殖,水生植物及水体富营养化间的关系,结果表明,在东湖Ⅰ、Ⅱ站,蚤类平均密度明显低于Ⅲ、Ⅳ站（P＜0．05）,而近邻剑水蚤在3个周年里一直占据桡足类的优势地位。Ⅲ站从1995年,Ⅳ站从1996年起,近邻剑水蚤均取代了广布中剑水蚤成为桡足类的第一优势种。甲壳动物的体长频度分布表明,在3个研究中,11－12月份和1－4月份体长大于1mm的甲壳动物频度均显著高于5－10月份,体长大于1mm的枝角类个体数以Ⅲ、Ⅳ站较多,而大于1mm的桡足则以Ⅰ、Ⅱ站较多。     

Sandhill Crane Abundance and Nesting Ecology at Grays Lake,Idaho

Abstract: We examined population size and factors influencing nest survival of greater sandhill cranes (Grus canadensis tabida) at Grays Lake National Wildlife Refuge, Idaho, USA, during 1997–2000. Average local population of cranes from late April to early May, 1998–2000, was 735 cranes, 34% higher than that reported for May 1970–1971. We estimated 228 (SE = 30) nests in the basin core (excluding renests), 14% higher than a 1971 estimate. Apparent nest success in our study (x̄ = 60%, n = 519 nests) was lower than reported for Grays Lake 30–50 years earlier. Daily survival rates (DSRs) of all nests averaged 0.9707 (41.2%). The best model explaining nest survival included year and water depth and their interaction. Nest survival was highest (DSR = 0.9827) in 1998 compared with other years (0.9698-0.9707). Nest survival changed little relative to water depth in 1998, when flooding was extensive and alternative prey (microtines) irrupted, but declined markedly with lower water levels in 2000, the driest year studied. Hypotheses relating nest survival to vegetation height, land use (idle, summer grazing, fall grazing), and date were not supported. In a before-after-control-impact design using 12 experimental fields, nest survival differed among years but not among management treatments (idle, fall graze, fall burn, and summer—graze—idle rotation), nor was there an interaction between year and treatments. However, DSRs in fall-burn fields declined from 0.9781 in 1997–1998 to 0.9503 in 1999–2000 (posttreatment). Changes in the predator community have likely contributed to declines in nest success since the 1950s and 1970s. Our results did not support earlier concerns about effects of habitat management practices on crane productivity. Nest survival could best be enhanced by managing spring water levels. Managers should continue censuses during late April to evaluate long-term relationships to habitat conditions and management.     

Vegetation development on newly embanked sandflats in the Grevelingen (The Netherlands) under different management practices

In 1971 the Grevelingen estuary was embanked. In the newly created lake Grevelingen the tidal movements stopped and a few thousand ha of sandflats fell permanently dry. Ca 40% of the surface of those flats was immediately afterwards sown with rye and other grasses to prevent wind erosion. This fixation of a rather uniform environment resulted in a monotonous vegetation cover. Grazing with domestic animals is now applied as management practice to create more environmental variation and thereby a higher species diversity.The present study gives the results of eleven years of comparing vegetation development under various management practices, including non-interference in the spontaneous and sown vegetation. Sequential vegetation mapping, repeated inventories of selected areas and studies in permannent plots are the main techniques used.On the unsown shore zones interesting vegetation types are developing where species diversity is higher than in the sown areas. In the shore zones not only a faster succession occurred compared with the sown areas, but also a shifting of environmental gradients, e.g. in moisture and salinity conditions, encouraged vegetation changes. After 10 yr grazed areas had a higher number of species than ungrazed equivalent areas. The results also indicated that grazing slows down the establishment of (tall) woody species and shrub development.Nomenclature of angiosperms and syntaxa follows Heukels & van Ooststroom (1977) and Westhoff & den Held (1975), respectively.The authors are indebted to Dr W. G. Beeftink (Yerseke) who initiated and supervised the early stages of the Grevelingen research work and W. de Munck (Yerseke) who assisted in the first steps. The logistic assistance of Rijkswaterstaat and Staatsbosbeheer made it all possible, especially the services of the bargemen A. van den Berg, G. W. van Leeuwen and J. M. Smits (Zonnemaire). Dr W. G. Beeftink, Dr D. C. P. Thalen (Leersum) and Dr A. D. Q. Agnew (Aberystwyth) reviewed earlier drafts and their constructive criticism is gratefully acknowledged.     

A microcosm study of nitrogen utilization in the Great Salt Lake,Utah

Microcosms were used to study the effects of two inorganic nitrogen sources (ammonia and nitrate) and two organic nitrogen sources (urea and glutamic acid) on the growth of algae and bacteria found in the Great Salt Lake, Utah. Ammonia, nitrate and urea stimulated bacterial growth indirectly through increased algal production of unknown organic substances. Glutamic acid, representing readily available organic carbon and nitrogen, stimulated the bacteria directly. No nitrification was observed in the microcosms although nitrite was found when the microcosms were supplemented with nitrate. Lake sediment contained a number of anaerobic bacteria producing hydrogen sulfide, methane and other gases. Production of these gases was stimulated in the columns with high algal and bacterial activity.     

Heterogeneity studies of Carchesium polypinum (Ciliophora: Peritrichida) in Donghu Lake

In this article, RAPD was employed to detect the DNA polymorphism of Carchesium polypinum in three lakes: Nanhu Lake (N), Shahu Lake (S) and Donghu Lake (D). The results were used to deduce the definition of the populations: (1) The 20 primers produced 172 clear bands with an average of 8.6 fragments ranging from 100bp to 1600bp. The other 11 primers produced 59 legible bands with an average of 5.4 fragments ranging from 100bp to 1 500bp; (2) SPSS 12.0 and RAPDistance 1.04 that had similar trees were composed of two parallel main branches. Samples from Shijizhong (Z) of D, Shuiguohu (H) of D and N clustered into a branch and another sample from D — Fengguangcun (F) — gathered with S or made another main branch itself. The result that the three samples from D were separated by the samples from other lakes suggested that the individuals of C. polypinum in D belong to several populations. This discovery will promote micro-hydrobiont population ecology research. In addition, it will help in the study of the essence of the transitional zone and its dispersal and vicariance behavior. We believe that this study will contribute to the study of population differentiation and the mechanism of speciation.     

Heterogeneity studies of Carchesium polypinum (Ciliophora: Peritrichida) in Donghu Lake

In this article, RAPD was employed to detect the DNA polymorphism of Carchesium polypinum in three lakes: Nanhu Lake (N), Shahu Lake (S) and Donghu Lake (D). The results were used to deduce the definition of the populations: (1) The 20 primers produced 172 clear bands with an average of 8.6 fragments ranging from 100bp to 1600bp. The other 11 primers produced 59 legible bands with an average of 5.4 fragments ranging from 100bp to 1 500bp; (2) SPSS 12.0 and RAPDistance 1.04 that had similar trees were composed of two parallel main branches. Samples from Shijizhong (Z) of D, Shuiguohu (H) of D and N clustered into a branch and another sample from D — Fengguangcun (F) — gathered with S or made another main branch itself. The result that the three samples from D were separated by the samples from other lakes suggested that the individuals of C. polypinum in D belong to several populations. This discovery will promote micro-hydrobiont population ecology research. In addition, it will help in the study of the essence of the transitional zone and its dispersal and vicariance behavior. We believe that this study will contribute to the study of population differentiation and the mechanism of speciation.     

Synopsis of scientific results of the sarec sponsored project on the ecology of Lake Kariba

A summary of current research on Lake Kariba is given. Lake Kariba is now a phosphorus limited oligotrophic lake, dependent on annual nutrient input for the maintenance of production. Nitrogen fixation by cyanobacteria has become an important source of nitrogen in the dry season and that fish harvesting is an important phosphorus sink. An up to date plankton composition list has been produced and plankton biomass determined. Diving studies indicate large biomass of bivalves. The aquatic vegetation displays both longitudinal as well as depth gradients, related to light regimes. Only preliminary data are available on mud/water interactions, but the available data indicate considerable fluxes in the river mouth stations and shallow protected littoral areas. The role of predatory birds and crocodiles in the fishery economy of the lake is evaluated and indicates no major conflict between these predators and human fishing interests. The research also draws attention to pesticides in Lake Kariba as indicated by work on fish eating birds and crocodile research. Since the publication of ‘Lake Kariba’ by Balon & Coche (1975) the research project, THE ECOLOGY OF LAKE KARIBA, being undertaken by the University Lake Kariba Research Station constitutes the first multidisciplinary study of the lake, 30 years after the Zambezi river was impounded at Kariba Gorge. It could have offered a unique opportunity of comparing the lake now with what it was soon after impoundment.     

阳宗海中紫色非硫光合细菌的生态研究

为得到高原深水湖泊中的微生物生态分布信息,运用统计学软件,在2002年对阳宗海中的紫色非硫光合细菌的数量进行了数学分析。影响湖泊中PNSB数量分布的主要因素是水平位点、深度和采水期,溶氧、温度、透明度、COD和叶绿素a含量等环境因子对PNSB数量也有影响。各环境因子如叶绿素a含量和透明度之间也有相关性,对其进行了分析并计算出环境因子之间关系的一元回归方程。     

Production and decomposition of eelgrass (Zostera marina L.) in saline Lake Grevelingen

Summary During five 28-hours measurements in 1981, the oxygen production and consumption in an eelgrass community in saline Lake Grevelingen were investigated using light plexiglass enclosures. Applying a conversion factor of 0.29 the amount of carbon fixed and the amount of organic carbon mineralized were estimated. Gross and net production were estimated over 24-hours periods.There appeared to be a good correlation between production and insolation on the water surface. For every measurement period the production as a function of light and aboveground eelgrass biomass in the enclosure were calculated. This showed a maximum of 5.10^–6 mg C.J.^–1 g dry weight^–1 in April and minimum of 1.4.10^–6 mg C.J.^–1 g^–1 in August.Using the calculated production coefficients, the insolation and the eelgrass biomass the gross production, net production and consumption during the growing season of 1976 were calculated. Gross production amounted to 340 gC.m^–2, and net production came to 130 g C.m^–2. Approximately 60 gC.m^–2 was respired by the eelgrass plants while the remaining 150 gC.m^–2 was consumed or mineralized by other organisms on the sampling spot. Approximately 120 g C.m^–2.yr^–1 was transported by wind and wave action towards the eastern part of the lake where it became anaerobically degraded. This resulted in the formation of sulfide and methane.Communication no. 236 of the Delta Institute for Hydrobiological Research, Yerseke, The Netherlands.     

Human rights,environment, and development: The dispossession of fishing communities on Lake Malawi

In a growing number of cases throughout Africa, communities' resource bases are being undermined or appropriated by outsiders, a process which seriously threatens the continuation of local cultures and livelihoods. In this article, we use a political ecology framework to examine how the linked processes of economic development, political power, and environmental change are transgressing the rights of fishing communities on the shores of Lake Malawi. In the cases described, these communities, or community members within them, find themselves powerless to prevent the expropriation of the resources over which they previously had either legal or customary control. Thus, it is not the economic processes of dispossession alone which lead to human rights violations but rather dispossession combined with an authoritarian political context.     

Isotopic change throughout the life history of a Lake Malawi cichlid fish

Clear changes in body size-isotope (carbon and nitrogen) trajectories of Pseudotropheus callainos , a cichlid belonging to the endemic haplochromine species radiation in Lake Malawi, were found that corresponded with an ontogenetic dietary shift from predominantly planktonic to benthic food sources. The results indicated that dietary switching was a proximate cause of isotopic change over the life history of this species and confirmed the value of stable isotope signatures for inferring diet. The data also illustrated that possible variability of signatures over the life history of a species should be considered when using stable isotope ratios to investigate fine-scale ecological differentiation among taxa.     

Sibling species complexes in sympatric populations of Petrotilapia Trewavas (Cichlidae, Lake Malawi)

The endemic Lake Malawi cichlid, Petrotilapia tridentiger Trewavas, was found to be a complex of sibling species. The various sympatric species show considerable homogeneity in body form and dentition but are separable on the basis of differences in adult coloration, size at maturity, depth distribution, size and degree of overlap of territories, aggression and courtship. Colour is considered to be important for specific mate recognition in this genus. Examination of wild populations is a valuable, perhaps essential, adjunct to classical taxonomy when dealing with the systematics of sibling species in Lake Malawi.     

Post-impoundment changes in the fish fauna of Lake Itezhi-tezhi, Zambia

The fish fauna of the newly inundated Lake Itezhi-tezhi, Zambia was observed between 1980 and 1985. Marked changes in the community structure were identified. The most obvious were a decline in species diversity and a shift in species composition from acommunity with a preponderance of Alesles lateralis (Boulenger) (Characidae), to one dominated by cichlids. These changes were primarily due to members of the families Cyprinidae, Mormyridae and Schilbeidae being unable to adapt to the new environmental conditions, such as spawning and feeding grounds, and their inability to cope with fluctuating water levels in the lake. It was suggested that a sound fishery data collection system be implemented to provide reliable information on which to base management policy.