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101.
The objective of the study was to determine which factors regulate zooplankton organisms along Lake Nasser. Temperature, pH, DO, conductivity, turbidity, nutrients, and zooplankton abundance were measured. Twenty-three species of zooplankton were recorded in Lake Nasser included in Copepoda, Cladocera and Rotifera. Copepoda represented the main bulk of the community. The lowest standing stock of zooplankton was noticed during spring due to the highest fish predation during this season associated with the lowest turbidity. Big difference in temperature in Lake Nasser along the year round is considered as a controlling factor related to range of tolerance of species. The oscillation of the lake water level and the different factors affect the standing stock of zooplankton in the lake. Thus, continuous monitoring of Lake Nasser biota should be undertaken to follow the changes in the ecosystem. 相似文献
102.
Biological mechanisms driving the seasonal changes in the internal loading of phosphorus in shallow lakes 总被引:1,自引:6,他引:1
XIE Ping 《中国科学D辑(英文版)》2006,49(Z1)
Because of the obvious importance of P as a nutrient that often accelerates growth of phytoplankton (including toxic cyanobacteria) and therefore worsens water quality, much interest has been devoted to P exchange across the sediment-water interface. Generally, the release mode of P from the sediment differed greatly between shallow and deep lakes, and much of the effort has been focused on iron and oxygen, and also on the relevant environmental factors, for example, turbulence and decomposition, but a large part of the P variation in shallow lakes remains unexplained. This paper reviews experimental and field studies on the mechanisms of P release from the sediment in the shallow temperate (in Europe) and subtropical (in the middle and lower reaches of the Yangtze River in China) lakes, and it is suggested that pH rather than DO might be more important in driving the seasonal dynamics of internal P loading in these shallow lakes, i.e., intense photosynthesis of phytoplankton increases pH of the lake water and thus may increase pH of the surface sediment, leading to enhanced release of P (especially iron-bound P) from the sediment. Based on the selective pump of P (but not N) from the sediment by algal blooms, it is concluded that photosynthesis which is closely related to eutrophication level is the driving force for the seasonal variation of internal P loading in shallow lakes. This is a new finding. Additionally, the selective pump of P from the sediment by algal blooms not only explains satisfactorily why both TP and PO4-P in the hypereutrophic Lake Donghu declined significantly since the mid-1980s when heavy cyanobacterial blooms were eliminated by the nontraditional biomanipulation (massive stocking of the filter-feeding silver and bighead carps), but also explains why TP in European lakes decreased remarkably in the spring clear-water phase with less phytoplankton during the seasonal succession of aquatic communities or when phytoplankton biomass was decreased by traditional biomanipulation. Compared with deep lakes, wax and wane of phytoplankton due to alternations in the ecosystem structure is also able to exert significant influences on the P exchange at the sediment-water interface in shallow lakes. In other words, biological activities are also able to drive P release from sediments, and such a static P release process is especially more prominent in eutrophic shallow lakes with dense phytoplankton. 相似文献
103.
环渤海地区海(咸)水入侵特征与防治对策 总被引:1,自引:0,他引:1
本文中阐述了环渤海沿海地区海(成)水入侵的主要方式、发展进程、影响因素等基本特征,提出海(成)水入侵的综合防治对策。研究区海(成)水入侵主要有面状、带状、脉状或树枝状和越流等4种入侵方式。气候、地形地貌、地质与水文地质是发生海(成)水入侵的基础条件,地下水超采等人类不合理工程经济活动是诱发海(成)水入侵的主要原因。通过调整产业结构、建立节水型社会体系,合理规划利用水土资源,建造阻成蓄淡工程,跨流域引水,以及建立健全监测预警系统等综合措施,防止海(成)水入侵的发展。 相似文献
104.
奉义以宁南清水河断陷盆地为例,研究西北干旱区储水盆地水循环特征与苦咸水成因机制。通过环境同位素特征分析,水化学模拟计算以及水文地质控制因素分析,阐明研究区地下水主要由大气降水补给形成,地表水难以形成持续性补给源;清水河平原地下水从形成上划分为:浅层现代水、深层古水、混合水。现状开采条件下,浅层现代水与深层占水的定量转化关系为山前洪积扇地下水7.6:2.4,平原下游地下水3,2:6.8,平原丰要开采区地下水5.2:4.8~6.6:3.4;山前洪积扇和冲积平原浅层地下水循环时间为7-28年,下游平原深层地下水循环时间为300年以上,上游冲积平原中深层地下水,总体上介于以上二者之间。各主要开采区,可更新能力在人工开采条件下明显增强,时间为60~75年;研究区苦咸水主要是地下水溶解了含水层介质中大昔的膏盐,矿化度增高所致。 相似文献
105.
冻融循环对盐渍土黏聚力影响的试验研究 总被引:1,自引:0,他引:1
通过室内试验,测试了冻融循环对不同含盐量和不同含盐类别盐渍土黏聚力的影响规律。从结晶体位置变化、微观结构、盐类性质及未冻结水含量三个方面分析了冻融循环对盐渍土黏聚力的作用机理。研究结果表明,在含水率一定的情况下,无论是向土中加入Na2SO4,或者是CaCl2,经冻融循环后黏聚力都随冻融次数的增加而减小,且第1次和第2次循环为主要减小阶段;加入CaCl2后黏聚力的减小程度比加入等量Na2SO4后小;冻融循环过程中结晶体析出时位置的变化是土体黏聚力和干密度减小的主要原因;经SEM图片分析,大孔隙占总孔隙面积的比例随冻融次数的增加而减小;盐渍土中CaCl2溶液的含量对冻融循环中黏聚力的变化有重要影响。 相似文献
106.
107.
Potential salinity limitations on nitrogen fixation in sediments from Mono Lake, California 总被引:2,自引:0,他引:2
David B. Herbst 《International Journal of Salt Lake Research》1998,7(3):261-274
Mono Lake is a hypersaline alkaline lake in the high altitude Great Basin desert of eastern California. Algal productivity
of the lake is nitrogen-limited, and a contributing source is derived from benthic nitrogen fixation. Lake level and salinity
have fluctuated with natural climatic variations but have also been affected by the diversion of tributary streams. This research
examines the influence of varied salinity and lake level on the potential for benthic nitrogen fixation in Mono Lake. A sediment-surface
microbial mat community was exposed directly, and in acclimated cultures, to a range of Mono Lake salinities under anaerobic
incubations and the activity of nitrogenase assayed by acetylene reduction. Activity was stimulated in light, but also occurred
in darkness. Over an experimental salinity range from 50 to 150 g L−1 TDS, nitrogenase activity was reduced by 90 per cent, with the activity persisting at the highest salinity being attributable
to dark fixation alone. Between a salinity of 50 g L−1, occurring in Mono Lake over 50 years ago, and 100 g L−1, nitrogenase activity was reduced by nearly half. Changes in the area of the littoral zone at varied lake levels also affect
the total amount of potential benthic nitrogen fixation in the lake. An accounting of yearly inputs of nitrogen to Mono Lake
suggests N2-fixation could contribute as much as 76–81 percent of the total. Inhibition of nitrogen fixation rates by increased salinity
could limit the long-term nutrient supply and benthic primary productivity of this ecosystem. 相似文献
108.
中国西北地区第四纪盐湖沉积中钙质超微化石的发现及其古环境意义 总被引:4,自引:0,他引:4
报导了中国西北地区的甘肃、青海、新疆等地陆相第四纪盐湖沉积中发现的钙质超微化石,它们主要是:Gephyrocapsaoceanica,Cocolithuspelagicus,Calcidiscusleptoporus,C.macintyrei,Reticulofenestraminutula等。上述钙质超微化石群具有以下特征:(1)化石丰度中等,属、种分异度低,化石保存差;(2)赋存化石的层位均为富含石膏盐层的微咸水咸水的沉积物,或为盐湖沉积;(3)产出化石地点远距该地质时期时的古海岸线。它们与古海域既无通道相连,亦非残留海。中国西北地区盐湖沉积中钙质超微化石的发现说明了中国东部地区第三纪沙河街组某些层位中的钙质超微化石不能作为“海相生物”的标志,否定了这些化石层位与“海侵”或“海泛”的关联。 相似文献
109.
BACKGROUNDANDSIGNIFICANCEOFSALINEWATERUTILIZATIONHeilonggangregion,asemi-aridareawith500-600mmannualprecipitation,liesintheEa... 相似文献
110.