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1.
Lake Beseka (Metahara), formerly, an alkaline soda lake in the Central Rift Valley of Ethiopia is recently undergoing unprecedented changes. The objective of this study was to investigate the current status on the plankton composition of Lake Beseka, in relation to the lake's environmental parameters. Samples for physicochemical and biological parameters were taken twice a year during both the rainy and dry seasons at two different sites (open and shore). Temperature, pH, conductivity, dissolved oxygen, alkalinity, salinity, ammonia, silica and soluble reactive phosphate showed significant variation (p < .05) between wet and dry seasons. The physicochemical parameters recorded during this study shows decreasing trend than the previous studies indicating the lakes ecosystem undergone fundamental changes over time. A total of 25 phytoplankton and 13 zooplankton genera were identified. The phytoplankton community of Lake Beseka had previously been dominated by Arthrospira fusiformis, but this time it was completely missing, and diatoms substituted for it. The decrease in pH and salinity of the lake's water could be responsible for these changes. In addition, cyclopoid copepods now predominate over zooplankton in Branchionus dimidiatus during periods of high salinity. Redundancy analysis showed that SRP, ammonia, nitrate and turbidity are important environmental factors that significantly influenced plankton abundance. This study provides new baseline information on the plankton composition of Lake Beseka, in relation to the lake's environmental parameters, which can be used to evaluate future community structure. 相似文献
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A. V. O. Ofulla D. Karanja R. Omondi T. Okurut A. Matano T. Jembe R. Abila P. Boera J. Gichuki 《Lakes & Reservoirs: Research and Management》2010,15(3):255-271
This study was conducted from September to December 2008 to investigate the relative abundance of malaria vectors and schistosomiasis host snails associated with aquatic weeds in Nyanza Gulf (Lake Victoria). Larval and adult’s stages of mosquitoes, lakeflies and snails were collected and identified with standard entomological and malacological techniques. The relative species composition and abundance of fish associated with macrophytes were also determined. Physico‐chemical parameters were determined with standard analytical methods. Community‐based surveys were also conducted, using standard questionnaires, focused group discussions and direct observations. The results of this study indicated that the abundance of malaria‐causing mosquitoes was low, accounting for only 0.4% of the total number of mosquitoes and lake flies collected from the gulf. Lake flies (Chaoborus and Chironomus spp.) were the most abundant flying insects associated with aquatic macrophytes (84.2%), followed by Culicines Culex spp. (12.2%) and Aedes spp. mosquitoes (3.2%). Biomphalaria sudanica and Bulinus africanus, the two most common hosts for schistosomiasis in the gulf, were detected in both types of macrophytes, but were most significantly attached to water hyacinth (P < 0.0001) and hippo grass (P = 0.0003). There were significantly fewer snails attached to the hippo grass, compared with those unattached in the open water (P < 0.05, GENMOD). Different habitats exhibited low Secchi disc transparency values, but elevated total phosphorous (TP), total nitrogen (TN), chlorophyll‐a concentrations, as well as algal cell counts. Furthermore, Oreochromis niloticus and Haplochromine fishes were more abundant in water hyacinth mats compared with hippo grass mats and open‐water habitats. The low mosquito abundance indicated that the sampled habitats were unsuitable for mosquito breeding, likely attributable to water turbulence and/or predation by larvivorous fish. The strong association between B. sudanica and B. africanus and aquatic macrophytes, and the observation that local communities perform many lakeshore‐related activities that bring them into contact with water, can potentially lead to a higher prevalence of schistosomiasis in the Nyanza Gulf region. 相似文献
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Naziriwo Betty Bbosa Wandiga Shem Oyoo Madadi Odongo Vicent Abongo Debra Atieno 《Lakes & Reservoirs: Research and Management》2009,14(2):127-137
Magnetic speciation technique was used for the determination of iron species in Nakivubo Channel and Lake Victoria waters. The method consisted of a column of supported Dowex 1-X18, 20–50 US mesh (Cl) surrounded by movable permanent magnets. Dowex was supported by a porous material to permit adequate passage of the eluent through the column. In the presence of an external magnetic field, enhanced capacity for adsorption of iron III was observed. The enhanced capacity is primarily due to the magnetic field produced and ion exchange sorption mechanism. The results show that, most of the Iron in Nakivubo Channel waters is in reduced ferrous form while, in the Lake Victoria waters, it exists in the oxidized ferric form. Physicochemical parameters for the field samples are discussed in this study. Turbidity levels in catchments with substantial vegetation were significantly lower than those without. pH values up to 13 was observed for some of the point source. The physicochemical parameters along Nakivubo Channel waters were relatively higher than the Lake Victoria waters indicating slow increasing pollution load along the Nakivubo Channel. 相似文献
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Naziriwo Betty Bbosa Wandiga Shem Oyoo 《Lakes & Reservoirs: Research and Management》2013,18(3):259-273
The current study was conducted for 2 years (2006 and 2007) during January, April and September to investigate seasonal variations in biological parameters and planktonic biodiversity observed at four sampling sites (MRM, M500, SRM and S500) in Lake Victoria. Blue‐green algae (Cyanophyta) dominated the lakeshore waters of Lake Victoria, comprising 54.1% of the total algal content, compared to 24.4% for diatoms and 14.7% for green algae (Chlorophyta). Euglenophytes and dinoflagellates both constitute <10% of the algal biomass. The algal distribution at the Sango Bay sampling sites, however, is different in that it is dominated by diatoms, in contrast to Murchison Bay, which was dominated by blue‐green algae. This study also investigated the influence of iron (Fe2+and Fe3+) and zinc (Zn2+) ions on four strains of microcystis (CYN 464, CYN 465, CYN 478 and CYN 522) isolated from Murchison Bay in Lake Victoria. The suggestion that iron species and zinc ions might limit phytoplankton growth in Lake Victoria was tested by enriching algal culture media with different metal concentrations. Based on measurements of the algal biomass of four species of Lake Victoria, the algal biomass of the four microcystis strains generally decreased with increased zinc and Fe2+ concentrations. The algal biomass of the four strains, however, increased with increased Fe3+ concentrations. This response to different metal concentrations provides evidence that high Zn2+ and Fe2+ ion concentrations limit phytoplankton growth and species distribution. The availability of Fe3+ ions is an important selective force on Lake Victoria phytoplankton communities. 相似文献
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Lake Lugano is located at the border between Italy and Switzerland and is divided into three basins by two narrowings. The geomorphologic characteristics of these basins are very different. The catchment area is characterized by calcareous rock, gneiss and porphyry; the population amounts to approximately 290 000 equivalent inhabitants. The external nutrient load derives from anthropogenic (85%), industrial (10%) and agricultural (5%) sources. The limnological studies carried out by Baldi et al. (1949) and EAWAG (1964) revealed early signs of eutrophication, with a phosphorous concentration of about 30–40 mg m–3 and an oxygen concentration of less than 4 g m–3 in the deepest hypolimnion. Subsequently Vollenweider et al. (1964) confirmed these data and was the first to point out the presence of a meromictic layer in the hypolimnion of the northern basin. From the 1960s, as a result of an increase in the population and internal migration, the lake became strongly eutrophic with the P concentration reaching 140 mg m–3 and the oxygen in the hypolimnion reduced to zero. Fifty‐five per cent of the P was from metabolic sources and 45% from detergents and cleaning products. In 1976, a partial diversion of waste water from the northern to the southern basin was begun, and gradually eight waste water treatment plants came into operation using mechanical, chemical and biological treatments. In 1986, Italy and Switzerland began to eliminate the P in detergents and cleaning products. Since 1995, the main sewage treatment plants have improved their efficiency by introducing P post‐precipitation, denitrification and filtration treatments. The recovery of the lake is due to be completed by the year 2005. Altogether, during the last 20 years recovery measures have reduced the external P load from about 250 to 70–80 tonnes year–1; the goal to be reached is 40 tonnes year–1. In‐lake phosphorous concentrations have decreased from 140 to 50–60 mg m–3, with the target at 30 mg m–3. Dissolved oxygen concentration is satisfactory only between the depths of 0 and 50 m, falling rapidly to zero in the deepest layers. Below a depth of 90 m, high CH4, HS–, NH4+, Fe2+ and Mn2+ concentrations exist. Primary production has decreased from 420 to 310 g Cass m–2 year–1, notwithstanding an increase in the thickness of the trophogenic layer. Structure and dynamic biomass show marked changes: phytoplankton dry weight has decreased from 16 to 7 g m–2, while zooplankton dry weight has increased from 3 to 4.5 g m–2. Chlorophyll concentration has fallen from 14 to 9 mg m–3 and Secchi disk transparency has increased from 3.5 to 5.5 m. The current sources of the external load are uncollected small urban conglomerations, storm‐water overflows from outfall sewers, and the residual load from sewage treatment plants, particularly those without P post‐precipitation. 相似文献
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白洋淀浮游生物群落动态变化与生物量模拟研究 总被引：1，自引：0，他引：1
为探究白洋淀浮游生物群落结构动态特征及其关键影响因子,基于2017年秋,2018年春、夏3个季节的水环境因子与浮游生物野外采样调查结果,采用冗余分析(ＲDA)、广义可加模型(GAMs)等方法探究了白洋淀不同季节的浮游生物群落动态变化,建立了浮游植物生物量与环境因子的非线性关系并进行了率定验证。结果表明:与1992年白洋淀干淀后重新蓄水时相比,浮游植物与浮游动物物种数分别下降了59%与37%,优势群落从绿藻门转化为蓝藻门。根据ＲDA排序结果可知,温度、透明度是影响浮游生物丰度的关键环境因子。运用GAMs构建了环境因子与浮游植物生物量的定量模型,最优模型结构为Biomass-phy～s(T)+s(TN)+s(Cond)+s(Biomass-zoo)+s(Biomass-pro)+te(Biomass-pro_TN)+te(Biomass-pro_Cond)+te(Biomass-pro_Biomass-zoo)。将2019年6月采样数据进行模型验证,计算模拟效果良好,实现了对浮游植物生物量的定量模拟,能够为白洋淀生态恢复与保护提供决策支持。 相似文献
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Bancy M. Mati Simon Mutie Hussein Gadain Patrick Home Felix Mtalo 《Lakes & Reservoirs: Research and Management》2008,13(2):169-177
The Mara River is the lifeline of the transboundary Mara basin across Kenya and Tanzania. The basin is considered one of the more serene subcatchments of the Lake Victoria Basin and ultimately the Nile Basin, and traverses the famous Maasai Mara and Serengeti National Parks. The basin also contains forests, large‐scale farms, smallholder farms, pastoral grazing lands, as well as hunter gatherers and fishers. There is growing concern, however, regarding land degradation in the basin, particularly deforestation in the headwaters, that is affecting the natural resource base and the river flows. Accurate scientific data are required to advise policy, and to plan appropriate mitigation measures. This study utilizes remote sensing and geographical information system (GIS) tools, and hydrological and ground‐truth studies to determine the magnitude of the land‐use/cover changes in the Mara River Basin, and the effects of these changes on the river flows over the last 30 years. The study results indicate that land‐use/cover changes have occurred. In 1973, for example, rangelands (savannah, grasslands and shrublands) covered 10 989 km2 (79%) of the total basin area. The rangelands had been reduced to 7245 km2 (52%) by 2000, however, while the forest areas were reduced by 32% over the same period. These changes have been attributed to the encroachment of agriculture, which has more than doubled (203%) its land area over the same period. The hydrology of the Mara River also has changed, with sharp increases in flood peak flows by 7%, and an earlier occurrence of these peaks by 4 days between 1973 and 2000. There is evidence of increased soil erosion in the upper catchments, with silt build‐up in the downstream floodplains. This has caused the Mara wetland to expand by 387%, adversely affecting riparian agriculture. There is need for urgent action to stem the land degradation of the Mara River Basin, including planning and implementing appropriate mitigation measures. 相似文献
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Spatial physicochemical parameters were determined from 39 sampling sites distributed throughout Lake Baringo during December 2010. Mean values of temperature, dissolved oxygen concentration and electrical conductivity decreased successively with depth, while the pH remained constant. Only the turbidity values increased marginally with depth. Of the surface water parameters, mean (range) values of dissolved oxygen (DO), pH, electrical conductivity, water transparency and turbidity were 6.9 (4.5–8.4) mg L?1, 8.3 (7.8–8.5), 573 (556–601)μS cm?1, 33 (28–37) cm and 43.3 (32.7–54.6) NTU, respectively. Mean and range values of total nitrogen (TN), nitrate‐nitrogen(NO3‐N), ammonia nitrogen (NH4‐N), total phosphorus (TP) and soluble reactive phosphorus (SRP) were 788.4 (278–4486) μg L?1, 4.5 (2.4–10.0) μg L?1, 42.6 (33.8–56.3) μg L?1, 102.9 (20.3–585.3) μg L?1 and 23.5 (15.2–30.5) μg L?1, respectively. Dissolved silica concentrations ranged from 19.7 to 32.7 mg L?1, with a mean value of 24.7 mg L?1. The chlorophyll‐a concentrations were quite low, ranging from 1.4 to 4.9 μg L?1, with a mean value of 4.2 μg L?1. In contrast to previous reported values, a key finding in the present study is a relatively high water transparency, indicating a relatively clear water column, due possibly to the fact that the sampling was conducted during the dry period. The nutrient levels remained low, and the chlorophyll‐a concentration also was an almost all time low value. A TP value of 20 μg L?1 and higher confirms strongly eutrophic conditions prevailing in the lake, with an extremely low potential for fish production and low species diversity, consistent with other studies. The results of the present study, therefore, reinforce the database for future management and monitoring plans for the Lake Baringo ecosystem, which lies adjacent to known geothermally active zones and a saline Lake Bogoria. 相似文献
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Mark Olokotum Marc Troussellier Arthur Escalas Sahima Hamlaoui William Okello Ronald Semyalo Jean-François Humbert Cécile Bernard 《Journal of Great Lakes research》2021,47(4):985-996
Eutrophication of Lake Victoria led to changes in its phytoplankton communities. However, different levels of eutrophication exist in the open lake and the bays, and between embayments. This study utilized spatial and temporal sampling of Napoleon Gulf and Murchison Bay, exhibiting different trophic conditions. Over one year, we investigated phytoplankton biomass, richness, diversity and dissimilarity, and related the dynamics of the dominant species to the limnological and climatic conditions. The results confirmed that Napoleon Gulf and Murchison Bay showed large differences in eutrophication status, with lower nutrient concentrations in Napoleon Gulf than in Murchison Bay, where a strong gradient was observed from inshore to offshore areas. These nutrient dynamics resulted in a 4 to 10 fold higher chlorophyll-a in Murchison Bay than in Napoleon Gulf. From the embayments, 135 phytoplankton taxa were recorded with no significant differences in alpha diversity. However, high dissimilarity in community structure was observed in beta diversity, mostly due to a turnover among the dominant toxigenic species. Thus, from a similar species pool, there was a shift in the dominant toxigenic cyanobacteria from Microcystis flos-aquae and M. aeruginosa in Murchison Bay, Dolichospermum circinale and Planktolyngbya circumcreta in Napoleon Gulf to D. circinale in the offshore stations. These cyanobacteria are toxigenic taxa with known health hazards. Using partial least square models, we showed that both climatic variables (e.g. wind, solar radiation) and levels of inorganic dissolved nutrients (e.g. SRP, NO3–, and NH4+) are the main drivers of differences and dominance in cyanobacteria communities in northern Lake Victoria. 相似文献
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Fredrick J. Muyodi Fredrick W. B. Bugenyi Robert E. Hecky 《Lakes & Reservoirs: Research and Management》2010,15(2):77-88
The Lake Victoria basin has experienced a myriad of environmental changes leading to its degradation, and necessitating various interventions to be implemented. The purpose of this study was to review early development initiatives, past and ongoing interventions in order to document experiences and lessons learned from them. The methods used in this study include review of published articles, project reports, and personal opinions of experts and project implementers in the lake basin. There are numerous threats to the lake basin, the major ones being poor land use and agricultural practices, catchment deforestation, destruction of wetlands, pollution loading, fishing malpractices and invasion by exotic aquatic weeds. These threats have resulted in rampant land and wetland degradation, leading to poor water quality and consequent water loss, a decline in the diversity of the commercial fisheries, and the lake’s biodiversity in general, unsustainable use of natural resources, increased poor human health and food insecurity, with high levels of poverty among the riparian communities. Initiatives for socio‐economic development within the lake basin began as early as the turn of the 20th century, while intervention studies started as early as the 1920s. Current lake management intervention projects, such as the Lake Victoria Environmental Management Project (LVEMP), undertaken by the riparian states of the East African Community, have invested heavily in the lake basin, with the goal of addressing the above‐noted threats to the lake. Some pilot projects undertaken through the LVEMP include: (i) water quality and quantity monitoring; (ii) industrial and municipal management; (iii) fisheries studies; (iv) water hyacinth control; (v) wetlands; (vi) land use; (vii) catchment afforestation; and (viii) micro‐projects to alleviate poverty, to cite a few examples. Phase 1 of the LVEMP was a major effort in the history of the lake basin; hence, its critical examination. To this end, this study highlights, in chronological order, the experiences, achievements, challenges and lessons learned with regard to Phase 1 of the LVEMP. 相似文献
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With the purpose of finding out whether seasonal water level fluctuations could affect water quality in a reservoir subjected to those changes, trends in environmental variables and in phytoplankton and zooplankton assemblages were analysed. The reservoir's hydrological cycle was characterized by three regimes. The maximum level phase lasted from January to the beginning of June, the emptying phase existed between mid‐June to the beginning of September and the minimum level phase lasted from mid‐September to the beginning of the first autumn/winter rain events. The highest values of total phosphorus, soluble reactive phosphorus, nitrate, water colour and chlorophyll a were found during the minimum level phase. The phytoplankton assemblage was dominated by taxa typical of meso‐eutrophic environments during the emptying and minimum level phases. However, during the maximum level phase, taxa generally found in more oligotrophic systems were observed here also. Similar to other disturbed systems, the zooplankton assemblage was dominated by Rotifera, except in summer and autumn when the cladoceran Ceriodaphnia quadrangula and/or the copepod Tropocyclops prasinus became dominant. Although those shifts seem to be related to water level variations, further research is needed to evaluate to what extent they might also be induced by other seasonal factors acting independently of water fluctuations. Based upon the obtained data, suggestions for reservoir management are proposed. 相似文献
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Kuanysh B. Isbekov Vyacheslav N. Tsoy Jean‐Francois Crtaux Nikolai V. Aladin Igor S. Plotnikov Guillaume Clos Muriel Berge‐Nguyen Saule Zh. Assylbekova 《Lakes & Reservoirs: Research and Management》2019,24(2):195-208
The water level variations of the Lake Balkhash, the Kapshagay Reservoir and the Ili River and the linkage with salinity and biological conditions are investigated in this work using different techniques: satellite radar altimetry, in situ gauges, historical archives of fish population counting and field works. We show that it is possible now to monitor, over decades, in near real time, with high precision, the water level changes in the Lake Balkhash from satellite altimetry, over the reservoir and also along the Ili River. The vulnerability of the lake fauna and flora populations is enhanced by the morphometry of the lake: shallow and separation of the eastern basin from the western basin through the narrow Uzun‐Aral strait. Water policy of the Ili River also plays a fundamental role in the evolution of the Balkhash Lake. The Ili River that provides 80% of the surface water of the lake is a transboundary river. Development of intense irrigated agriculture in the upstream part of this river, located in the Chinese territory, could lead in the future to high hydrological stress in the downstream regions with potentially high damage in the delta and for fishery production. We show here the recent evolution of the Lake Balkhash basin from satellite data. Some interannual oscillation of 6–8 years over the last decade has been highlighted, with a water level of the lake still at a high value, but prediction on increasing irrigation is also highlighting the vulnerability of this lake. Linkage between water level change along the river and the downstream waters is also investigated. It shows that the role of the reservoir is not fundamental in the understanding of the Lake Balkhash water level changes which is in contrast highly correlated to upstream river level changes. 相似文献
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洞庭湖是长江洪水的天然调蓄场所,不仅承接湘、资、沅、澧四水水沙,还纳入由荆江三口分泄的长江水沙,经湖泊调蓄后由城陵矶注入长江,形成了复杂的江湖关系,需要加强流域统一管理。通过分析洞庭湖区自然、经济状况及湖区湿地情况,结合1998年大水后湖区的治理情况及三峡工程蓄水运用后江湖关系的新变化,深入分析湖区湿地生态环境所面临的诸多问题,探讨如何在新一轮洞庭湖综合治理过程中,科学处理湖区综合治理与湿地生态环境保护与修复的关系。提出了洞庭湖统一管理措施,以便有效保护洞庭湖湿地生态环境与资源。 相似文献
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近年来干旱事件频发,在许多地区日益缺水的背景下,地下水的合理开发利用与妥善管理成为迫切需求。基于2018—2022 年鄱阳湖流域逐日地下水位,采用聚类分析、克里金空间插值、重心迁移等方法对流域不同时间尺度下地下水埋深时空分布特征进行分析。结果表明：鄱阳湖流域地下水埋深多年变化呈现平稳型、“V”型和“N”型三种模式,受2019年、2022 年干旱影响,流域中部地区出现短时间内地下水埋深迅速增大的情况。鄱阳湖流域地下水埋藏空间分布特征为中心深四周浅,地下水埋深由内向外逐渐减小,汛期地下水埋藏明显较非汛期浅,且地下水埋深中心向东北方向迁移。研究成果可为保障鄱阳湖流域水安全及可持续发展提供重要科学参考。 相似文献
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分析了流域水环境专业的社会需求,阐述了长江科学院流域水环境专业的定位和主要研究方向,分6个方面介绍了流域水环境研究所创建5 a来取得的主要科研成果:①湖库富营养化水体和藻类治理技术;②农村水电生态环境影响评价方法及保护对策;③河湖纳污能力计算方法和评价技术;④水库对河流水沙与营养物质连续传输影响及生态响应机制;⑤重金属及环境激素污染水土体治理及生态修复技术;⑥地下水污染治理技术。最后对流域水环境专业在治江科研工作的几个重点研究领域进行了讨论和展望。 相似文献