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Concentrations of heavy metals commonly known to impact the environment and other related trace elements were quantified in the water bodies of nine Ethiopian rift-valley lakes and six rivers (their inflows) as well as in effluents from two factories. In about half of the samples the concentrations of As was 10–700 g l–1 and Se, ranged from 10 to 28 g l–1, were much higher than the maximum permissible level (MPL) according to international standards for drinking water. Mercury (Hg) was detected in four lakes and one river with high values ranging from 2 to 165 g l–1. Concentrations of Mo in three soda lakes were as high as 544–2590 g l–1. Iron (Fe) was found in high concentrations (567–4969 g l–1) in three lakes, which are known to be discolored from inorganic colloids. Levels of Cd, Pb, and Cr ranged between 5 and 9, 12 and 20 and 104 and 121 g l–1, respectively. The rest of the heavy metals analyzed, Ba, Cu, Mn, Ni and Zn, were either not detected in the samples or were found in much lower concentrations than the MPL for drinking water. Effluent from a tannery contained about 15, 141, 523, and 19 g l–1 of As, Cr, Fe, and Se, respectively, and effluent from a textile factory contained high concentrations of As (10.6), Hg (3.8) and Se (20) g l–1. Compared to more industrialized regions and other African lakes the concentrations of heavy metals in Ethiopian rift-valley lakes (with the exception of the soda lakes) and their inflows were low. 相似文献
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Chemical and chlorophyll a concentrations of seven Ethiopian rift-valley lakes were studied during 1990–2000. Results were compared with studies made between 1960 and 1990 in an attempt to detect long-term changes. Three different trends are apparent in the salinities (and the correlates conductivity, alkalinity, sodium concentration) of these lakes over the last 40 years: three lakes (lakes Zwai, Shalla and Abaya) have maintained their salinity levels from the 1960s, two lakes (lakes Langano and Awassa) have become more dilute, and the salinity levels of Lake Chamo and the soda lake Abijata have increased. Concentrations of silicate decreased in almost all the lakes whereas soluble reactive phosphorus (SRP) increased in most lakes. Chlorophyll a concentrations were higher in the recent samples from all lakes except two, which in conjunction with results from SRP and silicate analyses suggest eutrophication in four out of the seven lakes studied. The study relates salinization in lakes with closed drainage to increased human activities in their catchments, intensified by changes in climate during the last three decades in sub-Saharan Africa. 相似文献
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Elizabeth K.; Getachew T.; Taylor W.D.; Zinabu G.-M. 《Journal of plankton research》1992,14(10):1473-1482
Lake Hayq was previously described as having exceptionally clearwater and very low phytoplankton biomass. It is now very different,with a shallow euphotic depth and abundant phytoplankton. Zooplanktonpopulations have changed as well; Daphnia and Diaphanosoma wererecorded before, whereas we found no Cladocera. Among the possiblecauses for this change in trophic status is the introductionof the planktivorous fish Oreochromis niloticus. 相似文献
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The Ethiopian Rift Valley lakes: chemical characteristics of a salinity-alkalinity series 总被引:3,自引:3,他引:0
The study on 10 lakes within the Ethiopian Rift Valley during March–May 1991 covered a range of conductivity (K25) between 286 and 49100 µS cm–1. HCO3
– — CO
inf3
sup2–
and Na+ were the dominant ions in all the lakes. Concentrations of K+, Cl– and SO
inf4
sup2–
increased with increasing salinity and alkalinity, whereas Ca2+ and Mg2+ decreased. Comparison of these data with previous records showed that a ten-fold dilution of total ionic concentration occurred over 30 years in Lake Metahara and about three-fold increase occurred over 65 years in Lake Abijata. Concentrations of soluble silica were generally high (12–222 mg SiO2 1–1) and increased with increasing salinity, except for Lake Chamo which showed SiO2 depletion (to < 1 mg SiO2 1 –1) over the past three decades.The relationship between ionic concentration and phosphorus was irregular although high phosphorus concentrations generally corresponded with increasing salinity. Fitting data to the Dillon & Rigler (1974) chlorophyll a — total phosphorus relationship suggested that lakes Zwai, Awassa and Chamo are phosphorus-limited, whereas others have surplus phosphorus. 相似文献
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Bacteria--chlorophyll relationships in Ethiopian lakes of varying salinity: are soda lakes different? 总被引:2,自引:0,他引:2
Some soda lakes in East Africa are extreme with respect to theirhigh abundance of bac teria and phytoplankton. We used regressionanalysis of 52 samples from 18 lakes in Ethiopia to demonstratethat soda lakes conform to a different relationship betweenbacterial abundance and phytoplankton biomass. The exponentof the power function relating bacteria and chlorophyll is muchsteeper for saline lakes, although still less than one. Thismay reflect that bacteria in eutrophic soda lakes are more substratelimited, and less controlled by graxers. 相似文献
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