Mineral springs and saline lakes of the Western Rift Valley, Uganda

Arad, Arnon; Morton, W. H.

doi:10.1016/0016-7037(69)90039-8

Cited by 40 publications

(20 citation statements)

References 7 publications

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“…It differs from the situation in the Western Rift with other inputs (e.g. K+, Mg 2+ ) as from the Virunga volcanic field (Talling & Talling, 1965;Arad & Morton, 1969). Nevertheless the concentration process may involve saline springs, thermal reflux pathways, and the alternate deposition and leaching of non-marine evaporites.…”

Section: Discussionmentioning

confidence: 77%

Chemical and algal relationships in a salinity series of Ethiopian inland waters

1988

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Most Ethiopian lakes are parts of closed drainage systems and collectively form an extensive salinity series, here treated comparatively for geographical, chemical and algal characteristics. Chemical data are presented for 28 lakes and numerous inflows, including original analyses for 15 lakes, in which total ionic concentration and electrical conductivity vary over 4 orders of magnitude. The principal determinant of a lake's position in the series is the open or closed nature of its individual drainage. At present there are three major closed systems (Awash R. -Afar drainage, northern rift lakes, southern rift lakes), numerous crater lakes with seepage -in and -out, and two cryptodepressions with marine inputs. Salinity is primarily determined by evaporative concentration, enhanced in lakes associated with past marine influence or recent volcanic activity by readily soluble materials in the catchment, and by some thermal-reflux pathways. However, anomalously dilute closed lakes exist, indicative of other processes of solute loss (e.g. past basin overflow, 'reverse weathering', seepageout).There are strong positive correlations between increasing salinity and the concentrations of Na + , alkalinity and Cl-. The last is used, in conjunction with other analyses of atmospheric precipitation, to estimate the marine and denudative contributions and the evaporative concentration factor, and to distinguish trends of ionic species during evaporative concentration. With several exceptions, affected by past penetration of sea water into the Danakil and L. Assal cryptodepressions, the most saline lakes are soda lakes with HCO + CO]-and Na + predominant and Ca 2+ and Mg 2 + largely eliminated. Soluble reactive silicate and phosphate tend to increase in concentration along the salinity series, but the unknown dynamics of algal growth are likely to introduce variance. Concentrations in some lakes are extremely high, e.g. > 40 mg SiO 2 1 -1 and > I mg PO 4 -P 1-'.Phytoplankters recorded from individual lakes are tabulated and where available the community biomass concentration as chlorophyll a is given. Lakes of high salinity-alkalinity are typically very productive in terms of phytoplankton biomass and photosynthetic rates (exceptions: the very deep L. Shala and the very saline L. Abhe), supported in part by relatively high concentrations of phosphorus and inorganic carbon. Many species are of restricted salinity-alkalinity range, being characteristic of waters where levels are low (e.g. desmids, Melosira spp.), intermediate (e.g. Planctonema lauterborn), or high (e.g. Spirulinaplatensis). Phytoflagellates are most strongly represented in waters with higher concentrations of the bivalent cations Ca 2 + and Mg 2 + . The common cyanophyte Microcystis aeruginosa can tolerate a wide salinity range, here as elsewhere.

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Section: Discussionmentioning

confidence: 77%

Chemical and algal relationships in a salinity series of Ethiopian inland waters

1988

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“…Others have studied the hydrology and chemistry of warm and hotsprings in Kenya including Lake Bogoria (Beadle, 1936), Lake Baringo (Worthington, 1932), Lake Nakurn (Koeman et al, 1972;Richardson and Richardson, 1972), and Lake Magadi (Baker, 1958;Coe, 1960;Talling and Talling, 1965;Beadle, 1974;Jones et al, 1977). Other scientists have studied the water chemistry for springs in Uganda (Arad and Morton, 1969;Viner, 1975) and Tanzania (White, 1957;Talling and Tailing, 1965). Generally, the characteristics of warm and thermal springs are insufficiently understood scientifically, particularly with regard to ecological effects and spatio-temporal changes in hydrology and water chemistry.…”

Section: Introductionmentioning

confidence: 94%

A spatio-chemical survey of hydrogeothermal springs in Lake Elementaita, Kenya

Mwaura

1999

International Journal of Salt Lake Research

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Abstract. The hydrochemistry of three areas of geothermal activity in the Lake Elementaita basin were surveyed. The results indicated warm temperatures between 30--40 ~ high alkalinity (1,200 mg CaCO3/1 ) and specific conductance (4,300-8,100/~S/cm). pH was above 9 with a high concentration of carbonates, chlorides and sulphates. Apart from playing a significant role in the lake chemistry, lacustrine springs provide a significant source of water supply, particularly during the dry season. However, there is a serious lack of scientific information on the hydrogeology and hydrochemistry of the thermal springs.

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“…Annual evaporation rates near Lake Edward basin are 2,000 mm; average annual rainfall is 900 mm, and average annual temperature is 23.5°C at the elevation of Lake Kitagata (Russell et al 2007). Present-day Lake Kitagata lacks permanent surface inflows and is fed by groundwater flow and runoff (Arad and Morton 1969;Russell et al 2007).…”

Section: Site Descriptionmentioning

confidence: 99%

“…Some lakes consist of brines with significant carbonate contents and relatively high pH (Arad and Morton 1969;MacIntyre and Melack 1982;Kilham 1982) and show regional chemical variations, notably in sulfate content (Arad and Morton 1969). Such variations are considered to be derived from regional differences in the Neogene volcanic rock suites (Arad and Morton 1969). Alkaline brines in volcanic terranes, such as the African crater lakes, are typically enriched with silica (MacIntyre and Melack 1982;Verschuren 1999, Russell et al 2007), due to interaction of alkaline brines with silicate minerals from volcanic rocks (Eugster 1967;Hay 1968;Eugster and Jones 1968;Jones et al 1967Jones et al , 1977Muraishi 1995).…”

Section: Introductionmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

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A Brine Evolution Model and Mineralogy of Chemical Sediments in a Volcanic Crater, Lake Kitagata, Uganda

Lowenstein

Russell

2010

Aquat Geochem

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Lake Kitagata, Uganda, is a hypersaline crater lake with Na-SO 4 -Cl-HCO 3 -CO 3 chemistry, high pH and relatively small amounts of SiO 2 . EQL/EVP, a brine evaporation equilibrium model (Risacher and Clement 2001), was used to model the major ion chemistry of the evolving brine and the order and masses of chemically precipitated sediments. Chemical sediments in a 1.6-m-long sediment core from Lake Kitagata occur as primary chemical mud (calcite, magadiite [NaSi 7 O 13 (OH) 3 Á3H 2 O], burkeite [Na 6 (CO 3 )(SO 4 ) 2 ]) and as diagenetic intrasediment growths (mirabilite (Na 2 SO 4 Á10H 2 O)). Predicted mineral assemblages formed by evaporative concentration were compared with those observed in salt crusts along the shoreline and in the core from the lake center. Most simulations match closely with observed natural assemblages. The dominant inflow water, groundwater, plays a significant role in driving the chemical evolution of Lake Kitagata water and mineral precipitation sequences. Simulated evaporation of Lake Kitagata waters cannot, however, explain the large masses of magadiite found in cores and the formation of burkeite earlier in the evaporation sequence than predicted. The masses and timing of formation of magadiite and burkeite may be explained by past groundwater inflow with higher alkalinity and SiO 2 concentrations than exist today.

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Mineral springs and saline lakes of the Western Rift Valley, Uganda

Cited by 40 publications

References 7 publications

Chemical and algal relationships in a salinity series of Ethiopian inland waters

Chemical and algal relationships in a salinity series of Ethiopian inland waters

A spatio-chemical survey of hydrogeothermal springs in Lake Elementaita, Kenya

A Brine Evolution Model and Mineralogy of Chemical Sediments in a Volcanic Crater, Lake Kitagata, Uganda

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