Geochemistry and natural ionic and isotopic tracing; two complementary ways to study the natural salinity regime of the hydrological system of Lake Chad

Roche, Michel-Alain

doi:10.1016/0022-1694(75)90131-6

Cited by 11 publications

(5 citation statements)

References 7 publications

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“…Although a geochemical interpretation is not attempted here, and the data are intended as a preliminary survey of the inorganic chemistry of the Boro River, the results of this investigation are nevertheless consistent with the model for physicochemical sedimentation on islands suggested by McCarthy & Metcalfe (unpublished data). The relative low ionic content of the Boro, reflecting the mineral poverty and the relative insolubility of rocks and soils present in the catchment above, the moderate alkalinity, and high silica content, stress the overall importance of chemical precipitation reactions in the control of salinity, similar to the situation seen in Lake Chad (Roche, 1975, Carmouze, Golteman & Pedro, 1977. These reactions, apart from the formation of amorphous silica, are unlikely to occur in the river.…”

Section: Mineral Equilibria and Evaporative Concentration Of Solutesmentioning

confidence: 78%

“…This was observed in April 1990 when the largest increase in the solute concentration gradients Assuming the concentration of CP is conservalive and the input source is rain-water, major solutes in the Boro should be concentrated by a factor 3-4. Concentration ratios (Table 3) indicate, however, that the Boro water is enriched by factors ranging from 1.1 to 3.4 with average values of 1.3-2.3, a situation very similar to Lake Chad (Roche, 1975). Chemical precipitation reactions seem to be one of the main mechanisms for removal of solutes and control of salinity.…”

Section: Mineral Equilibria and Evaporative Concentration Of Solutesmentioning

confidence: 97%

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Major ion chemistry of the lower Boro River, Okavango Delta, Botswana

Sawula

Martins

1991

Freshwater Biology

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1. The composition of surface waters of the Boro River, Okavango Delta, Botswana, was determined on five occasions during [1989][1990]. The waters could be characterized as calcium-sodiumbicarbonate, with moderate alkalinity, and moderate to high amounts of silica. Mean values of the major ions, in mgl"', were: 4.8, 1.3, Na^ 3.9, K^ 2.7, HCOJ 27, CP 1.0 and SiO^ 38; pH c. 7.2. The relative ionic composition of the waters changed gradually from the inlet in Seronga to the outlet at Boro/Thamalakane junction. There was a gradient of increasing concentrations of solutes resulting from the evaporative concentration of the waters in this semi-arid region with an almost permanent water deficit, and the total dissolved solutes increased fromc. 30to95mgr'.3. There were seasonal differences in solute concentrations, connected with the rainfall pattern and climatic cycle and an ill-defined relation with discharge. The chemical spectrum of the Boro, and the freshness of its waters, can be attributed to the major influence of precipitation within the basin and selective removal of solutes.4. Chemical equilibrium models indicate that amorphous silica and sepiolite are likely to precipitate from the Boro waters. Carbonate and silicate systems are responsible for the selective removal of solutes in the swamps, islands, or flood plains, as proposed by others in recent studies, but not in the Boro River waters.

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Section: Mineral Equilibria and Evaporative Concentration Of Solutesmentioning

confidence: 78%

Section: Mineral Equilibria and Evaporative Concentration Of Solutesmentioning

confidence: 97%

Major ion chemistry of the lower Boro River, Okavango Delta, Botswana

Sawula

Martins

1991

Freshwater Biology

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“…Although it is the terminal lake of an endorheic basin dominated by evaporation (∼ 2000 mm yr −1 ), Lake Chad waters remain surprisingly fresh (Carmouze, 1979;Roche, 1975). It has been suggested that the chemical regulation of Lake Chad is controlled both by geochemical precipitation and clay neoformation in the lake (Carmouze, 1983;Gac et al, 1977) and more significantly by infiltration of the lake water into the underlying Quaternary aquifer (Roche, 1975). The aquifer connected with the lake is the major source of water for domestic use but its waters in some areas show total dissolved salt concentrations above the recommended values (Abderamane et al, 2013).…”

Section: Introductionmentioning

confidence: 99%

Hydrological, chemical and isotopic budgets of Lake Chad: a quantitative assessment of evaporation, transpiration and infiltration fluxes

Bouchez¹,

Gonçalvès²,

Deschamps³

et al. 2015

Preprint

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Abstract. In the Sahelian belt, Lake Chad is a key water body for 13 million people who live on its resources. It experiences, however, substantial and frequent surface changes. Located at the center of one of the largest endorheic basins in the world, its waters remain surprisingly fresh. Its low salinity has been attributed to a low infiltration flow whose value remains poorly constrained. Understanding the lake's hydrological behavior in response to climate variability requires a better constraint of the factors that control its water and chemical balance. Based on the three-pool conceptualization of Lake Chad proposed by J. C. Bader, J. Lemoalle, and M. Leblanc (Bader et al., 2011), this study aims to quantify the total water outflow from the lake, the respective proportions of evaporation (E), transpiration (T) and infiltration (I), and the associated uncertainties. A Bayesian inversion method based on lake-level data was used, leading to total water loss estimates in each pool (ETI). Sodium and stable isotope mass balances were then used to separate total water losses into E, T and I components. Despite the scarcity of representative data available on the lake, the combination of these two geochemical tracers is relevant to assess the relative contribution of these three outflows involved in the control of the hydrological budget. Mean evapotranspiration rates were estimated at 2070 ± 100 and 2270 ± 100 mm yr−1 for the southern and northern pools respectively. Infiltration represents between 100 and 300 mm yr−1 but most of the water is evapotranspirated in the first few kilometers from the shorelines and does not efficiently recharge the Quaternary aquifer. Transpiration is shown to be significant, around 300 mm yr−1 and reaches 500 mm yr−1 in the vegetated zone of the archipelagos. Hydrological and chemical simulations reproduce the marked hydrological change between the normal lake state that occurred before 1972 and the small lake state after 1972 when the lake surface shrunk to a tenth of its size. According to our model, shrinking phases are efficient periods for salt evacuation from the lake towards the phreatic aquifer.

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“…Whenever it was possible annual weighted means have been computed: it is now well known that river mineralization is highly dependent upon discharge and hydrological events. This variation exists even for the major rivers (Gibbs, 1967;Roche, 1975). For example in the Mekong River at Phnom Penh total ionic contents ranging from 90 to 190 mg lr 1 were measured (Carbonnel and Meybeck, 1975) and the mean arithmetic total ionic content was 121 mg lr 1 versus 95 mg lr 1 for discharge weighted mean.…”

Section: Water Quality Datamentioning

confidence: 96%

“…Since Livingstone's review a lot of important work has been attempted on the world's biggest rivers: the Amazon (Gibbs, 1967(Gibbs, , 1972, Parana (Depetris and Griffin, 1968;Bonnetto et al, 1969), Danube (Liepolt, 1967), Mackenzie (Brunskill et al, 1975), Chari (Roche, 1975), Mekong (Meybeck and Carbonnel, 1975). The studies of river mineralization and dissolved transport have been undertaken mainly on rivers located in the same country where basins are sometimes similar, or they were based on worldwide river water quality data Brazhnikova, 1962, 1968;Langbein and Dawdy, 1964;Corbel, 1964;Judson and Ritter, 1964;van Denburgh and Feth, 1965;Leopold etal, 1964;Gibbs, 1970).…”

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confidence: 99%

TOTAL MINERAL DISSOLVED TRANSPORT BY WORLD MAJOR RIVERS / Transport en sels dissous des plus grands fleuves mondiaux

Meybeck

1976

Hydrological Sciences Bulletin

141

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World variations of dissolved transport Td [t km-2 year-1 ] and major ion content S [mg 1. ] with runoff g [1. s-1 km-2 ] and solid transport 77s [t km-2 year-1 ] are examined on the basis of 40 of the world's biggest rivers (basin area/4 >400 00 km 2 or discharge g>5 000 m 3 s-1). For each river estimates of A, Q, S, Td and 77s are given and two subsamples are considered according to the size of the rivers. For each subsample it is found that S is inversely related to q, Td is directly related to q and to Ts. The ratio Ts/Td is highly variable but generally increases when Ts increases. Climate dominates S variation and relief Td variation; wide scatterings of S and Td are due to the other factor. On a world scale relief is the main factor controlling variations of Td with 77s. The direct relationship between Td and Ts confirms the work of Alekin and Brazhnikova in the Soviet Union, while the inverse relationship found by Judson and Ritter in the conterminous USA seems to be a minor trend due to the influence of climate surpassing relief. The total sample of rivers considered covers 48 per cent of the continental area draining to the ocean and represents 44 per cent of the world's runoff. If this sample is taken as representative, dissolved transport of material appears to be dominant or equal to solid transport for about 35 per cent of the world's continental surface. A typology of dissolved transport by major rivers is given according to their morphoclimatic features. If chemical transport is a major process on the earth's surface, the solid material carried by the rivers to the ocean as a whole is five times more than the dissolved transport: 20 x 10 9 t year-1 according to Holeman as compared to 3.25 x 10 9 t year" 1 on the basis of these 40 rivers. Transport en sels dissous des plus grands fleuves mondiaux Resume. Les variations du transport dissous Td [t km-2 an-1 ] et de la concentration totale en sels dissous S [mg 1 _1 ], en fonction de l'écoulement q [1. s-1 km-2 ] et du transport solide 77s [t km-2 an-1 ] sont étudiées sur 40 des plus grands fleuves mondiaux (d'une superficie drainée supérieure à 400 000 km 2 ou d'un débit supérieur a 5 000 m 3 s-1). Sur l'ensemble des 40 fleuves les régressions suivantes ont été trouvées: S= 392

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Geochemistry and natural ionic and isotopic tracing; two complementary ways to study the natural salinity regime of the hydrological system of Lake Chad

Cited by 11 publications

References 7 publications

Major ion chemistry of the lower Boro River, Okavango Delta, Botswana

Major ion chemistry of the lower Boro River, Okavango Delta, Botswana

Hydrological, chemical and isotopic budgets of Lake Chad: a quantitative assessment of evaporation, transpiration and infiltration fluxes

TOTAL MINERAL DISSOLVED TRANSPORT BY WORLD MAJOR RIVERS / Transport en sels dissous des plus grands fleuves mondiaux

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