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Major ion chemistry of the lower Boro River, Okavango Delta, Botswana
Author(s) -
SAWULA G.,
MARTINS E.
Publication year - 1991
Publication title -
freshwater biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.297
H-Index - 156
eISSN - 1365-2427
pISSN - 0046-5070
DOI - 10.1111/j.1365-2427.1991.tb01413.x
Subject(s) - alkalinity , nitrate , chemistry , hydrology (agriculture) , environmental chemistry , bicarbonate , boro , precipitation , geology , boron , physics , geotechnical engineering , organic chemistry , meteorology
SUMMARY. 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 caicium—sodium—bicarbonate, with moderate alkalinity, and moderate to high amounts of silica. Mean values of the major ions, in mg1‐ −1 , were: Ca 2+ 4.8, Mg 2+ 1.3, Na + 3.9, K + 2.7, HCO 3 − 27, Cl − 1.0 and SiO 2 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 from c. 30 to 95 mg 1‐ −1 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.