Hydrochemical fluctuations and crustacean community composition in an ephemeral saline lake (Sua Pan,Makgadikgadi Botswana) |
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Authors: | Graham Paul McCulloch Kenneth Irvine Frank D Eckardt Rob Bryant |
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Institution: | (1) Department of Zoology, University of Dublin, Trinity College, Dublin, 2, Ireland;(2) Department of Environmental Sciences, University of Cape Town, Cape Town, South Africa;(3) Department of Geography, University of Sheffield, Sheffield, UK |
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Abstract: | Fluctuating hydrochemistry, as a result of extreme hydrological regimes, imposes major physiological constraints on the biota
of ephemeral saline lakes. While the inverse relationship between salinity and zooplankton species richness is well-known
across salinity gradients, few studies have documented closely the response of zooplankton to seasonal changes in salinity.
Weekly sampling during two flood seasons at Sua Pan, an intermittent saline lake in central Botswana demonstrated the importance
of spatial and temporal salinity gradients for crustacean community composition, associated with a decline in species richness,
from 11 to three species. Conductivity ranged between 320 and 125,800 μS cm−1 during seasonal flooding; changing from dominance by
and , Ca2+ and Mg2+, at the beginning of the floods, to NaCl dominated waters as the lake dried out and salinities increased. pH estimates generally
ranged between 8.6 and 10, with maximum values recorded during initial flooding. Crustaceans comprised mainly Branchinella spinosa, Moina belli, Lovenula africana and Limnocythere tudoranceai, all of which occurred across a wide range of salinities, while halotolerant freshwater species (Metadiaptomus transvaalensis, Leptestheria striatochonca and the ostracods Plesiocypridopsis aldabrae, Cypridopsis newtoni and a newly identified Potamocypris species) disappeared above conductivities of 1,500 μS cm−1. A unique crustacean composition in southern Africa was attributed to Sua Pans’ rare chemical composition among southern
African saline lakes; flood waters on Sua Pan contained a higher proportion of Na+ and , and less K+, Mg2+ and than over 80% of records from salt pans elsewhere in southern African. The freshwater species of crustaceans in Sua Pan were
similar to those found in other southern Africa lakes, and these similarities decreased in lakes with higher pH and proportions
of Na, and less SO4 and Mg in their chemical composition. The predominant saline tolerant species on Sua Pan, however, showed a greater similarity
to those in saline lakes in southern and East Africa with higher proportions of and, particularly, Mg2+ in their chemical composition.
Handling editor: J. M. Melack |
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Keywords: | Saline lake Ionic composition Zooplankton Makgadikgadi Species richness Salinity |
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