What causes the different colours of the salts pits in the Saloum Delta in Senegal?

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  • $\begingroup$ I read somewhere that these are dye pits $\endgroup$ – user889 Mar 21 '15 at 16:03
  • $\begingroup$ Could be bacteria? Different temperatures, salinites or other conditions could lead to different bacteria living there. $\endgroup$ – Gimelist Mar 22 '15 at 3:03
  • $\begingroup$ I initially thought they might be dying pits like Sabre Tooth states, based on pictures of such pits in North Africa, but its difficult to know how large these pits are without a reference for scale. Michael's comment about bacteria is an interesting possibility. With the yellow, red, orange & brown pits one thought was different combinations of iron oxides, ferric & ferrous, but then I don't know how to explain the green pits. $\endgroup$ – Fred Mar 22 '15 at 6:31
  • $\begingroup$ The delta is apparently a good example of an inverse delta, with very high salinity. So quite possibly this is an influencing factor? $\endgroup$ – mtb-za Mar 24 '15 at 9:02
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    $\begingroup$ Don't know about these in particular, but the colors in this image are due to algae (greens) and halophillic bacteria (red, orange). See wikipedia for more info. $\endgroup$ – rusty Sep 6 '15 at 21:44

Writing about the San Francisco Bay salt ponds, Dr R. J. Rusay notes:

Due to variable algal concentrations, vivid colors, from pale green to bright red are created. The color indicates the salinity of the ponds. Micro-organisms change their hues as the salinity of the pond increases. In low to mid-salinity ponds, green algae are predominant. In middle to high salinity ponds, an algae called Dunaliella salina shifts the color to red. Millions of tiny brine shrimp create an orange cast in mid-salinity ponds. Other bacteria such as Stichococcus also contribute tints.

Rusay says nothing about the Saloum Delta, but the explanation could be similar there.


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