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BOT RIVER ESTUARY: Water Quality

Physio-chemical Characteristics
Measurements of pH have made sporadically in the Botriviervlei since 1967 and the values range from 6,8 and 8,5.  This is in accordance with the charcterisation of the Bot River water as "turbid water" with pH "slightly acid to alkaline" (Heydorn and Tinley,1980). (Ref 2)
No evidence of stratification was found although in the case of ammonia, values were generally higher in bottom water samples than in samples from the surface, indicating reducing conditions in the sediments.  Silicates are probably of riverine origin indicated by the fact that much higher values were recorded at the head of the estuary than near the coastal dunes. (Ref 2)
The water from the Botriviervlei was always well oxygenated, the values ranging between  5,4 and 10,8 mg per litre.  Anoxic conditions were never encountered. (Ref 2)
Apart from the fact that there may be rapid and drastic changes in slainity due, for example, to such events as sudden floods or the opeing of the vlei to the sea after a lengthy jperiod of isolation, there appears to be an annual pattern of fluctuations in salinity.  This is linked to the annual rainfall regime.  Generally, salinities in summer tend to be rather high with peak vaues of around 40 parts per thousand being recorded in January to March.  The extent to which the vlei becomes saline, approaching or even exceeding the salinity of seawater, will depend on the amount of water that has entered the vlei the previous winter and the amount of evaporation in the following months.  With the onset of winter rains, alrge volumes of fresh water flow into the vlei and salinity drops, reaching its lowest values between September and November.  During this time salinities as low as 3 - 5 parts per thousand have been recorded.(Ref 2)
 

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