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GROEN RIVER ESTUARY: Water Quality |
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Physio-chemical Characteristics |
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During flow periods, which are infrequent, the estuary is flushed with feshwater with a corresponding lowering of salinity. When the mouth is breached during floods, sea water probabl y enters the lagoon once the level has dropped and the estuary becomes tidal, until such time as the mouth is closed by marine sediments. (Ref 1) |
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During no-flow periods, evaporation over the large shallow lagoon results in a steady escalation of salinity with time. It is during these periods, that the lagoon is fed by the springs situated on the floodplain about 2,5km from the mouth. These springs are, however, unable to compensate for the evaporative water loss and there is a net reduction in water volume with a corresponding rise in salinity in the lagoon. (Ref 1) |
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This situation was born out when AEF Heydorn and TJE Heinecken paid a fleeting visit to the Groen on 11 February 1981 with a party of Government Officials. At this time the salinity at the mouth of the lagoon was 117 parts per thousand, at the head of the lagoon 115 parts per thousand, at the spring in the northern channel47 parts per thousan, and at the spring in the southern channel 6 parts per thousand. When R Stauth visited the Groen at the end of March 1981 the salinity in the lagoon had further risen to 125 parts per thousand and much salt had crystallized out at the water's edge. (Ref 1) |
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The springs on the floodplain do, however, appear to maintain the upper reaches of the estuary in a biologically viable condition, particularly in the southern channel where the salinity did not rise from October 1980 to February 1981. During this period salinities lower down in the lagoon increased by up to 45 parts per thousand. (Ref 1) |
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Nutrients |
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The high oxygen levels measured throughout the estuary during the ECRU survey were probably due to dense concentrations of algae and phytoplankton resulting from eutrophication. Eutrophication is probably a feature of the Groen during no-flow periods when concentration of nutrients results from net evaporative water loss and a consequent reduction in water volume in the system. (Ref 1) |
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Pollution |
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There was no evidence of pollution (Ref 1) |
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