The effect of sedimentary processes on the ecology of the mangrove-fringed Kosi estuary/lake system, South Africa
Tóm tắt
The Kosi system is the only pristine estuarine system left inKwaZulu-Natal and possibly the whole of South Africa and isfacing increasing development pressure. Well-sortedunconsolidated quartz sand mantles the entire system with asapropelic ooze (gyttja) forming in the deeper lacustrine regionswhilst peat deposits occur on most of the low lying areas aroundthe lake shore. The lower part of the system comprises extensivetidal flats and mangal communities, whilst the upper partcomprises a series of linked, groundwater controlled, fresh tobrackish lakes. Fish traps, built from Avicennia marina, arelocated throughout the tidal sand-flats and lower lakes, causelocalised sedimentation and modify the tidal flow. Waves, formedfrom the prevailing winds, form both accretionary cusps and bermsas well as local beach erosion, especially in Lake Nhlange, whichhas the greatest fetch. Erosion and associated shallowing of thechannels linking the lakes is caused by excessive powerboatspeeds. Attempts to modify the physical character of the channels, eitherby dredging or erecting hard structures such wharfs orbreakwaters will irreparably alter the system by changing thephysical dynamics of the system, the most devestating resultbeing the increased bottom water renewal of Lake Mpungwini, whichwould result in more frequent fish kills.
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