Uilkraals Situation Assessment - Anchor Environmental

4.5 Waste treatmentWaste treatment is likely to be an important ecological service provided by the aquaticecosystems of the Uilkraals catchment, particularly in that agricultural return flows are dilutedand assimilated by the system. The value of this function is usually estimated in terms of thecost savings of treating the water before it is released. However, the quantity of pollutantsreleased into the system is unknown. It is important to note that the value of the system isonly measured in terms of the amount assimilated by the system. This capacity could bereduced under certain circumstances, resulting in decreased water quality downstream andexacerbating the negative impacts on downstream users that would already be caused byincreased pollution loads due to agricultural expansion.In order to effectively quantify the value of the waste treatment services water qualityassessments would have to identify any periods of elevated loads, which would signify whenthe Uilkraals system was not able to assimilate and dilute agricultural return flows, which havethe capacity to deliver of organic pollutants into the estuary.The capacity to assimilate pollutants could also be reduced under certain circumstances,resulting in decreased water quality downstream and exacerbating the negative impacts ondownstream users that would already be caused by increased pollution loads due toagricultural expansion.4.6 Export of materials and nutrientsThe export of sediments and nutrients to the marine zone is an important function of someriver systems. For example, the prawn fisheries of KwaZulu‐Natal depend on such exports(DWAF 2004b). However, this function is far more important on the east coast, which isrelatively nutrient‐poor, than on the west coast, where the outputs of estuaries do notcompete with the nutrients supplied by the Atlantic upwelling systems (Turpie & Clark 2007).It is unlikely that the export of materials and nutrients is important in this system because itslow mean annual runoff (MAR).4.7 Refugia areas and nursery valueRefugia areas are areas that help to maintain populations in a broader area. For example,wetlands within relatively arid areas may play an important seasonal role in the maintenanceof wild herbivores that are utilised in tourism operations well beyond the wetland. This isprobably not important in the study area apart from for fish. In the rivers, some of the smallertributaries have become important as refuge areas for endemic fish, although their ability torepopulate the rest of the river system is low at present. In the estuary, some inshore marinefish populations may utilise the estuary as a warmer refuge during upwelling events (Lamberth2003). The extent of this function in its contribution to marine populations is unknown.Uilkraals Estuary Situation Assessment36Anchor Environmental