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isolation, but only inasmuch as it contributes cumulatively to this service provided by
ecosystems in general.
4.5 Waste treatment
Waste treatment is likely to be an important ecological service provided by the aquatic
ecosystems of the Uilkraals catchment, particularly in that agricultural return flows are diluted
and assimilated by the system. The value of this function is usually estimated in terms of the
cost savings of treating the water before it is released. However, the quantity of pollutants
released into the system is unknown. It is important to note that the value of the system is
only measured in terms of the amount assimilated by the system. This capacity could be
reduced under certain circumstances, resulting in decreased water quality downstream and
exacerbating the negative impacts on downstream users that would already be caused by
increased pollution loads due to agricultural expansion.
In order to effectively quantify the value of the waste treatment services water quality
assessments would have to identify any periods of elevated loads, which would signify when
the Uilkraals system was not able to assimilate and dilute agricultural return flows, which have
the 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 on
downstream users that would already be caused by increased pollution loads due to
agricultural expansion.
4.6 Export of materials and nutrients
The export of sediments and nutrients to the marine zone is an important function of some
river 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 is
relatively nutrient-poor, than on the west coast, where the outputs of estuaries do not
compete 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 its
low mean annual runoff (MAR).
4.7 Refugia areas and nursery value
Refugia 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 maintenance
of wild herbivores that are utilised in tourism operations well beyond the wetland. This is
probably not important in the study area apart from for fish. In the rivers, some of the smaller
tributaries have become important as refuge areas for endemic fish, although their ability to
Uilkraals Estuary Situation Assessment
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