Management of multiple stressors to the lower reach of the Thukela River ecosystem.
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South Africa is a water scarce country which is experiencing an increase in the demand and development of water resources. The Thukela River in KwaZulu-Natal is the second largest river in South Africa and the largest in the KwaZulu-Natal Water Management Area. It is a key component of maintaining water security locally and in the rest of South Africa with several inter-basin transfer schemes. The lower reach of the Thukela River and associated estuary have been characterised as an ecologically important section of the Thukela River catchment as the river flows into the Indian Ocean and largely contributes to the formation of the Thukela Banks, a large mud bank off the coast that is also an important fisheries area. The eMandeni Stream is a tributary of the Thukela River, which has been augmented from a drainage line into a stream through the constant release of effluent from upstream industries and waste water treatment works. It is a highly impacted stream that flows into the lower reach of the Thukela River upstream of the Thukela Estuary. The aim of the study was to: 1) Review the historical and biodiversity information of the most developed areas within Thukela River catchment; 2) assess the trends in the wellbeing of the ecosystem of the lower reach of the Thukela River and 3) review a regional scale ecological risk assessment to evaluate the ecological consequences of alternative water use and protection scenarios on the water resources within the study area. The outcomes of the study indicate that the Thukela River is an important water resource for the people of South Africa and its growing economy, through the various goods and services it provides. Unfortunately, the uncontrolled use of the water resources often has a negative impact on the associated aquatic ecosystem. The aquatic ecosystem in many of the rivers’ reaches within the catchment are ecologically important and sensitive with various areas categorised as fish support and sanctuary areas. The lower reach of the Thukela River is currently in a fair state, but historical trends indicate that it has fluctuated between a fair and poor state. These results were generally lower than the results of the 2003-2004 Reserve study, and mostly did not attain the high C (fair state) recommended ecological reserve category set for this reach of the river. The eMandeni Stream is highly impacted by stressors associated with the upstream Isithebe Industrial complex, the waste water treatment works and the Sappi mill but only marginally impacts the Thukela River due to the size and dilution capacity of the Thukela River. Low flows will make the Thukela River more sensitive to these stressors and may impact on the health of the associate marine environment. The risk assessment highlighted the benefits to the Thukela River, if partially treated effluent from the Sappi mill was released into eMandeni Stream as a management option to consider. It is recommended that possible impacts to the Thukela Estuary and the offshore Thukela Bank need to be taken into consideration when any management decisions are made. The results of the risk assessment must be validated, and an updated Ecological Reserve study should be completed for the Thukela River, taking into consideration the freshwater requirements of the marine environment. Resource Quality Objective should also be established to enable decision makers to make informed decisions on the management of the Thukela system. The functionality of the UBTS fishways should be investigated as well as the impacts of the weir as a barrier for fish migration. Changes in water resource use practices is required to attain a better balance between the use and protection of the lower reach of the Thukela River and estuary.