|Characteristics of the Mbashe Catchment and Estuary, South Africa. Towards an assessment of catchment land use impact|
Verlé, K. (2013). Characteristics of the Mbashe Catchment and Estuary, South Africa. Towards an assessment of catchment land use impact. MSc Thesis. Universiteit Antwerpen/Universiteit Gent/VUB: Antwerpen, Gent, Brussel. 89, XXV pp.
catchment, ecosystem health, erosion, estuary, Mbashe, mangroves, land use
Estuaries provide essential ecosystem services and are valuable assets, but are under threat due to human activities. Activities in the catchment area have been found to have an impact on estuaries. Land use, transfer schemes, discharges and dam developments play a major role in changing ecosystems. The Mbashe Estuary situated in the former Transkei (Wild Coast) was ranked 28 in terms of national conservation importance. The estuaries along the Wild Coast have often been left out in historical research due to political instability and information on the Mbashe Catchment is limited. The overall aim of the study was to contribute to a health assessment of the Mbashe Estuary and to provide a link with the catchment area in terms of land use and status of the river. The anthropogenic driving forces in the catchment did not evolve considerably over the last decade and the Mbashe Estuary remained largely undisturbed. Land types of poor agricultural potential were found for 54% of the catchment. It could be estimated that 21% of the catchment area is under cultivation, which is similar to the situation in 1996. Furthermore, it is unlikely that large agricultural expansion will occur in the near future, because the soils with higher agricultural potential are mostly already under cultivation. The potential for local economic development is limited. Overall erosion is the major pressure on the Mbashe system. Tourism in the estuary is limited, but has the potential to quickly disturb the current equilibrium. Overall, water quality parameters measured in the Mbashe Estuary and River were within norms. However, a high turbidity (! 50 NTU) was found both in the river and in the estuary and high surface sediment loads at some locations. Soluble reactive phosphorus concentrations in the river as well as in the estuary were relatively high (> 40 "g.l-1), but dissolved inorganic nitrogen concentrations were low. Phytoplankton biomass was low both in the river and in the estuary. The mangrove indicators and sediment characteristics pointed towards an overall healthy forest. However, adult:seedling ratio was high and alive:dead ratio was low. Anoxic conditions in the soil were encountered. Furthermore, a dead patch of 0.47 ha of Avicennia marina trees was identified in 2012, likely caused by marine sediment deposition.