Mlawula Nature Reserve - Geology/Soils/Hydrology
The reserve is based predominantly on two geological formations, the Lubombo Mountains, being made up of rhyolites, and basalt valleys to the west. These formations evolved about 200 million years ago when Gondwanaland was beginning to break apart, and volcanic lava which formed the basalt rock of the eastern lowveld, was extruded. Later, as the edge of the African continent began to form, volcanoes along a line from the Limpopo to Zululand formed the rhyolitic rocks of the Lubombo. Subsequent erosion lowered the less resilient basalt, and left the harder rhyolites as escarpments.
The soil types found within the reserve vary greatly. Much of the area consists of rock outcrops and stony ground (raw mineral soil) but in the Ndzindza area, the soils found consist of either grey sand or sandy loam on hard rock (Lithosolic). In contrast, the Siphiso Valley area holds mainly brown to black loams or clay (Vertisolic). Grey, black and red clays (Vertisolic) as well as deep red, yellow and orange loams (Fersialitic) have also been recorded in the area. The larger watercourses are flanked by narrow strips of colluvial and alluvial soils
Soil erosion is a serious problem in places. The Siphiso valley contains large areas that have been subject to sheet, rill and gully erosion as a result of overgrazing. Badly drained roads also cause erosion in some areas.
The Mbuluzi, Mlawula, and Siphiso rivers flow through the reserve. The Siphiso represents the only river whose catchment area is nearly included in the reserve. The Mbuluzi and Mlawula rivers are perennial. The Mlawula only became so since the irrigation of the cane fields in 1979. The remaining rivers and streams dry up during the winter months, except in some stretches such as rhino pools and croc pool. There are a number of small pans in the reserve at Ndzindza and Mbuluzi. There are three dams on the Mlawula that were originally installed by cattle ranchers as well as a weir on the Mlawula River, adjacent to Mlawula Railway Station. The Mlawula and Mbuluzi rivers are polluted by sugar, fertilisers, molasses, and high sediment loads due to commercial agriculture. These pollutants reduce oxygen levels, increase nutrients levels and turbidity. These conditions result in algal blooms and fish kills. The Mlawula and Mbuluzi are also a permanent source of alien plant seeds.
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