Effects of informal and formal settlements on metal concentrations in the Ramsar accredited Nyl River floodplain, Limpopo Province, South Africa

Due to the limited water sources in South Africa and the increase in demand due to expanding informal and urban settlement, the conservation and adequate management of wetlands is crucial. Increased anthropogenic activities... [ view full abstract ]

Due to the limited water sources in South Africa and the increase in demand due to expanding informal and urban settlement, the conservation and adequate management of wetlands is crucial. Increased anthropogenic activities have led to elevated metal concentrations introduced into these fragile aquatic ecosystems. Humans rely on these ecosystems for ground water recharge, provision of water and in some instances food. Increased metal concentrations in water can cause bioaccumulation of metals in aquatic organisms and pose a potential threat to consumers. This paper looks at the effects of the associated anthropogenic activities of the town of Modimolle on water quality and the accumulation of 7 metals (Al, Cr, Cu, Fe, Mn, Sr and Zn) in Clarias gariepinus (Burchell, 1822), and Oreochromis mossambicus (Peters, 1852) at two sites (NRS1 and NRS2) in the Nyl River System. Metal concentrations in filtered water, gills, liver, skin and muscle tissue were determined using standard microwave digestion and ICP-MS techniques.
The results from the water analysis indicate that Al, Cr, Cu, Fe, Mn, Sr and Zn had elevated levels. The levels were above the South African water quality guideline values for aquatic ecosystems. These metals were then selected for analysis in the fish tissues. The selected metals are accumulating in all tissues at both sites within the system. Significant differences in interspecies metal accumulation were noted between sites. The organ responsible for the highest accumulated concentrations was the liver, followed by the gill, skin and muscle.
Though metal accumulation occurred at both sites, concentrations at NRS2 were significantly higher than that of NRS1, indicating that Modimolle does impact the system adversely.