Enrichment and geo-accumulation of trace and heavy metals in surface sediments along urbanised Austral wetlands

Urban wetlands are often polluted by heavy and trace metals being discharged from industries, urbanisation and agriculture, which tend to alter the sediment quality. Sediments are important as they act as a sink for nutrients in aquatic environments. Wetlands play an important role in maintaining ecological balance, preventing floods and droughts, providing shelter for various animals and plants and supporting human well-being through essential services such as carbon sequestration and water purification. The present study aimed to assess the spatiotemporal distribution and sediment pollution indices of trace and heavy metals in surface sediments and identify potential sources of contamination in urbanised Austral wetlands. Sediment samples were collected within the Riverside’s Wetlands, City of Nelspruit, South Africa, across three seasons (i.e. hot–dry, hot–wet and cool–dry seasons). A multivariate principal component analysis was used to determine the metal relationship. The metal pollution indices, such as contamination factor, enrichment factor, geo-accumulation factor and pollution load index were used to determine the pollution of metals in the sediments across different sites among seasons. The study found that only the lower Na concentration was observed during the cool-dry season, which was lower compared to the concentrations of other metals. The pollution indices indicated that wetland sediments were highly contaminated, mainly with Mn, Co, Cu, Pb, Zn, Al and Fe, especially during the cool–dry season. The current study highlights an urgent need to come up with immediate measures to control severe heavy metal pollution from the industrial emission into the wetlands. Those immediate measures should be carried out to minimise the rate of contamination and extent of future metal contamination.