Abstract
The Mkomazi River, South Africa, originates in the southern Drakensberg Mountains and extends 290km to the coast of KwaZulu-Natal before entering the Indian Ocean. Geochemical analysis of seven mud-sized borehole samples, ranging in age from greater than 6250 years BP to recent, from near the mouth of the Mkomazi River have been used to define Holocene values. These are compared to analyses of 24 modern mud-sized surface samples from the length of the Mkomazi River to assess potential anthropogenic pollution from agriculture, a paper factory and sewerage.
There is a relatively consistent downstream variation in the abundance of major and most trace elements in the Mkomazi River mud fraction due to increasing chemical and physical maturity. In addition the abundance of V, Co, Ni and Cu may be correlated to local geology. Otherwise the composition of mud-sized sediment is believed to be dominated by voluminous sediment sourced from the Karoo Supergroup and weathered during downstream transport. Samples which fall as outliers to the overall trends can be correlated to heavy mineral enrichment and coastal salt contamination.
More than 90% of analyses of modern mud-sized samples from near the mouth of the Mkomazi River plot within one standard deviation of the average Holocene value. This indicates that the modern day sediment load of the Mkomazi River is broadly similar to Holocene sediment at the mouth of the river. An exception is Cu which has modern values greater than Holocene values plus one standard deviation. While this may be cause for monitoring the absolute values are well within internationally acceptable levels. There is no indication for significant anthropogenic pollution of sediment within the Mkomazi River.
