Gary Caitcheon

Major element chemistry of sediments from the Darling–Barwon river and its tributaries: implications for sediment and phosphorus sources

In 1991, one of Australias longest rivers, the Darling–Barwon, experienced one of the worlds largest recorded algal blooms. Nearly 1000 km of river were affected. At the time of the bloom phosphorus originating from anthropogenic sources was believed to be the principal cause. In this study we have used major element chemistry to examine the sources of sediment and sediment-associated phosphorus delivered to the Darling–Barwon River. We show that the sediments are derived primarily from the sedimentary and granitic bedrock areas of the catchment, not the intensively farmed basalt areas. We also show that the sediment currently in transport in the Darling–Barwon does not originate from contemporary upland erosion, but is probably derived from lowland areas of the catchment that contain more weathered material. Phosphorus concentrations in the sediments are consistent with those in natural soils of the region, and evidence from two sediment cores indicates that phosphorus concentrations have not changed significantly in the last 200 years. The implications of these findings for algal growth control strategies are discussed. Copyright