Clay mineral source tracing and characterisation of Burdekin River (NE Australia) and flood plume fine sediment

The purpose of this study is to define the relative contributions of fine (< 10 mu m) suspended sediment from tributaries within the Burdekin River catchment, NE Australia, and subsequent delivery to the Great Barrier Reef (GBR) lagoon. The temporal variability in these contributions was also investigated. Sediments in river and flood plume water samples were analysed for particle size and clay mineral abundance at 31 sites across the Burdekin catchment. Sampling sites included minor tributaries, sub-catchment, reservoir and end-of-river outlets, and the adjacent coastal flood plume. Samples were collected during multiple wet season streamflow events from 2005-2011. Particle size data were used to calculate catchment-wide fine sediment (< 10 mu m) and clay-only (< 4 mu m) budgets, and a clay mineral ratio was used to distinguish geological source areas. This sediment source tracing study identified basaltic, granitic and sedimentary geologies as the dominant sources of end-of-river and flood plume fine sediments (< 10 mu m) across the Burdekin. A clay mineral ratio (illite/illite + expandable clays) clearly distinguished between the two main catchment source areas (Upper Burdekin and Bowen River sub-catchments), highlighting the importance of considering both of these sources for management of the finer sediment fractions that are potentially more ecologically damaging in the marine environment. This ratio also highlighted the relative enrichment of expandable clays (i.e. those containing a 'shink-swell' smectitic component) along the salinity gradient within remaining flood plume fine sediment. The distinctive geological source-related 'fingerprints' found in this study validate the relative proportions of clay minerals as a valuable tracing tool in large and geologically complex catchment settings and across freshwater-marine continuums.