Paired geochemical tracing and load monitoring analysis for identifying sediment sources in a large catchment draining into the Great Barrier Reef Lagoon

• Sediment tracing was applied to gauged river catchments with load monitoring data.
• Sediment tracing identifies preferential delivery of clay though large impoundment.
• Recognized uncertainty of load monitoring data was constrained by tracing results.
• Dominant spatial source of fine sediments was identified and discussed.

While sediment tracing has been typically applied to identify sediment sources that are difficult to measure by gauging (monitoring), it can also be useful in estimating relative sediment yields from gauged river catchments. The major and trace element composition of river sediments from eleven locations in the 130000 km2 Burdekin River catchment, northeastern Australia was analysed to examine relative contributions from upstream source areas in the 2011/12 water year. Sediment tracing results are compared against estimates derived from sediment load monitoring at three locations. Comparisons show that there is good agreement between tracing results and monitoring data at one of the tributary confluences. At the second site, notable contrasts were found between the load estimates from the monitoring and tracing data. At this site a large impoundment occurs between the upstream sampling/gauging sites for source sediments and the downstream sampling/gauging sites for target sediments. The contrast is likely caused by temporal variations in particle size distributions of suspended sediment from each river and differential trapping efficiencies in the impoundment for sediment derived from the different tributaries. In the absence of the detailed particle size data and trapping efficiency estimates, sediment tracing provides the unique opportunity to elucidate source contributions of the finer fractions of suspended sediment. At a third site, where there were recognised measurement gaps in the monitoring data during large discharge events, the relative load estimates from the tracing data provided a means of constraining the recognized uncertainty of monitored load estimates. We conclude that sediment tracing can be used as a valuable adjunct to monitoring data particularly in remote, large and data-sparse catchments. Both tracing results and monitoring data show that the Upper Burdekin River and Bowen-Bogie Rivers were the dominant source of the < 10 μm sediments being delivered to the GBR lagoon from the Burdekin River catchment in the 2011/12 water year. More substantial contribution from the Belyando-Suttor Rivers indicated by the tracing results than the monitoring data is attributed to preferential delivery of the 1–10 μm sediments through the impoundment and has uncovered a knowledge gap in sediment budgets in the catchment.