The role of coastal floodplains in generating sediment and nutrient fluxes to the Great Barrier Reef lagoon in Australia

Floodplains adjacent to the Great Barrier Reef (GBR) lagoon in Australia are sources of pollutants that may degrade this unique marine ecosystem. Much of the contaminant load is transported to the ocean in large flood events, where over bank flows are not well recorded by standard river gauges. This paper describes the estimation of flood discharge and measurements of sediment and nutrient concentrations in flood waters on the Tully and Murray floodplains in northern Queensland, Australia. These data were combined to estimate the loads of sediment and nutrient delivered to the GBR lagoon during three floods in 2007. We found that the floods made a very significant contribution (>50%) to the marine load and that there was more dissolved organic nitrogen (DON) than dissolved inorganic nitrogen (DIN). As this is the opposite of their concentrations in river water, DON loads to the ocean may be nearly twice those previously estimated from riverine data.