Review: Sediment-related controls on the health of the great barrier reef

Linking terrestrial soil erosion to the degradation of marine ecosystems relies on a long chain of evidence. Here, this chain of evidence is reviewed for Australia’s Great Barrier Reef and its catchments. Excessive sediment delivery to the marine environment is one component of an interlinked group of stressors that include coral bleaching, damage by storms, and plagues of crown-of-thorns starfish. Sediment and the pollutants they carry are one of the drivers of marine ecosystem decline and adversely impact recovery following disturbance by other stressors. Significantly, a portion of the N species carried by fine sediment in the freshwater system is released in the marine environment, thereby perturbing marine ecology. Available controls on sediment and pollutant delivery are hillslope erosion rates, gully and streambank erosion rates, sediment deposition rates in sediment sinks including footslopes, floodplains, and water reservoirs, and the application rates of pesticides and fertilizers. By reducing sediment fluxes through the combined strategies of erosion control and deposition enhancement, near- and offshore impacts can be reduced. Gully and streambank erosion are more significant sources of fine sediment than hillslope erosion. Fertilizer and non-fertilizer N and pesticides carried by sediment play an important role in coral reef degradation. A graphic summary of the spatial configuration the sources and sinks is provided to guide the prioritization of interventions. The scale of intervention required to achieve the desired marine outcome is so large that a combined voluntary and regulatory approach is needed.