Sediment Sources to the Great Barrier Reef – what if the coastal zone is a major sediment source rather than a sink?

Abstract

Sediment budgets constructed for the catchments draining to the Great Barrier Reef World Heritage Area (GBRWHA) have tended to assume that coastal plains can typically be considered to act as sediment sinks, where a significant proportion of sediment sourced from the catchment tends to be deposited. In this paper, we present preliminary evidence from the coastal plain around Princess Charlotte Bay (PCB) in the northern Great Barrier Reef (GBR), which suggests that rather than acting as a sediment sink, the extensive coastal plain through which the major rivers draining the Normanby Basin flow, is in fact a major sediment source. Geochemical tracing data suggests that the coastal plain source is in fact responsible for delivering up to four times more sediment to PCB than the entire catchment in recent decades. More research is required to disentangle the drivers of this erosion and the relationship between floods, tides and storm surges as the primary mechanism responsible for removing the sediment from the coastal plain and transferring it to the PCB. We also speculate that such processes may be much more widespread than previously thought throughout the coastline adjacent to the GBRWHA, and suggest that much greater focus needs to be placed on understanding the processes within the coastal zone interface between the Reef Catchments and the GBR lagoon.