What’s really damaging the Reef? Tracing the origin and fate of the environmentally detrimental sediment

Stephen Lewis
Led by: Dr Stephen Lewis, JCU


Project Summary

Recent research has shown that only a portion of the fine sediment fraction delivered from rivers draining into the Great Barrier Reef Lagoon (GBRL) reaches coral reefs and seagrass meadows. The specific sources of this sediment, which affects the health of corals and seagrasses, are as yet unresolved. This project will, for the first time characterise and trace the origin(s) and fate of this environmentally detrimental sediment using samples collected in flood plumes and during resuspension events. This will enable direct spatial targeting of the sources of this material to achieve maximum benefits to GBR health from catchment management actions.

Problem Statements


Recent research tracing the sources of sediments exported from the mouth of the larger rivers draining into the Great Barrier Reef Lagoon (GBRL) including the Burdekin, Normanby, Fitzroy, Johnstone and Herbert Rivers, have identified both the dominant erosion processes and sources of the sediment. This work has provided important knowledge on specific areas contributing higher sediment yields; however the transport, fate and impacts of recently delivered catchment sediments within the GBRL have received less attention. The available data show that most (>80%) of the sediment load from rivers is deposited and largely retained near the river mouth with a much smaller proportion transported further afield; this sediment fraction has certain properties (i.e. particle size, clay mineralogy, organic content) which allow it to be transported greater distances in the marine environment where it can reach coral reefs and seagrass meadows. Furthermore this sediment is likely to be more easily resuspended and influence water clarity along the inner shelf of the GBR over both short (flood plume) and longer (months following plume) timeframes. Unfortunately, little data exist on this ‘environmentally detrimental sediment’ and its within-catchment origin is unknown. If its origin were known targeted catchment works could be used to reduce these specific sediment sources.

How Research Addresses Problem

We will characterise the physical, biogeochemical and isotopic composition of suspended sediment samples from flood plumes and resuspension events. This characterisation will Alignment with NESP Research Priorities enable us to trace the within-catchment source of the sediments and give insight into the various sediment and nutrient transformations that occur as fine clay-sized sediment moves from ‘catchment to reef’. This project will test our hypothesis that the composition of newly delivered clay-sized sediment to the GBRL changes during transport, deposition and resuspension, with increasing importance of the biological component. Newly designed sediment traps that for the first time allow for collection of sediment in resuspension events will be utilised. Particle size, clay mineralogy, biogeochemical and isotopic characteristics of the analysed samples will be used to identify the ‘most environmentally detrimental sediment’ in terms of transportability and nutrient bioavailability. The organic component of the floc aggregates will also be characterised to determine if they are of catchment or marine origin and how they change during successive resuspension events. Combined with existing sediment tracing data from the catchments, this new information will then be used to identify the origin of this problematic sediment so that catchment management priorities can be further refined. In addition to providing critical information for targeting catchment sources of environmentally detrimental sediment, this work also has significant applicability to port management and dredging as it examines the changing sedimentary nature of resuspension events throughout the year

Alignment with NESP Research Priorities

1b) Determining the source and marine fate of environmentally relevant sediments.

1a) Local scale identification of priority contaminant export loss (hot spots) for better targeting of on-ground works and extension activity.

4b) Quantify sediment transport pathways and water quality over relevant timeframes to better understand interactions with, and contributions to, the broader catchment inputs within the GBR.

Project Keywords

Sediment floc aggregates; Sediment tracing; Resuspension; Turbidity; Flood plume.

Project Funding

This project is jointly funded through JCU, GU, DEHP, DSITI and the Australian Government’s National Environmental Science Programme.

Project Publications






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