Reducing end-of-catchment fine sediment loads and ecosystem impacts
Led by: Dr Johanna Johnson, RRRC
A wide range of NESP TWQ Hub projects have focused on the source, transport, fate and impact of sediments on estuarine, coastal and reef ecosystems. These projects have responded to the Reef 2050 Plan water quality targets and Water Quality Improvement Plan aiming to reduce the loss of sediments from catchments to the marine environment. To better manage sediment losses and prioritise remedial actions, it is important to be able to understand and contextualise all of the issues that are involved in this sediment story, from managing catchment sources to defining which types of sediment cause the most harm in the marine environment. The synthesis report will include a list of gully prioritisation tools and sampling methods for detecting sediment and bioavailable nutrients. This project will provide a narrative and synthesis to bring all these threads together. Synthesis of this new knowledge will provide advice on practical on-ground actions for land and sea managers, policy implications and identify remaining gaps for future research and management investments.
Significant effort over the last decade has been directed at reducing nitrogen run-off to the GBR from catchments. A 25% reduction in anthropogenic end-of-catchment fine sediments loads is a target for 2025 under the Ref 2050 Water Quality Improvement Plan (WQIP). The 2017-2018 Reef Report Card shows that despite this considerable investment, progress towards this target is limited. A wide range of projects from repairing gullies in grazing lands to tracking the dispersion of fine soil particles have been commissioned to engender improved land management practices in the grazing lands from which problematic sediments originate.
Throughout the NESP Tropical Water Quality Hub, a cluster of research projects have been developed around the research priority to seek solutions to sediment reduction through an understanding of sediment sources, sediment suspension, the impacts of dredging, gully rehabilitation and improved management in upper and lower catchments of the Great Barrier Reef. In addition to managing the sources of sediment, research has also examined where sediment disperses in the marine environment and how to monitor, measure and report on its dispersion and impact upon coral and seagrass communities.
The objectives and outcomes of this project are to:
- Synthesise the NESP TWQ Hub funded research outcomes that have advanced the science towards reducing end-of-catchment sediment loads (and associated particulate nutrients) impacting on coastal and reef ecosystems;
- Highlight the interactions between sediment and bioavailable particulate nitrogen (BPN), including the interactions between sediment, BPN and dissolved nutrients that are critical to understanding the effectiveness of rehabilitation works; and
- Provide a summary of future research and activities required for on-ground investment.
The synthesis project will have the capacity to draw together information from projects across the entire scope of the NESP TWQ Hub, plus external material where relevant, including relevant ecosystem impacts documented by the Marine Monitoring Program. This synthesis will take a source-to-sea approach, beginning with the tracing of sediment source hot-spots in catchments; approaches for remediation of those sources; delivery of sediments and transformation/desorption of nutrients attached to sediment; fate and dispersion of catchment-derived sediments in the marine environment; impacts upon key marine habitats (coral and seagrass) and the spatial extent of these impacts in the GBRWHA; and methods for measuring and reporting upon reduced light availability as a result of catchment-derived sediment in the marine environment. Synthesis outputs will consider relevant existing tools, such as the GBRF prioritisation tool and incorporate information from FORAGE, Groundcover and Erodible. The synthesis may, where identified as important, analyse existing data that makes a beneficial contribution to the synthesis.
Outcomes from the following NESP TWQ Hub projects will inform the synthesis products:
- Project 1.2: Developing an approach to evaluate the effectiveness of investments in riparian management in the GBR catchments.
- Project 1.3: A validation of coral geochemical records to reconstruct suspended sediment loads to the Great Barrier Reef.
- Project 1.7: Reducing sediment sources to the Reef: testing the effectiveness of managing alluvial gully erosion.
- Project 2.1.4: Demonstration and evaluation of gully remediation on downstream water quality and agricultural production in GBR rangelands.
- Project 2.3.1 / Project 5.3: Benthic light as ecologically-validated GBR-wide indicator for water quality: drivers, thresholds and cumulative risks.
- Project 3.3: Light thresholds for seagrasses of the GBR: a synthesis and guiding document for managing seagrass.
- Project 3.4: Developing and refining biological indicators for seagrass condition assessments in an integrated monitoring program.
- Project 2.1.5: What’s really damaging the reef? Tracing the origin and fate of the environmentally detrimental sediment.
- Project 2.1.9: Risk assessing dredging activities.
- Project 2.1.10: Achieving maximum reductions of sediment loads to the GBR on the shortest possible timescales: the application and adaptation of mine site rehabilitation approaches to alluvial gully rehabilitation in the Bowen catchment.
- Project 3.1.4: Optimizing the management of riparian zones to improve the health of the Great Barrier Reef.
- Project 3.1.7: Reducing sediment loads to the Great Barrier Reef – developing optimal approaches for treating alluvial gully erosion.
- Project 3.2.1 / Project 5.4: Deriving ecologically relevant load targets to meet desired ecosystem condition for the GBR: a case study for seagrass meadows in the Burdekin region.
- Project 4.9: Gully characterisation framework to underpin GBR catchment water quality management.
- Project 4.11: Sources, transformations and fate of dissolved organic carbon – implications for the reef.
- Project 5.8: What’s really damaging the reef? Tracing the origin and fate of the environmentally detrimental sediment and associated bioavailable nutrients.
- Project 5.9: Gully remediation effectiveness.
- Project 5.10: Development and application of automated tools for high-resolution gully mapping and classification from LiDAR data.
- Bioavailable Nutrients outputs (DES/NESP TWQ Hub).
Key project deliverables:
This synthesis will make a significant contribution to the next Scientific Consensus Statement of which sediment management and reduction is a key component. It will also help inform investments in improved water quality required under the Reef Trust Partnership and this synthesis will be conducted in parallel with the Major Investment Project (MIP) being conducted in the Burdekin catchment by NQ Dry Tropics.
NESP 2017 Research Priority Alignment
This project aligns with NESP 2017 Research Priority: Improved understanding of the impacts, including cumulative impacts, and pressures on priority freshwater, coastal and marine ecosystems and species (Theme 1)
This project aligns with TWQ Hub 2018 Research Priority 3. Improving water quality emanating from catchments.
Sediment; Catchment; Great Barrier Reef; Ecosystem; Gully.
This project is jointly funded through JCU, CSIRO, GU, AIMS, DES, DES – OGBR, C2O and the Australian Government’s National Environmental Science Program.