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| April 2006 | National Research Flagship | www.csiro.au/healthycountry/ |
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| April 2006 | National Research Flagship | www.csiro.au/healthycountry/ |
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Assessing land condition and sediment delivery in Great Barrier Reef catchments
The transport of sediment and nutrients to the GBR lagoon has quadrupled since the introduction of European-style agriculture. It is strongly seasonal and driven by major episodic rainfall events. It is also influenced by land condition and management, climate and geomorphology. The challenge in
managing the land-ocean system in the region is to make assessments at large
spatial and temporal scales in a system driven by a highly variable climate.
Using the Burdekin-Fitzroy Basins, this study examined the
potential for using Earth Observation - remote sensing, supplemented with
long-term in-situ observations.
Findings: dynamics of vegetation, run-off and sediment As expected, analysis of vegetation greenness using satellite imagery showed a strong correlation with rainfall. However, the analysis also showed that the maximum green flush occurs some three months after and in response to rainfall, and that the year-to-year variations in both rainfall and vegetation response exceed the variations associated with the seasonal cycle. Hence, the system is predominantly driven by interannual variability, largely associated with major episodic rainfall events in the wet season. Managing the land-ocean connection in the GBR lagoon is therefore linked with the problem of predicting these large events and the system response to them. The study examined the performance between 1981 and 2004 of a standard seasonal climate prediction approach based on the Southern Oscillation Index (SOI). It was found that SOI is a fairly weak predictor of rainfall and vegetation greenness, highlighting the need for improved seasonal climate prediction approaches. Sediment dynamics in the lagoon were also analysed using a method developed by the team and based on the long-term record (1981-2004) from NOAA-AVHRR* satellites. Results were compared with more modern sensors that provided higher-quality but shorter records of sediment level. Behaviour of the sediment plumes is consistent in the long-term: the Burdekin plume has a systematic northward trend, while the Fitzroy Estuary sediment is dominated by macrotidal activity. Long-term trends indicate that much sediment activity occurs in the shallow parts of the lagoon as a result of tidal and wind re-suspension. The study also discerned limitations of existing approaches for measuring sediment levels in the highly turbid, near-coastal waters of the GBR lagoon, caused by inadequate knowledge of and accounting for the optical properties of these waters. A symptom of these weaknesses is a tendency in the remote sensing record of sediment levels to saturate at high sediment loadings. Ongoing work is improving this situation. An estimate of ground cover at the onset of the wet season is also needed for input into models of sediment movement, particularly to characterise the extent to which vegetation suppresses erosion.
Findings support the use of long-term remote sensing to discern patterns and trends in vegetation cover and sediment levels in the GBR lagoon, while recognising the different spectral properties and interpretation algorithms among the various available satellite-borne sensors. The project identified several significant weaknesses in standard indices. For example, standard global products assume a correlation between suspended matter and chlorophyll which is only true for clear ocean waters and not appropriate in the GBR region. Also, GBR-lagoon-specific algorithms that independently estimate all optical components for determining the colour of water would improve detection sensitivity and estimation of sediment composition. Future monitoring for land-ocean dynamics in GBR catchments would integrate monitoring of real-time landscape, vegetation, riparian and in-stream processes, together with a system for tracking sediment, run-off, coloured dissolved organic matter and nutrient-driven algal blooms. Short-term monitoring could include determining risks of impacts from land management activities, and monitoring to establish sediment and nutrient budgets to provide risk assessments of sediment and nutrient inflows, and weather and tidal conditions. The Report: Use of Earth Observation to Assess Land Condition and Sediment Delivery in Great Barrier Reef Catchments: a Feasibility Study. MR Raupach, B Schoettker, PR Briggs, JL Lovell, EA King, K Oubelkheir, A Marks, VE Brando, G Byrne, PA Dyce, AG Dekker, DJ Barrett, J Brodie
For more information please contact: |
IN THIS EDITION:
Building a Water Resources Observation Network Science supporting the Living Murray Giving revegetation strategies the edge Real-time monitoring helps irrigators to be water wise Determining requirements for managed aquifer recharge in WA Assessing land condition and sediment delivery in Great Barrier Reef catchments A community creating its future options WaterSmart Irrigation in the Murray Meet some scientists from the Water for a Healthy Country Flagship Meet some students from the Water for a Healthy Country Flagship |
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Water for a Healthy
Country Flagship |
Phone: +61 02 6246 4565 Fax: +61 03 6246 4564 | editor.healthycountry@csiro.au www.csiro.au/healthycountry/ |
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Transport of water,
sediments and nutrients from land to river, estuary and sea have important
physical and ecological consequences in the Great Barrier Reef (GBR) lagoon.
Understanding the processes behind these consequences - how they vary and
how they respond to other influences - is critical to better managing the
system and monitoring water quality targets as outlined in the GBR Water
Quality Protection Plan. Improved understanding and better monitoring are
important steps in reducing the flow of sediments and nutrients to the GBR
lagoon, one of the goals of the Water for a Healthy Country Flagship.
Roles of Earth
observation
