Soil sampling conducted across the BBB

The Department of Resources has collected soil samples across the BBB to help assess and understand the variability of soils in the region.

The Department of Resources has collected soil samples across the BBB to help assess and understand the variability of soils in the region.

Soil scientists from the Department of Resources are collecting soil data in Great Barrier Reef catchments where data is limited or outdated. 

The collection and interpretation of soil and land resource information is required to assess the variability of soils and landscapes, and to demonstrate how this variation affects land use, for example agricultural suitability, land management and land degradation risks. 

This field work is part of the 2020–21 Soil and land conservation technical support for priority hotspots in reef catchments project.

In April, the Department of Resources team spent time in the BBB, in particular the Broken River and Little Bowen River catchments. They worked closely with LDC field officers to shortlist sampling locations and liaise with landholders to coordinate the visits. 

Site data will help support soil characterisation and understanding in the district as well as improve input data and information into mapping products and extension activities.

This fieldwork complements updated soil conservation fact sheets which are available to the public.

  • Soils will be described for: texture, colour, mottles, structure, segregations, coarse fragments, field pH,permeability and drainage.
  • Site analysis includes: location, slope, landform element, landform pattern, surface condition, erosion, geology, lithology and vegetation (where present).
  • Representative soil core depths: 0-10 cm, 10-20 cm, 20-30 cm, 50-60 cm, 80-90 cm, 110-120 cm, 140-150 cm
  • Analyses will include: pH, salinity, exchangeable cations, particle size analysis, moisture content, organic carbon, phosphorus and nitrogen 

Results will be available in July after the samples have been analysed in a soil laboratory. 

The results will be stored on the Queensland Government’s Soil and Land Resource Information (SALI) database and is made available to the public through the Queensland Globe website and the Queensland Spatial Catalogue.

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Figure 1. Total fine sediment reduction by project type and erosion source. Inset shows the proportion of the total project area for each project type.

These estimates have been calculated using two methods: 

1) The pollutant reduction component of the Alluvium/Great Barrier Reef Foundation (GBRF) investment tool for hillslope and streambank erosion management projects; 

2) The Reef Trust Gully Toolbox method for gully erosion management projects. The LDC Water Quality Report 2020 (Waterhouse et al., 2020) highlights that a number of assumptions underlay these calculations, therefore these figures should be treated as the best available estimate of sediment reductions to date.

Preventing sediment from reaching the Great Barrier Reef

Each wet season sediment is washed into local waterways and out to the Great Barrier Reef (GBR). 

Most sediment is very fine, and can stay suspended for a long time and can travel great distances. Valuable topsoil is lost from production, and increased concentrations on the reef can be harmful to seagrasses and corals. 

Landholders in the BBB have completed 69 on-ground water quality practice changes, and it is estimated that these have contributed a fine sediment reduction of 6,154 tonnes per year from reaching the GBR. 

Of this, approximately half of the sediment savings are attributable to grazing land management changes on hillslopes and streambanks, and the other half as a result of gully remediation treatments across a broad range of scales, as shown in the graphs above. 

The table below also highlights the relatively small area of intervention in the gully management projects compared to the large sediment savings that these can achieve - 60 per cent of the sediment savings over only 4 per cent of the project area.

Table 1. Estimated sediment reductions (tonnes) from projects completed in the LDC Project to date.

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*GLMWW = Grazing Land Management Wire and Water

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*The Exploring New Incentives activity area has provided an opportunity for graziers to adopt improved land management practices through a range of activities. For some of these properties, it was the first time they signed contracts for on-ground works.

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The LDC project monitors four gully sites (represented in this table) with gold standard equipment and analysis, carried out by CSIRO.

Results have been compiled in a preliminary report from Bartley et al (2020), with the final report expected to be released by the end of 2020. The preliminary report shows all four sites have indicators of improvements, notably the Strathbogie and Mt Wickham sites.

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Reef regulations - grazing, standard conditions

  1. For land in good or fair condition (more than 50 per cent ground cover at 30 September), continue using measures to maintain land condition.
  2. For land in poor condition (less than 50 per cent ground cover at 30 September), steps must be taken to improve land condition.
  3. For land in degraded condition (less than 20 per cent ground cover at 30 September), steps must be taken to improve land condition OR prevent areas from further degrading or expanding.
  4. Keep records of measures taken and also of agricultural chemicals, fertiliser and mill mud or mill ash applied to land.
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