Early data shows encouraging progress at Mt Pleasant Learning Hub

The 2019-20 wet season monitoring results are in for the Mt Pleasant Learning Hub and they show an improvement in vegetation on the hillslope and the gully of the treatment site.

The Mount Pleasant Learning Hub, featuring Mulloon Institute landscape rehydration techniques, has been designed to reinstate the hydrological function of the landscape.

Treatment works were completed in 2019. The site is a good demonstration of what can be achieved to improve water quality on a stable gully system that is no longer active.

Data reported through CSIRO from the 2019-20 wet season shows improvements in vegetation on the hillslope and the gully of the treatment site. 

Two biodiversity assessments were conducted by James Cook University (JCU) officers at the rehydration site and reference sites pre-wet November 2019 and post-wet May 2020, with interesting results. 

Monitoring rehydration

Data reported through CSIRO from the 2019-20 wet season showed improvements in the Mt Pleasant vegetation, on the hillslope and in the gully. 

This site has the lowest fine sediment concentrations measured across all BBB gully remediation sites, measuring a mere ~60mg/L. This is almost 800 times less fine sediment concentrations than the two largest gully sites being monitored through the LDC project, attributable to the land condition of the catchment feeding into this system. 

Agrotek soil moisture probes continue to validate the rehydration treatment is consistently maintaining total soil moisture levels (through the top 80cm profile) in excess of 7 per cent  higher than the control site (41.47 per cent compared to 34.17 per cent volumetric water content). 

This means that for each cubic metre of topsoil, the treatment site is holding more than three additional cups of moisture on average than the control site. This is great for plant growth, ground cover and biodiversity habitat.

Biodiversity surveys

JCU undertook two biodiversity assessments at the rehydration site and reference sites (pre-wet November 2019 and post-wet May 2020 assessment). 

It is challenging to detect significant changes at this scale in coarse biodiversity metrics within short timeframes. Looking closely at specific fauna, it was found that the rehydration site supported a higher abundance of amphibians, while reference sites supported a higher abundance of reptiles. 

Mammal and bird abundance and richness were similar between treatments. Amphibian abundance was significantly higher at the rehydration site during the post-wet survey. 

This increase in amphibian activity is likely to be a  result of the persistent water bodies around the log dams in the rehydration site. Therefore it can be concluded that the restoration structures have successfully retained water after heavy rains, slowing down drainage, and making ephemeral water bodies accessible for wildlife, especially frogs. 

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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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