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Sustainability Research Unit

05/05/2017

The rehabilitation of mine land after a mine has closed can take several years to achieve and cost millions of rands; however, according to a study undertaken by researchers at the University of Pretoria (UP), the application of dung beetles and dung can go a long way towards helping nutrient- deprived soil regain its former glory.

Environmental consulting company Confluent Environmental MD Dr Jackie Dabrowski, who is also a research associate at UP and the Nelson Mandela Metropolitan University, led a four-person research group in a three-year study into the effects of using dung beetles and dung to rehabilitate degraded soil on coal mines.

The research is funded by coal research association Coaltech.

The study concludes at the end of this year, and has thus far proved to be a highly viable option as a complementary method for the rehabilitation of degraded soil, according to Dabrowski. She explains that dung beetles and their natural and speedy act of burying dung improves three of the most compromised soil health factors affecting rehabilitated mines: soil compaction, water infiltration and plant biomass development.

These three problems are most prevalent in rehabilitated mine soil, as soil is stockpiled for several decades (sometimes as long as 50 years) when an area is mined. This removal of soil and subsequent long-term stockpiling lead to a number of detrimental effects, such as a high degree of compaction and mixing of soil horizons. Top soil, otherwise known as the A-horizon (which is rich in nutrients), is mixed with subsoils (much poorer in nutrients) and leads, in turn, to greater compaction and severe loss of nutrients and organic matter.

Once this mixed soil is eventually replaced over the mined-out area, Dabrowski says, it is of such a poor quality that vegetation (chiefly, grass) struggles to grow, and requires a multi- step approach to improve the various elements required for vegetation to thrive. For example, she points out that conventional methods to improve nutrient levels in the soil, such as the addition of fertilisers, and compaction using a mechanical ripper, are both costly and have to be repeated several times to achieve a satisfactory, yet temporary, outcome.

However, she notes that, with the simple act of introducing dung beetles and cattle dung pads on the affected land, nature can take its course, and these interventions potentially have a longer-term effect on the environment.

There are 650 different species of dung beetle in South Africa, and it is the most commonly unseen tunnelling species (not the type most commonly seen rolling dung balls on the soil surface) that has proved most successful in rehabilitating mine land soil. These lesser known, and lesser seen, dung beetles have the ability to seek out dung by smell and fly several kilometres to locate it.

She says that, once these dung beetles find dung pads, they immediately walk into them, take out a chunk and bury the dung at a depth of 10 cm to 20 cm. This act of tunnelling and burying dung introduces both aeration and nutrients back into the soil and the buried dung acts as a natural fertiliser. “This is happening in the plant root zone, so the benefit to plant growth and nutrient content and overall biomass is really well established.”

Dung beetles have the ability to bury large amounts of dung in a short timeframe. “If there are warm temperatures and sufficient rainfall, then they can bury a 1 kg dung pad within 12 hours,” Dabrowski notes.

She explains further that the beneficial impacts include a reduction in soil compaction as the dung beetles create a number of micro- and macropores, owing to the different sizes of dung beetle species burrowing into the ground. “These different-sized tunnels persist in the soil for a number of months after the activity of the dung beetles.”

These tunnels assist in water infiltration and reduce soil compaction – the most profound problem on rehabilitated mine land. For dung beetles to be used successfully to rehabilitate mine land, Dabrowski explains, a breeding programme will need to be established to ensure sufficient numbers of dung beetles are introduced onto the affected land. A dung source needs to be provided in the form of grazing cattle, or through the collection and placement of dung on the land. Both these options bring with them job creation potential, as they require low levels of skills and investment.

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