Surface Environment

Recharge factors of 23.5 per cent and 12.9 per cent were calculated at the two rehabilitated pits with complete data. The higher value reflected surface drainage towards the pit centre and eroded topsoil; the lower one, a deep pit floor with well compacted spoil and intact cover. The rates are site specific and no generic formula could be derived.

Experimental studies tested ways to alleviate compaction on mine soils by combining mechanical treatment with organic material. Survival of 16 pasture species was recorded on mechanically ameliorated compacted soil, dry matter and leaf area were measured for tall fescue and cocksfoot at different levels of organic material, and soil fertility, bulk density and root biomass were tracked under irrigated and dryland grass.

Grazing trials on tall fescue pasture irrigated with gypsiferous mine water on rehabilitated mined land, run over several seasons. The work covers steer stocking rates, dry matter intake by cattle, and the factors that control pasture quality and intake, among them nitrogen fertilisation, stage of growth, sward structure and grazing intensity. Findings are reported study by study.

Ants, termites, dung beetles and earthworms are known to improve soil health, but none had been deliberately applied as part of a mine reclamation strategy. Experimental and field scale studies asked whether dung beetles maintain their burial activity, and the soil services that follow, in soils typical of rehabilitated mine land, and set out recommendations for using them alongside existing methods.

Stockpiling degraded every soil property measured across four Witbank area mines. Clay content of topsoil and subsoil rose by 50 to 60 per cent, surface bulk density increased from stockpiling through to rehabilitation, and effective depth on rehabilitated areas was under 17 cm in most cases. Topsoil organic carbon fell by almost half and microbial species numbers dropped in the stockpiles.

Gas sampling on coal mine dumps found rehabilitation very effective at cutting emissions. Even incomplete rehabilitation held carbon dioxide below about 1 kg per square metre a year, against over 100 on unrehabilitated ground and as much as 7 000 where combustion was active, though burning areas were small. Sulphur oxides, nitrogen oxides, ammonia and methane were low.

Grazing pressure on the rehabilitated block ran at roughly three times the estimated carrying capacity. The sward was dominated by low quality grasses with a high proportion of bare ground and a raised erosion risk. Fenced exclosures over one year changed the abundance of a few species, but the vegetation showed no clear direction of recovery.

Hydrogen for biological sulphate removal can be generated on site by electrolysis more cheaply than it can be bought. Stainless steel electrodes in acid mine drainage gave hydrogen at about a third of the bought in price while oxidising ferrous iron to ferric, which helps downstream treatment. Iron and zinc electrodes dissolved too quickly to be viable.

Heat exchanger material governs how fast ice scale forms during eutectic freeze crystallisation of dilute brine. Induction time fell as thermal conductivity rose, so copper scaled first, while aluminium gave the lowest scaling rate because its low surface energy pushed ice crystallisation into the bulk. Stainless steel delayed onset but scaled heavily once nucleation started.

Compared against concrete and gabions on cost, construction time, footprint, durability and safety, the Dongalock product proved cheaper and quicker to install in small and medium incised valley bottom wetlands, and needs no heavy plant, so local enterprises can build it. Concrete still suits large wetlands carrying high water velocities.

A digital wetland map and linked database were compiled for the Upper Olifants River Catchment from existing literature, existing wetland layers and aerial photography. Wetlands cover about 2 147 km2, some 14 per cent of the 15 158 km2 catchment. The wetland layer is about 70 per cent accurate and its attributes about 60 per cent, so it suits baseline screening rather than site assessment.

Ecological integrity of a Mpumalanga wetland affected by coal mining was assessed before and after rehabilitation, using water quality, bacterial consortium, freshwater algae and vegetation indicators. The work sits within a wider programme to give the coal sector and regulators practical ways of limiting and mitigating mining impacts on wetlands.