Rehabilitation studies on saline land caused by potash mining activity
Thorpe, Mark Bramley
The salinity at the waste management areas at potash mines is extreme. Saturated brine seeps from the tailings pile and contaminates the surrounding land killing vegetation and affecting soil structure. Conventional saline land reclamation practices cannot be applied directly because of the high salt concentrations and the continued inputs. Some major modifications of saline land reclamation practices are, therefore, required. Some of the factors affecting the movement of NaCl into areas of comparatively low salinity surrounded by extreme salinity were investigated. Methods of rehabilitating extremely saline areas with high NaCl inputs, by applying amendments and using salt tolerant vegetation, were investigated using field plots, a greenhouse column study, laboratory testing of the salinity tolerance of vegetation and the Trasee /Tracon computer model. The movement of Na upwards in the profile of an area of low salinity was affected by the [Na] in the base of the profile and climate, in the form of evapotranspirational losses. The vegetation cover did not affect the movement of Na. To maintain low [Na] in the soil profiles, the [Na] in the saline base must be kept low and, where possible, the water table kept low. In the revegetation trials, the movement of Na into the sewage sludge amendments was slower than into the topsoil amendments. This affected the vegetation which became established on the two amendments. The vegetation on the topsoil amendment was all killed after 3 months but the vegetation on the sewage sludge amendment remained for the 3 years of the field trial. Of the five species of grass planted, Agropyron trachycaulum and Elymus junceus proved to be best suited to the saline conditions on the sewage sludge amendment. These species also showed considerable salt tolerance at germination and at the mature stage in the laboratory. The greenhouse column study also showed that the movement of Na in to the topsoil was faster than into the sewage sludge amendment. The surface of the sewage sludge amendment dried out, reducing evaporation from that amendment, indicating that evaporation driving the mass flow of water and Na into the amendment might be the key factor affecting the movement of Na in to the two materials. The Trasee /Tracon computer model indicated that the surface evaporation from the sewage sludge was less than from the topsoil. The model accurately simulated Na movement in both the field and column studies. Potential revegetation scenarios are also discussed.