Comparison of Amendments and Management Practices for Long‐Term Reclamation of Abandoned Mine Lands

Abstract

AbstractAbandoned mine lands containing pyritic spoil may become toxic due to production of sulfuric acid and subsequent high levels of heavy metals. A field study was initiated to compare the long‐term (10 yr) effectiveness of digested municipal sewage sludge (224 Mg ha−1), powerplant fly ash (448 Mg ha−1), papermill sludge composted with either coarse or line wood bark (67, 90, and 112 Mg ha−1), and limed topsoil (20‐cm depth) in maintaining a grass‐legume mixture on toxic abandoned mine spoil (initial pH 3.4). Management of reclaimed plots included an additional one‐time application of N, P, and K according to soil test 1 yr after reclamation and annual cutting of vegetation that was either removed from the plot or left on the surface. Soil was sampled at depths of 0 to 10 and 10 to 20 cm, with the lower sample representing soil (except for the topsoil treatment) to which the amendments had not been mixed. These soil samples were analyzed for pH and plant nutrients. Dry matter production declined sharply after 3 yr and then recovered the last 2 yr due to favorable weather, although to only two‐thirds of the initial levels. The topsoil and sewage sludge amendments maintained overall highest yields and highest percent vegetative cover (93 and 91%, respectively). Amended spoil experienced a gradual pH increase over the study period with the topsoil amendment exhibiting the highest pH (7.0) and fly ash the lowest pH (5.1) after 10 yr. The topsoil and sewage sludge amendments generally maintained the highest soil K, Ca, and Mg concentrations, while the sewage sludge and fly ash amendments had the highest P concentrations. pH values and P, K, Ca, and concentrations in the 0‐ to 10‐cm soil horizon were higher than in the 10‐ to 20‐cm horizon. Management did not result in differences in plant uptake of nutrients and metals, but a one‐time addition of lime and fertilizer did increase vegetative yields. We conclude that the papermill sludge and sewage sludge amendments were roughly equivalent to limed topsoil for the successful long‐term reclamation of toxic mine spoil. The fly ash amendment was least successful due to its inability to provide pH and nutrient levels sufficient for the maintenance of good vegetative growth.