PS 3-35 - Put the lime in the mine waste: Results of a four-year revegetation experiment on abandoned coal mine overburden

Abstract: The Appalachian Region has been greatly affected by surface and coal mining, including the dumping of mine waste, or overburden, in valleys next to streams. Overburden piles contain loose acidic soils contaminated with heavy metals, bear little to no vegetation, and easily erode into streams. Reclamation of large sites involves voluminous topsoil, plant material, labor, and cost, while small, isolated sites are often neglected.



In 2018, an isolated overburden pile above a first-order stream in southwestern Pennsylvania was selected to test methods for low-cost and low-impact revegetation and stabilization. Five soil treatments (control, lime, straw, mycorrhizae, and combination of treatments) and four plant types (little bluestem, lavender, annual ryegrass, and native seed mix) were used across 60 0.61-m2 plots in the complete random design experiment. In Summer 2022, we measured the height of the tallest stem, abundance of stems, and assessed plant cover. The effects of soil treatment were determined by using the Kruskal-Wallis and Dunn tests to identify significant effects of treatment combinations.



Soil treatments that displayed the most plant growth were the lime and combination treatments, while little bluestem and the native seed mix were the most successful plant treatments across all soil treatments. There was a difference in little bluestem abundance (P=2.2 x 10-16) and cover (P=2.2 x 10^-16) across soil treatments , but the soil treatments were not significantly different from each other. Similarly, native seed mix abundance (P=4.681 x 10-16) and cover (P=4.681 x 10-16) were not the same across soil treatments, yet no soil treatments were significantly different from each other. The combination soil treatment was the most effective at facilitating plant growth; however, this treatment is the least cost effective ($21,808 per acre) compared to the lime alone ($1,993 per acre).



Mitigation of soil pH with lime and use of native plants, especially grasses, produced the most cost-effective revegetation outcome in this experiment. Given the high temperatures of the dark-colored overburden in the Summer and lack of organic material in the overburden, straw, wood mulch, or a similar material should improve plant success. At approximately $2,550 per acre for use of lime and little bluestem seed, isolated coal mine overburden sites could grow this important native grass for soil binding, soil organic matter, surface temperature reduction, and shading to improve conditions for other plant species to eventually colonize the material.