Designing Amendments to Improve Plant Performance for Mine Tailings Revegetation

To provide recommendations for establishment of plants on a low pH mine tailings, we conducted greenhouse studies on the effects of gasified conifer softwood waste biochar (BC) plus other amendments to improve the survival and growth of plants. Experiment 1 indicated that 1% lime (by weight) raised tailings pH, permitting Douglas fir (Pseudotsuga menziesii) seedling growth. However, high biosolids (BS, 2% by weight) were phytotoxic likely due to salts associated with high electrical conductivity (EC). Biochar (BC. 1, 2.5 or 5% by weight) plus lime and BS, caused an additional increase in pH, a decrease in EC, and enhanced growth of Douglas fir. Experiment 2 with Douglas fir had additional amendments: lime ( 0.5 and 1% by weight), two nutrient sources (BS and mineral fertilizer), three nutrient levels, (0.2, 0.5, 2%), BC (0 and 2.5%), and Locally-Sourced Microbes (LSM) or no LSM. While there were many interactions among amendments, in general Douglas fir growth again was enhanced with lime, biochar, and lower concentrations of nutrients. LSM had no effect on Douglas fir seedlings in either study. These studies indicated optimum additions of BC in combination with other amendments to enhance revegetation of low pH, metal-contaminated mine tailings.

Impact/Purpose

Past mining activities in the United States have left a legacy of heavy metal contaminated tailings, which need to be cleaned up to allow for healthy plants on the site, and to prevent water and soil pollution. The EPA has regulatory authority, especially under Comprehensive Environmental Response, Compensation, and Liability Act (Superfund) to oversee cleanup of these sites; and responsibility to regions, states and local communities under the Office of Research and Development’s Safe and Healthy Community Research Program to develop new techniques to assist in this cleanup. Of special concern to EPA’s Region 10 is the Formosa mine superfund site in south-central Oregon, which has a large area of degraded tailings where it is difficult to establish vegetation. This research was designed to determine if a newly developed technique, addition of biochar to tailings, could assist revegetation efforts. We evaluated the potential for biochar made from conifer wood, along with agricultural lime and nutrient sources (biosolids or mineral fertilizer), to enhance the survival and growth of Douglas fir seedlings in mine tailings from the Formosa mine site. This studies were a preliminary greenhouse screening of plants using a variety of combinations of amendments to provide information for a full-scale on-site revegetation study. The soil had an extremely low pH ( ? 2.6), but addition of 1.0% lime raised pH to above 6.5. The increase in pH decreased concentrations of heavy metals (e.g., Al and Cu) in the tailing leachate, and was necessary for seedling survival and growth. A high level of added nutrients (2%) inhibited plant growth, especially at the higher pH. Addition of biochar enhanced seedling survival, new shoot growth, and new growth K concentration, at least in part by reducing the detrimental effects of high nutrients. This study demonstrated that biochar, along with lime and nutrients, can enhance early seedling growth in mine affected soils by improving soil physical and chemical characteristics, providing immediately useful information to alleviate a tailing pollution problem in Region 10. More broadly, the study illustrated the potential for techniques developed under ORD’s biochar research program to enhance plant growth by improving tailing chemistry, thus increasing the potential for success of vegetation reestablishment to degraded mine tailings across the United States.

Citation

Johnson, M., D. Olszyk, T. Shiroyama, M. Bollman, M. Nash, V. Manning, K. Trippe, D. Watts, AND J. Novak. Designing Amendments to Improve Plant Performance for Mine Tailings Revegetation. John Wiley & Sons, Inc., Hoboken, NJ, 6(3):e20409, (2023). [DOI: 10.1002/agg2.20409]

DOI: Designing Amendments to Improve Plant Performance for Mine Tailings Revegetation