Biochar and Other Amendments For Douglas fir Survival and Growth on Acidic Mine Tailings

In the western US and in other nations, there are many abandoned mine sites with heavy metal contaminated tailings that prevent the reestablishment of vegetation and contaminate local ground and surface waters. Successful growth of plants on these sites is often limited by low tailings pH and high tailings heavy metal concentrations, poor structure, compaction, diminished water holding capacity, and limited fertility, carbon, and microbial activity. In a field study at an abandoned mine, we evaluated the effects of a mixture of amendments (lime, biosolids, biochar, locally sourced microbes) on tailings pH and metal concentrations and subsequent impacts on injury, growth and needle elemental concentrations for Douglas fir [Pseudotsuga menziesii (Mirb.) Franco] over multiple years. One year post tree planting, the tailings had increased pH, lowered metal availability, and increased moisture retention resulting in seedling survival, growth, and adequate needle nutrient contents for growth; while reducing needle heavy metal concentrations, such as Cu. However, four years post planting, tree growth slowed and trees exhibited nutrient deficiency which may be alleviated by additional fertilization. This study highlights the potential for amendments that include biochar, to enhance plant growth by improving soil chemistry and physical conditions. Our amendment recipe includes approximately 2.5% biochar (by weight), along with lime (1%) and biosolids (0.25%), to promote tree survival and growth on mine tailings. This study also points out the necessity for long-term monitoring of plant responses so that if needed, additional amendments such as biosolids or lime can be added to sustain tree growth.

Impact/Purpose

Past mining activities in the United States have left a legacy of heavy metal contaminated soils, which need to be cleaned up to allow for healthy plants on the site and to prevent water and soil pollution. 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 on the soil surface where it is difficult to establish vegetation. Successful growth of plants at this sites is limited by low tailing pH and high tailing heavy metal concentrations, poor structure, diminished water holding capacity, and limited fertility, carbon, and microbial activity. In a field study at the abandoned mine, we evaluated the effects of a mixture of amendments (lime, biosolids, biochar, locally-sourced microbes) on tailing pH and metal concentrations and subsequent impacts on injury, growth and needle elemental concentrations for Douglas fir [Pseudotsuga menziesii (Mirb.) Franco] over multiple years. One year post tree planting, the tailings had increased pH, lowered metal availability, and increased moisture retention resulting in seedling survival, growth, and adequate needle nutrient contents for growth; while reducing needle heavy metal concentrations, such as Cu. However, four years post planting, tree growth slowed and trees exhibited nutrient deficiency which may be alleviated by additional fertilization. This study highlighted the potential for amendments including biochar, to enhance plant growth by improving soil chemistry, and provides a recipe of approximately 2.5% biochar (by weight), along with lime (1%) and biosolids (0.25%), to promote tree survival and growth on mine tailings. The study also points out the necessity for long-term studies to monitor plant response over time and to add additional amendments to sustain tree growth.

Citation

Olszyk, D., M. Bollman, M. Nash, K. Trippe, V. Manning, D. Watts, J. Novak, AND M. Johnson. Biochar and Other Amendments For Douglas fir Survival and Growth on Acidic Mine Tailings. SETAC Europe, 33rd Annual Meeting, N/A, Dublin, IRELAND, April 30 - May 04, 2023.