Health Assessment of Nickel-Contaminated Soils Linked to Chemical and Biological Characteristics

Soils contaminated historically by refinery nickel (Ni) emissions were subjected to laboratory assays evaluating soil health, including microbial function, biomass, and community diversity, based on high-throughput DNA sequencing. The assays showed that soils with >500 mg kg(-1) total Ni had lower microbial biomass and respiration rates as well as reduced microbial diversity and shifts in prevalent phyla compared with most soils with lower Ni. Soil testing for nutrient status suggested additional limitations due to factors other than Ni contamination, including deficiencies of Mn and other essential elements that could possibly explain reduced microbial function even in relatively uncontaminated soils. A greenhouse soybean assay showed greater Ni uptake from soils with the highest total and 0.01 M CaCl2-extractable Ni, with one of the high-Ni soils (1900 mg kg(-1) total Ni) having a level of CaCl2-extractable Ni predicted to reduce soybean growth by >25%. The study revealed that conventional macroscopic measures of soil health were reflected at the microscopic scale by differences in microbial community composition and diversity as evidenced by DNA analysis. Although soil health indicators were affected by high Ni bioavailability, other factors attributable to local differences in fertility status and organic matter content appeared to have strong influences on these indicators.