The biggest difference came from aluminum in the top organic layer of soil, with concentrations declining at 14 locations by an average of 40 %. (scientificamerican.com)
Scientists took samples from the top organic layer of soil and the underlying mineral layer. (scientificamerican.com)
«In the boreal region, there is a thick organic layer on the surface comprised of litter and soil, that in some cases is hundreds to thousands of years old,» Mack said. (sciencedaily.com)