When Soil Goes to Sleep: Looking Into It Across An Anthropogenic Threshold.

The soil on our planet is a dynamic and multipart interactive environment of minerals, organic material, water, gasses, and living organisms. This complex nature of soil environment is particularly important with regard to the services it provides for food and biomass production, environmental interaction (storage, transformation and filtering), biological habitat and gene pool, and source of raw material. Due to this epic importance of soil in sustaining life on the planet, we therefore have to understand its sensitivity towards various human actions. In this study, to assess when soil geos to functionally sleep across a long-term pollution (copper) gradient, a number of soil chemical (Total and bioavailable copper, and pH), physical (texture, organic carbon, and EGME surface area), biological (earthworm density, plant species richness, and bacterial richness and diversity), and functional markers (soil-water retention, pore size distribution, air permeability and gas diffusivity) were extensively measured. The experimental site (7200 m²) is located at Hygum, Denmark, which was contaminated with CuSo₄ during timber preservation operations from 1911 to 1924. Total Cu concentration varied from 21.5-3837 mg kg^-1, and all measuremnts were carried out at 5 points along this gradient. The soil texture was a sandy loam with soil organic carbon increased from 1.97 to 3.47%, whereas total porosity decreased from 0.54 to 0.47 cm³ cm^-3 along the gradient. Biotic functions of soil were found significantly affected (negative) with increasing soil Cu concentrations along the gradient. The resulting soil functional markers were also significantly affected with increasing Cu concentrations of soil mainly due to severe deterioration of soil biotic functions. The combined evaluation of the results suggests a threshold level for soil copper concentration around 500 mg kg^-1 beyond which soil functions significantly impedes.