Impacts of thermal and smouldering remediation on plant growth and soil ecology

Thermal (<1000°C) and smouldering (600-1100°C) remediation strategies potentially remove significant quantities of persistent organic pollutants from contaminated sites, reducing environmental and public health impacts while improving suitability for subsequent land use. However, high temperatures change the chemical and biological quality of soils, thus making restoration more difficult and costly. Here, we quantified the effects of soil heating (ambient to 1000°C) and smouldering remediation (>1000°C), which involved flameless combustion of hydrocarbon laden soils, on two topsoil types. The experimental aim was to determine the thermal-related effects on soil ecology, including geochemical properties and microbial activity, and plant growth, which can inform restoration efforts as to limited factors. There was a negative trend in plant growth with treatment temperature with red clover (Trifolium pratense) and red fescue (Festuca rubra). This appears to be related to geochemical changes in the soil, particularly atmospheric losses of nitrogen and reduced nutrient availability (e.g., Cu, Zn, and P). Consequently the ability of soils to immediately recover with active microbial communities rapidly declined when heated ≥500°C. Microcosm experiments, such as these, inform engineers and land-use managers of chemical and biological impacts, and provide guidance as to the nutritional and biological requirements for effective land restoration and rehabilitation.