Micromorphological investigations into root penetration in a landfill mineral cap, Hertfordshire, UK

A micromorphological study of the soil fabric of a landfill mineral cap in Hertfordshire, UK is described. The study was undertaken to examine the nature of the cap and roots within it, and whether micromorphology could help in the explanation for root penetration. The results from thin section description supported by macro and micro image analysis clearly demonstrated that rooting was associated with zones of weakness in the cap, due to the heterogeneous particle/pore size distribution, low bulk density and presence of organic matter. The study of the material fabric also suggested evidence of pedological activity within the cap, further indicating that the mineral cap had not been engineered sufficiently to prevent the risk of root penetration. A greater uniformity of particle size within the cap material with a reduced clay and stone fraction were identified as potential solutions to avoid the extent of root penetration. The study demonstrated the value of observing and quantifying the undisturbed fabric of the micro structure in the examination of mineral cap fabric, and diagenetic and pedological processes acting on it.