Development of soil physical structure and biological functionality in mining spoils affected by soil erosion in a Mediterranean-Continental environment

The main aim of this work was to analyse the development of soil functionality (aggregate development and soil biological functionality) on mining spoils 18 years after reclamation affected by different levels of soil erosion (rill erosion rate from 0 up to 70 t ha− 1 year− 1) in a Mediterranean-Continental environment. For this purpose, different parameters were determined: the size distribution and stability of soil aggregates [mean weight diameter (MWD), microparticles and macroparticles proportions (MIP and MAP), and aggregate stability (AS)]; soil microbial population size [microbial biomass C (MBC)] and activity [basal respiration (BR) and dehydrogenase activity (DHA)]; and soil hydrolase activities [phosphatase (PHA), β-glucosidase (β-GA) and urease (UA)]. Soil ecological trends obtained from Principal Component Analysis revealed the accumulation of organic matter from restored vegetation as the triggering factor for the development of soil aggregation and biological functionality. The spatial differentiation of reclaimed vegetation was the principal source of variability for these soil forming processes, which were also conditioned by the presence of variations on soil particle size distribution. Erosion-related exponential decreases of AS, BR, DHA, PHA, β-GA and UA were identified. In fact, limitations of vegetation development caused by accelerated soil erosion drastically constrained the development and spatial organisation of both physical structure and soil biological functionality, by preventing the accumulation of soil organic matter. Although soil forming processes in uneroded conditions occurred, soil functionality levels were rather low, probably due to the small amounts of soil organic matter reached, generally < 2%. This stresses the importance of including organic amendments during restoration works in Mediterranean environments.