Seasonality, altitude and human activities control soil quality in a national park surrounded by an urban area

Maintaining high soil quality is necessary to let healthy living ecosystems and to protect them from disturbances. The present research aimed to: test the quality of soils located inside the Vesuvius National Park (Southern Italy), an example of a peculiar volcanic system of great naturalistic interest affected by high touristic pressure and human impact, by the analyses of 25 parameters. Other goals of the research were to identify the main drivers among site-specific factors (altitude, seasonality, touristic impact) in defining soil quality and to individuate a Minimum Data Set (MDS) able to assess soil quality inside the Vesuvius National Park. The soil quality index (SQI) was calculated by linear scoring technique applying the “more is better” or “less is better” functions. In order to individuate the MDS, two statistical approaches were performed. In the first approach, not redundant parameters and showing the highest loading values were considered (MDS1); whereas, in the second approach, those with the highest sum of correlation coefficients were considered (MDS2). The SQI, calculated for all the parameters, showed intermediate values (0.44–0.67) reflecting the combination of the good level of naturalness and the metal accumulation. Seasonality affected the soil quality with high value in autumn, when the microclimatic conditions were less suitable for microorganisms and the soil metal contamination degree was lower than in spring. Anyway, also the touristic season inside the National Park affected the qualities of the soils along the two roads as they were similar regardless on accessibility and duration of the traffic flow. Also altitude that, regulating the microclimatic conditions, conditioned the type and density of plant cover affected soil quality. In fact, at low altitude most favourable conditions occurred for soil microbial biomass growth and activities. The MDS1 (C content, total Ni concentration, qCO2 and percentage effect of root elongation for S. saccharatum L.) appeared sufficiently informative to evaluate soil quality.