WINTER SURVIVAL OF MICROBIAL CONTAMINANTS IN SOIL

摘要

The aim of this study was to evaluate, at site scale, the influence of freezing and freeze/thaw cycles on the survival offecal coliforms and fecal enterococci in soil, in a climate change perspective. Viable cells of both fecal indicators werecounted in ten different soil profiles and at different depths, before and after a winter season. Before the winter periodand during grazing, viable cells of fecal coliforms and fecal enterococci were detected only in the first 10 cm belowground, while, after the winter period and before the new seasonal grazing, a lower number of viable cells of both fecalindicators was detected only in some of the soil profiles, and within the first 5 cm. Thus, a significant decrease in viablecells was observed in all soil profiles, due to cold shock, freezing, prolonged exposure to subzero temperatures, andalternating freezing and thawing periods, even though this decrease was not uniform at site scale. Taking intoconsideration the results of specific investigations, we hypothesised that the non-uniform spatial distribution of grassroots within the studied soil ccould play an important role in influencing this phenomenon, while several abioticfactors, such as organic matter, grain size and specific weight of particles, total porosity, and relative density, did notplay any significant role. In a climate change perspective, taking into account also the local trend in air temperature, adifferent distribution of microbial pollution over time is expected in spring waters, and a higher risk of transmission ofinfections is expected throughout the year. The progressive increase in air temperature, with emphasis on the minimumone, will cause a progressive decrease in freezing and freeze/thawing at higher altitudes, therefore minimising coldshocks on microbial cells, and causing spring water pollution also during winter, differently from the actualobservations.