Depth transfer of fecal indicator organisms in an arable clayey soil

Abstract

In clayey soils, shrinking cracks formed during dry periods in the summer are the most important form of macropores. They may contribute under disadvantageous conditions to the movement of fecal microorganisms and therefore to the contamination of groundwater. For this reason, a field experiment was carried out on a highly clayey arable soil to investigate the effect of the factors slurry addition, sampling date, depth, and season. Under worst case conditions, i.e. a soil at field capacity, irrigated directly after application of fresh cattle slurry with high rates of water, the numbers of spores, total coliforms, fecal coliforms and fecal streptococci were not significantly increased at depths of 15 cm, 45 cm and 75 cm in spring (with less shrinking cracks) or in autumn (with more shrinking cracks). The close correlations between the numbers of spores, total coliforms, aerobic bacteria and microbial biomass C indicate that spore forming organisms and most total coliforms belong to the autochthonous soil microflora and cannot indicate fecal pollution.