Microbial and chemical tracer movement through Granular, Ultic, and Recent Soils

Abstract

The ability of New Zealand soils to renovate dairy‐shed effluent following application to land is being evaluated. We investigated the pattern of transport of faecal coliforms, a host‐specific Salmonella bacteriophage and a non‐reactive chemical tracer (Br–), when applied to large, intact lysimeter soil cores (460 mm dia. × 520–700 mm high) of three contrasting soils. The soils were imperfectly drained Ultic and Granular Soils and a well‐drained Recent Soil. A depth of 25 mm of dairy‐shed effluent containing faecal coliforms and spiked with bacteriophage and Br⁻ was applied to the soil at a rate of 5 mm h⁻¹ followed by up to 1 pore volume of simulated rainfall applied at 5 mm h⁻¹. This application rate is generally much slower than the soil's saturated hydraulic conductivity except in the Ultic Soil where saturated hydraulic conductivity is slower. Resulting leachates, collected continuously, were analysed for the microbial and bromide tracers. The phage tracer moved rapidly through all soils, peaking early in the leachates and then tailing off in a pattern indicative of bypass flow. Faecal coliforms also moved rapidly through the Ultic and Granular Soils but numbers were much lower or not detectable in leachate from the Recent Soil. In contrast, bromide moved uniformly through Granular and Recent Soils but peaked early at about 0.5–0.8 pore volume. The microbial data suggest the soil structure in the Ultic and Granular Soils makes them vulnerable to leaching of microbes into shallow water bodies.

Keywords:

• microbial contamination
• soil
• bypass flow
• dairy‐shed effluent