Bacterial leaching from dairy shed effluent applied to a fine sandy loam under irrigated pasture

Abstract

This experiment investigated bacterial transport from land-applied dairy shed effluent (DSE), via field lysimeter studies, using 2 contrasting irrigation methods. Transient water flow and bacterial transport were studied, and the factors controlling faecal coliform (FC) transport are discussed. Two trials (Trial 1, summer; Trial 2, autumn) were carried out, using 6 undisturbed soil monolith lysimeters, 500 mm diameter by 700 mm deep, with a free-draining, Templeton fine sandy loam. DSE with inert chemical tracers was applied at the start of both trials using the same method, followed with repeated 14-day cycles of either flood or spray irrigation of water. A bacterial tracer, antibiotic-resistant faecal coliform, was added to the DSE in Trial 2 only, to distinguish applied FC from external or resident FC. Leachates were collected after each water application (or heavy rainfall when applicable) for enumeration of FC and measurement of tracers. All lysimeters were instrumented for monitoring volumetric water content, matric potential, and soil temperature at 4 depths (100, 250, 450, and 600 mm). The results showed that bacteria could readily penetrate through 700-mm-deep soil columns, when facilitated by water flow. The highest post-water irrigation concentration was 3.4 × 103 cfu/100 mL under flood irrigation, which resulted in more bacterial and Br– leaching than spray irrigation. Trial 2 (autumn) results also showed significant differences between irrigation treatments in lysimeters sharing similar drainage class (moderate or moderately rapid), flood irrigation again gave more bacterial and tracer (Cl–) leaching. In the summer trial, FC in leachate as high as 1.4 × 106 cfu/100 mL, similar to the concentration of DSE, was detected in one lysimeter that had a higher clay content in the topsoil immediately after DSE application, and before any water irrigation. This indicates that applied DSE leached through preferential flow paths without any dilution. Bacterial concentration in the leachate was positively correlated with both volumetric water content and water potential, and sometimes drainage rate. Greater bacterial leaching was found in the lysimeter with rapid whole-column effective hydraulic conductivity, Keff, for both flood and spray treatments. Occasionally, the effect of Keff on water movement and bacterial transport overrode the effect of irrigation. The ‘seasonal condition’ of the soil (including variation in initial water content) also influenced bacterial leaching, with less risk of leaching in autumn than in summer. These findings contribute to our increased understanding of bacterial transport processes on the field scale.

Leaching of Cryptosporidium parvum Oocysts, Escherichia coli, and a Salmonella enterica Serovar Typhimurium Bacteriophage through Intact Soil Cores following Surface Application and Injection of Slurry

“…Studies have shown that leaching of bio-colloids such as E. coli is strongly influenced by soil wetness conditions at the time of animal slurry application as well as the time between slurry application and rainfall occurring after spreading: i.e., the wetter the soil, the higher the leaching of bacteria (43,57). Correspondently, a significant leaching of bacteriophage PRD1 has been observed in connection with rainfall (62).…”

“…Microbial transport in intact soils has been studied under simulated rain conditions (58,59,65) or with a combination of rainfall and irrigation (43,44), whereas little information is available about microbial transport under natural climate conditions (57,62). Studies have shown that leaching of bio-colloids such as E. coli is strongly influenced by soil wetness conditions at the time of animal slurry application as well as the time between slurry application and rainfall occurring after spreading: i.e., the wetter the soil, the higher the leaching of bacteria (43,57).…”

Leaching and ponding of viral contaminants following land application of biosolids on sandy-loam soil

“…Preferential flow was reported in earlier lysimeter work McLeod et al, 2001McLeod et al, , 2003McLeod et al, , 2004Pang et al, 2008;Jiang et al, 2008). The transport rate measured in laboratory scale experiments may be considerably lower than the transport rate in the natural environment because the preferential flow pathways allow contaminants to bypass the soil matrix.…”

“…Soil depth in these lysimeters ranged from 40 to 100 cm with diameters ranging from 30 to 60 cm (volume ranged from 0.028 to 0.28 m 3 ). Most studies were performed indoors except for the work reported by Jiang et al (2008) and Carlander et al (2000). The focus of their work was on the transport of fecal coliforms, Escherichia coli and salmonella phage from dairy manure or pure cultures.…”

“…Several researchers have evaluated lysimeters containing undisturbed soil to investigate manure contaminant and microbial tracer transport in soil systems Carlander et al, 2000;McLeod et al, 2001McLeod et al, , 2003McLeod et al, , 2004Pang et al, 2008;Jiang et al, 2008). Soil depth in these lysimeters ranged from 40 to 100 cm with diameters ranging from 30 to 60 cm (volume ranged from 0.028 to 0.28 m 3 ).…”