Submitted to: BARC Poster Day
Publication Type: Abstract Only
Publication Acceptance Date: May 1, 2003
Publication Date: May 1, 2003
Citation: Guber, A.K., Shelton, D.R., Pachepsky, Y.A. 2003. Movement of manure-borne bacteria in soils as a colloid-facilitated transport affected by soil structure. BARC Poster Day.
Manure is a source of several bacteria that can potentially contribute to surface and ground water contamination. Results of the majority of studies of bacterial transport in soils are only partially applicable to manure-borne bacteria because microorganisms are released along with manure particulates as manure dissolves. We hypothesized that transport of manure-borne bacteria in soils could be viewed as colloid-facilitated transport. Such transport is known to be affected by pore structure, because only pathways formed by large pores can serve as conduits for colloidal particles. Therefore, we suggested that transport of manure-borne bacteria could be affected by soil structure. To test the two hypotheses, column experiments were conducted with sandy loam and clay loam soils. Aggregated soil samples and soil samples passed through 2-mm sieve were packed uniformly in 20-cm columns. Soil in columns was subject to capillary saturation during 48 hours, and remained saturated after that. A pulse of KCl solution followed by a pulse of E. coli strain solution with or without liquid manure was passed through columns. Volumes of the pulses were equal to one pore volume of soil in columns. E. coli concentrations, pH and turbidity were measured in influent and in effluent. Columns were cut into 2-cm layers after the experiment to measure viable bacteria concentrations and water content in soil.
Effluent chloride concentration was larger in aggregated than in sieved soils for the same effluent amount. This meant that vertical transport of chloride had occurred only in a limited portion of total pore space of aggregated soil. Effluent bacteria concentrations were negligible in sandy loam and sieved clay loam soil columns. Distinct peaks of viable bacteria were observed in effluents from the aggregated clay loam soil. The peak of the effluent bacteria concentration was observed much earlier and was substantially larger in columns with manure added than without it. Peaks of E. coli concentrations coincided with turbidity peaks, reflecting similarity in manure colloid transport and E. coli transport. After experiments in sieved soil columns, viable bacteria were found in the upper 4 cm layer. Bacteria were distributed relatively uniformly along columns with aggregated clay loam soil. The velocity of bacteria transport was about 1.5 larger than water flow rate in the experiment with manure and about 2 times less than the water flow in experiment without manure.
Our data support the hypotheses that transport of manure-borne bacteria in soils is substantially affected by the transport of manure colloids, and as such may be quite significant depending on soil structure.