TRANSPORT OF MANURE-BORNE CRYPTOSPORIDIUM PARVUM OOCYSTS THROUGH SATURATED AND UNSATURATED SOIL COLUMNS

Authors: Pachepsky, Yakov; Shelton, Daniel; Kuczynska, Ewa; ROUHI, SEYED - NVS&WCD, VIRGINIA

Submitted to: International Agrophysics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/2/2005
Publication Date: 9/2/2005
Citation: Pachepsky, Y.A., Shelton, D.R., Kuczynska, E., Rouhi, S.A. 2005. Transport of manure-borne cryptosporidium parvum oocysts through saturated and unsaturated soil columns. International Agrophysics. 19:1-7.

Interpretive Summary: Cryptosporidium parvum is an animal parasite that is pathogenic for humans at its oocyst stage of development. The oocysts are released in water as manure dissolves and are able to survive in wide variety of environments. Soils seemingly play an important role in preventing the oocysts from entering ground and surface water. There is no published information about the transport and retention of manure-borne oocysts in soils. Transport and retention of pure oocysts has been shown to be affected by the soil water saturation. Our objective was to assess the effect of water saturation on transport of manure-borne oocyst through soil cores. Manure seeded with oocysts was applied on the surface of 10-cm columns filled with sandy loam soil and clay loam soils. Cores were initially saturated, and eight-hour rainfall simulation provided saturated flow in one set of columns whereas the flow in another set of columns was unsaturated due to suction applied at the bottom. The retention of oocysts in columns appeared to be much less than equilibrium laboratory experiments suggested. It was substantial, nevertheless, and oocysts stayed mostly within top 8 cm of soil columns. Cumulative oocyst contents in leachates from unsaturated columns were less than 0.1% whereas the saturated columns allowed breakthrough of 0.4% and 1.3% in sandy loam and clay loam soil cores, respectively. We simulated the oocyst transport with a commonly used model and found it mimicking the profile distributions of oocysts very well, but failing to simulate breakthrough of small amounts of oocysts occurring probably due to a preferential flow. Soil water saturation substantially affected the manure-borne oocyst transport.

Technical Abstract: Release of the manure-borne Cryptosporidium parvum oocysts is the most probable cause of further ground and surface water contamination with this pathogen. Our objective was to assess the effect of water saturation on transport of manure-borne oocyst through soil cores. Manure seeded with oocysts was applied on the surface of 10-cm columns filled with sandy loam soil and clay loam soils. Cores were initially saturated and eight-hour rainfall simulation provided saturated flow in one set of columns whereas the other set had suction ca. 5 kPa applied at the bottom. The convective-dispersion model with exponential boundary release, instantaneous adsorption and first-order kinetic removal of oocysts was used to simulate the transport. Transport parameters were found by fitting an analytical solution to the oocyst profile distributions. Oocysts stayed mostly within top 8 cm of soil columns. Cumulative oocyst contents in leachates from unsaturated columns were less than 0.1% whereas the saturated columns allowed breakthrough of 0.4% and 1.3% in sandy loam and clay loam soil cores, respectively. The model mimicked the profile distributions of oocysts very well, but failed to simulate breakthrough of small amounts of oocysts occurring probably due to a preferential flow. Values of retardation coefficient were less than unity in saturated columns and greater than unity in unsaturated columns. Values of the soil partition coefficient Kd derived from the retardation coefficient values were much less than earlier reported values from batch experiments with the same soils. Removal rates were much higher in saturated than in unsaturated columns. Soil water saturation strongly affected the manure-borne oocyst transport.