Importance of manure properties on survival and transport of manure bacteria through the vadose zone
Survival and transport of pathogens from manure in the environment depend on a number of complex phenomena. An important question is how the properties of such a complex environment as the soil-manure medium impact the transport of bacteria within the vadose zone. The physical configuration of soil, soil chemistry, and the properties of bacterial cells are of importance in the retention of bacteria in soils. Transport of bacteria in soils obeys the general laws pertinent to macropore flow and the interaction between particles and surfaces of variable charge. Detailed characterization of the variable properties within the structured soil profile is difficult. Application of manure results in potentially significant changes in the physical and electrochemical properties of the soils. The objective of the present thesis was to establish whether the composition of manure influenced the contaminant potential of faecal bacteria from manure, and what likely mechanisms were involved. The investigation focused on the transport and survival of bacteria as affected by manure. The effect of manure composition on soil transport properties, and on the surface properties of bacteria, and the consequences for bacteria transport were investigated in a series of experiments in the field, in undisturbed columns and samples of sieved aggregates. Another series of experiments focused on the effect of manure composition on survival of the faecal bacteria in soil. Manure properties were found to have a significant influence on the soil properties relevant to bacterial transport. The amount of manure dry matter had a significant impact on the partitioning of precipitation into infiltration (manure with large dry matter content) and surface runoff (manure with little dry matter content). The physico-chemical properties of manure, and the presence of soluble and insoluble organic components in the manure, influenced the interaction between bacteria and the soil environment by affecting the surface charges on the bacteria or enhancing their hydrophobicity. Survival of faecal bacteria was affected by the physical and chemical conditions existing prior to manure application as well as by conditions imposed by mixing soil and manure. Competition with the soil bacteria appeared to be an important factor influencing survival.