Studies were initiated to determine the release behavior of Cryptosporidium oocysts and Giardia
cysts from dairy calf
manure to waters of various salinities. Experiments were conducted by sprinkling a particular aqueous
solution over a
manure disk and collecting the runoff water. Effluent concentrations of
manure and (oo)
cysts were initially several orders of magnitude below their starting concentration in the
manure, after continued application of water the concentrations gradually decreased, and then exhibited persistent concentration tailing.
Solution salinity significantly affected the shape and magnitude of the
manure and (oo)
cyst concentration curves. Increases in
solution salinity tended to decrease the
manure and (oo)
cyst concentrations at a particular time. This was attributed to a stabilization of
manure by compression of the double layer thickness between negatively charged components of the
manure phase. Calculated release efficiencies of the (oo)
cysts (relative to
manure release) also decreased with increasing
solution salinity. Experimental observations indicate that onlythe surface layer of
manure was depleted of finer
manure materials and (oo)
cysts and that the
manure will act as a long-term source of contamination. A conceptual model to describe and predict
manure and (oo)
cyst release rates and cumulative loading for the various
solution salinities was proposed and applied to the experimental data. The calibrated model yielded a reasonable description of the experimental results.