OCCURRENCE OF CRYPTOSPORIDIUM OOCYSTS AND GIARDIA CYSTS IN THE RIVER MEUSE AND REMOVAL IN THE BIESBOSCH RESERVOIRS

The first results from an ongoing research project, carried out by the Water Storage Corporation Brabantse Biesbosch and several partners, are presented. The main research objectives are to gather information on the occurrence of Cryptosporidium and Giardia in the raw-water source (River Meuse), to determine the removal of the parasites in the Biesbosch reservoirs and to detect correlations between water-quality parameters and (oo)cyst densities. Cryptosporidium and Giardia densities in the Meuse were found to peak in winter, In the last of the three interconnected reservoirs (oo)cysts were intermittently present throughout the year. Giardia levels were higher than Cryptosporidium levels, while both were lower than reported in most other surveys. It is concluded that water storage in reservoirs with long retention times markedly reduces Giardia and Cryptosporidium concentrations.