<i>Cryptosporidium</i> and <i>Giardia</i> Concentrations: 13-Year Longitudinal Analysis of Monitoring in Eight Independent Streams

Abstract

Since the 1990s, a major Australian water agency has monitored the concentrations of Cryptosporidium and Giardia in eight tributaries to its principal water supply reservoir. The accumulated data have recently been made available for analysis, resulting in this paper. The eight catchments total over 7,700 km2 (∼3,000 mi2) producing an average of approximately 1,800&nbsp;ML/day (475&nbsp;mgd) of water treated downstream to supply a population of nearly 4&nbsp;million. Beginning in 2002, weekly 10&nbsp;L samples from each of the eight sites were analyzed. Significantly, recovery efficiency of both organisms was measured for every sample. Data analyzed in this project encompassed all samples from 2002 through 2014. Data were analyzed to identify chronological variations in the concentration of both organisms and in terms of cumulative frequency analysis. These analyses permitted the identification of differences in concentration patterns related to catchment characteristics, including identification of temporal patterns related to season or weather, estimation of the most common (median) concentrations, and the degree of variation typical of each sampling location. Clear differences were apparent between typical concentrations and variabilities among the eight stations. Giardia concentrations were characteristically higher than Cryptosporidium. The data clearly illustrate the continuous long-term presence of Cryptosporidium and Giardia, despite the many nondetect analytical results. The concentrations and variabilities of both organisms were in the midrange of what has been reported at locations throughout the US. These comparisons, made possible by measurement of true concentration by including recovery efficiency measurement for every sample, will form the basis for further investigation of individual catchment characteristics and conditions in an effort to account for differences in observed concentration patterns.