Identifying mechanisms associated with spatial and temporal variation in Cryptosporidium occurrence in the South Nation River basin

Cryptosporidium is a relatively host specific parasite, and profiling of Cryptosporidium oocysts from water has been used to track host sources of fecal contamination of surface water. Occurrences of the genus Cryptosporidium, as well as the distribution of individual species and/or genotypes are variable across space and time. Variables affecting the hydrology in the basin can potentially influence this observed variability. To address this issue, Cryptosporidium was monitored at twelve sites within the South Nation River basin (Ontario, Canada) on a biweekly basis between May 30 and November 30, 2005. Cryptosporidium oocysts were detected in 38% of the samples, with a parasite load ranging from 0.04 to 61 oocysts/L. Variations in Cryptosporidium occurrence in the basin are due to the dynamic processes influenced by multiple hydrological and ecological variables. Stream order was identified as one of the variables contributing to spatial affinity within the basin. Occurrences of Cryptosporidium were higher in the fall months (September, October and November) and appear to be influenced by river discharge rates within the basin. Variables contributing to the hydrology of the basin can influence the occurrence of Cryptosporidium and other pathogens within a watershed. Understanding the causes of variation in pathogen occurrence allows for improved public and environmental risk assessment models. © 2008 American Water Works Association.