GIARDIA AND CRYPTOSPORIDIUM OCCURRENCE AND LEVELS DURING STORM EVENTS

摘要

The often quoted saying in water quality "dilution is the solution to pollution" may be deceiving when it comes to understanding the effects of rainfall events on protozoa levels in source waters and sewage effluents. Storm event sampling was conducted at eight locations to compare the effects of storm events on protozoa occurrence and concentrations in a creek, river, and sewage treatment plant effluent. The occurrence and concentrations of Giardia and Cryptosporidium increased during storm events compared to stable flow periods. The protozoa concentrations typically increased by more than a factor of 10 during storm events. These increases suggest that overall loading to the watershed during storm events increase to such a point that dilution by increased stream flow will not reduce protozoa concentrations. Water quality and stream measurements during the study showed that flow, turbidity, fecal coliforms, and total coliforms correlated with protozoa concentrations. This observation suggests that these parameters may serve as indicators of periods of increased protozoa levels in the source water in the studied watershed areas. Storm event profiles were collected on various occasions to better determine the effects of hydrograph position on protozoa concentration. The recording of three different protozoa concentration profiles during three different events demonstrated the importance of combination of watershed characteristics and existing hydrological conditions on source water levels of protozoa. Given these observations, understanding the watershed's characteristics that affect the loading of protozoa and the existing hydrological conditions are imperative. This knowledge may ultimately allow utilities to predict periods of greatest protozoa loading and source water concentrations and guide source water management programs or alternative intake strategies to prevent these loading scenarios.