Physical chemical and biological monitoring and analysis of four small New England watersheds during baseflow and stormflow conditions
As prolifically documented in the literature, wet weather events have a significant effect on the physical, chemical and biological properties of streams, thereby affecting the overall water quality of the stream as well as the receiving body of water. These effects are of particular importance when the receiving water body is a reservoir used as a source of drinking water in which a decrease in water quality could pose a significant risk to human health. Pathogens such as Cryptosporidium and Giardia are of particular importance to water supply authorities for their specific and direct threat to human health. Cryptosporidium and Giardia are known waterborne pathogens, whose effects on immunocompromised individuals can be life threatening. Because of the risk posed to human health by these pathogens, it is imperative to gain a solid understanding of the environmental factors affecting die-off and transport, and thus the ultimate concentrations in receiving waters. Testing for these pathogens is both expensive and time consuming. It is therefore also important to determine if other, more easily measured parameters can act as surrogates for these pathogens.
Documentation of outbreaks resulting from exposure to these resistant pathogens is plentiful and has in part been paralleled by the study described herein. However, this research was necessary owing to the reliance of Southern New England on surface water to supply drinking water to its population and has several focus points that have yet to be evaluated in the existing literature. Specific objectives of this research were to (1) identify and better understand factors affecting Cryptosporidium and Giardia concentrations entering the studied surface water supplies and; (2) develop a sampling protocol for future use by researchers and water utilities to most accurately determine nutrient and microbial concentrations entering a water supply. Factors evaluated included event rainfall, antecedent rainfall, streamflow, land use characteristics, and the validity of indicator organisms to predict the presence of Cryptosporidium and Giardia. The study sites for this research were four small streams in Massachusetts in watersheds with varying land use characteristics. This research focused on gaining a better understanding of the effects of rainfall on in-stream parameter concentrations for streams receiving water running off of areas with distinct land-uses. The effects of rainfall were investigated through field measurements and statistical analyses. The transport of Cryptosporidium and Giardia to receiving waters, as well as understanding the factors impacting their detection, were main focus areas of this research.
Study results suggest that the occurrence of Cryptosporidium and Giardia in the tributaries of small watersheds is not easily explained by basic hydrologic conditions, precipitation, land use, or the presence/absence of standard in-stream indicator organisms. Total event rainfall did not significantly affect the presence, absence or concentration of Cryptosporidium or Giardia. However, 72-hr antecedent rainfall totals greater than 20 mm were observed for all but one of the events where Cryptosporidium and/or Giardia were detected. Clostridium perfringens concentrations greater than 100 cfu/100mL was the only water quality parameter (both nutrient as well as microorganism) to provide an accurate indication for the potential presence of Cryptosporidium or Giardia. If present in the near stream area, even small amounts of precipitation when paired with wet antecedent conditions, were likely to result in transport and thus elevated in-stream concentrations of Cryptosporidium and Giardia. Concentrations were typically higher on the rising limb or near the peak of the storm hydrograph, suggesting that the nutrients and microorganisms evaluated were carried into the stream with the first flush. This flushing phenomenon was further evidenced by the clockwise hysteresis loops produced for all events that presented a single peak hydrograph. Cryptosporidium and Giardia were generally (6 out of 7 events) observed at higher concentrations at the downstream sampling location. Occurrence of Cryptosporidium and Giardia in surface waters appeared to be largely a factor of infectivity rates of wild and domesticated animals living within the watershed and their annual cycles. The animal population may have increased the probability of detecting Cryptosporidium or Giardia during the late winter and early spring. For watersheds where reservoirs are the major source of water withdrawals, sampling should be based on hydrodynamics of the reservoir and travel times from the tributaries to the intake. Attention should also be paid to antecedent rainfall conditions and time of year. This dissertation outlines the research objectives, reviews pertinent literature, describes the research design and methods as well as presents results and conclusions.