Virus Transport: Integrating Laboratory and Field-Scale Observations with Modeling
Our primary objectives are to develop insights into basic processes that control large-scale virus export and transport and to quantify fluxes to the Great Lakes using process-based models. Virus transport is controlled by mechanical dispersion, preferential flow, time-dependent nonreversible and reversible attachment, and apparent mass transfer to immobile domains within the aquifer. Successful modeling requires separation of viral specific properties from lumped transport parameters. Our working hypothesis is that viral and bacterial transport is controlled by physical and chemical heterogeneity. We are using viral tracer studies and transport modeling to examine the impact of septic tanks along the diversity of Great Lakes shorelines. Our key questions are related to the level of characterization required to develop an accurate virus transport model and to the factors that influence scale-up as we move from the laboratory to a field setting.
Ecology and Hydrology of Pathogens and Improved Understanding and Forecasting of Viral and Bacterial Sources and Transport in the Great Lakes
We conducted large-scale virus transport experiments in 2006 to understand the influence of physical and chemical heterogeneity on virus transport relative to the transport of the conservative tracer Rhodamine-WT. In order to assess the effects of CSO events to water quality at beaches along Lake Michigan around the discharge site of the Grand River, a tracer study was conducted on May 8, 2006. A conventional dye, Rhodamine WT was injected in conjunction with a bacteriophage, PRD-1 into the Grand River at the city of Grand Rapids. Although PRD-1 has often been in groundwater study, its transport and survival behaviors in surface water have not been studied extensively and this is the first study that uses PRD-1 as a tracer in a complex surface water system.
Bacteriophage PRD-1 were aliquoted into 16 one-liter bottles and poured into the river from the Ann Street bridge, Grand Rapids, MI, which is located approximately 2 km and 4.54 km upstream of the Sixth Street dam and the first sampling location- Wealthy Bridge, respectively.
Grab samples were collected from three locations at each sampling site. All samples were kept on ice and transported to the laboratory within 12 hours after collection and were analyzed within 48 hours of collection. Both rhodamine WT and PRD-1 exhibited a classic pattern. Maximum concentration values dropped as a function of distance from injection point as the result of dispersion, dilution and inactivation (in the case of PRD-1). Comparison of rhodamine WT and PRD-1 showed identical distribution pattern. Arrival (± 17 min) and peak time (± 17 min) at each site are quite similar. Rhodamine traveled at approximately 0.49 km h-1 (range: 0.45-0.59 km h-1) while PRD-1 traveled at 0.50 km h-1 (range: 0.46 – 0.58 km h-1). We were able to use watershed modeling coupled with a transient storage formulation to describe the flow-weighted average concentrations of both Rhodamine WT and bacteriophage P22 in three different reaches of the river. Our model showed that travel times were similar for both tracers and that a constant (first-order) inactivation rate in the range 0.3 – 0.6 per day described the inactivation of P22 in the river. These models will be used to predict risk at recreational beaches and parks.
In addition we have been conducting laboratory-scale flume studies to track the deposition and resuspension of seeded bacterial, viral and parasitic model organisms at various flow rates into and from two types of sediment commonly found in the lower Grand River watershed (sand and loamy/sand).
