Human and bovine viruses in the Milwaukee River watershed: hydrologically relevant representation and relations with environmental variables

Abstract

To examine the occurrence, hydrologic variability, and seasonal variability of human and bovine viruses in surface water, three stream locations were monitored in the Milwaukee River watershed in Wisconsin, USA, from February 2007 through June 2008. Monitoring sites included an urban subwatershed, a rural subwatershed, and the Milwaukee River at the mouth. To collect samples that characterize variability throughout changing hydrologic periods, a process control system was developed for unattended, large-volume (56-2800 L) filtration over extended durations. This system provided flow-weighted mean concentrations during runoff and extended (24-h) low-flow periods. Human viruses and bovine viruses were detected by real-time qPCR in 49% and 41% of samples (n=63), respectively. All human viruses analyzed were detected at least once including adenovirus (40% of samples), GI norovirus (10%), enterovirus (8%), rotavirus (6%), GII norovirus (1.6%) and hepatitis A virus (1.6%). Three of seven bovine viruses analyzed were detected including bovine polyomavirus (32%), bovine rotavirus (19%), and bovine viral diarrhea virus type 1 (5%). Human viruses were present in 63% of runoff samples resulting from precipitation and snowmelt, and 20% of low-flow samples. Maximum human virus concentrations exceeded 300 genomic copies/L. Bovine viruses were present in 46% of runoff samples resulting from precipitation and snowmelt and 14% of low-flow samples. The maximum bovine virus concentration was 11 genomic copies/L. Statistical modeling indicated that stream flow, precipitation, and season explained the variability of human viruses in the watershed, and hydrologic condition (runoff event or low-flow) and season explained the variability of the sum of human and bovine viruses; however, no model was identified that could explain the variability of bovine viruses alone. Understanding the factors that affect virus fate and transport in rivers will aid watershed management for minimizing human exposure and disease transmission.

Keywords: Automated sampling; Human viruses; Hydrologic event; Seasonality; Watershed.

Fig. 1

Sampling locations and land cover in the Milwaukee River watershed. Map comprised of various spatial datasets: state boundaries (Instituto Nacional de Estadística Geografía e Informática et al., 2006), county boundaries (National Atlas of the United States, 2005), hydrography (U.S. Environmental Protection Agency and U.S. Geological Survey, 2005), land cover (Fry et al., 2011), and watershed boundaries

Fig. 2

Diagram of the automated large-volume virus sample collection and filtration system. “P” and “G” designations for the filter sets refer to prefilter and glass-wool filter, respectively.

Fig. 3

Example of quality control results from the automated virus sample filtration process at Underwood Creek in June, 2007.

Fig. 4

Occurrence (fraction of samples that were virus positive), mean concentrations and maximum concentrations (genomic copies/L) of human and bovine viruses at three sites in the Milwaukee River watershed, Wisconsin from February 2007 to June 2008. BPyV represents bovine polyomavirus, BRA represents bovine rotavirus group A, BVDV1 represents bovine viral diarrhea virus type 1.

Fig. 5

Variability and magnitude in loadings of human and bovine viruses during event and low flow periods for the Milwaukee River watershed and two subwatersheds representing urban and agricultural land use. The box represents the 25th to 75th quantiles with a horizontal line for the median. The whiskers represent data beyond the box within 1.5 times the interquartile range. Circles are data points beyond the upper or lower limits of the whiskers. ND indicates no viruses detected.

Fig. 6

Time series of human and bovine virus concentrations with streamflow for the Milwaukee River watershed and two subwatersheds representing urban and agricultural land use. Sampling periods are indicated by the width of red shading (low flow) and blue shading (runoff events) of the hydrographs. ND indicates no pathogens detected.