Microbial Source Tracking Pilot Study Developed for the Upper Mississippi River Bacteria TMDL and Protection Plan

A pilot study was undertaken to investigate the use of microbial source tracking of fecal contamination for Total Maximum Daily Load (TMDL) studies in Minnesota. The Minnesota Pollution Control Agency (MPCA) and Minnesota Department of Health (MDH) collaborated with Dr. Michael Sadowsky from the University of Minnesota's Department of Soil, Water and Climate, and The BioTechnology Institute. Three Bacteroides primers were used to identify the source of fecal contamination: bovine (cow), porcine (swine), and humans (and cats/dogs1). For the pilot study, 19 sites were selected and a total of 50 samples were taken from the sites over four sampling days (Table 1). Sites were selected to provide a cross-section of rural and urban drainage characteristics, and samples from the Mississippi River, tributaries, and stormsewer. MDH source water protection areas were also targeted. Up to four samples were collected from each site, to include a stormflow and baseflow sample from both June and fall. At least one liter of surface water was collected for each sample. Samples were collected from the middle of the river/stream/stormsewer at most of the sites. Four of the 19 sites entailed collecting the sample from off of boat launches or loading docks using a 12 foot dip pole extended towards the center of the river/stream, ultimately collecting the sample at minimum 25 to 50 feet from shore in flowing water. This sampling approach provides data on which sources were found at the monitoring site. However, the limited number of samples taken does not provide information about which sources were not found at the monitoring site during that time period. Relative concentrations of markers were compared in the data evaluation. The bovine marker was found at twelve of the nineteen monitoring sites. Four of the five Mississippi River sites tested positive for the bovine marker, and six of the eleven tributary sites tested positive. Two of the three stormsewer sites also tested positive for the bovine marker. There were several sites that tested positive for the bovine marker that do not have any obvious sources of fecal contamination from cattle. The porcine marker was found at only one site. The humans (and cats/dogs) marker was found at thirteen of the nineteen monitoring sites. Two of the five Mississippi River sites tested positive for the humans (and cats/dogs) marker, and five of the eleven tributary sites tested positive. All of the samples taken from stormsewers showed the presence of human (and cat/dog) sources.