A study of the contamination of suspended fluvial sediments with enteric bacteria in agricultural drains

The pollution of bathing beaches on the Great Lakes and inland waters occurs often as a result of the discharge of rivers and streams into near-shore waters. Depending on wind direction and speed, plumes of turbidity can be observed to be impacting directly on bathing beaches. The immediate impairment of the beach is the aesthetics, when water clarity diminishes to only a few centimetres. However, the major water quality parameters which increase are fecal coliforms and Escherichia coli. Total viable bacteria increase in conjunction with these parameters. This study was initiated to determine to what extent the particulates contributing to the turbidity of the water were perhaps transporting bacteria to the beach waters. Samples were collected from three agricultural drains suspected of impacting bathing beaches with elevated bacterial levels. The samples were analyzed by electronic zone sensing to size and count the suspended particulates. Analyses of the samples involved direct viable cell count and Salmonella determinations using epi-fluorescence and immunofluorescence microscopy to establish the numbers of bacteria sorbed to the suspended particulates of the agricultural drains. In addition, a bacterial transport study was conducted. An antibiotic-labelled Escherichia coli was sorbed to agricultural drain sediment in the laboratory. This bacteria-particulate mixture was inserted into the Desjardine Drain 5 km from the discharge of the drain to the Old Ausable River. Results of particulate analysis showed that four basic size ranges existed. Microscopic analyses of the size ranges of particulates colonized by bacteria were shown to range from 103 to 105 bacterial cells per mm2 of particulate surface area. Some differences were observed between the agricultural drains studied, which may be related to the clay content of the sediments of the specific drain. Some seasonal differences were also detected. The summer and autumn had the highest degree of particulate colonization while the particulates analyzed during the spring studies possessed fewer bacteria. The results of the bacterial transport study demonstrated that the fecal associated bacterium, Escherichia coli, could travel 5 km from the point of insertion to the beaches of Lake Huron and that the bacteria remained viable in the drain for at least eighty-five days. In conclusion, suspended particulates, contributing to the turbidity of agricultural drains, serve to transport high levels of bacteria to the receiving waters and often travel many kilometres from the point of entry of the bacteria into the drain.