Nematodes from river drift and surface drinking water supplies in southern Ontario

Sixty-six genera of nematodes representing 37 families were collected over a 13-month period from untreated and treated water from three water treatment plants in southern Ontario. Two plants receive water from the Grand River which drains agricultural, residential and industrial regions, the third from a small stream in an agricultural district. Specimens were isolated by filtration from weekly samples of untreated and treated water, most were identified to genus but a few to species.Estimated mean density in the organic drift of the river ranged from 0.58 individuals per litre in winter, when it was under ice, to 10.57 per litre during the spring thaw. Most of the 66 genera found passed through the treatment plants and over 50% of these were still motile.Eleven genera were abundant at some time of the year, six known only from soil-dwelling forms and five from aquatic or soil/aquatic species. There was no indication that sewage purification works were a major source of any genus. There were a few plant parasites.Aquatic nematodes occurred during most of the year although they were more abundant during the warmer months, high densities of soil nematodes were a feature of the spring thaw and rains and during heavy autumn rains. More than 50% of the specimens were juveniles and some common genera lacked males.