OCCURRENCE OF NEMATODES IN BENTHIC DEPOSITS

This paper describes a method which has been developed and found satisfactory for sampling and separation of nematodes in benthic deposits of shallow streams with sandy bottoms. A simple scoop is described for obtaining an undisturbed sample. A modification of the centrifugal flotation technique described was found more quantitative than other methods. A 3-min flotation at 2900 g in a sugar solution was followed by filtration of the supernatant through a 5μ membrane filter for separation. Enumeration was carried out after staining with eosin-Y dye. The method can safely be used to make a quantitative determination of the concentration of nematodes in benthic samples. Nematodes were found to be present in all sections of the stream system investigated. The concentration of nematodes in water and benthic samples were significantly higher below the outfall of a waste treatment plant than above the outfall. The concentrations of nematodes in the benthos during the fall months were found to be about twice that observed during summer months. This was attributed to the more favorable temperatures during the fall. During the same period, the nematode concentration in the stream benthos did not bear any constant ratio to that in the water. The nematodes in the benthos were severely affected by high flows in the stream because of the erosive action of such high discharges. The concentration of nematodes in the benthos was observed to increase during low flows. The variation found in physical properties such as effective size and uniformity coefficient and chemical properties such as chemical oxygen demand, total nitrogen, and pH of the bottom material were found to have no direct relationship to the nematode concentration. © 1969.