ACCURACY AND PRECISION IN SAMPLING HYPORHEIC FAUNA

A series of interstitial faunal samples was taken from a riffle in the Speed River, southern Ontario, Canada, to compare the field performan ce of four hyporheic samplers: the standpipe, colonization, and freeze corers and a pump sampler. Each of the samplers proved useful for col lecting purely qualitative data, but statistical differences in some o f the measured quantitative parameters were identified. The colonizati on corer significantly underestimated invertebrate density at each of the depths tested (20, 40, and 60 cm below the surface of the river be d). Taxonomic richness did not differ among the samplers. A sampling b ias in the pump sampling method was identified in terms of both the pr oportion of insect larvae captured and the mean chironomid body size a nd is probably the result of a filtering effect of the interstices. Sa mpling precision estimates of density, richness, and organismal size r anged from 20 to 40%, but no pattern among the four samplers for any o f the measures was observed. We conclude that, whereas the standpipe a nd freeze coring methods most effectively characterize the hyporheos, one of the other methods might prove acceptable under specific field c ircumstances or under certain practical constraints.