The occurrence of benthos deep in the substratum of a stream

(1) The vertical distribution of the benthic fauna of the Speed River, Ontario, was studied over a 13-month period from October 1970 to October 1971. Various physical and chemical parameters of this interstitial environment were also measured. (2) Several new techniques for sampling the interstitial environment of rivers were devised. These methods and their relative efficiencies are considered. (3) The validity of the terms 'hyporheal' and 'hyporheic' are discussed and the term 'hyporheos' is offered to replace the former. (4) A brief resume of interstitial sampling methods is given with comments on their limitations for sampling deep heterogeneous substrates. (5) Chemical parameters are thought to be more important in the control and distribution of the fauna than physical parameters. (6) It is suggested that many larvae of stream-dwelling chironomids have overwintering stages when they penetrate deep into the substrate to: (a) actively feed on the trapped organic detritus; (b) follow an optimum temperature for development. (7) It is suggested that the shape of an organism determines its success as a hyporheic form and examples are given. (8) The numbers of animals occurring in the sub-benthic populations are shown to be very large indeed. For the Speed River, estimates of between 184,760 and 797,960 animals/m3 are made for different times of the year. Dry weight biomass is estimated to vary between 30.9 g and 253.2 g/m3 throughout the year. (9) Sub-benthic or hyporheic populations are shown to exist in at least three other Canadian rivers. Some of the animals found are shown to be common to two or more of these rivers. (10) The inefficiencies of many conventional benthic samplers in sampling the total biomass of certain streams with hyporheic populations is discussed