An Ecological Analysis of Lotic Environments: I. Design and Testing

ABSTRACT

A biotic analysis of lotic environments was designed, using ecological tolerances and requirements of the numerically dominant macrobenthic invertebrates. This method, “Ecological Community Analysis” (ECA), uses the habitat, habits, mode of feeding, temperature preference and silt- and hypoxia-tolerances of the dominant organisms to isolate the most important environmental factors associated with biotic communities.

ECA showed that above a mainstream impoundment on the Speed River (Southern Ontario) the benthos was dominated by lotic-selecting, warm-water and hypoxia-intolerant organisms. Presence of these organisms indicates that the biologically relevant environmental factors at the upstream station were: swift current, warm water and high dissolved oxygen levels. Two stations, 100 m and 400 m below the dam, were characterized by higher proportions, relative to other stations, of cool water, shredding, and algae-tolerant organisms. Significantly higher proportions of climbing and lentic-selecting invertebrates were also found below the dam. Partial recovery to control conditions occurred 1500 m downstream.

Water temperature and filamentous algal growth are deemed the two most important factors in this system. Major differences between upstream and downstream communities can be ascribed to the dense mats of Cladophora sp. which often cover the substrate below the dam.