Benthic Invertebrate Community Structure

Fundamental to the scientific method is the use of controls or control conditions against which results obtained under test conditions are compared. In field studies, all variables cannot be controlled and replicates cannot be randomly assigned to treatments, so an attempt is made to choose test and control conditions (often represented by different sites) that are as similar as possible; the variable of interest is then manipulated, and uncontrolled variables are assumed to fluctuate similarly. Traditionally, this problem has been solved in aquatic studies by choosing adjacent sites in streams (i.e. upstream and downstream comparisons, Norris et al. 1982), by dividing lakes into halves (Schindler 1974), or by using mesocosms (Graney et al. 1984). Such approaches have several problems (Cooper and Barmuta 1993); a major issue in streams is confounded designs (Eberhardt 1978), often called “pseudoreplication” (Hurlbert 1984).