Use of Detrended Correspondence Analysis in Evaluating Factors Controlling Species Composition of Periphyton

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Abstract
Detrended correspondence analysis (DCA) was evaluated for its usefulness in elucidating relationships among samples and among species of periphyton in an oligotrophic stream, and for its effectiveness in displaying major gradients where an experimental gradient (copper) affecting species composition was imposed. It was highly sensitive to differences among samples and consistently provided ecologically meaningful species ordinations. Gradients related to seasonality of taxa and year-to-year differences in population densities were evident in DCA ordinations if data for all sampling dates were included, and these gradients complicated interpretation of the copper gradient. Clear discontinuities between samples in control and copper-treated stream sections existed only if data for each sampling date were ordinated separately. Prior to copper exposure, stage of succession of the community was the major gradient displayed in species ordinations. During periods of exposure, sensitivity of taxa to copper was the primary factor controlling the spatial distribution of periphyton. Stage of succession was a secondary gradient during exposure and complicated interpretation of the copper gradient after a major disturbance event (flooding).