MULTIVARIATE ANALYSIS OF PERIPHYTON ASSEMBLAGES IN RELATION TO ENVIRONMENTAL GRADIENTS IN COLORADO ROCKY MOUNTAIN STREAMS 1

Abstract

We assessed relationships between chemical and physical characteristics and periphyton assemblages in stream reaches of the mineral belt in the Southern Rockies ecoregion of Colorado, United States. Using canonical ordination analyses, we contrasted results wherein assemblage structure was assessed using community metrics or species abundances. Our objectives were to identify community metrics or individual species diagnostic of the primary environmental stressors in these streams, to compare the sensitivity of these two approaches to determining the primary stressors, and to determine how these approaches may be used to differentiate the effects of these environmental stressors from other gradients. For periphyton metrics, the first axis extracted by redundancy analysis correlated with total phosphorus, substrate coarseness and embeddedness, and riparian vegetation condition, whereas the second axis correlated with dissolved metals. For species abundances, the three axes extracted by canonical correspondence analysis (CCA) were correlated with (1) stream size and types of in‐stream habitats; (2) total phosphorus, dissolved ions, and riparian disturbance by agriculture; and (3) sediment coarseness and embeddedness and riparian vegetation condition. Concentrations of dissolved metals were not correlated with the CCA axes. Analyses of species abundances were sensitive to effects associated with nutrients, substrates, and riparian vegetation, whereas analyses of periphyton metrics were sensitive not only to these nutrient and physical habitat effects but also to toxicological effects associated with metals. As a result, the analyses of periphyton metrics may be used to identify which metrics would be useful for a periphyton index of biotic integrity and would also be individually diagnostic of the larger scale stressors in these streams, nutrient, substrate, and riparian vegetation effects of livestock grazing and increased metal concentrations associated with metal mining.