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ANALYSIS OF MACROINVERTEBRATE ASSEMBLAGES IN RELATION TO ENVIRONMENTAL GRADIENTS IN ROCKY MOUNTAIN STREAMS
Citation:
Griffith, M. B., P R. Kaufmann, A. T. Herlihy, AND B H. Hill. ANALYSIS OF MACROINVERTEBRATE ASSEMBLAGES IN RELATION TO ENVIRONMENTAL GRADIENTS IN ROCKY MOUNTAIN STREAMS. ECOLOGICAL APPLICATIONS 11(2):489-505, (2001).
Impact/Purpose:
The goal of this research is to develop methods and indicators that are useful for evaluating the condition of aquatic communities, for assessing the restoration of aquatic communities in response to mitigation and best management practices, and for determining the exposure of aquatic communities to different classes of stressors (i.e., pesticides, sedimentation, habitat alteration).
Description:
Using redundancy analysis (RDA) and canonical correspondence analysis (CCA), we assessed relationships among chemical and physical characteristics and macroinvertebrate assemblages at stream sites sampled by the Regional Environmental Monitoring and Assessment Program (R-EMAP) in the mineral belt of the Southern Rockies Ecoregion in Colorado. We contrasted results of analyses where community structure was summarized as community metrics and analyses based on genera abundances. Our objective was to identify metrics or taxa diagnostic of major environmental stressors in these streams. When RDA was used to analyze the community metrics data, three axes were significant, accounting for 96% of the metric- environment relation. The first RDA axis was correlated with dissolved cadmium, sediment zinc, and total suspended solids, variables that indicate it was related to mining effects. The second and third RDA axes were correlated with water temperature, mean substrate embeddedness, mean canopy density at the banks, and a riparian human disturbance index for agriculture, variables associated with riparian and substrate alterations associated with grazing by livestock. When CCA was used to analyze the genera abundance data, four axes were significant, accounting for 45% of the species-environment relation. The CCA axes were correlated with total and dissolved iron, water temperature, dissolved and total organic carbon, mean bank height, and mean water surface gradient, variables associated with riparian disturbance from livestock grazing, but not with mining effects. Because CCA measures variation in community structure in terms of changes in the absolute abundances of different genera relative to one another, that analysis of genera abundances was sensitive to the effects of riparian disturbance and stream size, but not to the general toxicological effects associated with mining that reduced the abundances of all genera. Community metrics measure various aspects of community structure, including taxa richness, taxa relative abundances, and taxa relative dominance, and these metrics were sensitive to the effects of mining, riparian disturbance, and stream size. Some community metrics, such as the percentage abundance of the most dominant taxon, the total number of individuals, the total number of taxa, and the number of chironomid taxa, may be used to diagnose the environmental stressors in these streams, while the results of the CCA for genera abundances may be used to design new metrics for this purpose.