Periphyton and phytoplankton samples were collected and analyzed from 393 locations in three mid-continent (US) great rivers: the Upper Mississippi, Missouri and Ohio. From the 410 taxa identified, 303 taxa were common enough for multivariate analyses. Algae assemblages were quantified by multiple metrics including biovolume (based on algal shape formulae and cell measurements), relative biovolume, cell density, relative cell density, entity density (based on numbers of colonies, filaments or free-living cells), and relative entity density. Relationships between algal metrics and both water quality (e.g., nutrients, ionic properties, physicochemical parameters) and landscape-scale stressor data (e.g., proportions watershed with agriculture and urban development, impoundment, pollution point-sources) were examined using multivariate analyses. Overall, algal metrics were more closely related to water quality than to landscape stressors. Phytoplankton cell density was the best indicator of water quality with 45% of the variance in the taxonomic data explained. We suspect that relationships between periphyton and water quality were weaker because water grab samples did not reflect the prevailing conditions to which the periphyton had been exposed. Phytoplankton also had a slightly stronger relationship to landscape-scale stressor data than did periphyton. Biovolume metrics were the best periphytic indicators of water quality and stressors. Absolute algal metrics, especially cell density, consistently had stronger relationships to water quality and stressors than relative (percentage-based) metrics.
Bibliographical noteFunding Information:
We thank the field crews who collected the EMAP-GRE data. M. Agbeti of Bio-Limno Research and Consulting and E. Ruzycki (NRRI) supported algal analyses. N. Danz helped with calculations and development of the algae database. This research was supported by a grant to E. Reavie from the U.S. Environmental Protection Agency under Cooperative Agreement CR-83272401. This document has not been subjected to the Agency's required peer and policy review and therefore does not necessarily reflect the view of the Agency, and no official endorsement should be inferred. This is contribution number 493 of the Center for Water and the Environment, Natural Resources Research Institute, University of Minnesota Duluth.
- Great rivers
- Water quality