title: THE POTENTIAL INDICATOR VALUE OF RARE TAXA RICHNESS IN DIATOM-BASED STREAM BIOASSESSMENT1.
abstract: Despite their recognized contribution to species richness, the importance of rare taxa richness in bioassessment is unclear. This study aimed to characterize the environmental factors affecting the number of rare diatom taxa in western U.S. streams and rivers, and to evaluate whether this number can be used to differentiate streams with contrasting human disturbance. Three different categories of rare taxa were used: satellite (taxa with low occurrence and low abundance), rural (taxa with high occurrence and low abundance), and urban (taxa with low occurrence and high abundance). Common taxa were included as a separate category of core taxa (taxa with high occurrence and high abundance). We analyzed 987 diatom samples collected over the period of 5 years (2000-2004) for the U.S. Environmental Protection Agency's (EPA) Western Environmental Monitoring and Assessment Program (WEMAP). The results showed that rural taxa richness (number of rural taxa per site) increased along a longitudinal gradient from mountainous, fast-flowing oligotrophic streams with fewer fine substrates to large, slow-moving, nutrient-rich rivers with abundance of fine substrates. Rural taxa richness was the only rarity metric that distinguished least disturbed (reference) sites from the most disturbed (impacted) sites, but it was significantly different only in the mountains ecoregion. Core taxa richness distinguished reference from impacted sites in the West and in each one of the three ecoregions (mountains, plains, and xeric). Our findings revealed that rural taxa richness can be used as an indicator of human disturbance in streams/rivers, especially in the mountains ecoregion, and that rarity definition is important in bioassessment.
authors.affiliation: Environmental Sciences and Management, Portland State University, Portland, Oregon 97207, USADepartment of Biological and Environmental Sciences, Georgia College and State University, Milledgeville, Georgia 31061, USADepartment of Biological Sciences, California State University San Marcos, San Marcos, California 92096, USADepartment of Biology, North Central College, Naperville, Illinois 60540, USA.
authors.forename: Nadezhda D
authors.initials: ND
authors.lastname: Gillett
authors.affiliation: Environmental Sciences and Management, Portland State University, Portland, Oregon 97207, USADepartment of Biological and Environmental Sciences, Georgia College and State University, Milledgeville, Georgia 31061, USADepartment of Biological Sciences, California State University San Marcos, San Marcos, California 92096, USADepartment of Biology, North Central College, Naperville, Illinois 60540, USA.
authors.forename: Yangdong
authors.initials: Y
authors.lastname: Pan
authors.affiliation: Environmental Sciences and Management, Portland State University, Portland, Oregon 97207, USADepartment of Biological and Environmental Sciences, Georgia College and State University, Milledgeville, Georgia 31061, USADepartment of Biological Sciences, California State University San Marcos, San Marcos, California 92096, USADepartment of Biology, North Central College, Naperville, Illinois 60540, USA.
authors.forename: Kalina M
authors.initials: KM
authors.lastname: Manoylov
authors.affiliation: Environmental Sciences and Management, Portland State University, Portland, Oregon 97207, USADepartment of Biological and Environmental Sciences, Georgia College and State University, Milledgeville, Georgia 31061, USADepartment of Biological Sciences, California State University San Marcos, San Marcos, California 92096, USADepartment of Biology, North Central College, Naperville, Illinois 60540, USA.
authors.forename: Rosalina
authors.initials: R
authors.lastname: Stancheva
authors.affiliation: Environmental Sciences and Management, Portland State University, Portland, Oregon 97207, USADepartment of Biological and Environmental Sciences, Georgia College and State University, Milledgeville, Georgia 31061, USADepartment of Biological Sciences, California State University San Marcos, San Marcos, California 92096, USADepartment of Biology, North Central College, Naperville, Illinois 60540, USA.
authors.forename: Christine L
authors.initials: CL
authors.lastname: Weilhoefer
keywords: Western Environmental Monitoring and Assessment Program; bioassessment; diatoms; rare taxa; streams/rivers