Using genus-level taxonomy and traits for cost-effective ecological assessments of diatom assemblage condition

Difficulty in diatom species identification and nomenclature can lead to major inconsistencies in taxonomic datasets. These inconsistencies may hinder the use of diatoms in large-extent bioassessments such as the U.S. Environmental Protection Agency’s (U.S. EPA) National Aquatic Resource Surveys. We addressed this problem by developing diatom multimetric indices (MMIs) of ecological condition using genus-level taxonomy and trait-based information (e.g., tube-living, motile and/or nitrogen-fixing diatoms) collected from the 2008-09 U.S. EPA National Rivers and Stream Assessment (NRSA). The MMIs were designed to assess ecological condition for >3,000 rivers and streams across the U.S. Genus-level, trait-based indices have the advantage over traditional species-based indices of using genus-level data which require less work-effort and expertise and therefore are less costly to analyze. Using genus-level taxonomy also eliminates the persistent taxonomic biases introduced over vast geographic extents because genus-level identifications are less prone to taxonomic errors, thus improving the taxonomic consistency and quality of large datasets involving multiple analysts. The genus-level trait MMIs responded well to increases in multiple stressors; discriminating least-disturbed from most-disturbed sites. This new indicator will allow for the use of diatoms in future NRSA surveys. Similar genus-level MMIs are also being developed for use in the U.S. EPA’s National Wetland Condition Assessment. Our genus-based approach can be effective for spatially extensive assessments and facilitates including of diatoms into assessment programs that have limited monitoring resources.

Impact/Purpose

For large-scale and long-term assessment programs that require multiple taxonomic laboratories to process samples, such as the United StatesEnvironmental Protection Agency’s (U.S. EPA’s) National Rivers and Streams Assessment (NRSA), discrepancies in species-level identification ornomenclature can preclude the use of diatom data in regional and national assessments. To address this problem, ORISE post-doctoral associate LuisaRiato, and Ryan Hill, Alan Herlihy, David Peck, Philip Kaufmann, John Stoddard and Steven Paulsen of EPA-ORD-PESD, developed diatom multimetricindices (MMIs) using genus-level diatom taxonomy and trait-based autecological information, effectively circumventing the problem of taxonomicinconsistencies in the National River and Stream Assessment diatom datasets from 2008-2009 and 2013-2014. The MMIs are designed to assess river andstream ecological condition in three large ecoregions across the conterminous United States. In contrast to traditional species-level approaches, trait-basedapproaches can use genus-level data, which is simpler and less-expensive to obtain, and can eliminate discrepancies in species-level identification ornomenclature that can reduce confidence and defensibility of the datasets. The authors applied their trait-based MMI to NRSA data collected within threelarge ecoregions within the U.S. - the East, Plains and West. The MMI for the East had the greatest ability to discriminate reference from disturbed sites,followed by MMIs for the Plains and West, respectively. MMI performance was comparable to that observed in existing NRSA fish and macroinvertebrateMMIs. The authors also demonstrate that trait-based MMI’s can be effective for large-scale assessments, and may allow programs such as NRSA toassess historical trends in freshwater condition by revisiting older diatom datasets, where inconsistencies in species-level identification, and recentadvances in standardization of identification may have rendered historical datasets unreliable and inconsistent with current standards. The approachdeveloped in this study requires less labor, and could allow the inclusion of diatoms in state or regional programs with limited time and financial resources

Citation

Riato, L., R. Hill, A. Herlihy, D. Peck, P. Kaufmann, J. Stoddard, AND S. Paulsen. Using genus-level taxonomy and traits for cost-effective ecological assessments of diatom assemblage condition. Society of Limnology, Foz do Iguaçu, N/A, BRAZIL, May 05 - 09, 2024.