Evaluation of a combined macrophyte–epiphyte bioassay for assessing nutrient enrichment in the Portneuf River, Idaho, USA
We describe and evaluate a laboratory bioassay that uses Lemna minor L. and attached epiphytes to characterize the status of ambient and nutrient-enriched water from the Portneuf River, Idaho. Specifically, we measured morphological (number of fronds, longest surface axis, and root length) and population-level (number of plants and dry mass) responses of L. minor and community-level (ash-free dry mass [AFDM] and chlorophyll a [Chl a]) responses of epiphytes to nutrient enrichment. Overall, measures of macrophyte biomass and abundance increased with increasing concentrations of dissolved phosphorus (P) and responded more predictably to nutrient enrichment than morphological measures. Epiphyte AFDM and Chl a were also greatest in P-enriched water; enrichments of N alone produced no measurable epiphytic response. The epiphyte biomass response did not directly mirror macrophyte biomass responses, illustrating the value of a combined macrophyte–epiphyte assay to more fully evaluate nutrient management strategies. Finally, the most P-enriched waters not only supported greater standing stocks of macrophyte and epiphytes but also had significantly higher water column dissolved oxygen and dissolved organic carbon concentrations and a lower pH. Advantages of this macrophyte–epiphyte bioassay over more traditional single-species assays include the use of a more realistic level of biological organization, a relatively short assay schedule (~10 days), and the inclusion of multiple biological response and water-quality measures.
KeywordsNutrient bioassay Lemna minor Aquatic epiphytes Duckweed Macrophytes Eutrophication
This work was supported by the National Science Foundation Undergraduate Mentoring in Environmental Biology program (UMEB 03-05289), the NSF-Idaho EPSCoR program (EPS 04-47689), the Inland Northwest Research Alliance (Department of Energy Contract #DE-FG02-05ER64132), the Center for Ecological Research and Education and the Stream Ecology Center at Idaho State University, and the Idaho Department of Environmental Quality. Field and laboratory support was also provided by the City of Pocatello, the Idaho Association of Soil Conservation Districts, and Three Rivers RC&D. The authors would also like to thank Kelsey Flandro, Stacey Raben, Jennifer Cornell, Heather Bechtold, and Colin Warnock for field and laboratory assistance. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the US Government.
- APHA. (2005). Standard methods for the examination of water and wastewater (21st ed.). Washington DC: American Public Health Association, American Water Works Association, and Water Environment Federation.Google Scholar
- Hooper, F. F. (1969). Eutrophication indices and their relation to other indices of ecosystem change. In Review of eutrophication: Causes, consequences, correctives. Proceedings from a Symposium (pp. 225–235). Washington DC: National Academy of Sciences Publication 1700.Google Scholar
- Les, D. H., Crawford, D. J., Landolt, E., Gabel, J. D., & Kimball, R. T. (2002). Phylogeny and systematics of Lemnaceae, the duckweed family. Systematic Botany, 27, 221–240.Google Scholar
- Miller, W. E, Greene, J. C., & Shiroyama, T. (1978). The Selenastrum capricornutum Printz algal assay bottle test. Experimental design, application and data interpretation protocol. U.S. Environmental Protection Agency, EPA-600/9-78-018.Google Scholar
- R Development Core Team. (2011). R: A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna. ISBN 3-900051-07-0. http://www.r-project.org. Accessed 14 March 2012.
- Ramsey, F. L., & Schafer, D. W. (2002). The statistical sleuth. A course in methods of data analysis. Pacific Grove: Duxbury Press.Google Scholar
- Ray, A. M. (2010). Portneuf River total maximum daily load revision and addendum. Idaho Department of Environmental Quality. http://www.epa.gov/waters/tmdldocs/portneuf_river_revision_addendum_final.pdf. Accessed 3 October 2013.
- Szabó, S., Braun, M., & Borics, G. (1999). Elemental flux between algae and duckweeds (Lemna gibba) during competition. Archiv für Hydrobiologie, 146, 355–367.Google Scholar
- USEPA. (2000). Nutrient criteria technical guidance manual: Rivers and streams. U.S. Environmental Protection Agency, EPA-822-B-00-002. http://www.epa.gov/waterscience/criteria/nutrient/guidance/rivers/index.html. Accessed 3 October 2013.
- USEPA. (2013). National summary of impaired waters and TMDL information. U.S. Environmental Protection Agency. http://iaspub.epa.gov/waters10/attains_nation_cy.control?p_report_type=T. Accessed 3 October 2013.
- Wetzel, R. G. (2001). Limnology: Lake and river ecosystems. San Diego: Academic Press.Google Scholar