Article

Environmental Monitoring and Assessment

, Volume 186, Issue 7, pp 4081-4096

Evaluation of a combined macrophyte–epiphyte bioassay for assessing nutrient enrichment in the Portneuf River, Idaho, USA

  • Andrew M. RayAffiliated withDepartment of Biological Sciences, Center for Ecological Research and Education, Idaho State UniversityNational Park Service, Greater Yellowstone Network Email author 
  • , Christopher A. MebaneAffiliated withU.S. Geological Survey
  • , Flint RabenAffiliated withDepartment of Biological Sciences, Center for Ecological Research and Education, Idaho State University
  • , Kathryn M. IrvineAffiliated withU.S. Geological Survey
  • , Amy M. MarcarelliAffiliated withDepartment of Biological Sciences, Center for Ecological Research and Education, Idaho State UniversityDepartment of Biological Sciences, Michigan Technological University

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Abstract

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.

Keywords

Nutrient bioassay Lemna minor Aquatic epiphytes Duckweed Macrophytes Eutrophication