title: Understanding the combined influence of fine sediment and glyphosate herbicide on stream periphyton communities.
abstract: Pesticides and deposited fine sediment have independently been associated with changes in relative abundance and species richness in aquatic ecosystems, but the interplay between these two stressors in agricultural streams is poorly understood. A 28-day experiment in outdoor stream mesocosms examined the effects of four levels each of fine sediment coverage (0, 25, 75, 100%) and glyphosate-based herbicide concentration (0, 50, 200, 370 μg/L) on periphyton communities (algae and bacteria) in a fully factorial, repeated-measures design. Our aims were to determine whether (i) increased levels of sediment and glyphosate had individual and/or additive effects, (ii) increased sediment reduced the toxicity of glyphosate (antagonistic multiple stressor interaction), or (iii) sediment-adsorbed glyphosate prolonged the effects of exposure (synergistic interaction). We also assigned all algal taxa to three ecological guilds (low-profile, high-profile and motile growth forms) and separately determined their responses to the treatments. As individual stressors, sediment addition affected all algal community-level metrics, whereas glyphosate addition only affected algal community evenness. Bacterial taxon richness was unaffected by either stressor. In combination, however, significant overall sediment by glyphosate interactions were detected, demonstrating synergistic (algal evenness, high-profile and motile guilds) or antagonistic effects (low-profile guild). Our experiment underscores the importance of considering both structural and functional indicators, including algal guild representation, when assessing the mechanisms by which periphyton communities respond to multiple stressors.
authors.affiliation: Department of Zoology, University of Otago, PO Box 56, Dunedin 9054, New Zealand. fsmagbanua@gmail.com
authors.forename: Francis S
authors.initials: FS
authors.lastname: Magbanua
authors.forename: Colin R
authors.initials: CR
authors.lastname: Townsend
authors.forename: Kimberly J
authors.initials: KJ
authors.lastname: Hageman
authors.forename: Katharina
authors.initials: K
authors.lastname: Lange
authors.forename: Gavin
authors.initials: G
authors.lastname: Lear
authors.forename: Gillian D
authors.initials: GD
authors.lastname: Lewis
authors.forename: Christoph D
authors.initials: CD
authors.lastname: Matthaei
mesh_terms: D000327:Adsorption; D001419:Bacteria / Q000187:drug effects; D017753:Ecosystem; D019015:Geologic Sediments / Q000382:microbiology; D005998:Glycine / Q000031:analogs & derivatives* / Q000633:toxicity; D006540:Herbicides / Q000633:toxicity; D010839:Phytoplankton / Q000187:drug effects; D014874:Water Pollutants, Chemical / Q000633:toxicity*; D000097797:Glyphosate
chemical_list: D005998:Glycine; D006540:Herbicides; D014874:Water Pollutants, Chemical; D000097797:Glyphosate
keywords: Algal guilds; Antagonism; Bacteria; Multiple stressors; Outdoor mesocosms; Synergism