title: Spatial and temporal variation of algal assemblages in six Midwest agricultural streams having varying levels of atrazine and other physicochemical attributes.
abstract: Potential effects of pesticides on stream algae occur alongside complex environmental influences; in situ studies examining these effects together are few, and have not typically controlled for collinearity of variables. We monitored the dynamics of periphyton, phytoplankton, and environmental factors including atrazine, and other water chemistry variables at 6 agricultural streams in the Midwest US from spring to summer of 2011 and 2012, and used variation partitioning of community models to determine the community inertia that is explained uniquely and/or jointly by atrazine and other environmental factors or groups of factors. Periphyton and phytoplankton assemblages were significantly structured by year, day of year, and site, and exhibited dynamic synchrony both between site-years and between periphyton and phytoplankton in the same site-year. The majority of inertia in the models (55.4% for periphyton, 68.4% for phytoplankton) was unexplained. The explained inertia in the models was predominantly shared (confounded) between variables and variable groups (13.3, 30.9%); the magnitude of inertia that was explained uniquely by variable groups (15.1, 18.3%) was of the order hydroclimate>chemistry>geography>atrazine for periphyton, and chemistry>hydroclimate>geography>atrazine for phytoplankton. The variables most influential to the assemblage structure included flow and velocity variables, and time since pulses above certain thresholds of nitrate+nitrite, total phosphorus, total suspended solids, and atrazine. Time since a ≥30 μg/L atrazine pulse uniquely explained more inertia than time since pulses ≥ 10 μg/L or daily or historic atrazine concentrations; this result is consistent with studies concluding that the effects of atrazine on algae typically only occur at ≥30 μg/L and are recovered from.
authors.affiliation: Waterborne Environmental, Inc., 2001 South First Street, Suite 109, Champaign, IL 61820, United States. Electronic address: andrusm@waterborne-env.com.
authors.forename: J Malia
authors.initials: JM
authors.lastname: Andrus
authors.affiliation: Rhithron Associates, Inc., 33 Fort Missoula Rd., Missoula, MT 59804, United States; Algal Analysis, LLC, Missoula, MT, United States. Electronic address: dwinter1@juno.com.
authors.forename: Diane
authors.initials: D
authors.lastname: Winter
authors.affiliation: MapTech, Inc., 3154 State Street, Blacksburg, VA 24060, United States. Electronic address: mscanlan@maptech-inc.com.
authors.forename: Michael
authors.initials: M
authors.lastname: Scanlan
authors.affiliation: Rhithron Associates, Inc., 33 Fort Missoula Rd., Missoula, MT 59804, United States. Electronic address: ssullivan@rhithron.com.
authors.forename: Sean
authors.initials: S
authors.lastname: Sullivan
authors.affiliation: Rhithron Associates, Inc., 33 Fort Missoula Rd., Missoula, MT 59804, United States. Electronic address: wbollman@rhithron.com.
authors.forename: Wease
authors.initials: W
authors.lastname: Bollman
authors.affiliation: Inovatia, Inc., 120 East Davis Street, Fayette, MO 65248, United States. Electronic address: jwaggoner@inovatia.com.
authors.forename: J B
authors.initials: JB
authors.lastname: Waggoner
authors.affiliation: Syngenta Crop Protection, LLC, 410 Swing Rd., Greensboro, NC 27419, United States. Electronic address: alan.hosmer@syngenta.com.
authors.forename: Alan J
authors.initials: AJ
authors.lastname: Hosmer
authors.affiliation: Syngenta Crop Protection, LLC, 410 Swing Rd., Greensboro, NC 27419, United States. Electronic address: richard.brain@syngenta.com.
authors.forename: Richard A
authors.initials: RA
authors.lastname: Brain
mesh_terms: D000383:Agriculture; D001280:Atrazine / Q000032:analysis / Q000633:toxicity*; D004784:Environmental Monitoring / Q000379:methods*; D006540:Herbicides / Q000032:analysis / Q000633:toxicity*; D058086:Microalgae / Q000145:classification / Q000254:growth & development*; D015146:Midwestern United States; D010839:Phytoplankton / Q000145:classification / Q000254:growth & development; D045483:Rivers / Q000737:chemistry; D062211:Spatio-Temporal Analysis; D014874:Water Pollutants, Chemical / Q000633:toxicity
chemical_list: D006540:Herbicides; D014874:Water Pollutants, Chemical; D001280:Atrazine
keywords: Algae; Atrazine; Midwest; Multiple stressors; Stream; Variance partitioning