title: Modelling the effect of fluctuating herbicide concentrations on algae growth.
abstract: Herbicide concentrations fluctuate widely in watercourses after crop applications and rain events. The level of concentrations in pulses can exceed the water chronic quality criteria. In the present study, we proposed modelling the effects of successive pulse exposure on algae. The deterministic model proposed is based on two parameters: (i) the typical growth rate of the algae, obtained by monitoring growth rates of several successive batch cultures in growth media, characterizing both the growth of the control and during the recovery periods; (ii) the growth rate of the algae exposed to pulses, determined from a dose-response curve obtained with a standard toxicity test. We focused on the herbicide isoproturon and on the freshwater alga Scenedesmus vacuolatus, and we validated the model prediction based on effect measured during five sequential pulse exposures in laboratory. The comparison between the laboratory and the modelled effects illustrated that the results yielded were consistent, making the model suitable for effect prediction of the herbicide photosystem II inhibitor isoproturon on the alga S. vacuolatus. More generally, modelling showed that both pulse duration and level of concentration play a crucial role. The application of the model to a real case demonstrated that both the highest peaks and the low peaks with a long duration affect principally the cell density inhibition of the alga S. vacuolatus. It is therefore essential to detect these characteristic pulses when monitoring of herbicide concentrations are conducted in rivers.
authors.affiliation: Institut des dynamiques de la surface terrestre (IDYST), Faculté des Géosciences et de l'Environment, Université de Lausanne, Géopolis, Quartier Mouline, CH-1015 Lausanne, Switzerland. Electronic address: pierre-jean.copin@unil.ch.
authors.forename: Pierre-Jean
authors.initials: PJ
authors.lastname: Copin
authors.affiliation: Laboratoire de technologie écologique, Institut d'ingénierie de l'environnement, Faculté de l'environnement naturel, architectural et construit (ENAC), Ecole Polytechnique Fédérale de Lausanne (EPFL), 1015 Lausanne, Switzerland. Electronic address: sylvain.coutu@epfl.ch.
authors.forename: Sylvain
authors.initials: S
authors.lastname: Coutu
authors.affiliation: Institut des dynamiques de la surface terrestre (IDYST), Faculté des Géosciences et de l'Environment, Université de Lausanne, Géopolis, Quartier Mouline, CH-1015 Lausanne, Switzerland. Electronic address: nathalie.chevre@unil.ch.
authors.forename: Nathalie
authors.initials: N
authors.lastname: Chèvre
mesh_terms: D002452:Cell Count; D005618:Fresh Water; D006540:Herbicides / Q000633:toxicity*; D008954:Models, Biological; D010671:Phenylurea Compounds / Q000633:toxicity*; D045483:Rivers; D044444:Scenedesmus / Q000187:drug effects* / Q000254:growth & development; D018675:Toxicity Tests; D014874:Water Pollutants, Chemical / Q000633:toxicity*
chemical_list: D006540:Herbicides; D010671:Phenylurea Compounds; D014874:Water Pollutants, Chemical; C028904:isoproturon
keywords: Cell density inhibition; Isoproturon; Modelling; Pulse; Recovery; Scenedesmus vacuolatus