title: Influence of isolation on the recovery of pond mesocosms from the application of an insecticide. I. Study design and planktonic community responses.
abstract: The influence of relative isolation on the ecological recovery of freshwater outdoor mesocosm communities after an acute toxic stress was assessed in a 14-month-long study. A single concentration of deltamethrin was applied to 8 out of 16 outdoor 9-m3 mesocosms to create a rapid decrease of the abundance of arthropods. To discriminate between external and internal recovery mechanisms, four treated and four untreated (control) mesocosms were covered with 1-mm mesh screen lids. The dynamics of planktonic communities were monitored in the four types of ponds. The abundance of many phytoplankton taxa increased after deltamethrin addition, but the magnitude of most increases was relatively small, probably due to low nutrient availability and the survival of rotifers. The greatest impact on zooplankton was seen in Daphniidae and, to a lesser extent, calanoid copepods. Recovery (defined as when statistical analysis failed to detect a difference in the abundance between the deltamethrin-treated ponds and corresponding control ponds for two consecutive sampling dates) of Daphniidae was observed in the water column 105 and 77 d after deltamethrin addition in open and covered mesocosms, respectively, and <42 d for both open and covered ponds at the surface of the sediments. Rotifers did not proliferate, probably because of the survival of predators (e.g., cyclopoid copepods). These results confirm that the recovery of planktonic communities after exposure to a strong temporary chemical stress mostly depends upon internal mechanisms (except for larvae of the insect Chaoborus sp.) and that recovery dynamics are controlled by biotic factors, such as the presence of dormant forms and selective survival of predators.
authors.affiliation: UMR985 INRA-Agrocampus Ecobiologie et Qualité des Hydrosystèmes Continentaux, Equipe Ecotoxicologie et Qualité des Milieux Aquatiques, 65 Rue de Saint-Brieuc, F35042 Rennes, France.
authors.forename: Mark L
authors.initials: ML
authors.lastname: Hanson
authors.forename: David W
authors.initials: DW
authors.lastname: Graham
authors.forename: Emmanuelle
authors.initials: E
authors.lastname: Babin
authors.forename: Didier
authors.initials: D
authors.lastname: Azam
authors.forename: Marie-Agnes
authors.initials: MA
authors.lastname: Coutellec
authors.forename: Charles W
authors.initials: CW
authors.lastname: Knapp
authors.forename: Laurent
authors.initials: L
authors.lastname: Lagadic
authors.forename: Thierry
authors.initials: T
authors.lastname: Caquet
mesh_terms: D005618:Fresh Water; D007306:Insecticides / Q000633:toxicity*; D009570:Nitriles / Q000633:toxicity*; D010933:Plankton / Q000187:drug effects*; D011722:Pyrethrins / Q000633:toxicity*; D014874:Water Pollutants, Chemical / Q000633:toxicity*
chemical_list: D007306:Insecticides; D009570:Nitriles; D011722:Pyrethrins; D014874:Water Pollutants, Chemical; C017180:decamethrin