Effects of photosystem II inhibitors and their mixture on freshwater phytoplankton succession in outdoor mesocosms

Abstract

Effects of three photosystem II inhibitors and of their mixture on a freshwater phytoplankton community were studied in outdoor mesocosms. Atrazine, isoproturon, and diuron were applied as 30% hazardous concentrations (HC30s) obtained from species-sensitivity distributions. Taking concentration addition into account, the mixture comprised one-third of the HC30 of each substance. Effects were investigated during a five-week period of constant concentrations and a five-month posttreatment period when the herbicides dissipated. Total abundance, species composition, and diversity and recovery of the community were evaluated. Ordination techniques, such as principal component analysis and principal response curve, were applied to compare the various treatments on the community level. The three herbicides stimulated comparable effects on total abundance and diversity of phytoplankton during the period of constant exposure because of the susceptibility of the dominant cryptophytes Chroomonas acuta and Cryptomonas erosa et ovata and the prasinophyte Nephroselmis cf. olivacea. Moreover, concentration addition described combined effects of atrazine, isoproturon, and diuron on total abundance and diversity in the constant-exposure period, because their mixture induced effects on abundance and diversity similar to those of the single substances. Principal component and principal response curve analyses revealed that the community structure of diuron- and isoproturon-treated phytoplankton recovered two weeks after constant exposure, which might be related to the fast dissipation of the phenylureas. Species compositions of mixture- and atrazine-treated communities were not comparable to that of the control community five months after the end of constant exposure. This might be explained by the slower dissipation of atrazine relative to the phenylureas and by differences in the species sensitivities, resulting in a different succession of phytoplankton.

Assessing triclosan-induced ecological and trans-generational effects in natural phytoplankton communities: a trait-based field method

“…We consider however more likely that the low exposure level and the very short time characterising our exposure design were not sufficient to induce disappearance of an entire functional group over the course of 2-3 generations. This idea is supported by previous studies: treatment of phytoplankton communities in outdoor mesocosms with herbicides, for example, resulted in limited effects on biodiversity after short periods of time, with many treatments increasing Shannon diversity for longer exposure time (Knauert et al 2009). A positive control, with a known effect on community biodiversity, would have allowed to directly test the importance of methodological constraints in detecting extinction of one or more functional groups and, although challenging, should be included in future similar studies, also to assess the impact of extinction on inferred community effects.…”

“…More experimental studies should address in the future the relative importance and interaction of physiological acclimation, evolutionary processes and ecological dynamics in explaining community effects of micropollutants like TCS, in order to scale the effects of stressors through community level dynamics and link between response-and-effect traits (the Price equation is only one of the possible ways forward in this direction). The study of resilience and recovery time in complex natural systems also appears critical, especially after exposure to mixtures that may affect the structure and functioning of communities more deeply and unpredictably (Knauert et al 2009). …”

Mixture toxicity from photosystem II inhibitors on microalgal community succession is predictable by concentration addition

“…Knauert et al [39] concluded that CA is applicable for both effects on photosynthesis as well as higher-order ecological effects such as total abundance and diversity [20] in a phytoplankton community after exposure to non-congeneric PSII inhibitors at the level of HC30. We now may conclude that this phenomenon is not restricted to a single effect level.…”

Impact of contaminated-sediment resuspension on phytoplankton in the Biguglia lagoon (Corsica, Mediterranean Sea)

“…Phytoplankton responses to contaminants can, for example, be influenced by species interactions (Leboulanger et al, 2001;Ortmann et al, 2012), grazing pressure (Munoz et al, 2001), temperature (Bérard et al, 1999), water chemistry (Knauer et al, 2007), light exposure history (Guasch and Sabater, 1998;Laviale et al, 2010) or contamination exposure history (Dorigo et al, 2004;Serra et al, 2009). In addition, in its natural environment, phytoplankton is exposed to contaminant mixtures and, depending on the mixture, additive, synergistic or antagonistic effects may result from contaminant interactions (DeLorenzo and Fleming, 2008;Knauert et al, 2009;Relyea, 2009).…”