Abstract

In surface waters within agricultural catchments, periphyton - i.e., biofilms containing algae, heterotrophs, and associated detritus - is subjected to multiple stressors including herbicides. Although herbicide effects on periphyton are frequently studied, the focus has been on photosynthesis-inhibiting herbicides while other modes of toxic action have received little attention. Against this background, a 21-days-lasting bioassay was conducted, during which mature periphytic communities were exposed to the carotenoid-biosynthesis-inhibiting herbicide diflufenican for 12 days (up to 10 mu g/L; n = 4), followed by a 9-days-lasting recovery phase in herbicide-free medium. Variables related to periphytic functioning (photosynthetic efficiency and non-photochemical quenching) and structure (pigment concentrations, biomass, and algal community structure) were quantified every third day during both experimental phases. Exposure to >= 0.2 mu g diflufenican/L resulted in 20-25% and 25-30% lowered carotenoid and chlorophyll a concentrations, respectively, likely explained by a reduced algal biovolume as well as diflufenican's mode of toxic action and thus a shift towards a higher heterotrophy of the communities. Despite these adverse effects on the photosynthetic apparatus, the photosynthetic efficiency increased by up to similar to 15% under diflufenican exposure judged on higher chlorophyll fluorescence. This may be explained by an up to similar to 60% reduced non-photochemical quenching as well as binding of diflufenican to the pigment-protein membrane complex of the photosystem II, two processes causing higher chlorophyll fluorescence. Additionally, phototrophs may have actively increased energy assimilation to cope with higher energy demands under chemical stress. Although periphyton showed some recovery potential following the exposure phase, observed as increasing chlorophyll a concentrations and non-photochemical quenching, periphyton may not be able to quickly recover from stress given the persistent increase in the photosynthetic efficiency. While the processes underlying the observed effects yet remain speculative, the results suggest a shift towards a higher degree of heterotrophy in periphytic communities ultimately increasing the importance of heterotrophic ecosystem functions at impacted sites over the long term.

Keywords

Algae; Biofilm; Carotenoid-biosynthesis-inhibitor; Chlorophyll fluorescence; Herbicide; PAM fluorometry; Photosynthesis

Published in

Aquatic Toxicology
2018, Volume: 203, pages: 187-193
Publisher: ELSEVIER SCIENCE BV

SLU Authors

• Feckler, Alexander

  • Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences
    

• Rakovic, Jelena

  • Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences
    
  • Department of Soil and Environment, Swedish University of Agricultural Sciences
    

• Kahlert, Maria

  • Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences
    

• Tröger, Rikard

  • Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences
    

• Bundschuh, Mirco

  • Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences
    

Sustainable Development Goals

Protect, restore and promote sustainable use of terrestrial ecosystems, sustainably manage forests, combat desertification, and halt and reverse land degradation and halt biodiversity loss


UKÄ Subject classification

Environmental Sciences
Ecology


Publication identifier

DOI: https://doi.org/10.1016/j.aquatox.2018.08.015

Permanent link to this page (URI)

https://res.slu.se/id/publ/96817