The effects of nickel on the structure and functioning of a freshwater plankton community under high dissolved organic carbon conditions: a microcosm experiment

In the present study, we aimed to test the protectiveness of the bioavailability-normalisation procedure, with its associated hazardous concentrations for x% of the species (HCx), that is currently implemented to derive environmental threshold concentrations for Ni in European environmental legislative frameworks. We exposed a natural plankton-dominated community to three constant Ni concentrations during a 56d-microcosm experiment under high DOC conditions. The effects of the bioavailability-normalised HC5 and HC50 were evaluated at the level of the community structure, community functioning  and individual species abundances.

Scientific abstract

In the present study, we aimed to test the protectiveness of the bioavailability-normalisation procedure, with its associated hazardous concentrations for x% of the species (HCx), that is currently implemented to derive environmental threshold concentrations for Ni in European environmental legislative frameworks. We exposed a natural plankton-dominated community to three constant Ni concentrations, i.e. a control with no Ni added (background Ni between 1.2 and 4 µg/L) and the bioavailability-normalized HC5 and HC50 of 24 and 97 µg dissolved Ni/L, respectively, during a 56d-microcosm experiment under high DOC conditions (dissolved organic carbon 14 mg/L at test initiation). The effects of the bioavailability-normalised HC5 and HC50 were evaluated at the level of the community structure (community composition and plankton group abundances), community functioning (measured as indirect physicochemical proxies for overnight respiration and carbon fluxes) and individual species abundances. The bioavailability-normalised HC50-treatment had clear effects (defined as effects occurring on at least two consecutive sampling days) on both the structure and functioning of the investigated aquatic community. Through its effect on community functioning (i.e. reduced pH and DOC), Ni also influenced its own bioavailability. Clear direct effects of Ni were observed for only three species (i.e. the cyanobacteria Oscillatoria sp. 1 and the rotifers 'Asplanchna/Testidunela sp' and 'Trichocerca group similis'). Most other effects occurring in the plankton community in the HC50 treatment were indirect and likely driven by the direct effect of Ni on the cyanobacteria Oscillatoria sp. 1, which was the dominant phytoplankton species in the control microcosms. In contrast to this, the bioavailability-normalised HC5 did not induce clear effects on community structure and functioning endpoints, as these were only affected on individual sampling days. Clear (direct) effects were observed for only two plankton species (i.e. the rotifer Trichocerca group similis and the cyanobacteria Oscillatoria sp. 1), but their abundances recovered to control levels at the end of the study. In addition, a few species (1 phytoplankton and 3 zooplankton species) were affected in the HC5 treatment only on the last sampling day. It is uncertain whether or not these species would have shown clear effects over a longer exposure duration. Thus, our study shows that the bioavailability-normalised HC5 of Ni at high DOC induced clear effects on a few individual species. However, the overall conclusion is that the bioavailability-normalised HC5 of Ni as derived with the procedure that is currently implemented in European legislative frameworks protects against clear effects on community structure and function.

Full reference (link):

Nys, C., Van Regenmortel, T., De Schamphelaere, K.A.C. (2019). The effects of nickel on the structure and functioning of a freshwater plankton community under high dissolved organic carbon conditions: a microcosm experiment. ENVIRONMENTAL SCIENCE & TECHNOLOGY.