Impact of interaction between Limnoperna fortunei and Roundup Max® on freshwater phytoplankton: an in situ approach in Salto Grande reservoir (Argentina)

GATTÁS, FLORENCIA; DE STEFANO, LUCÍA; A. VINOCUR; BORDET, FACUNDO; ESPINOSA, MARÍA SOLEDAD; H. PIZARRO; CATALDO, D.

CHEMOSPHERE

PERGAMON-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 2018 vol. 209 p. 748 - 757

0045-6535

Mesocosms in situ approaches are useful tools to study multiple stressors effects in freshwaters. We assessed the joint impact of the glyphosate-based commercial formulation Roundup Max® and the invasive mussel Limnoperna fortunei over phytoplankton and water quality of Salto Grande reservoir through a 7-day experiment carried out in situ conditions by means of 400-L mesocosms. The following treatments were applied by triplicate: addition of 250 mussels (treatment M); addition of 5 mg L-1 of the active ingredient (a.i.) present in Roundup Max® (R); addition of 250 mussels and 5 mg L-1 of the a.i. in Roundup Max® (MR), and controls, without any addition (C). R had higher total phosphorus (TP) and ammonium nitrogen (N-NH4+) in water due to the herbicide input, and a significant increase in algal abundance, biovolume and chlorophyll a levels (Chl-a). In M, mussels? grazing over phytoplankton and posterior phosphates (SRP) release were evidenced, and a decrease in species diversity with respect to C (also observed in R). In MR, besides higher TP and N-NH4+, there was a decrease in biovolume and an antagonistic effect over Chl-a, and a synergistic effect over phytoplankton abundance. Significant decreases in species diversity and evenness were detected due to the explosive growth of a small and opportunistic Chlorophyta (Spermatozopsis exsultans). Negative selectivity of L. fortunei over S. exsultans, release of potential competitors by grazing, nutrients availability provided by Roundup Max® (and release of competitors by toxicity), may have favored the dominance of this species