Effects of multiple stressors on aquatic microbiota: an experimental approach.

Abstract

Anthropogenic stressors from industry, agriculture, and urbanization are primary drivers of negative impacts, these multiple stressors that produce cumulative and synergistic effects on aquatic microbiota. This study evaluated the effects of different stressors on aquatic microbial communities through experimental approaches involving freshwater microcosms and phototrophic biofilms. First, the impacts of glyphosate on different components (richness, density and beta diversity) of the aquatic microbiota (i.e., cyanobacteria, autotrophic and heterotrophic nanoflagellates, algae, ciliates, testate amoebae, rotifers, and copepods) were investigated, under different contamination scenarios over time.: (i) control (no glyphosate), (ii) low glyphosate content (30 µg/L-1), (iii) high glyphosate content (500 µg/L-1), (iv) the maximum allowed in Brazil (65 µg/L-1) over time: first day (T1), after three days (T3), and after seven days (T7). Glyphosate exposure promoted contrasting responses among biological groups, highlighting the complexity of community-level responses to contamination. Positive effects were observed for autotrophic and heterotrophic nanoflagellates, whereas negative effects were detected for total microfauna, while for other organisms, the responses are oscillatory (e.g., testate amoebae). Changes in species composition were observed for testate amoebae (species replacement) and cyanobacteria (richness difference), both of which contributed significantly to the variation in beta diversity under pesticide exposure. In a second experiment, the effects of copper, salinity, and temperature on the Gross Primary Production (GPP) of phototrophic biofilms were evaluated under different stressor sequences and temporal intervals. The results demonstrated that biofilm responses depended not only on stressor identity, but also on stressor chronology. The Copper/Salinity combination showed the strongest negative effects on GPP, particularly when copper was applied first. In addition, the sequential combination Salinity͢͢͢͢→ Copper→ Temperature consistently resulted in the lowest GPP values. Resistance generally increased with longer intervals between stress events, whereas the influence of stressor order on resilience decreased over time, suggesting that recovery dynamics play an important role in responses to sequential disturbances. Together, these findings demonstrate that the effects of multiple stressors on aquatic microbiota depend on the affected biological compartment, stressor identity, and temporal dynamics of exposure. Understanding how sequential and cumulative disturbances affect ecological stability is essential for predicting ecosystem responses under increasing anthropogenic pressure and climate change.