Interdisciplinary strategy to survey phytoplankton dynamics of a eutrophic lake under rain forcing: description of the instrumental set-up and first results

Abstract

Abstract. We present an interdisciplinary investigation of the links between rain macro and microphysical properties, meteorological parameters, and a mountain lake to assess the impact of precipitation events on phytoplankton dynamics and, in particular, on cyanobacteria. In order to document this interdisciplinary scientific question, the Aydat lake in the French massif central mountains has been instrumented in 2020 with a set of high-resolution atmospheric radars, disdrometer, and precipitation collector. In parallel, the lake was monitored with a suite of sensors and water sampling. To illustrate the potential of this original experimental setup, we present a rain case study that occurred in September 2020 and during which three contrasted sub-periods were identified. Using our high temporal-resolution monitoring, we show that the air mass origin mainly influences the rain nutrient composition, which depends on the type of rain, convective or stratiform. Our results also highlighted a non-negligible presence of photosynthetic cells in all rains, but their very low abundance can probably not impact the phytoplankton dynamics. Nevertheless, rain events indirectly impacted phytoplankton assemblages. Indeed, among all phytoplankton genera, three cyanobacteria, Microcystis, Coelomoron, and Merismopedia, showed a similar pattern with a systematic punctual decrease of their abundance at the lake surface immediately after rain events, suggesting a different impact of rain events according to the cyanobacterial genus considered. These various phytoplankton responses subjected to the same rainfall event could play a key role in phytoplankton dynamics in the temperate zone. Our results highlight the interest in high-frequency and time resolution monitoring of both atmosphere and lake to better understand the cyanobacteria adaptive strategies following rain events.

The aeromicrobiome: the selective and dynamic outer-layer of the Earth’s microbiome

“…For bacteria, wet deposition is associated with highest fluxes, reaching up to ~10 7 -10 8 cells/m 2 /h (Reche et al, 2018;Woo and Yamamoto, 2020;Péguilhan et al, 2021). The microbial mixture permanently deposited from air on surfaces brings invaders and competitors to surface environments (Hervas and Casamayor, 2009;Morris and Sands, 2017;Noirmain et al, 2022). The continuous flow of foreign genetic material from atmospheric deposition is hypothesized to contribute to ecosystems stability and microbial evolution (Jalasvuori, 2020).…”