Multiple interacting environmental drivers reduce the impact of solar UVR on primary productivity in Mediterranean lakes

Abstract

Increases in rainfall, continental runoff, and atmospheric dust deposition are reducing water transparency in lakes worldwide (i.e. higher attenuation Kd). Also, ongoing alterations in multiple environmental drivers due to global change are unpredictably impacting phytoplankton responses and lakes functioning. Although both issues demand urgent research, it remains untested how the interplay between Kd and multiple interacting drivers affect primary productivity (Pc). We manipulated four environmental drivers in an in situ experiment—quality of solar ultraviolet radiation (UVR), nutrient concentration (Nut), CO2 partial pressure (CO2), and light regime (Mix)—to determine how the Pc of nine freshwater phytoplankton communities, found along a Kd gradient in Mediterranean ecosystems, changed as the number of interacting drivers increased. Our findings indicated that UVR was the dominant driver, its effect being between 3–60 times stronger, on average, than that of any other driver tested. Also, UVR had the largest difference in driver magnitude of all the treatments tested. A future UVR × CO2 × Mix × Nut scenario exerted a more inhibitory effect on Pc as the water column became darker. However, the magnitude of this synergistic effect was 40–60% lower than that exerted by double and triple interactions and by UVR acting independently. These results illustrate that although future global-change conditions could reduce Pc in Mediterranean lakes, multiple interacting drivers can temper the impact of a severely detrimental driver (i.e. UVR), particularly as the water column darkens.

Multiple-stressors effects on Iberian freshwaters: A review of current knowledge and future research priorities

“…Investigating more autotrophic responses. Although some recent progress has been made (Cabrerizo et al, 2020;Romero et al, 2018), there is still a low representation of autotrophic organisms in the Iberian context. Given that some widely used WFD indicators data include autotrophic organisms (diatoms and macrophytes), we underscore the need of addressing multiple-stressor effects based on these low-cost, observational sources.…”

“…Considering more high-order stressor interactions. Most of the reviewed studies focused on pairwise interactions, whereas global change can yield more complex interactions (Cabrerizo et al, 2020;Rillig et al, 2019;Romero et al, 2019). Factorial designs including three or four stressors will require more resources (time, sampling effort, materials and personnel) and are often difficult to interpret and communicate to managers.…”

Macrophyte meadows mediate the response of the sediment microbial community to ultraviolet radiation

“…The most studied foreseeable environmental changes in lakes are warming, eutrophication, salinization, and changes in light quality (Jeppesen et al, 2014;Carrillo et al, 2015;Rojo et al, 2019). In this regard, Mediterranean shallow lakes or wetlands represent a paradigmatic case because they are already suffering the concomitant effects of these mentioned factors (Giorgi & Lionello, 2008;Parcerisas et al, 2012;IPCC, 2014;Cabrerizo et al, 2020). Moreover, these processes occur in ecosystems sited in areas with abusive anthropogenic nitrogen inputs (i.e.…”