We quantified dry and wet atmospheric deposition of soluble reactive phosphorus (SRP) to the Southwest Mediterranean region during one year and assessed its effect on bacterial abundance and phytoplankton specific biomass during one ice-free period in a high mountain lake located in an area highly influenced by Saharan dust outbreaks. Dry deposition of SRP represented 79% of total SRP inputs and it showed a seasonal pattern similar to Saharan dust export to this region, with maxima during spring and summer. Bacterial abundance was significantly correlated with SRP atmospheric deposition, suggesting the influence of this input on bacterioplankton dynamics. The field evidence was experimentally corroborated using bacterial regrowth cultures performed with dust-amended lake water. Dust addition significantly increased SRP concentration in lake water and it stimulated bacterial abundance. Regarding phytoplankton community, only one species, the chrysophyte Chromulina nevadensis, was significantly related to SRP inputs and, consequently, there was a significant decrease in phytoplankton species diversity after atmospheric SRP inputs. Since changes in climate will presumably lead to an alteration in dust export, these results point to the need of further studies on the potential effects of this alteration on bacterioplankton and phytoplankton dynamics in remote oligotrophic systems.
