Experimental evidence of dust‐driven shifts in production, chlorophyll <i>a</i>, and community composition in mountain lakes

Abstract Drought and human land use have increased dust emissions in the western United States. However, the ecological sensitivity of remote lakes to dust deposition is not well understood and to date has largely been assessed through spatial and temporal correlations. Using in situ bioassays, we investigated the effects of dust enrichment on the production, chlorophyll a (Chl a ) concentration, and taxonomic composition of phytoplankton and microbial communities in three western US mountain lakes. We found that dust‐derived nutrients increased Chl a concentration in all three lakes, but the magnitude of the effect varied from 32% to 226%. This variation was related to pre‐existing lake conditions, such as trophic status, pH, and nutrient limitation. In Castle Lake, co‐limited by N and P, dust bioassays showed an increase in Chl a content per cell but suppressed primary production and increased dark 14 C uptake. In contrast, both Flathead Lake and The Loch were primarily P‐limited and exhibited increases in Chl a concentration. The contrasting Chl a and primary production results from Castle Lake are consistent with the alleviation of nitrogen limitation where energy Adenosine triphosphate (ATP) is used for nutrient assimilation instead of carbon fixation. Dust additions also altered the algal and microbial communities. The latter included the addition of new phyla (e.g., Deinococcota ), indicating that dust‐delivered microbes have the potential to thrive in receiving lakes. Our study provides the first short‐term experimental in situ evidence of rapid ecosystem effects in mountain lakes following dust exposure. The results emphasize the need for continued research in this area to understand interactions of both the short‐ and long‐term consequences of dust‐induced perturbations in remote lakes in the context of global changes.