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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, chlorophylla(Chla) concentration, and taxonomic composition of phytoplankton and microbial communities in three western US mountain lakes. We found that dust‐derived nutrients increased Chlaconcentration 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 Chlacontent per cell but suppressed primary production and increased dark¹⁴C uptake. In contrast, both Flathead Lake and The Loch were primarily P‐limited and exhibited increases in Chlaconcentration. The contrasting Chlaand 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. 

Abstract Wildfire smoke often covers areas larger than the burned area, yet the impacts of smoke on nearby aquatic ecosystems are understudied. In the summer of 2018, wildfire smoke covered Castle Lake (California, USA) for 55 days. We quantified the influence of smoke on the lake by comparing the physics, chemistry, productivity, and animal ecology in the prior four years (2014–2017) to the smoke year (2018). Smoke reduced incident ultraviolet-B (UV-B) radiation by 31% and photosynthetically active radiation (PAR) by 11%. Similarly, underwater UV-B and PAR decreased by 65 and 44%, respectively, and lake heat content decreased by 7%. While the nutrient limitation of primary production did not change, shallow production in the offshore habitat increased by 109%, likely due to a release from photoinhibition. In contrast, deep-water, primary production decreased and the deep-water peak in chlorophylladid not develop, likely due to reduced PAR. Despite the structural changes in primary production, light, and temperature, we observed little significant change in zooplankton biomass, community composition, or migration pattern. Trout were absent from the littoral-benthic habitat during the smoke period. The duration and intensity of smoke influences light regimes, heat content, and productivity, with differing responses to consumers.