Dust provides ecosystem-sustaining nutrients to landscapes underlain by intensively weathered soils. Here we show that dust may also be crucial in montane forest ecosystems, dominating nutrient budgets despite continuous replacement of depleted soils with fresh bedrock via erosion. Strontium and neodymium isotopes in modern dust show that Asian sources contribute 18-45% of dust deposition across our Sierra Nevada, California study sites. The remaining dust originates regionally from the nearby Central Valley. Measured dust fluxes are greater than or equal to modern erosional outputs from hillslopes to channels, and account for 10-20% of estimated millennial-average inputs of bedrock P. Our results demonstrate that exogenic dust can drive the evolution of nutrient budgets in montane ecosystems, with implications for predicting forest response to changes in climate and land use.

The generation and transport of mineral dust is strongly related to climate on seasonal, year-to-year, and glacial-interglacial timescales. The modern dust cycle is influenced by soil moisture, which is partly a function of drought duration and severity. The production and transport of dust can therefore be amplified by global and regional droughts, thereby moderating ecosystem vulnerability to disturbance through the influence of dust on nutrient delivery to ecosystems. In this work, we use strontium and neodymium isotopes in combination with trace element concentrations in modern dust samples collected in 2015 to quantify the role of regionally versus globally supplied dust in nutrient delivery to a montane ecosystem. The study sites lie along an elevational transect in the southern Sierra Nevada, USA, with samples spanning the dry seasons of 2014 (Aciego et al., 2017) and 2015 (this study), when the region was experiencing a historic drought. The goal of our research was to quantify the spatial and temporal variability and sensitivity of the dust cycle to short term changes at nutrient-limited sites. We find that, during the dry season of 2015, Asian sources contributed between 10 and 40% of dust to sites located along this elevational transect, and importantly increased in importance during the summer growing season compared to regional dust sources. These changes are likely related to the prolonged drought in Asia in 2015, highlighting both the sensitivity of dust production and transport to drought and the teleconnections of dust transport in terrestrial ecosystems.