Altitudinal Contrasts in Drought-Driven Aeolian Microbial Inputs to Montane Soil Ecology: Impacts of a 500-Year Drought in the Sierra Nevada, California

Abstract:

Mounting evidence shows that California is currently experiencing the most severe drought since 1580, and it is likely that extreme droughts will become more common as the climate changes. Any drought – particularly one of this magnitude – can elevate dust transport, from fallow croplands and bare natural ecosystems, to sometimes distant locations. The transported dust may bring nutrients and microorganisms, with unknown, but potentially transformational, impacts on the ecosystems where dust is deposited. In this project, we are measuring the mass, provenance (using isotopic chemistry), chemical makeup, and microbial composition of dust transported to the Sierra Nevada mountain range.

Dust is being collected at three sites along an elevational gradient in the Southern Sierra Critical Zone Observatory (SSCZO), ranging from 400 m to 2000 m elevation. At each site, dust has been collected monthly in Summer 2014 from passive dust collectors and from filters (1 um pore size) on the eddy covariance tower active CO₂ samplers. To complement dust collection, soil samples (10 cm depth) have been collected within the footprint of the towers. Dust fluxes were found to be highest at the 2000 meter-high site, with a maximum of 231 mg dust collected in July 2014. The lowest dust fluxes were found at the medium elevation site, at 1100 m, with 21 mg dust in July. The provenance of dust samples will be determined using radiogenic strontium (Sr) and neodymium (Nd) isotopic tracers. Nutrients and microbial composition of dust and soil samples will also be analyzed. This approach will allow us to identify the effects of mega-droughts on i) dust-related contributions to the geobiology and biogeochemistry of soils and ecosystems, ii) the role of local versus distant dust sources of microorganisms, including bacteria, archaea and fungi, and of nutrients to the Sierra Nevada, and iii) the role of elevation in determining the ecological effects of mega-drought-induced dust transport. In the future, we will endeavor to compare the data collected during this year of extreme drought to data collected in wetter years.