RAPID: Sources and ecosystem significance of dust inputs during extremely wet and dry years in the Sierra Nevada, California

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Investigators have shown that, during drought, dust is important to soils in the Sierra Nevada, California (CA) and it is entering the Sierra from both the Central Valley (CA) and from the Gobi Desert, China, and that both sources bring in high-nutrient dust. These results are based on analyses of dust collected at the peak of the recent 2012-2016 drought, raising the question of whether the same trends would be observed during a wet year. Here, the team will collect new dust samples monthly to bi-monthly during the summer of 2017, following the recent wet winter of 2016-2017, from the same four elevations of the Southern Sierra Critical Zone Observatory that were used in previous research. In addition, they will collect shallow topsoil samples for comparison. They will then begin to describe the microbial community of the dust and soil from 2017, and to analyze the origin of dust entering the Sierra in the dry seasons of 2015, a dry year, and 2017, a wet year. The research will involve three graduate students and a postdoctoral scientist, as well as underserved minority undergraduates from both University of California (UC) Riverside and Merced, both Hispanic Serving Institutions. This project will be an excellent opportunity for educational and professional development. Additionally, the participating postdoctoral scientist takes part in a residential summer institute in Earth System Science for American Indian and Alaska Native high school students at UC Irvine. The research from this project will be disseminated during the summer institute in an effort to interest students in the interplay between climate and Earth surface processes. Dust has long been recognized as a vital source of nutrients in slowly eroding tropical ecosystems where intense weathering limits nutrient inputs from underlying bedrock. Investigators' recent work along an actively eroding montane landscape in the Sierra Nevada, California (CA) revealed large contributions of dust from both regional and transoceanic sources; growth-limiting nutrients (e.g., phosphorus) were determined to be supplied at rates on par with those from underlying bedrock weathering. This work also shows that microbial communities in dust varied between elevations, and community composition contained very few overlapping sequences with co-located soil communities. Also, the contributions from the Central Valley to mid-elevation sites increased substantially over the summer dry period, suggesting that the relative importance of regional dust sources to these ecosystems increases as the time since the last significant precipitation event increases. Analyses thus far have been based on dust inputs collected (2014) at the peak of the recent 2012-2016 drought, raising the question of whether findings are sensitive to changes in dust sources and emissions. The proposed work will begin to evaluate this question by analyzing the provenance and nutrients of dust collected during another drought-year summer (2015), and collecting new samples throughout the summer of 2017, after a wet year, with the goal of analyzing them in the near future.