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

研究人员已经证明，在干旱期间，沙尘对加州内华达山脉（CA）的土壤很重要，而且它正在从中央山谷（CA）和中国戈壁沙漠进入塞拉利昂，这两个来源都带来了高营养的沙尘。这些结果是基于对最近的2012-2016年干旱高峰期收集的尘埃的分析，提出了一个问题，即在潮湿的年份是否会观察到同样的趋势。在这里，该团队将在2016-2017年最近潮湿的冬季之后，于2017年夏季每月到双月收集新的尘埃样本，这些样本来自先前研究中使用的南塞拉临界区天文台的相同四个高度。此外，他们将收集浅层表土样本进行比较。然后，他们将开始描述2017年以来灰尘和土壤的微生物群落，并分析2015年旱季（干旱年）和2017年（潮湿年）进入塞拉的灰尘的来源。这项研究将涉及三名研究生和一名博士后科学家，以及来自加州大学河滨分校和默塞德分校两所西班牙裔服务机构的服务不足的少数族裔本科生。这个项目将是一个教育和专业发展的绝佳机会。此外，参与的博士后科学家还将参加加州大学欧文分校为美国印第安人和阿拉斯加原住民高中生举办的地球系统科学住宿暑期学院。该项目的研究成果将在夏季研究所期间传播，以使学生对气候与地球表面过程之间的相互作用产生兴趣。长期以来，人们一直认为，在缓慢侵蚀的热带生态系统中，尘土是营养物质的重要来源，在热带生态系统中，强烈的风化限制了来自底层基岩的营养物质的输入。研究人员最近在加州内华达山脉（Sierra Nevada， CA）一处受到积极侵蚀的山地地貌进行了研究，发现来自区域和跨洋的沙尘对该地区的影响很大；限制生长的营养物质（如磷）的供给速率与下垫基岩风化的供给速率相同。该研究还表明，不同海拔高度粉尘中微生物群落存在差异，群落组成与同地土壤群落很少重叠。此外，在夏季干旱期，中央山谷对中高海拔地区的贡献显著增加，表明区域沙尘源对这些生态系统的相对重要性随着上一次显著降水事件的时间增加而增加。迄今为止的分析是基于最近的2012-2016年干旱高峰期收集的沙尘输入（2014年），这就提出了一个问题，即研究结果是否对沙尘源和排放的变化敏感。拟议的工作将通过分析另一个干旱年夏季（2015年）收集的尘埃的来源和营养物质，并在整个2017年夏季收集新样本，在一个潮湿的年份之后，开始评估这个问题，目标是在不久的将来分析它们。

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.