ABSTRACT

Humans? changes to the sulfur (S) cycle are changing from mining and fossil fuel emissions to sulfur additions in croplands. Now, similar to nitrogen and phosphorus, large amounts of S are also applied to some crops as fertilizers or other soil additives. In locations where atmospheric S deposition is down due to air quality policies, farmers now add S fertilizers to meet plant requirements. Often two-to-ten times the amount of S that was in rain before the Clean Air Act, S applications to croplands may have negative consequences for areas downstream. In particular, transport of excess S into wetlands can cause movement of heavy metals into the food chain, which is dangerous for animals and people. There has not been thorough study of how agricultural S additions behave in the environment and the consequences of their use. This project will fill that knowledge gap by addressing three primary objectives. The first is to develop scientific methods to measure key S cycling processes and chemical forms in crop systems. The second is to create exercises that provide middle school and undergraduate students with experience doing environmental research. The final objective is to hold workshops for farmers to discuss research findings and inform crop S management. Together, these activities will improve understanding and promote interaction to address how humans are changing the S cycle.

The proposed research addresses a major knowledge gap in the field of biogeochemistry: quantifying how reactive S additions to agricultural systems behave in the environment and investigating the processes that control their ultimate fates and ecological consequences. The early career PI will build on her body of research in the Napa River Watershed (California, USA)?a perfect regional agricultural system where wine grapes are grown exclusively and S is applied ubiquitously at 150 kg ha-1 yr-1, on average. She has designed a focused field- and laboratory-based investigation that relies on her background in biogeochemistry and leverages her growing network of academic and stakeholder collaborators to build capacity within her research group, field of study, and the agricultural sector. Specifically, the PI will increase scientific knowledge in three main areas: (1) developing methods to quantify sulfate reduction in soil microaggregates; (2) determining chemical and S stable isotopic composition of organic S exported from agricultural systems; and (3) identifying how the forms of S and S stable isotopic composition of soils and solution waters vary not only across one agricultural area (the Napa River Watershed) but also across other croplands in the U.S. where S is used heavily. Integrated with the research activities, the PI will lead the following education and outreach efforts: (1) creating work-based learning field trips and data exploration exercises for 280 7th grade students at the Silverado Middle School where ~60% of the students are Hispanic and many are the children of workers in the local agricultural industry; (2) designing a publicly-available case study module that builds quantitative and critical thinking skills for undergraduate environmental studies students; and (3) leveraging collaborations with the Sustainability Innovation Lab at Colorado and University of California Extension to hold stakeholder workshops that communicate project findings and inform solutions for sustainable S management. In addition, the PI will continue her commitment to recruiting students from underrepresented groups to participate in this project and train them to become the next generation of interdisciplinary scholars. Ultimately, this effort will yield a broad understanding of where, when, and how S reacts in the environment?advancing knowledge of how humans are changing a fundamental element cycle and informing what to do about it.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

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