From Early Earth to Acid Rain and Agriculture: A Broad Look at the Changing Global Sulfur Cycle

Sulfur (S) is a key component of life and an element that has been dramatically changed by human industrial activities, including mining and fossil fuel combustion. Today, the nature of how humans alter the global S cycle is changing. As atmospheric S deposition has declined in response to air quality regulations in the United States and Europe, there has been an increase in S fertilizer applications reported in many large-scale regional crop systems. In addition, intensification of agriculture has driven increased S inputs for other uses: as a pesticide, regulator of soil pH, and soil conditioner. Given that excess S can cause soil acidification and mobilization of heavy metals in ecosystems, it is critical to develop methods to trace the “fingerprint” of agricultural S through complex landscapes, quantify S forms and transformations in soils and surface waters, and determine the consequences of its use. In this talk, I will describe both new trend analyses and process-based studies that provide compelling evidence for how the forms, amounts, flows, and consequences of S have changed from what they were in the 1960s and 1970s when the dominant human manipulation of the S cycle was through mining and fossil fuel emissions. I will highlight studies from my research group that show exciting new methodological developments using radio- and stable isotopes of S adapted from the marine literature to trace S applications through large agricultural regions. I will also discuss the collaborative actions that researchers, land managers, and regulators may take to address the consequences of excess S in the environment. Finally, I will touch on the potential extension of these new studies to probe the potential consequences of S in geoengineering applications. Ultimately, I will make the case for how an element that has been far less investigated than carbon, nitrogen, and phosphorus should be a priority for study in the coming years.

To be added to the EPS colloquium mailing list, please contact Caroline Carr (carolinecarr@fas.harvard.edu).