Reduced sulfur gases are precursors to sulfate aerosols that act as cloud condensation nuclei and affect Earth’s radiative balance. The diminishing anthropogenic atmospheric sulfur inputs due to long-standing acid rain abatement activities increase the influence of natural emissions on the remaining sulfur budget. Most previous terrestrial observations of reduced sulfur gas fluxes focus on wetland ecosystems where sulfur gas emissions are highest. The diffuse natural production of sulfur gas from more widespread oxic ecosystems needs to be characterized. Here we report in situ fluxes of sulfur gases and CO2 from grasslands outside of Santa Cruz, CA, USA (36.96°N, 122.08°W). Monthly measurements were made using static flux chambers from March 2012 to March 2014. A large net emission of dimethyl sulfide (DMS) was observed during the growing season. During the non-growing dry season, small but quantifiable carbonyl sulfide (COS) exchange rates were correlated with soil temperature. When soil moisture was artificially increased in senescent grassland plots, the relative exchange of COS-CO2 increased and then returned to the original ratio within 2 h. Sulfur gas fluxes during wet season soil moisture transition events (i.e. after precipitation) indicate that understudied aerobic environments may provide an important contribution to atmospheric COS consumption and DMS production.
We thank the California State Parks Service for site access; J. Chalfant, M. Schulz, C. Lawrence, J. Rhim, L. Ledesma, J. Kim, K. Barnash, J.E. Campbell, and T. Bhattacharya for field assistance; C. Lewis for suggestions on experimental design; W. Silver for sample processing support; M. Berkelhammer for data sharing; J. Muhle and R. Weiss for standard calibration; and A. Goldstein, R. Amundsen, E. Brzostek, and 2 anonymous reviewers for manuscript feedback. This work was supported by the Martin Foundation, the NSF-EAR Grant Number 0819972, and NSF-AGS Grant Number 1433257. Data presented in this work can be found in the UC3 archival system Merritt data repository.