Canopy-scale GPP from Measurements of Carbonyl Sulfide in a Freshwater Marsh

Abstract:

We demonstrate the application of carbonyl sulfide (COS) measurements to obtain new estimates of canopy-scale Gross Primary Production (GPP). We measured net ecosystem fluxes of COS and CO2 at an established flux tower site in a freshwater marsh in southern California during the growing season. The ecosystem acted as a strong sink of COS. The daytime variations mirrored those of CO2, however, COS uptake continued at night whereas the CO2 flux became very small. During the first part of the field campaign, the marsh was inundated which essentially eliminated surface fluxes, providing ideal test conditions for the COS-based flux partitioning method. The GPP estimates obtained from measured COS fluxes agreed well with thoses calculated using CO2-based partitioning methods. One of the most widely used flux partitioning methods, using the relationship of night-time fluxes and temperature, did poorly due to lack of turbulence at night. Our results demonstrate that adding COS to flux tower measurements would provide valuable observation-based constraints on the land carbon cycle.