Measuring isotopic N2O, CO2 and CH4 soil flux with cavity ring-down spectroscopy
Atmospheric concentrations of N2O, CO2and CH4 are currently steadily increasing, and in the case of N2O, the increase in emissions is mainly linked to the increased use of fertilizers in agricultural soils. Stable isotope analysis of these trace gases is a valuable tool to better understand production and consumption pathways in soils and this process understanding will ultimately help to reduce greenhouse gas emissions from crop production. Here we present the integration of two cavity ring-down spectrometers (CRDS) for continuous stable isotope analysis of N2O, CO2 and CH4 with 12 automated soil flux chambers. The measurements were performed at a long-term field experiment site located at Ultuna, Uppsala, Sweden. The site has been in agricultural use (predominantly C3 crops) for at least 300 years before the establishment of the experimental trial. Nitrous oxide concentrations, bulk δ15N and δ18O as well as the site specific isotopic composition (δ15Nα, δ15Nβ) were measured with a Picarro G5131-i CRDS instrument.Carbon dioxide and methane concentrations and the stable carbon isotope composition (δ13C) were measured with a Picarro G2201-i dual carbon isotope analyzer. The analyzers were coupled in parallel and integrated with 12 EoSense eosAC automated soil flux chambers coupled to an EoSense eosMX multiplexer. The chamber measurements were performed in a recirculation configuration. Each chamber was located on one of four fertilizer treatments (Unfertilized, Calcium Nitrate, Ammonium Sulphate, Calcium Cyanamide). We will present concentration and isotope data from this field study and discuss the potential and technical considerations for continuous isotopic flux measurements in an agricultural setting.