Evaluation of laser-based spectrometers for greenhouse gas flux measurements in coastal marshes

Precise and rapid analyses of greenhouse gases (GHGs) will advance understanding of the net climatic forcing of coastal marsh ecosystems. We examined the ability of a cavity ring down spectroscopy (CRDS) analyzer (Model G2508, Picarro) to measure carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O) fluxes in real-time from coastal marshes through comparisons with a Shimadzu GC-2014 (GC) in a marsh mesocosm experiment and with a similar laser-based N₂O analyzer (Model N₂O/CO, Los Gatos Research) in both mesocosm and field experiments. Minimum (analytical) detectable fluxes for all gases were more than one order of magnitude lower for the Picarro than the GC. In mesocosms, the Picarro analyzer detected several CO₂, CH₄, and N₂O fluxes that the GC could not, but larger N₂O fluxes (218-409 µmol m^-2 h^-1) were similar between analyzers. Minimum detectable fluxes for the Picarro were 1 order of magnitude higher than the Los Gatos analyzer for N₂O. The Picarro and Los Gatos N₂O fluxes (3-132 µmol m^-2 h^-1) differed in two mesocosm nitrogen addition experiments, but were similar in a mesocosm with larger N₂O fluxes (326-491 µmol m^-2 h^-1). In a field comparison, Picarro and Los Gatos N₂O fluxes (13 ± µmol m^-2 h^-1) differed in plots receiving low nitrogen loads but were similar in plots with higher nitrogen loads and fluxes roughly double in magnitude. Both the Picarro and Los Gatos analyzers offer efficient and precise alternatives to GCbased methods, but the former uniquely enables simultaneous measurements of three major GHGs in coastal marshes.