Hubbard Brook Experimental Forest: Ice Storm Experiment Trace Gas

Trace gas fluxes were measured using the in situ
chamber design similar to that described by Bowden and others (1990,
1991). Static gas soil sampling chambers (four per plot) of 20 cm
diameter (ID) polyvinyl chloride (PVC) were placed on permanently
installed PVC base rings immediately prior to measurement. At 0, 10,
20, and 30 min following placement of the chamber on the base, 8-mL
gas samples were collected from gas sampling ports in the center of
the chamber top by syringe. Samples were transferred to evacuated
glass vials and stored at room temperature prior to analysis by gas
chromatography (GC). CO2, N2O, and CH4 were analyzed on a Shimadzu
GC-14 GC with thermal conductivity (CO2), electron capture (N2O), and
flame ionization (CH4) detectors. These GC’s were capable of detecting
ambient levels of these gases. Fluxes were calculated from the linear
rate of change in gas concentration, the chamber internal volume and
soil surface area. Flux rate calculations were not corrected for
actual in situ temperature and pressure. Single points were removed
from regressions if they were more than six times higher or lower than
the other three values or if they contradicted a clear trend in the
other three points. This procedure prevents inclusion of high flux
rates based on non-significant regressions. Non-significant
regressions were used in flux calculations to avoid biasing the
statistical distribution of rates by setting all non-significant
regressions to zero. Gas samples were collected prior to any icing
treatment in September and October 2015, and then for 2 years after
the icing treatments were initially applied (1st icing: 1/27/16; 2nd
icing, only in MIDx2 plots: 1/14/17) in August 2016, July 2017, and
October 2017.