5 research outputs found
Carbon dioxide flux measurements from a coastal Douglas-fir forest floor
Soils can store large quantities of carbon in the form of decaying organic matter
originally derived from vegetation. In order to gain a better understanding of the
importance of soils in the carbon cycle, it is necessary to examine processes that directly
affect the exchange of carbon between the soil and the atmosphere. During the year
2000, measurements of forest floor CO₂ flux and below-ground CO₂ storage were
obtained beneath the canopy of a 33-m tall coastal temperate Douglas-fir forest. The
study took place at a micrometeorological tower flux site in operation since late 1997
obtaining year-round eddy covariance (EC) measurements of above-canopy CO₂ and
energy fluxes. An automated soil chamber system was designed and constructed which
could obtain half hourly measurements of CO₂ flux from six locations with each chamber
covering 0.2 m . These soil chambers were installed in late April and operated until mid-
December, spanning a large portion of the growing season. EC measurements of CO₂
flux 2.6 m above the forest floor over a two month period in the late summer and early
autumn were obtained to compare the two measurement techniques. Below-ground CO₂
mixing ratios of soil air were measured periodically at six depths between 0.02 to 1 m
using gas diffusion probes and a simple syringe sampling technique.
Maximum CO₂ fluxes measured by the soil chambers varied by a factor of three,
with two of the chambers measuring up to 16 pmol m⁻² s⁻¹ during the warmest times of
the year, indicating high spatial variability in soil CO₂ flux. Forest floor CO₂ fluxes
measured by each of the chambers showed different sensitivities to soil temperature and
there was clear evidence of hysteresis in the flux-temperature relationship over the year.
Due to the very low windspeeds below the forest canopy, reliable below-canopy EC
measurements of forest floor CO₂ flux were very difficult to obtain. Measurements of
below-ground CO₂ mixing ratio revealed that the amount of CO₂present in the soil
increased rapidly with depth near the surface and increased less rapidly deeper in the soil.
Using estimated values of the CO₂ diffusivity and measured fluxes as inputs into a simple
model, it appears that about 50% of the CO₂ produced below-ground comes from
between the soil surface and the 0.15 m depth. Results from this study suggests that CO₂
fluxes from this forest floor are large compared to other, less productive ecosystems.Land and Food Systems, Faculty ofGraduat