6. Conclusions
This study shows the eddy covariance method can be used in a saturated
end-member, complex, mountain region. This method led to less than 30%
closure error in the spring and summer months showing that most of the
energy coming into the system can be quantified and partitioned between
latent, ground, and sensible heat fluxes. This closure error is within
the ranges found at other study sites in mountain regions and riparian
areas of 10 to 30% closure error (Eshonkulov et al., 2019; Nagler et
al., 2005; Scott et al., 2004; Scott et al., 2008; Wilson et al., 2002)
and the daily ET values for the range of the study period are similar to
those found at the Niwot Ridge AmeriFlux site (about 0 to 5mm/day). This
closure error is likely to decrease if we measured the snowpack energy
flux and the energy involved in heating standing water prior to surface
runoff.
We also show that in a saturated end-member site, ET will not be as
variable as precipitation and precipitation is not the main driver of
ET, as it may be in other Rocky Mountain locations. This site is not
water-limited and thus useful for constraining ET in the rest of the
East River Basin and is behavior that may be applicable across other
western US headwater catchments for constraining ET estimations.
Using precipitation, change in soil moisture, and ET values, we can
estimate groundwater contributions to ET showing that groundwater may
increase ET values by up to 76%. This shows the necessity in
constraining these variables at high-elevation basins and additional
observations are needed to better estimate ET from groundwater across
the rest of the East River Basin.
Both precipitation and ET are highly variable across the basin with an
increase in ET of 13-22% when the missing data is estimated through
gap-filling and a difference in precipitation of about 140-660mm
depending on the water year and meteorological station used. This
variability can change a wet year from a gaining system into a losing
system creating complications for estimating water availability and
planning downstream water consumption. These results again highlight the
need for additional eddy covariance observations and meteorological
stations in both the East River and other high-elevation basins.
Comparison of the East River eddy flux estimations with those from the
other two eddy flux towers in the Rocky Mountains allow for constraining
ET across the rest of the East River basin and other similar mountain
headwater regions. ET values in the East River basin should be equal to
or less than those at the eddy flux location. ET at higher elevations
should be similar to the magnitudes of ET seen at Niwot Ridge given the
similarities between Niwot Ridge and the high-elevation locations in the
East River basin.
The ability to quantify these fluxes, particularly ET, is useful for
estimating water availability downstream from headwaters catchments.
Though this study presents a useful dataset for water and energy fluxes
in complex headwater regions, access to more eddy covariance towers in
diverse locations across the basin, would allow for better estimations
of ET and other water and energy fluxes across an entire basin leading
to better water availability predictions that are useful for downstream
water planning.