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.