How Evapotranspiration And Deep Percolation Impact The Precipitation-Runoff Response, Aquifer Recharge, And Linked Nutrient-Water Cycling At The Subalpine Como Creek Drainage In The Colorado Front Range
Abstract
Here we evaluate how evapotranspiration (ET) and deep percolation (DP) impact the precipitation-runoff response, aquifer recharge, and linked nutrient-water cycling at the 664-ha sub-alpine Como Creek drainage in the Colorado Front Range. ET is measured continuously using eddy covariance, soil moisture (SM) is measured using 2-m vertical sensor arrays, groundwater (GW) by a series of piezometers, and precipitation (P) is measured daily along with snow-water equivalent (SWE). From 2004 to 2009, annual P averaged 813 mm and ET averaged 590 mm, with ET thus representing 72.5% of annual P. Using multiple linear regression analysis, discharge (Q) was found to be modeled reasonably well with the independent variables of ET (p < 0.01), P (p < 0.01), and SM (p < 0.01). The final linear model had a reasonable fit (r2=0.57) indicating ET, P and SM to be good predictors of Q, with ET and SM having a positive coefficient, and somewhat surprisingly P having a negative coefficient. We found ET to be positively correlated with summer P (r2=0.45), but not well correlated with annual or winter P. Our vertical soil moisture arrays show that summer precipitation over 5 years never penetrated more than 50 cm in depth. Thus, during the summer, water flux in the root zone becomes decoupled from the ground water system and subsequent precipitation does little to contribute to streamflow for the current year, but serves to offset ET, which may explain the decrease in Q with increasing P. Newly installed piezometers (12, at depths ranging from 5 to 30 m) provide evidence that this portion of the basin is largely a loosing reach during snowmelt, with GW in the piezometers increasing 5-7 m. After peak snowmelt however, the reach starts gaining again with piezometer levels dropping. Time series plots reveal a strong relationship between SWE and Q with larger SWE often resulting in larger Q. Thus, surface-groundwater interactions are tightly coupled during snowmelt, with snowmelt first replenishing the subsurface water deficit before contributing to discharge. The deepest two piezometers (18 and 29 m) were not showing any significant water level declines by early August 2011, suggesting that water loss to DP is a potential important component of the water balance in the Como Creek catchment. Wet precipitation chemistry from the National Atmospheric Deposition Program monitors in the basin show that atmospheric deposition of inorganic nitrogen has increased several-fold in the last 25 years. However, in contrast to higher-elevation catchments, which have seen a dramatic increase in the nitrate content of surface waters, we see no such increase in the nitrate content of Como Creek. The reason may be that snowmelt first infiltrates into the subsurface, where ammonium and nitrate are assimilated.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFM.H33E1357Z
- Keywords:
-
- 0495 BIOGEOSCIENCES / Water/energy interactions;
- 1655 GLOBAL CHANGE / Water cycles;
- 1852 HYDROLOGY / Plant uptake;
- 1863 HYDROLOGY / Snow and ice