Seasonality and evaporation of water resources in Reynolds Creek Experimental Watershed and Critical Zone Observatory, Southwestern Idaho, USA

Authors: SCHLEGEL, MELISSA - Idaho State University; SOUZA, JENNIFER - Idaho State University; WARIX, SARA - Idaho State University; MACNEILLE, RUTH - Idaho State University; MURRAY, ERIN - Idaho State University; RADKE, ANNA - Idaho State University; GODSEY, SARAH - Idaho State University; SEYFRIED, MARK - Retired ARS Employee; FINNEY, BRUCE - Idaho State University; Flerchinger, Gerald; LOHSE, KATHLEEN - Idaho State University

Submitted to: Vadose Zone Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/4/2023
Publication Date: 8/31/2023
Citation: Schlegel, M., Souza, J., Warix, S., MacNeille, R., Murray, E., Radke, A., Godsey, S., Seyfried, M., Finney, B., Flerchinger, G.N., Lohse, K. 2023. Seasonality and evaporation of water resources in Reynolds Creek Experimental Watershed and Critical Zone Observatory, Southwestern Idaho, USA. Vadose Zone Journal. 22(6). Article e20278. https://doi.org/10.1002/vzj2.20278.
DOI: https://doi.org/10.1002/vzj2.20278

Interpretive Summary: Stable isotopes of hydrogen and oxygen within water are created when it undergoes evaporation and condensation. The ratio of these isotopes can create a signature that assists in tracking the source of the water within the soil and groundwater. This paper summarizes a data set compiled from several studies within the Reynolds Creek Experimental Watershed (RCEW) located in southwest Idaho. The dataset can be used to identify the season (winter versus summer) and source (precipitation, surface water, or spring) of water supplied to soil and ground water. For example, isotope signatures of precipitation varied with season. Soil, groundwater and spring water were shown to be more similar to the November through April precipitation, suggesting that the source water for these waters originated during winter and spring periods. The dataset was published so that other researches can use it for more detailed studies that help better understand the hydrology within the RCEW and how it compares to regional hydrology.

Technical Abstract: The Reynolds Creek Experimental Watershed (RCEW) and Critical Zone Observatory (CZO), located south of the western Snake River Plain in southwestern Idaho in the intermountain western United States, is the site of over 60 years of research aimed at understanding integrated earth processes in a semi-arid climate to aid sustainable use of environmental resources. Meteoric water lines (MWLs) are frequently used to interpret hydrologic processes, though equilibrium and nonequilibrium processes affect the linear function, revealing seasonal and climatological effects, necessitating the development of local meteoric water lines (LMWLs). At RCEW-CZO, a RCEW LMWL was developed using orthogonal regression with assumed error in both predictor and response variable from several years of precipitation (2015, 2017, 2020, 2021) primarily at three different elevations (1203m, 1585m, 2043m). As most precipitation is evaporated or intercepted by vegetation in the driest months, a groundwater recharge RCEW LMWL (RCEW LMWL - GWR) was also developed using precipitation from the wettest months (November through April). The RCEW LMWL (d18O = 7.41 * d2H - 3.05) is different from the RCEW LMWL-GWR (d18O = 8.21 * d2H + 9.69) primarily due to seasonality of precipitation (November through April average d18O value -14.73‰ vs. May through October average d18O value -11.36‰). The RCEW LMWLs compare favorably to LMWLs developed for the region and climate. Surface, spring and subsurface water data sets within the RCEW-CZO exhibit evaporative effects and a precipitation source primarily from cooler meteoric water. Variability between the RCEW LMWL and the RCEW LMWL-GWR, in conjunction with an isotopically depleted precipitation source for the RCEW-CZO comparative groups, illustrate that some semi-arid hydrologic systems may most appropriately be compared to MWLs developed from precipitation only from the wettest seasons. The data set is found at https://scholarworks.boisestate.edu/reynoldscreek/29/ (DOI: 10.18122/reynoldscreek.29.boisestate).