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ARS Home » Pacific West Area » Boise, Idaho » Northwest Watershed Research Center » Research » Publications at this Location » Publication #304036
Title: Simulation of long-term soil water dynamics at Reynolds Creek, Idaho: Implications for rangeland productivity

Author
item FINZEL, JULIE - University Of California - Cooperative Extension Service
item Seyfried, Mark
item Weltz, Mark
item LAUNCHBAUGH, KAREN - University Of Idaho

Submitted to: Ecohydrology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/29/2015
Publication Date: 9/27/2015
Citation: Finzel, J., Seyfried, M.S., Weltz, M.A., Launchbaugh, K. 2015. Simulation of long-term soil water dynamics at Reynolds Creek, Idaho: Implications for rangeland productivity. Ecohydrology. 9:673-687.

Interpretive Summary: Plant productivity, forage availability and soil carbon dynamics are all strongly controlled by soil moisture in semi-arid rangelands. Sagebrush ecosystems are among the most extensive in the western USA. In this study, the Soil Ecohydrology Model (SEM) was used to simulate soil water and estimate plant growth using a yield index at three sagebrush steppe sites, representing a range of vegetation and climate conditions. SEM is a capacitance parameter model that uses a water balance approach to simulate daily changes in soil moisture and a modification of the de Wit equation to estimate plant yield. Model simulated soil water results were evaluated using long-term (>30 years) measured soil moisture data. We found that SEM accurately captured soil water dynamics and simulated total soil water storage accurately at all three sites, with R2 values greater than 0.8, Nash Sutcliffe efficiencies around 0.8 and average deviations of about 1.5 cm. The results indicate that loss of water by deep percolation is very rare at these sites. Estimated yield indices indicated no long-term trend in plant production due to water availability. We also found that, in this environment, seasonal yield could be estimated with reasonable accuracy at the outset of the growing season for about half of the years simulated due to either a very high or very low level of pre growing season precipitation.

Technical Abstract: Plant productivity, forage availability and soil carbon dynamics are all strongly controlled by soil moisture in semi-arid rangelands. Sagebrush ecosystems are among the most extensive in the western USA. In this study, the Soil Ecohydrology Model (SEM) was used to simulate soil water and estimate plant growth using a yield index at three sagebrush steppe sites, representing a range of vegetation and climate conditions. SEM is a capacitance parameter model that uses a water balance approach to simulate daily changes in soil moisture and a modification of the de Wit equation to estimate plant yield. Model simulated soil water results were evaluated using long-term (>30 years) measured soil moisture data. We found that SEM accurately captured soil water dynamics and simulated total soil water storage accurately at all three sites, with R2 values greater than 0.8, Nash Sutcliffe efficiencies around 0.8 and average deviations of about 1.5 cm. The results indicate that loss of water by deep percolation is very rare at these sites. Estimated yield indices indicated no long-term trend in plant production due to water availability. We also found that, in this environment, seasonal yield could be estimated with reasonable accuracy at the outset of the growing season for about half of the years simulated due to either a very high or very low level of pre growing season precipitation.