Five decades of soil moisture dynamics in a northern forest

Background/Question/Methods

Forest ecohydrological dynamics are highly dependent upon the availability of soil water. At the Marcell Experimental Forest (MEF), the seasonal patterns of soil moisture across landscape and depth have been monitored since 1961. This highly unique dataset was used to analyze the influence of time-lagged precipitation and modified Thornthwaite modeled potential evapotranspiration on seasonal soil moisture at three depths (0-15cm, 76-107cm, and 198-229cm) across ten forested study sites. Models were created using multiple linear regression; model robustness was chosen based upon least squares estimates and Akaike Information Criterion (AIC).

Results/Conclusions

Precipitation and PET were found to significantly account for 5 to 75% of the variability in seasonal soil moisture (p < 0.05). As anticipated, soil moisture at deeper depths was influenced by the longest lags in both precipitation and PET, suggesting that deep soil water is a reflection of precipitation that occurred up to two years prior to measurement. Soil moisture at the shallower depths was more correlated with precipitation that occurred within one month prior to measurement. Correlations were the strongest with September and November precipitation, where precipitation and PET mechanistically dominate soil moisture. May soil moisture had the weakest correlations, a likely result given the large contributions of meltwater that influence the hydrology during leaf-out. These general models will be used to create a 3-dimensional of time-series model of soil moisture at the MEF.