Soil water potential response to double funneling of precipitation on a forested, Mid-Atlantic hillslope
Date
2019
Authors
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Publisher
University of Delaware
Abstract
Soil matric potential measurements were taken on a hillslope beneath a 74 cm diameter at breast height (dbh) Fagus grandifolia Ehrh. (American beech) tree between January 2012 and November 2014. Thirty-six sensors were installed in three transects at four locations downslope from the tree, at three depths (30, 45 and 60 cm). Data were examined for temporal persistence and variability, preferential flow, and change in soil water storage and drainage. Results indicate that as sensors reveal greater soil wetness, both temporal variability and the root mean square error of mean relative difference increase. This indicates that short term increases in soil moisture are responsible for the observed variability. Additionally, stemflow infiltration is observed as a short-lived increase in storage, with significant drainage occurring within the first thirty minutes. Preferential flow occurred along consistent flow paths which were identified not only by the occurrences of out-of-sequence flow, but also indicated by temporal persistence and storage/drainage. Finally, year-to-year variation indicated the relationship of preferential flow occurrences and timing of precipitation; 2013 had significantly more precipitation early in the growing season and led the three study years in the occurrence of both preferential and sequential flow responses. Further investigation into the five identified precipitation classes indicate that precipitation events over 30mm which included extreme events such as Hurricane Sandy, have more common occurrences of preferential flow smaller magnitude events. Thus, the major conclusion of this study is stemflow infiltration and transport increases the moisture along a set group of sensors that coincide with the location of roots > 2.54cm in diameter. Additionally, stemflow infiltration and transport causes a short-term increase in soil water storage, with sensors identified along the preferential flow path having higher soil storage maximum values, larger post rain fall drainage (WD0.5) and additional drainage after soil moisture levels return to antecedent conditions. Precipitation events with magnitudes greater than 30mm tend to have higher instances of preferential flow as well as larger increases in maximum soil water storage than smaller magnitude events. Finally, year to year variability is more related to changes in yearly precipitation event timing, which has implications for changing precipitation regimes.