HIGHLIGHTING GROUNDWATER USE BY TREES IN A FORESTED WATERSHED IN THE VIRGINIA COASTAL PLAIN

Groundwater use by forests in humid regions is an often-ignored but substantial part of the water balance, particularly in areas with fast-draining sandy soils. To explore the extent and magnitude of groundwater use by forests, we established four observational sites near beech trees to observe continuous signals of soil moisture and depth to groundwater. By installing water level loggers in groundwater wells and soil moisture sensors (depths of 10cm, 25cm, 50cm), time series of groundwater depth and changes to soil moisture were compiled. These data were collected over the 2022 summer and fall seasons to explore the distribution of soil moisture between different sites and to examine the frequency and magnitude of groundwater consumption by trees in areas of shallow groundwater. Soil moisture in areas of shallow groundwater showed consistently higher water content with depth, indicating more available moisture for root water uptake. Soil moisture in areas of deep groundwater were lower with depth, which indications that trees in these environments may experience water stress. Using the depth to groundwater data in R, the day-to-day changes in storage, amount of groundwater recharge, and groundwater consumption for evapotranspiration over each day is calculated. Preliminary analysis indicates that temporally variable groundwater use by forests depends on depth to groundwater and weather conditions. Understanding when and where trees use groundwater can help constrain the water balance in forested watersheds and aid our understanding of the buffering effects of groundwater use by forests during droughts.