SPATIAL VARIABILITY OF SOIL MOISTURE IN A DECIDUOUS FOREST: INTEGRATING TIME-LAPSE RESISTIVITY, TEMPERATURE, AND THROUGHFALL MEASUREMENTS

In deciduous forests, soil moisture is an important driver of energy and carbon cycling, as well as ecosystem dynamics. The amount and distribution of soil moisture also influences soil microbial activity, nutrient fluxes, and groundwater recharge. Characterizing the interactions between vegetation and soil moisture is critical to forecast water resources and ecosystem health in a changing climate. However, these interactions are difficult to measure, both in time and space. Recent studies have shown the ability of electrical resistivity tomography to characterize the spatial and temporal dynamics of soil moisture dynamics below a range of different vegetation types. In this study, we investigated the spatial variability of the soil water budget of a deciduous forest in lower Mid-Michigan. For the duration of the 2012 growing season, bi-weekly measurements of canopy throughfall, soil temperature and soil moisture were collected along a 125 m long transect that extended from the forest into an adjacent grassland. The canopy throughfall data were collected using a series of 24 innovative funnels that integrated over four-week time periods. At the same locations (19 in the forest and 5 in the grassland), soil temperature was measured at 5 cm depth. Subsurface distribution of soil moisture was estimated by inversion of weekly electrical resistivity datasets. Additional equipment and data included two tipping bucket rain gauges, leaf area index measurements, vertical soil temperature profiles, and capacitance water content probes. Fluid salinity, temperature, and pressure (depth) were continuously monitored for the water table below the forest and grassland. Our results highlight the strong correlation of the shallow subsurface soil moisture distribution with rainfall intensity and vegetation cover.