WATER CYCLING ON CULTIVATED LAND: AN INVESTIGATION OF THE TWO WATER WORLDS HYPOTHESIS IN CENTRAL OHIO

We honor Frank Schwartz’s cutting-edge research and leadership in hydrogeology by investigating the novel idea of the two water world (TWW) hypothesis to advance knowledge of small scale water cycling. The TWW hypothesis recognizes distinct pools of water within the shallow subsurface. In contrast to the translatory flow model, the TWW hypothesis states that two pools of water, termed soil water and mobile water, differ in flow characteristics, quantity, and δ¹⁸O and δD isotopic composition. Using the differentiation in isotopic signature, recent studies have investigated impacts of physiochemical characteristics, soil moisture content, climate and vegetation on hydrologic cycling at the hillslope scale. This study focuses on delineating water flow through a field of Zea mays, corn, in the temperate climate of central Ohio. Sampling of precipitation, soil, vegetation, stream and tile drainage water occurred throughout the growing season, May 2018 to September 2018. Isotopic composition of corn water and soil water at different profile depths (10cm, 20cm, 40cm, 60cm) were compared to a local meteoric water line (LMWL) previously established by our research group. Soil moisture content and water potential were monitored using METER Environment EC-5 and TEROS-21 sensors. Water was extracted from soil and vegetation samples via cryogenic extraction and analyzed on a Picarro Wavelength Scanned-Cavity Ring Down Spectroscopy Analyzer for Isotopic Water-Model L2130-i. Due to corn root length, corn water uptake was dependent on the soil water characteristics of the upper 40cm of the soil profile. Elevated levels of precipitation in the early growing season resulted in soil moisture content frequently reporting near field capacity and soil water potential consistently remained near -10kpa. In late June water potential began to decline and vary in the soil profile, coinciding with reduced rainfall frequency and greater variation in soil moisture content. Differentiation in isotopic signature was not observed when moisture content remained near field capacity, however significant differences in the soil water profile were observed when the frequency of precipitation decreased and soil moisture declined. Ongoing isotopic analysis will be used to differentiate which water pools corn utilizes in the soil profile.