Quantifying hydrologic pathway and source connectivity dynamics in tile-drainage: implications for P concentrations

Authors: NAZARI, SAEID - University Of Kentucky; FORD, WILLIAM - University Of Kentucky; King, Kevin

Submitted to: Vadose Zone Hydrol
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/22/2021
Publication Date: 8/4/2021
Citation: Nazari, S., Ford, W., King, K.W. 2021. Quantifying hydrologic pathway and source connectivity dynamics in tile-drainage: implications for P concentrations. Vadose Zone Hydrol. 20(5). Article e20154. https://doi.org/10.1002/vzj2.20154.
DOI: https://doi.org/10.1002/vzj2.20154

Interpretive Summary: Artificial subsurface (tile) drainage is necessary for viable crop production in the poorly drained humid regions of the world. Identifying and representing the processes associated with water movement to tile drainage through the soil profile is important for understanding nutrient transport and development of conservation practices and simulation technologies. Fine resolution tile drainage, nutrient concentration, and specific conductance were collected from an edge-of-field tile site and used to develop a framework that considers matrix and preferential flow in combination with the age of the water, that is recent rainfall or older soil water. The developed framework significantly improved the representation and prediction of tile drainage discharge as well as nutrient transport. These findings will be useful for simulation model developers seeking to better represent the hydrologic cycle in tile drained landscapes as well as conservationists wanting to identify and develop practices to address water quality concerns.

Technical Abstract: Flow pathways and source water connectivity dynamics are widely recognized to impact tile-drainage water quality. In this study, we developed and evaluated a framework that couples event-based hydrograph recession and specific conductance end-member mixing analysis (SC-EMMA) to provide a more robust framework for quantifying both flow pathway dynamics and source connectivity of drainage water in tile-drained landscapes. High-frequency (30-minute) flow and conductivity data was collected from an edge-of-field a tile-main at the edge-of-field for a sitelocated in northwestern Ohio and the newly developed framework was applied for data collected in water year 2019. Multiple linear regression (MLR) analysis was employed to evaluate the impact of pathway-connectivity dynamics on flow-weighted mean dissolved reactive P (DRP) flow-weighted mean concentrations, which were collected as part of the USDA-ARS edge-of-field monitoring network. The hydrograph recession and SC-EMMA results highlighted intra and inter-event differences between quick (preferential) flow and new (precipitation) water transported during events, challenging a common assumption that new-water is always reflective of drainage through preferential flow paths. The analysis of hydrologic flow pathways demonstrated Qquick-old, Qquick-new, Qslow-old and Qslow-new were significant contributors to tile-discharge, contributing 9%, 39%, 42% and 10% of tile discharge on average, with high greater inter-event variability as a function of antecedent conditions and event precipitation. The MLR results highlighted that pathway-connectivity hydrograph components improved prediction of DRP concentrations over hydrograph recession and SC-EMMA results in isolation. Our findings also highlight the importance of matrix-macropore flow and preferential flow of new water to groundwater recharge to strongly impact drainage hydrographs and DRP concentrations.