Wide-ranging timescales of subsurface phosphorus transport from field to stream in a tile drained landscape

Authors: DECKER, LAUREN - The Ohio State University; SAWYER, AUDREY - The Ohio State University; WELCH, SUSAN - The Ohio State University; ZHU, JUNFENG - University Of Kentucky; BINLEY, ANDREW - University Of Lancaster; FIELD, HANNA - The Ohio State University; Hanrahan, Brittany; King, Kevin

Submitted to: Journal of Hydrology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/23/2024
Publication Date: 4/8/2024
Citation: Decker, L., Sawyer, A.H., Welch, S.A., Zhu, J., Binley, A., Field, H., Hanrahan, B.R., King, K.W. 2024. Wide-ranging timescales of subsurface phosphorus transport from field to stream in a tile drained landscape. Journal of Hydrology. 635. Article 131185. https://doi.org/10.1016/j.jhydrol.2024.131185.
DOI: https://doi.org/10.1016/j.jhydrol.2024.131185

Interpretive Summary: Improved drainage, defined as artificial subsurface (tile) drainage, is necessary to remove excess water for crop production agriculture in the poorly drained, humid regions of the world. However, nutrient transport in and through tile drainage systems has been linked to downstream water quality issues. A combination of conservative tracers and dissolved phosphorus applied over a tile drainage system on a privately owned crop production farm in northwest Ohio showed a distinct and rapid macropore connection between the soil surface and tile drainage network located approximately three feet below the surface. Movement of both soluble and sediment bound tracers were observed. These findings are important for understanding the transport mechanisms controlling nutrient movement to surface waters, especially in those watersheds where artificial tile drainage is necessary. The findings are also important for researchers, conservationists, extension, and practitioners as they develop, assess, and implement conservation practices aimed at addressing nutrient transport.

Technical Abstract: Many agricultural riparian zones have been heavily modified to improve drainage by installing tile drains, which form direct subsurface flow paths for nutrient transport from farm fields to adjacent streams. Our goal is to understand the transport of phosphorus along these flow paths by combining a novel mixture of tracers (including conservative chloride, potassium phosphate, and fluorescent micrometer-sized particles) on a farm field and sampling their breakthrough curves at the end of the tile drain 30 meters away. Simultaneously, we performed a 26-hour time-lapse electrical resistivity survey to monitor the saline tracer migration in three dimensions every 0.5 to 1 hour. Chloride and dissolved phosphorus were rapidly transported to the tile drain outlet via preferential flow paths, including soil macropores and the tile drain structure itself: mean arrival time of both solutes was approximately 20 minutes. Little removal of dissolved phosphorus was observed compared to the conservative tracer. Analysis of electrical resistivity imagery shows fast downward movement of chloride to the tile drain depth but also prolonged retention of the tail of the chloride plume in the soils after the injection. Particles were recovered in tile drain effluent during the initial pulse and in soil cores taken at the tracer injection area to understand the movement of fine particulate matter and associated P through subsurface macropores. Additional water samples collected at the tile outlet during successive storm events indicate remobilization of solutes and particles over longer timescales.