Evaluating hydrologic response in tile drained landscapes: Implications for phosphorus transport

Authors: MACRAE, MERRIN - University Of Waterloo; ALI, GENEVIEVE - University Of Manitoba; King, Kevin; PLACH, JANINA - University Of Waterloo; PLUER, WILLIAM - University Of Waterloo; Williams, Mark; MORRISON, MATTHEW - University Of Waterloo; TANG, WEIGANG - McMaster University

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/6/2019
Publication Date: 8/19/2019
Citation: Macrae, M., Ali, G., King, K.W., Plach, J., Pluer, W., Williams, M.R., Morrison, M., Tang, W. 2019. Evaluating hydrologic response in tile drained landscapes: Implications for phosphorus transport. Journal of Environmental Quality. 48(5):1347-1355. https://doi.org/10.2134/jeq2019.02.0060.
DOI: https://doi.org/10.2134/jeq2019.02.0060

Interpretive Summary: Water quality issues, particularly those associated with phosphorus, continue to plague inland water bodies worldwide. In the Lake Erie Watershed, phosphorus is transported in both surface runoff and subsurface tile discharge. Using, edge-of-field data from agricultural production systems in Ohio, USA and Ontario, Canada, four surface-tile discharge response types were identified and were dependent on soil type and seasonality. However, phosphorus transport was not strongly correlated with any of the discharge response types, suggesting that factors other than surface-tile hydrology may be more important to phosphorus transport. These results should be useful to those designing and implementing management practices to address hydrology and phosphorus transport in tile drained landscapes.

Technical Abstract: Phosphorus (P) loss in agricultural discharge has typically been associated with overland flow; however, tile drains have been identified as a key P pathway due to preferential transport. Identifying when and where these pathways are active may establish high-risk periods and regions that are vulnerable for P loss. A synthesis of high-frequency, runoff data from eight cropped fields across the Great Lakes Region of North America over a two-year period showed that both overland and tile flow occurred year-round, although tile flow occurred more frequently. The timing of surface and tile flow activation relative to one another was classified into four response types to infer hydrological processes. Response types were found to vary with season and soil texture. In most events across all sites, tile responses preceded overland flow, whereas the occurrence of overland flow prior to tile flow was uncommon. The simultaneous activation of pathways, indicating rapid connectivity through the vadose zone, was seldom observed at the loam sites but occurred at clay sites during spring and summer. Overland flow at the loam sites was often generated as saturation-excess, a phenomenon rarely observed in the clay sites. Contrary to expectations, differences in P loads in tiles were not apparent under the different response types. This may be due to the frequency of the water quality sampling, or may indicate that factors other than surface-tile hydrologic connectivity drive tile P concentrations. Region-specific soil type and seasonality should be considered when designing management strategies to reduce P loading via tile drains.