Impacts of preferential flow and agroecosystem management on subsurface particulate phosphorus loadings in tile‐drained landscapes

Abstract

Recent research on tile-drainage has placed emphasis on dissolved reactive phosphorus (DRP) delivery and transport pathways but less emphasis on particulate P (PP), resulting in its exclusion from agricultural water management models. In this study, we quantified the fluxes, mechanisms, and factors driving PP delivery into tiles through statistical analysis of a long-term hydrologic and water quality dataset. The dataset includes 5 yr of surface and tile discharge, total P (TP), DRP, total nitrogen (TN), and dissolved inorganic N concentrations from two edge-of-field study sites with contrasting soil and management practices. Hydrograph recession techniques were coupled with multiple linear regression for understanding hydrologic flow pathways, and empirical mode decomposition (EMD) time-series analysis was used to determine the significance of PP seasonality processes and the effect of management practices. The analysis of hydrologic flow pathways demonstrated that quickflow contributed 66 and 36% of subsurface discharge in the clay and loam sites, respectively. Phosphorus loading analysis showed that macropore flow plays a significant role in PP delivery to subsurface P loading and that PP significantly contributed to TP and DRP delivery; however, greater PP loadings were observed at the clay site despite greater subsurface discharge and soil test P levels at the loam site. Furthermore, PP delivery was significantly affected by environmental conditions and management practices. We highlight the efficacy of hydrograph recession analysis for identifying macropore and diffuse drainage, of P/N ratios to characterize sediment delivery mechanisms in tiles, and of EMD to detect management impacts on TP and DRP at the field scale.

Quantifying hydrologic pathway and source connectivity dynamics in tile drainage: Implications for phosphorus concentrations

“…However, in agroecosystem models, they often require long-term records for rigorous calibration and validation and neglect or oversimplify simulation of processes including matrix-macropore interaction, resulting in uncertainties during model evaluation (Djabelkhir et al, 2017;Pferdmenges et al, 2020). Utilization of hydrograph recession analysis has been identified as an effective method to quantify event-scale matrix and macropore pathway contributions (Ford et al, 2019;Husic et al, 2019;Nazari et al, 2020). In hydrograph recession, hydrographs are conceptualized as the drainage of a series of reservoirs that have variable hydraulic conductivities and storage volumes (Husic et al, 2019).…”

“…Hydrograph recessions from events throughout the monitoring period were compiled to develop a master recession curve. We assumed two flow pathways reflecting reservoirs for matrix and macropore flow, consistent with previous studies (Nazari et al, 2020;Schilling & Helmers, 2008;Vidon & Cuadra, 2010;Williams et al, 2016). Recession coefficients (k) for a linear reservoir are defined by the equation Q = Q 0 e -kt (Gregor & Malik, 2012).…”

One size does not fit all: Toward regional conservation practice guidance to reduce phosphorus loss risk in the Lake Erie watershed

“…Artificial drainage, either in the surface or subsurface, increases the connectivity of the landscape, allowing P that would formerly have been retained on fields to be transmitted to surface water (King et al., 2015). However, the net impact of tile drains and surface drains on P export to Lake Erie is a question that has not been fully resolved (King et al., 2015; Kleinman et al., 2015; Nazari et al., 2020; Reid et al. 2012).…”

“…The methods used are described in Supplemental Material. NE, northeast; SW, southwest a question that has not been fully resolved (King et al, 2015;Kleinman et al, 2015;Nazari et al, 2020;Reid et al 2012). There is limited evidence that tile drains increase total water export from the landscape (Blann et al, 2009) or increase peak flows (Irwin & Whiteley 1983).…”

“…No‐till can increase dissolved P loss by (a) inducing P stratification in surface soils when P is surface applied, (b) maintaining macropores (biopores and physical pores) that allow for rapid flow from the surface to tile drains, and (c) lessening the physicochemical removal of DRP from water during transport by suspended sediments by reducing the overall presence of sediments in runoff. Given these mechanisms, the high density of preferential flowpaths and drainage tiles in the southwestern management region produces conditions that are conducive to significant P losses through tile drains (King et al., 2015; Nazari et al., 2020). There has been discussion that a return to periodic tillage may reduce P stratification and temporarily disrupt macropore connectivity, thereby reducing P losses to tile drains.…”