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

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

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/15/2020
Publication Date: 6/24/2020
Citation: Nazari, S., Ford, W., King, K.W. 2020. Impacts of preferential flow and agroecosystem management on subsurface particulate phosphorus loadings in tile-drained landscapes. Journal of Environmental Quality. https://doi.org/10.1002/jeq2.20116.
DOI: https://doi.org/10.1002/jeq2.20116

Interpretive Summary: Phosphorus transport has been identified as the leading cause of harmful and nuisance algal blooms in Lake Erie. However, most of the attention has been focused on dissolved phosphorus with little attention on particulate phosphorus. Data from two edge-of-field study sites in the Lake Erie basin indicated that preferential or quick flow is a significant transport pathway for tile drainage. Furthermore, particulate P delivery from subsurface tile drainage can be significant and impacted by field scale management. Understanding the mechanisms governing particulate phosphorus transport will permit the development and enhancement of prediction technologies, providing researchers, policy makers, etc valuable information and resources to evaluate the impacts of different management practices on phosphorus delivery in tile drained landscapes and meet the 40% binational reduction goals to Lake Erie.

Technical Abstract: Midwestern tile-drained landscapes are well recognized to export high levels of phosphorus, leading to proliferation Harmful and Nuisance Algal Blooms (HNABs). The focus of monitoring plans and recent studies have been mostly on dissolved reactive phosphorus (DRP) delivery and transport pathways, and less emphasis is placed on particulate P (PP), resulting in their exclusion from agricultural water management models. In this study, we aim to quantify the fluxes, mechanisms and factors driving PP delivery into tiles through statistical analysis of long-term hydrologic and water quality dataset including five-year surface and tile discharge, TP, DRP, total nitrogen (TN) and dissolve inorganic nitrogen (DIN) concentrations from two edge-of-field study sites with contrasting soil (clay vs. loam) and management (conservation vs. conventional tillage) practices. Hydrograph separation techniques were coupled with multiple linear regression (MLR) for understanding flow pathway analysis and Empirical Mode Decomposition (EMD) time-series analysis was used to determine significance of PP seasonal processes and the effect of management practices. The pathway hydrologic analysis highlighted that quickflow contributed to 66% and 36% of subsurface discharge in the clay and loam site, respectively. P loading analysis showed that macropore flow plays a significant role in PP delivery to subsurface P loading, and PP significantly contributed to TP-DRP delivery in both sites; however, higher PP loadings were observed at the clay site despite higher subsurface discharge and soil test P levels at the loam site. Furthermore, PP delivery was significantly impacted by environmental conditions and management practices. We highlight the efficacy of hydrograph recession analysis for identifying macropore and diffuse drainage, as well as the efficacy of P:N ratio to characterize sediment delivery mechanisms in tiles, we suggest future studies should use high-resolution data collection and isotopic tracers in order to improve characterization of intra-event processes and short-term effect of practices such as tillage in order to improve understanding and management of PP in tile-drained landscapes.