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

Abstract

Flowpathways and source water connectivity dynamics are widely recognized to affect tile-drainage water quality. In this study, we developed and evaluated a framework that couples event-based hydrograph recession and specific conductance endmember 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-min) flow and conductivity data were collected from an edge-of-field tile main located in northwestern Ohio, and the newly developed framework was applied for data collected in water year 2019. Multiple linear regression (MLR) analysis was used to evaluate the impact of pathwayconnectivity dynamics on flow-weighted mean dissolved reactive P (DRP) 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 interevent differences between quick (preferential) flow and new (precipitation) water transported during events, challenging a common assumption that new water reflects drainage through preferential flow paths. The analysis of hydrologic flow pathways demonstrated matrix-macropore exchange (Q quick-old ), preferential flow of new water (Q quick-new ), slow flow of old water (Q slow-old ), and slow flow of new water (Q slow-new ) contributed 9, 39, 42, and 10% to tile discharge, on average, with interevent variability. Matrix water that is transported to tile drains via macropore flowpaths was found to be activated throughout the year, even under drier antecedent conditions, suggesting that matrix-macropore exchange was more sensitive to within-event hydrological processes as compared with antecedent conditions. The MLR results highlighted that pathway-connectivity hydrograph fractions improved prediction of DRP concentrations, although improvement may be more pronounced in landscapes with higher rates of matrix-macropore exchange.

Impact of water source dynamics on dissolved reactive phosphorus loadings in heterogenous karst agroecosystems with phosphatic limestones

“…These results suggest that deeper soil layers enriched in WEP are activated at the tail end of the event and increase DRP loadings. This finding suggests temporal variability in matrix‐macropore exchange in the soil profile, which is supported by studies that have shown matrix‐macropore exchange increases within increasing soil moisture (e.g., Nazari et al, 2021). Future tracer‐based approaches should focus on using tracers that can discriminate hydrologic connectivity within the soil profile to improve DRP source apportionment predictions.…”

“…These results suggest that deeper soil layers enriched in WEP are activated at the tail end of the event and increase DRP loadings. This finding suggests temporal variability in matrix-macropore exchange in the soil profile, which is supported by studies that have shown matrix-macropore exchange increases within increasing soil moisture (e.g., Nazari et al, 2021).…”

“…This finding suggests mixing of heterogenous DRP sources occurred in both quickflow and slowflow pathways. For instance, quickflow may have reflected mixing of precipitation water rapidly pirated through sinkholes and matrix water that exchanges with macropores (Nazari et al, 2021) that is then transported to seeps and springs. Therefore, we conclude that although hydrograph recessions have been successful in a variety of karst springs and watersheds to improve understanding of hydrological pathway impacts on contaminant transport (Husic et al, 2019;Jarvie et al, 2014;Mellander et al, 2012Mellander et al, , 2013, they may provide limited insights for DRP dynamics in heterogenous karst watersheds with phosphatic limestone parent materials.…”

Using stable water isotopes to evaluate water flow and nonpoint source pollutant contributions in three southern Ontario agricultural headwater streams

“…However, hydrograph shape alone does not determine the age distribution of water contributions and pre‐event water can also quickly be transported to the stream by tiles, causing a quick discharge response. Recent work by Nazari et al (2021) monitoring tile discharge at the field has shown considerable contributions on the rising limb were attributed to matrix flow, indicating pre‐event water can be a quick source of discharge during events. In other studies examining tile‐drained catchments, pre‐event water contributions can be significant during events (Klaus et al, 2013).…”

Tile Drainage Flow Partitioning and Phosphorus Export in Vermont USA

“…Previous studies have used two different hydrograph separation methods for estimating PFP contributions to TD, and until recently the two have yet to be combined to clarify matrix-PFP interactions and their impact on P transport [17]. The first method, hydrograph recession analysis (HRA), separates matrix and PFP contributions into slow flow (SF) and quick flow (QF), respectively, by examining the hydraulics of the system.…”