Tile Drainage Increases Total Runoff and Phosphorus Export During Wet Years in the Western Lake Erie Basin

Samuel A Miller,Steve W Lyon

doi:10.3389/frwa.2021.757106

Abstract

Artificial subsurface (tile) drainage is used in many agricultural areas where soils have naturally poor drainage to increase crop yield and field trafficability. Studies at the field scale indicate that tile drains disproportionately export large soluble reactive phosphorus (SRP) and nitrate loads to downstream waterbodies relative to other surface and subsurface runoff pathways, but knowledge gaps remain understanding the impact of tile drainage to nutrient export at watershed scales. The Western Lake Erie Basin is susceptible to summertime eutrophic conditions driven by non-point source nutrient pollution due to a shallow mean water depth and land use dominated by agriculture. The purpose of this study is to analyze the impact of tile drainage on downstream discharge, nutrient concentrations, and nutrient loads for 16 watersheds that drain to the Western Lake Erie Basin. Daily discharge and nutrient concentrations were summarized annually and during the main nutrient loading period (March–July) for 2 years representing normal nutrient loading period precipitation (2018) and above normal precipitation (2019). Results indicate positive correlations between watershed tile drainage percentage and runoff metrics during 2019, but no relationship during 2018. Additionally, SRP concentration and load were positively correlated to watershed tile drainage percentage in 2019, but not in 2018. Watershed tile drainage percentage was correlated with nitrate concentration and load for both years. The SRP concentration-discharge relationships suggested relatively weak, chemodynamic behavior, implying a slight enriching effect where SRP concentrations were greater at higher stream discharge conditions during both years. In contrast, nitrate concentration-discharge relationships suggested strong, enriching chemodynamic behavior during 2018, but chemostatic behavior during 2019. The difference in SRP and nitrate export patterns in the 2 years analyzed highlights the importance of implementing appropriate best management practices that target specific nutrients and treat primary delivery pathways to effectively improve downstream aquatic health conditions.

Highlights

Increased severity and frequency of Harmful Algal Blooms (HABs) caused by elevated toxinproducing phytoplankton and cyanobacterial biomass occurred in a majority of lakes around the globe from 1984 to 2012 (Ho et al, 2019)
In 2019, which had above average annual precipitation and March–July precipitation, watershed tile drainage percentage was significantly correlated with annual and March–July runoff and annual and March–July runoff ratios (Figure 3)
The lack of relationship between tile drainage and annual or March–July runoff and runoff ratios during 2018 suggests that the presence of tile drainage amplifies the flashiness during wetter than average years in this region, while the effect is less noticeable in years with normal amounts of precipitation

Summary

Introduction

Increased severity and frequency of Harmful Algal Blooms (HABs) caused by elevated toxinproducing phytoplankton and cyanobacterial biomass occurred in a majority of lakes around the globe from 1984 to 2012 (Ho et al, 2019). Tile Drainage Effects on Runoff runoff from residential lawns, fertilizer or manure runoff from farm fields and runoff or leaks from animal agriculture manure lagoons are the main HAB drivers in agricultural landscapes. Direct HAB remediation is costly and typically involves either biological, physical, or chemical control measures; mitigating nutrient losses at the source in agricultural fields could prove to be a cost-effective alternative to reduce HABs in receiving waters and lakes. It seems that a combination of both hydrologic and nutrient management practices are likely needed to reduce nutrient losses from agricultural fields and improve downstream aquatic health (Hanrahan et al, 2019)

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Conclusion