Abstracts Geography

Characterization of Agricultural Subsurface Drainage WaterQuality and Controlled Drainage in the Western Lake ErieBasin

by Lindsay Anne Pease

Subsurface drainage, while an important and necessary agricultural production practice in the Midwest, contributes significant loads nitrate (NO3) and soluble phosphorus (P) to surface waters. Controlled drainage is one management strategy which is recommended to reduce NO3 soluble P losses from subsurface drainage waters. Under climate change, the Midwest is expected to experience higher intensity rainfall events along with an increased chance of drought. The impact that these changes will have on subsurface hydrology is critical for ensuring agricultural resiliency to future climate. This research used multiple linear regression analysis to evaluate impacts of climate, field management, and landscape on NO3 and soluble P concentrations in subsurface drainage water in the Western Lake Erie Basin. Parameters significantly impacting NO3 concentrations included rainfall, fertilizer application rate & timing, Soil Test P, soil texture, season, drain spacing, site relief, tillage, temperature, crop, and drainage water management. The results of this study indicate that BMPs specifically targeted at reducing losses of fertilizer, soil matrix flow of NO3, and soluble P losses via preferential flow pathways will have the greatest impact on NO3 and soluble P concentrations.Controlled drainage significantly reduced seasonal accumulated subsurface discharge from 178 to 54.2 mm in winter, from 24.3 to 8.12 mm in summer, and from 155 to 115 mm in the critical discharge period. Controlled drainage significantly reduced NO3 load from 10.8 kg ha-1 to 3.64 kg ha-1 in winter, and from 1.28 kg ha-1 to 0.385 kg ha-1 in summer. Controlled drainage significantly reduced soluble P load from 0.042 kg ha-1 to 0.013 kg ha-1 in winter, 0.008 kg ha-1 to 0.003 kg ha-1 in summer, and from 0.039 kg ha-1 to 0.028 kg ha-1 in the critical discharge period (March through June). The highest reductions in discharge NO3 load and soluble P load through use of controlled drainage were observed during winter indicating that management during the winter and management of controlled drainage systems through at least April 1 is critical for achieving maximum water quality benefits from this practice. This study used the hydrologic DRAINMOD model to simulate subsurface drainage discharge in controlled and conventional drainage systems under future climate projected by 20 General Circulation Models (GCMs). Despite increases in rainfall throughout the year, by mid-century subsurface drainage discharge was projected to decrease by 6% and 7 % under Representative Concentration Pathway (RCP) 4.5 and RCP 8.5, respectively. By the late-21st century, subsurface discharge is projected to decrease 7% and 11% for RCP 4.5 and RCP 8.5, respectively. Reductions in subsurface discharge were attributed to increased temperature and evapotranspiration. The performance of controlled drainage systems will not change over the next century. The role of controlled drainage as a means to potentially store water in the soil profile could become critically important over the next… Advisors/Committee Members: Martin, Jay (Advisor), Fausey, Norman (Advisor).