Nitrate reduction in a reconstructed floodplain oxbow fed by tile drainage

Abstract

Conservation practices are needed to reduce the loss of nitrate via subsurface tile drainage systems and in this study we evaluated nitrate retention in a reconstructed oxbow in central Iowa that was engineered to receive inputs from two drainage tiles. Our objectives were to evaluate the hydrogeology and nitrate loading patterns and quantify the average and seasonal nitrate retention efficiency in the reconstructed oxbow. Over a two-year period, water and nitrate concentrations and loads into the oxbow were dominated by tile drainage inputs compared to groundwater seepage. Nitrate concentrations were highest in tile drainage water (9 to 17 mg/l), similar in upgradient groundwater and in the oxbow itself (4-8 mg/l) and lowest in downgradient groundwater (0.2 mg/l). Using N:Cl ratios, we estimated nitrate retention efficiency from May to September to range from 44% to 47% in 2014 and 2015, respectively, and found that on a monthly basis, greater retention efficiencies were measured in late summer and early fall. The nitrate retention efficiency was similar to other practices such as bioreactors, wetlands and saturated buffers. Given ecosystem benefits of oxbows and similar costs compared to bioreactors, we believe that reconstructing oxbows to receive tile drainage water should be considered a viable practice for tile drainage treatment in agricultural areas.

Floods, drying, habitat connectivity, and fish occupancy dynamics in restored and unrestored oxbows of West Central Iowa, USA

“…Numerous studies have illustrated the importance of oxbows and analogous standing water bodies in floodplains as habitat for Topeka shiners in today's agriculturally dominated Midwestern landscape (Bakevich et al, ; Clark, ; Natural Resource Conservation Service, ; Simpson et al, ). The restoration of oxbows and similar water bodies is now an important part of the Topeka shiner conservation strategy (Kenney, , ; Natural Resource Conservation Service, ), as well as a promising approach for the reduction of nutrient loading to streams and rivers (Jones, Kult, & Laubach, ; Schilling, Kult, Wilke, Streeter, & Vogelgesang, ). The results suggest that the hydrodynamics that affect connections with nearby streams should be an important consideration for future oxbow restorations, and efforts to predict the hydrodynamic characteristics of different oxbow locations, elevations relative to the stream, groundwater characteristics, and perhaps other considerations would be useful.…”

Human amplified changes in precipitation–runoff patterns in large river basins of the Midwestern United States

“…Decreased residence time of water in the soil has substantially increased nutrient export from agricultural landscapes (Randall and Mulla, 2001;Kreiling and Houser, 2016;Schilling et al, 2017). Though artificial drainage reduces field erosion by reducing surface runoff, it has been shown to essentially have shifted the sediment source from fields to channels (Belmont, 2011;Belmont and Foufoula-Georgiou, 2017).…”

“…Linkages between artificial agricultural drainage and increased nutrient export have been well documented (David et al, 1997;Goolsby et al, 1999;Kreiling and Houser, 2016;Letey et al, 1977;Randall and Mulla, 2001;Royer et al, 2006;Schilling et al, 2017;Sims et al, 1998). Less research has focused on the implications of hydrologic change for sediment loads in agricultural landscapes.…”

Assessment of Spatial Nitrate Patterns in An Eastern Iowa Watershed Using Boat-Deployed Sensors

“…Our data also demonstrate that a fixed-location study based in the uppermost 60 km of either stream would show little seasonal variation (Figures 7 and 8). Dilution from groundwater and biotic uptake have been reported as the dominant drivers for in-stream NO 3 -N reduction in Iowa with a smaller proportion of NO 3 -N reduction from denitrification [22,26,27].…”