Effect of replacing surface inlets with blind or gravel inlets on sediment and phosphorus subsurface drainage losses

Authors: Feyereisen, Gary; Francesconi, Wendy; Smith, Douglas; Schneider, Sharon; KRUEGER, E. - Oklahoma State University; Wente, Christopher - Chris

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/30/2014
Publication Date: 3/11/2015
Publication URL: http://handle.nal.usda.gov/10113/60620
Citation: Feyereisen, G.W., Francesconi, W., Smith, D.R., Papiernik, S.K., Krueger, E.S., Wente, C.D. 2015. Effect of replacing surface inlets with blind or gravel inlets on sediment and phosphorus subsurface drainage losses. Journal of Environmental Quality. 44(2):594-604.

Interpretive Summary: In the prairie pothole region of the Midwestern U.S. cropland, subsurface drainage systems often include surface inlets in the bottom of low lying areas that drain ponded water after intense storms. The type of inlet design affects the transport of sediment, nutrients, agrochemicals, and bacteria from the field surface to the subsurface drainage system, bypassing the filtering capacity of the soil. This study was conducted to examine whether modifying the open inlets, sometimes called tile riser inlets, by burying them in gravel capped with 30 cm of sandy clay loam soil or in very coarse sand/fine gravel could reduce suspended sediment and phosphorus concentrations and loads in the drainage effluent. In Indiana, USA, a pair of closed depressions in adjacent fields were fitted with both open inlet tile risers and blind inlets and monitored for flow and water chemistry. Paired comparisons on a storm event basis during the growing season showed that suspended sediment loads were reduced by 64% for the closed versus open inlets. Total phosphorus (TP) and soluble reactive phosphorus (SRP) loads were 66 and 50% less for the closed inlets, respectively. In Minnesota, USA, suspended sediment and SRP concentrations were monitored for three years prior to and following installation of closed inlets in an unreplicated large-field on-farm study. The results confirm the reduction in suspended sediment concentrations/loads observed in Indiana. The SRP concentrations were not different during the non-snowmelt season. The Minnesota results indicate that SRP concentrations during spring snowmelt are higher than during the remainder of the year and that snowmelt losses are a sizable portion of the annual sediment and SRP budgets. Replacing open inlet tile risers in closed depressions with the blind inlet designs studied reduced sediment and phosphorus loads from agricultural closed depressions. The results of this study clearly indicate the consequences of replacing open inlets with blind inlets, information germane to conservation practioners, producers, land improvement contractors, policy makers, and researchers.

Technical Abstract: Open surface inlets that connect to subsurface tile drainage systems provide a direct pathway for sediment, nutrients, and agrochemicals to surface waters. This study was conducted to determine whether modifying open inlets by burying them in gravel capped with 30 cm of sandy clay loam soil or in very coarse sand/fine gravel could reduce suspended sediment and phosphorus concentrations and loads in the drainage effluent. In Indiana, USA, a pair of closed depressions in adjacent fields were fitted with both open inlet tile risers and blind inlets and monitored for flow and water chemistry. Paired comparisons on a storm event basis during the growing season showed that suspended sediment loads were reduced by 64% for the closed versus open inlets. Total phosphorus (TP) and soluble reactive phosphorus (SRP) loads were 66 and 50% less for the closed inlets, respectively. In Minnesota, USA, suspended sediment and SRP concentrations were monitored for three years prior to and following installation of closed inlets in an unreplicated large-field on-farm study. The results confirm the reduction in suspended sediment concentrations/loads observed in Indiana. The SRP concentrations were not different during the non-snowmelt season. The Minnesota results indicate that SRP concentrations during spring snowmelt are higher than during the remainder of the year and that snowmelt losses are a sizable portion of the annual sediment and SRP budgets. Replacing open inlet tile risers in closed depressions with the blind inlet designs studied reduced sediment and phosphorus loads from agricultural closed depressions.