Subsurface tile drainage is an essential water management practice in many high production fields. When nutrients are carried off those fields, it can cause problems in local waterways when nitrates get into the runoff. Drainage water management is one of those practices described to justify the use of resources to reduce those problems.
Category: Research
Utilization of Steel Slag in Blind Inlets for Dissolved Phosphorus Removal
Blind inlets are implemented to promote obstruction-free surface drainage of field depressions as an alternative to tile risers for the removal of sediment and particulate phosphorus (P) through an aggregate bed. However, conventional limestone used in blind inlets does not remove dissolved P, which is a stronger eutrophication agent than particulate P. Steel slag has been suggested as an alternative to limestone in blind inlets for removing dissolved P. The objectives of this study were to construct a blind inlet with steel slag and evaluate its ability to remove dissolved P, nitrogen (N), and herbicides. A blind inlet was constructed with steel slag in late 2015; data from only 2018 are reported due to inflow sampling issues. The blind inlet removed at least 45% of the dissolved P load and was still effective after three years. The dissolved P removal efficiency was greater with higher inflow P concentrations. More than 70% of glyphosate and its metabolite, and dicamba were removed. Total N was removed in the form of organic N and ammonium, although N cycling processes within the blind inlet appeared to produce nitrate. Higher dissolved atrazine and organic carbon loads were measured in outflow than inflow, likely due to the deposition of sediment-bound particulate forms not measured in inflow, which then solubilized with time. At a cost similar to local aggregate, steel slag in blind inlets represents a simple update for improving dissolved P removal.
The Past, Present and Future of Blind Inlets as a Surface Water Best Management Practice
Drainage of tile-riser inlets allow direct discharge of surface water into tile drainage systems, effectively bypassing soil filtration processes and negatively affecting water quality. Blind inlets have gained recent popularity in allowing for both depression drainage and removal of suspended particulate matter by filtration through a sand/gravel layer. This paper summarizes blind inlet development and all published studies, provides new data from dissection of the longest-operating blind inlet that was recently de-commissioned, and discusses new ideas for the future of blind inlets, given certain shortcomings. Previous studies, as well as current soil analysis of the 12-yr old blind inlet, confirmed the ability of blind inlets to reduce sediment and particulate phosphorus (P), with an overall removal efficiency of at least 40% for each. In addition to sediment and particulate P, soil sampling revealed the ability of the blind inlet to capture several pesticides: glyphosate, atrazine, S-metolachlor, and metabolites. Traditional blind inlet sand media are unable to remove appreciable amounts of dissolved P compared to alternative media such as steel slag. Enhanced removal of dissolved constituents could be easily achieved through the use of P sorption materials and organic materials such as biochar, as well as a combination with tile-drain filters.
Livingston Blind Inlets
Blind inlets are an alternative to a tile riser to drain small impressions, but in reverse. Blind inlets reduce the direct connectivity to contaminants getting into streams. Interrupting the connectivity helps to reduce loads of sediment, nutrients and pesticides running into water systems. An ARS scientist has shown a Blind Inlet Study Site, sediment and nutrient loss data.
Delaying Drainage from Prairie Potholes Protects Water Quality
After a storm, a tile riser drains a pothole in a wheat field. Tile risers are perforated pipes extending a foot or more above the soil. Water flows into the holes in the pipe and then typically flows unimpeded and unfiltered into subsurface drains and eventually into streams, causing pollution. An ARS scientist has shown that a blind inlet provides a solution.
Drainage Water Management for Water Quality Protection
Highlights of major areas within drainage water management that show promise for water quality protection, emphasizing the array of options, established and nascent. Included in this resource are eight components of drainage water management where land managers can positively impact water quality.
Drainage Water Management Effects on Tile Discharge and Water Quality
Drainage water management (DWM) has received considerable attention as a potential best management practice (BMP) for improving water quality in tile-drained landscapes. The objective of this study was to evaluate the effects of DWM on subsurface drain discharge as well as on nitrogen (N) and phosphorus (P) loads in drainage water. Tile discharge and nutrient concentrations were measured from two adjacent tile drainage outlets in an Ohio, USA headwater watershed for 7 years (2006–2012). A control structure was installed in 2009 to allow DWM at one of the outlets from 2009 to 2012. A before-after control–impact (BACI) study design was used to assess the impact of DWM on tile discharge and nutrient loads. Results showed that DWM significantly decreased annual tile discharge between 11 and 178 mm, which was equivalent to an 8 to 34% reduction inflow. DWM significantly decreased annual NO3 N loads by −1.3 to 26.8 kg ha−1 (−8 to 44%) and annual dissolved P loads by 0.04 to 0.51 kg ha−1 (40 to 68%). Nutrient concentrations were not significantly affected by DWM indicating that decreases in nutrient loads were primarily due to reductions in tile discharge rather than changes in concentration. Results from the current study support the use of DWM as a BMP to decrease N and P loads in subsurface drain discharge throughout the U.S. Midwest. Future research should focus on quantifying the effect of DWM on nutrient transport in other flow paths (e.g., lateral seepage, surface runoff) to further evaluate its use as a BMP in tile-drained landscapes.
