Treatment Systems 1: Blind Inlets.

In freshwater ecosystems, phosphorus is generally the nutrient most limiting algal growth. Agricultural drainage systems in the upper Midwestern US are generally designed to drain water as quickly as possible, in order to ensure trafficability and minimize crop damage due to flooding. An unintended consequence of this hydraulic efficiency is that contaminants, including sediment and phosphorus are also transported away from agricultural fields rapidly. For example, in fields with closed depressional areas, which are common throughout the young glacial till landscapes of the Midwest, the most common practice to drain the water is a tile riser. Tile risers are a direct conduit for surface water to the subsurface tile drainage systems, and thus, to the agricultural drainage ditch network. Researchers in Indiana and Minnesota have independently come up with solutions to break the direct connection between surface runoff and subsurface tile systems. In the case of Indiana, the practice, known as blind inlets, has been shown to reduce soluble and total P loadings by nearly 80% compared to tile risers. In Minnesota, the practice known as French drains, has been shown to reduce soluble P by 20% and total suspended solids by 79%. Reducing the direct connection between surface runoff and subsurface tile risers is an important technology that can effectively reduce phosphorus loading to agricultural drainage ditches.