|What are Saturated Buffers?|
What are Saturated Buffers?
The riparian zone is water’s finish line into our waterways. Each time it crosses, it carries on downstream while water quality gets stuck in last place. However, this does not have to be the indefinite story. Saturated buffers are a conservation option that remove little to no land from production, require little maintenance, and do no affect crop yields when placed in ideal sites. They have four main components, (1) a non-perforated drain pipe, (2) water control structure, (3) distribution pipe, and (4) a vegetated buffer. The tile drained water is directed to the control structure via the drain pipe. That water is then diverted into the perforated distribution pipe, where it is slowly pushed through the vegetated buffer. While crossing the buffer, denitrification occurs (a microbial facilitated process of nitrate being converted to nitrogen gas) along with nitrate uptake by the plants within the buffer.
Saturated buffers have been effective at removing nitrate, where an average of 42% of the nitrate load is removed. The amount of nitrate removed can increase if longer distribution pipes are laid. The more water that can permeate into the buffer, the more chance there is for denitrification to occur. An effort is being made it locate suitable sites across Iowa using four criteria (see the Saturated Buffer Viewer for initial efforts). denitrification occurs (a microbial facilitated process of nitrate being converted to nitrogen gas) along with nitrate uptake by the plants within the buffer
First, a buffer and tile outlet should already be in place. The vegetated buffer must be at least 30 feet wide and the tile outlet must drain enough area to provide sufficient flow. Second, soils must promote gradual, lateral movement to the water body (e.g. loam soil). Clayey soils may not allow movement, and sandy soils to gravel will result in too quick of movement. There also needs to be at least 1.2% of organic matter within the top 2.5 feet of soils to encourage denitrification. Carbon enhancement, using woodchips, has been suggested if organic matter lacks. Third, the buffer should be lower than the adjacent field to avoid inundation. If the slope is not ideal, seasonal, manual adjustment of the water control structure can allow adequate drainage. Lastly, stream banks should be stable and not exceed 8 feet in height. This provision ensures no seepage through the stream bank which can results in bank failures. While this has not been a recorded issue, it is still a safety precaution.
The overall cost of installing saturated buffers depends on the size of the water control structure and length of distribution pipe. The excavation work will also vary from site to site. The video put out my Transforming Drainage answers some questions about installation and cost (see it here).
Currently, projects are being conducted to test the siting criteria and improve the NRCS practice standard. The bank height criterium is being tested to gather a better understanding of bank stability and if sites with steeper banks may be suitable. The NRCS is also working to measure how much nitrate is removed versus how much water passes through the buffer. Saturated buffers can remove considerable amounts of nitrate from tile drained water. When located in ideal sites, they do not require regular maintenance and have the chance to greatly impact water quality throughout the Midwest and further.
If you would like more information about saturated buffers, please contact Dan Jaynes with the ARS-USDA at NLAE.