Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 8/1/2008
Publication Date: 9/3/2008
Citation: Smith, D.R., Heathman, G.C., Livingston, S.J., Larose, M. 2008. Factors Influencing Nutrient Losses in the St. Joseph River Watershed [abstract]. The National Sedimentation Laboratory: 50 Years of Soil and Water Research in a Changing Agricultural Environment. September 3-5, 2008, Oxford, Mississippi. 2008 CDROM.
Technical Abstract: Agricultural drainage ditches are a common landscape feature in the glacial till soils of the upper Midwestern United States. Many of these ditches have had vegetative buffer strips placed along the banks, presumably to filter sediments and other contaminants as surface runoff flows from adjacent fields to the ditches. However, local microtopography analysis often indicates that surface runoff will be held back by localized high spots that run along the top of the banks of these ditches. These high spots are a result of the initial construction of the ditch and/or more recent ditch maintenance activities such as dredging. A survey of two ditches in the St. Joseph River watershed indicated that these localized high spots were observed at approximately 90% of more than 100 ditch transects. This may often result in the ponding of water behind within the vegetative buffer strip. Furthermore, to alleviate this ponding, farmers will often times install tile risers in these areas to shunt the ponded water into the drainage ditch. This being the case, surface runoff water is conveyed to agricultural drainage ditches by one of four mechanisms: 1) from tile risers placed in potholes that are upto several km away from the drainage ditch; 2) from tile risers placed in the vegetative buffer strips; 3) as drainage from roads and fields that are transported through roadside ditches; or 4) where microtopography permits direct flow from fields into drainage ditches. While the buffer strips may not filter contaminants from surface runoff water as effectively as initially expected, they do provide an extremely beneficial purpose by acting as natural setbacks when producers are carrying out field activities. These vegetative buffer strips keep producers from tilling right next to the agricultural ditches, as well as from placing pesticides or fertilizers directly into the drainage ditches. Given this information, future efforts should be placed on maintaining these vegetative buffer strips as vegetated setback, as well as to try and ensure buffering or setbacks are used for other sources of surface runoff water to agricultural drainage ditches.