ARS | Publication request: Nutrient Transport in Dredged Reaches of Agricultural Drainage Ditches

Submitted to: Soil and Water Conservation Society
Publication Type: Abstract Only
Publication Acceptance Date: April 1, 2009
Publication Date: July 11, 2009
Citation: Smith, D.R., Huang, C. 2009. Nutrient Transport in Dredged Reaches of Agricultural Drainage Ditches [abstract]. Soil and Water Conservation Society and CEAP meeting, July 11-15, 2009. Dearborn, Michigan. 2009 CDROM.

Technical Abstract: Agricultural drainage ditches are a vital component of many of the more productive agricultural landscapes in the United States. These systems often require intensive management to ensure adequate removal of water from the system, but little is known about how ditch management affects nutrient losses. In this study, we monitored nutrient transport in three drainage ditches for five years, during which time three dredging activities occurred in two of the ditches. There were significant decreases in NH4-N (96%; P < 0.01), NO3-N (90%; P < 0.05), TKN (93%; P < 0.001), soluble P (95%; P < 0.05) and total P (93%, P < 0.05) transport as measured by change in monthly mass loss for three study reaches. Removal of nutrients by sediments and associated biota is typically negligible in agricultural stream systems, and is a result of steady state conditions. We therefore propose that the removal of nutrients in the water column of the dredged study reaches was due to a flux in the biogeochemical properties of the sediments, chiefly: (1) oxidation of the reduced exposed sediments; (2) deposition of “fresh” sediments in the ditch; (3) recolonization of filamentous algae and higher plants; and (4) the formation of biofilms on the sediments exposed by dredging. Whereas it is inadvisable to apply fertilizers immediately before or after dredging occurs, due to increased susceptibility to higher in-stream nutrient concentrations, within 2 or three months after dredging, this risk appears to have been minimized or even reversed.