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United States Department of Agriculture

Agricultural Research Service

Research Project: CONSERVATION EFFECTS ASSESSMENT FOR THE ST. JOSEPH RIVER WATERSHED

Location: National Soil Erosion Research Lab

Title: Short-term and long-term impacts of dredging on nutrient transport in agricultural ditches of the Lake Erie Basin, USA

Author
item Smith, Douglas

Submitted to: American Society of Limnology and Oceanography
Publication Type: Abstract Only
Publication Acceptance Date: March 15, 2008
Publication Date: June 8, 2008
Citation: Smith, D.R. 2008. Short-term and long-term impacts of dredging on nutrient transport in agricultural ditches of the Lake Erie Basin, USA. American Society of Limnology and Oceanography, Society of Canadian Limnolgists, North American Benthological Society. June 8-13, 2008, St. John's, Newfoundland, Canada. 2008 CDROM.

Technical Abstract: Agricultural drainage ditches are a common landscape feature in the Midwestern United States. Compared to natural streams in more pristine environments, little is known about nutrient fate and transport in these highly enriched systems, especially following human induced manipulations. Drainage ditches can be dredged every five to fifty years, often removing more than 25 cm of sediments, as well as the vegetation and other biota in the sediments. We conducted studies to evaluate the immediate (days) and long-term (months and years) impacts of dredging on nutrient fate and transport from these systems. Using a flume, sediments collected from ditches after dredging removed less P from the water column than sediments collected before dredging. Similar results were observed for nitrification and Denitrification for these two sets of sediments. For long-term information, two monitoring stations were established up-stream and downstream of a dredged section of ditch. In the year after the dredging, N transport appeared to be relatively unaltered compared to other years, whereas there was a loss of P mass (-12 kg soluble P and -5 kg total P) during the monitored period the year after dredging. There are several factors that likely contributed to this finding, including revegetation of the ditch and a relatively dry year compared to other years. Results from this research show that human manipulations of drainage ditches may result in greater nutrient transport to receiving waters over the short term; however, this is most likely offset as the systems recover (i.e. revegetation), at least with respect to P.

Last Modified: 7/23/2014