GLOBES Research Summary
Sarah Roley
Email: sroley@nd.edu
Department: Biological Sciences
Advisor: Jennifer Tank
Restoration of Ecosystem Function in an Agricultural Landscape
Intensely farmed landscapes export excess nutrients and sediments to streams and the resulting nutrient pollution and sedimentation can result in eutrophication. In eutrophied systems, nutrients fuel overabundant algal growth and their subsequent decomposition robs the water column of oxygen. Other effects include community shifts to toxic species of algae, reduced fish and crustacean populations, human health risks, and aesthetic problems (Carpenter et al. 1998). The hypoxic zone in the Gulf of Mexico is an example of extreme eutrophication, which encompassed over 20,000 square kilometers in 2007 (Louisiana Universities Marine Consortium 2007). Most of the excess nitrogen responsible for Gulf eutrophication originates from the Corn Belt (particularly Indiana, Illinois, and Iowa) in the Mississippi River basin (Rabalais et al. 2002, Turner and Rabalais 2003).
One suggested technique for reducing export of nitrogen and sediments is the two-stage ditch (Powell et al. 2007). A typical agricultural first-order stream is a drainage ditch, designed to move water quickly downstream. These channels are effective for moving water, but have minimal capacity for nutrient processing or sediment retention (Triska et al. 2007). In the two-stage ditch, the channel is bordered by benches, or small floodplains, that convey peak stream flows without overtopping the stream bank. During storms, water gets trapped on the benches, where sediments can settle out and nutrient processing can occur. In addition, two-stage ditch banks are more stable than those in a typical agricultural stream.
In cooperation with The Nature Conservancy (TNC), I am examining the results of the two-stage manipulation on an Indiana stream. Our study site is upstream of the Tippecanoe River, which is rich in mussel and fish diversity. If this technique is effective at removing nitrogen and sediments, the TNC will implement it across the Tippecanoe River Basin to maintain the water quality and habitat in the River. The results will be applicable to other agricultural watersheds, as well.
The two-stage ditch was constructed in November 2007, after one year of data collection. We are measuring in-stream and bench denitrification, sediment composition, whole-stream metabolism, and water retention time. Denitrification is the process that converts nitrate (NO-3) to N2 gas (Wetzel 2001), and it is the only process that removes nitrogen from the system completely. Whole-stream metabolism measurements include community respiration and primary production, which demonstrate how much nitrogen is assimilated into plant matter. We will continue collecting data for 3 years, post-manipulation, to determine how the two-stage ditch affects ecosystem function, and if it is effective at nitrogen removal and sediment retention.
Carpenter, S. R., N. F. Caraco, D. L. Correll, R. W. Howarth, A. N. Sharpley, and V. H. Smith. 1998. Nonpoint pollution of surface waters with phosphorus and nitrogen. Ecological Applications 8:559-568.
Louisiana Universities Marine Consortium. 2007. Hypoxia in the northern Gulf of Mexico: Mapping the “dead zone” 2007. http://www.gulfhypoxia.net/
Powell, G.E., A.D. Ward, D.E. Mecklenburg, and A.D. Jayakaran. 2007. Two-stage channel systems: Part 1, a practical approach for sizing agricultural ditches. Journal of Soil and Water Conservation. 62:277-285.
Rabalais, N. N., R. E. Turner, and W. J. Wiseman. 2002. Gulf of Mexico hypoxia, aka "The dead zone". Annual Review of Ecology and Systematics 33:235-263.
Triska, F.J., J.H Duff., R.W.Sheibley, A.P.Jackman, and R.J. Avanzino. 2007. Din-retetion-transport through four hydrologically connected zones in a headwater catchment of the upper Mississippi River. Journal of the American Water Resources Association. 43: 60-71.
Turner, R. E., and N. N. Rabalais. 2003. Linking landscape and water quality in the Mississippi river basin for 200 years. BioScience 53:563-572.
Wetzel, R.G. 2001. Limnology: Lake and river ecosystems, 3rd ed. Academic Press, San Diego, CA.
Research Publications and Presentations
Roley, S.S., Tank, J.L., Johnson, L.T., Beaulieu, J.J., Stephen, M.L. (2008, May 26). Two-stage ditch restoration: a potential strategy to reduce nitrogen export from agricultural streams. North American Benthological Society Annual Meeting. Salt Lake City, UT
Roley, S.S. and Newman, R.M. 2008. Predicting Eurasian watermilfoil invasions in Minnesota. Lake and Reservoir Management. 24:361-369.
Roley, S.S. and Stephen, M.L. (2008, September). The ecological importance of floodplains and their influence on nitrogen dynamics. Presented at a Two-Stage Ditch Seminar, hosted by The Nature Conservancy. Pokagon State Park, IN.