Research

Pollution and Eutrophication of Freshwaters

The Dead Zone

In the Gulf of Mexico an expansive area—“the dead zone”—has developed in recent years.  As a result of oxygen depletion, many forms of ocean life in this formerly productive fishing ground have died or migrated elsewhere.  The dead zone is caused by excess nitrogen and phosphorous that has moved from Midwestern farm fields downstream via the Mississippi River and ultimately into the Gulf of Mexico. Agricultural run-off from feedlots and fertilizer are the primary sources of this excess nitrogen and phosphorous. These nutrients move over the landscape through agricultural ditches, streams and rivers and are eventually deposited in lakes wetlands, and other waterways, if they do not find there way all the way to the Gulf of Mexico.  Thus over-fertilization—or eutrophication to scientists—causes both local and regional pollution.  In affected waterways, very tiny plants—phytoplankton--grow rapidly and densely.  This enhanced plant growth, often called an algal bloom, reduces dissolved oxygen in the water when dead plant material decomposes, and can cause other organisms to die.   The “dead zone” in the Gulf of Mexico is well-known, but eutrophication of our waters is occurring worldwide and is altering freshwater ecosystems and the services they provide to humans.  Drinking water quality is often reduced, swimming becomes dangerous, and harvests of fish, shellfish, waterfowl and other ecosystem goods are devastated.

Mitigating Nitrogen Pollution

At CAC, researchers are working to better understand eutrophication, and are testing strategies to reduce the nitrogen pollution in run-off.  Jennifer Tank is leading investigations on the fate of nitrogen run-off as it travels downstream from midwestern farm fields.  Tank and her research team have discovered that some nitrogen is being taken up by plants in and around streams and rivers.  In addition, bacteria remove nitrogen when they convert nitrates into gaseous nitrogen. Using nitrogen tracers, the researchers are tracking nitrogen as it moves through streams to determine where nitrogen is retained.  These results will then be extended to  watershed-wide geographic models that include water flow and land use to predict nitrogen retention in the watershed. Using this model, researchers will identify possible strategies for increasing nitrogen uptake and denitrification before it pollutes our waters and damages ecosystems.   In collaboration with The Nature Conservancy, Tank and her students, who are supported by CAC fellowships, are using a large experiment in Indiana to test how much widened and reshaped farm ditches—so-called two stage ditches—can reduce the run-off of nitrogen.  By working collaboratively with farmers, engineers, and other stakeholders, Tank and The Nature Conservancy will discover the most cost effective ways to reduce run-off.

Greener Alternatives to Chemical Pollutants

Other common causes of water pollution include point source pollution from manufacturing and industry.  Currently many of the chemicals used in manufacturing and industry are highly toxic.  Chemical engineers at the University of Notre Dame, led by Joan Brennecke, Edward Maginn and others, are designing a new class of chemicals that promise to be a “greener” alternative than many solvents widely used in industry.  CAC ecologists, led by Gary Lamberti and Charles Kulpa, are testing these new ionic liquids for their toxicity in aquatic systems and providing the engineers valuable feedback about the toxicity of the various ionic liquids. This feedback is used to guide the chemical design process, and provide advice about potential environmental harm before chemicals are adopted for use by industry.  Such proactive combinations of engineering and environmental analyses are rare, and provide an excellent model to prevent future human health and environmental disasters.

Links

• LINX
• TNC Indiana
• Interdisciplinary Graduate Program in Interfaces of Ecology, Engineering, and Geology

 Selected Publications

Bernot, M.J., Tank, J.L.; Royer, TV, David, MB. 2006. Nutrient uptake in streams draining agricultural catchments of the midwestern United States. Freshwater Biology 51 (3): 499-509.

Hamilton, S.K.; Tank, J.L. Raikow, D.E. Siler, E.R Dorn, N.J., Leonard, N.E. 2004. The role of instream vs allochthonous N in stream food webs: modeling the results of an isotope addition experiment. Journal of the North American Benthological Society 23 (3): 429-448.

Dodds, W.K., Marti, E,Tank, J.L., Pontius, J, Hamilton, S.K., Grimm, N.B., Bowden, W.B., McDowell, W.H., Peterson, B.J., Valett, H.M., Webster, J.R., Gregory, S. 2004. Carbon and nitrogen stoichiometry and nitrogen cycling rates in streams. Oecologia 140 (3): 458-467.

Hall, R., Tank, J.L., Dybdahl, M.F. 2003. Exotic snails dominate nitrogen and carbon cycling in a highly productive stream. Frontiers in Ecology and the Environment 1 (8): 407-411.

Frost, PC; Larson, JH; Johnston, CA; Young, KC; Maurice, PA; Lamberti, GA; Bridgham, SD. 2006. Landscape predictors of stream dissolved organic matter concentration and physicochemistry in a Lake Superior river watershed. Aquatic Sciences 68 (1): 40-51.

Bernot, R.J., Brueseke, M.A., Evans-White, M.A., Lamberti, G.A. 2005. Acute and chronic toxicity of imidazolium-based ionic liquids on Daphnia magna. Environmental Toxicology and Chemistry 24 (1): 87-92.

Bernot, RJ; Kennedy, EE; Lamberti, GA. 2005. Effects of ionic liquids on the survival, movement, and feeding behavior of the freshwater snail, Physa acuta. Environmental Toxicology and Chemistry 24 (7): 1759-1765.