GLOBES Research Summary

Sarah Roley

Department: Biological Sciences

The effect of floodplain restoration on ecosystem function and downstream biota

Intensely farmed landscapes export excess nutrients and sediments to streams and downstream water bodies, which can impair aquatic organisms. For example, excess nitrogen (N) can fuel overabundant algal growth, particularly in coastal systems, and their subsequent decomposition robs the water column of oxygen. In addition, excess N can contaminate drinking water, produce toxic species of algae, and decrease freshwater biodiversity. I study how aquatic organisms are affected by intensive agricultural land use, and how to manage landscapes to reduce those effects.

Two Stage Ditch Irrigation Specifically, I am studying the efficacy of two-stage ditch restoration for nitrogen removal. The two-stage ditch was developed by agricultural engineers to alleviate channel instability in incised, trapezoid-shaped ditches by constructing floodplains (Fig. 1). During high flows, water spreads onto the floodplains, slowing water velocity, decreasing erosive power, and allowing sediments to settle out of the water column onto the floodplains (Powell et al. 2007). The construction of floodplains also adds bioreactive surface area, which may increase N removal via soil denitrification. In partnership with The Nature Conservancy (TNC), I am testing this hypothesis by quantifying N removal in an agricultural stream before and after the restoration of stream floodplains.

Although water quality responses to row crop agriculture are well-documented, less is known about the response of individual species to agriculturally-driven environmental stressors. Freshwater invertebrates are one of the most imperiled groups of organisms in the world, but they have received relatively little scientific attention. Without knowledge of environmental stressors, conservation is challenging.

I study the clubshell mussel (Pleurobema clava), a federally endangered species that has been eliminated from most of its native range. One of the last remaining populations is located in the Tippecanoe River in Indiana, yet the mussels have been declining since the early 1990’s. Its decline may be due, in part, to environmental stressors influencing its unique habitat requirements: P. clava spends its adult life buried beneath coarse sand and cobble, and depends upon percolation of surface water for food particles and dissolved oxygen (DO). Current land use in the Tippecanoe River basin is dominated by row crop agriculture; thus sedimentation and eutrophication may be contributing to the decline of P. clava. Sedimentation can negatively affect P. clava by filling interstitial spaces in the benthos, thereby hindering percolation of oxygen-rich stream water and food. Additionally, sediment decomposition can rob the sediments of oxygen and release ammonium (NH4+) via remineralization of organic matter; the un-ionized form, ammonia (NH3), is toxic to juvenile and adult mussels (Newton and Bartsch 2007). Excess ammonia can also result directly from fertilizer run-off. In cooperation with the Center for Aquatic Conservation, I am testing these hypotheses by characterizing sediment, pore water, and surface water conditions at sites where the clubshell thrive and at sites where they have died out.

References:

Newton, T. J., and M. R. Bartsch. 2007. Lethal and sublethal effects of ammonia to juvenile Lampsilis mussels (Unionidae) in sediment and water-only exposures. Environmental Toxicology and Chemistry 26:2057-2065.

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.

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.