Excess nutrient effects in streams

detrital_streamThis research addresses the following questions:

  • How do excess nutrients affect the functioning of aquatic systems? What thresholds in concentrations need to be avoided to maintain stream health?
  • How does the relative supply of nitrogen (N) and phosphorus (P) affect ecosystem functioning?


Nutrient pollution is a leading source of impairment to streams in the U.S. (U.S. EPA and USGS reports) and globally. Human activities increase the concentrations of N and P in aquatic systems as well as their relative concentrations, which differ by watershed land use. We investigated the relative importance of N and P and the ratio of N:P in driving ecosystem responses in detritus-based streams. This research stemmed from prior studies in which we enriched a stream for 5 years with both N and P at a fixed ratio in a paired watershed design; a nearby stream served as a reference. Our previous results showed significant effects on heterotrophic microorganisms, stream macroinvertebrates, and energy flow pathways (Gulis et al. 2003, Cross et al. 2006, Rosemond et al. 2008, Davis et al. 2010, Suberkropp et al. 2010). In more recent studies, laboratory incubations, and whole-stream nutrient additions were used to determine the concentrations and ratios of N and P that elicit undesirable ecosystem changes. We have identified important mechanisms by which changes occur. Knowledge of these threshold concentrations and ratios can guide management of aquatic ecosystems to maintain water quality for wildlife conservation and human utilization. We have found that nutrient enrichment affects all components of stream food webs, with differential effects of N and P.


Most recent collaborators: PI’s: Jon Benstead (University of Alabama), Vlad Gulis (Coastal Carolina University), John Maerz (UGA); Project postdoctoral associate: John Kominoski (now faculty at FIU); Graduate students: David Manning, Phillip Bumpers, James Wood, Mick Demi (University of Alabama); Undergraduate students: Keith Kinek, Jenna Martin. Additional and former collaborators: PI’s: J. Bruce Wallace, Keller Suberkropp, Pat Mulholland, Marsha Black; Former graduate students/collaborators: Cynthia Tant, Wyatt Cross, Jennifer Greenwood, John Davis, Brent Johnson.

ADR is also participating in a synthesis of nutrient effects in streams from experiments around the world that is being led by Lydia Zyglin and involves several other collaborators (Marcelo Ardon, John Kominoski, Bill McDowell, Sherri Johnson, Walter Dodds, Jay Jones, Tamara Harms, Ayesha Burdett, Becky Bixby, David Van Horn, Scott Cooper, Natalie Griffiths, Amelia Ward, Ryan Utz, Jenn Follstad Shah, Laura Johnson and Matt Trentman).