SREL Reprint #3872

Anaemic streams: iron and essential trace metals frequently limit primary producer biomass

David M. Costello1, Olufemi J. Akinnifesi1, Renn C. Schipper1, Paisley Kostick1, Jordyn T. Stoll1,2, Scott D. Tiegs3, Amy M. Marcarelli4, Sally A. Entrekin5, Raven L. Bier6, Krista A. Capps6,7, and Dean E. Fletcher6

1Department of Biological Sciences, Kent State University, Kent, Ohio, USA
2Department of Biology, Grand Valley State University, Allendale, Michigan, USA
3Department of Biological Sciences, Oakland University, Rochester, Michigan, USA
4Department of Biological Sciences, Michigan Technological University, Houghton, Michigan, USA
5Department of Entomology, Virginia Polytechnic Institute, Blacksburg, Virginia, USA
6Savannah River Ecology Laboratory, University of Georgia, Aiken, South Carolina, USA
7Odum School of Ecology, University of Georgia, Athens, Georgia, USA

Abstract: Metals are essential for microbial metabolism, yet their role as limiting nutrients in freshwater streams remains poorly understood. We quantified the prevalence of metal and nutrient (co-)limitation of primary producers in 41 streams. Metal limitation was widespread with Fe limitation eliciting the strongest and most consistent biomass responses (50% of streams). Zn limitation was also common (33% of streams), marking the first evidence of Zn-limited stream biofilms at this spatial scale. Metals were often co-limiting with N and P, highlighting interactions between macro-and micronutrients. Diatoms were more responsive to Zn and cyanobacteria reached higher biomass with N and P enrichment, emphasizing divergent nutrient responses among taxa. Predictive modelling indicated that Fe and Zn limitation could be forecasted from environmental variables related to macronutrient supply. These findings challenge the long-standing assumption that stream primary producers are rarely metal-limited and suggest that trace metals may play an underappreciated role in regulating stream productivity, community composition and nutrient cycling.

Keywords: biofilm; co-limitation; metals; nitrogen limitation; phosphorus limitation; zinc

SREL Reprint #3872

Costello, D. M., O. J. Akinnifesi, R. C. Schipper, P. Kostick, J. T. Stoll, S. D. Tiegs, A. M. Marcarelli, S. A. Entrekin, R. L. Bier, K. A. Capps, and D. E. Fletcher. 2026. Anaemic streams: iron and essential trace metals frequently limit primary producer biomass. Ecology Letters 29(e70357).

This information was provided by the University of Georgia's Savannah River Ecology Laboratory (srel.uga.edu).