Effects of experimental nutrient loading on phosphorus uptake by biofilms: Evidence for nutrient saturation in mid-Atlantic streams

Keith J. Price, Hunter J. Carrick

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8 Scopus citations


Biofilms generally account for the majority of P assimilation in streams. However, relatively few direct measurements have been made that link nutrient loadings to biofilm assimilation. We measured P uptake rates for natural benthic biofilms sampled from 8 streams situated along a productivity gradient in the mid-Atlantic region, where point-source nutrient loadings were applied with an in situ enrichment system (ISES). ISES consisted of vials spiked with increasing concentrations of P with and without N. Short-term radiotracer H333PO4) experiments were conducted to measure P uptake by biofilms growing on the surface of the vials collected from the streams. The relationship between P uptake and P loading in each stream was explained using simple linear regression. In all streams, P uptake rates declined with increased experimental P loading and as a function of stream productivity. Biofilms had significantly higher uptake rates overall in low- vs high-productivity streams (1.29 and 0.84 log10[nmol P μg-1 chlorophyll d-1], respectively) (F1,30 = 6.21, p = 0.018). These results indicated that assemblages in low-productivity streams were physiologically adapted to use new P additions, whereas biofilms in productive streams showed signs of P saturation such that these assemblages had reduced demand for new P loadings. N loading synergistically affected biofilm P uptake ability in high-productivity streams, where N appeared to have been a secondarily limiting nutrient. Our work emphasizes that P uptake was heterogeneous across landscapes. P-saturation was common in high-productivity streams (embedded in agriculturally dominated watersheds) and was mediated by N-enrichment and nutrient stoichiometry.

Original languageEnglish
Pages (from-to)503-517
Number of pages15
JournalFreshwater Science
Issue number2
StatePublished - Jun 2016


  • Biogeochemistry
  • Mid-Atlantic region
  • Nitrogen
  • Periphyton
  • Stoichiometry


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