, Volume 826, Issue 1, pp 233–246 | Cite as

Acidification, stress, and detrital processing: implications for ecosystem function in headwater streams

  • H. Maurice ValettEmail author
  • Damon T. Ely
Primary Research Paper


Environmental influences like acidification promote stress at the ecosystem level that manifests as reduction in metabolic and biogeochemical efficiency. Headwater streams along a chronic acidity gradient were assessed to explore how stress alters microbial abundance and activity and their influence on ecosystem structure and function. Streams draining deciduous forests were investigated during autumn when channels were filled by leaf litter. Whole-system measures of respiration were coupled to estimates of fungal biomass in leaf biofilms to generate an ecosystem-level measure of metabolic efficiency (qCO2E, g CO2–C g C−1 d−1). Stable isotope releases of nitrate nitrogen (15N–NO3) were performed to address nitrate uptake (\({\text{U}}_{{{\text{NO}}_{ 3} }}\)) across streams. Fungal stocks decreased across five streams as pH declined (6.98–5.34). Whole-system respiration decreased fivefold with increasing acidity, while qCO2E did not respond consistently to acidification, but was correlated with stream temperature. Across streams, concentrations of nitrogen (N) were low and \({\text{U}}_{{{\text{NO}}_{ 3} }}\) related to nutrient availability and not to stream acidity. Results illustrate that acidification alters ecosystem processes through influences on microbial abundance and metabolic activity, while scarce N availability and low \({\text{U}}_{{{\text{NO}}_{ 3} }}\) characterized biogeochemical behavior during autumnal periods of maximal detrital stocks.


Metabolic efficiency N uptake Stress Acidification Streams Fungi 



We thank JR Webster, E.F. Benfield, B.R. Niederlhener, D. Von Schiller, and the students of the Virginia Tech Stream Team for conceptual and operational support. HM Valett also thanks Marc Peipoch for comments on an earlier draft of the manuscript. This research was supported by National Science Foundation (NSF) awards DEB080836 to DT Ely and HM Valett, DEB0841809 to KS Simon and HM Valett, NSF EPSCoR Track-1 NSF-IIA-1443108, and the Montana Institute on Ecosystems. The datasets generated and/or analyzed during the current study are available through DataONE (

Supplementary material

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Supplementary material 1 (PPTX 361 kb)


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Authors and Affiliations

  1. 1.Division of Biological SciencesUniversity of MontanaMissoulaUSA
  2. 2.Department of BiologyState University of New York OrangeMiddletownUSA

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