The method controls the story - Sampling method impacts on the detection of pore-water nitrogen concentrations in streambeds

Research output: Contribution to journalReview articlepeer-review


  • Julia L.A. Knapp
  • Felicity Shelley
  • Jay Zarnetske
  • Joseph Lee-Cullin
  • Silvia Folegot
  • Marie Kurz
  • Jorg Lewandowski
  • Judson Harvey
  • Adam Ward
  • Clara Mendoza-Lera
  • Thibault Datry
  • Daren Gooddy
  • Jennifer Drummond
  • Eugènia Martí
  • Sandy Milner
  • David Hannah
  • Stefan Krause

External organisations

  • Universitat Tubingen
  • School of Geography and Water
  • University of Leeds
  • School of Biological and Chemical Sciences Queen Mary University of London
  • Michigan State University
  • Department for Urban and Environmental Sociology
  • The Academy of Natural Sciences of Drexel University
  • Leibniz-Institute of Freshwater Ecology and Inland Fisheries
  • U.S. Geological Survey
  • Indiana University
  • Irstea, UR MALY
  • British Geological Survey
  • Centre for Advanced Studies of Blanes (CEAB-CSIC)


Biogeochemical gradients in streambeds are steep and can vary over short distances often making adequate characterisation of sediment biogeochemical processes challenging. This paper provides an overview and comparison of streambed pore-water sampling methods, highlighting their capacity to address gaps in our understanding of streambed biogeochemical processes. This work reviews and critiques available pore-water sampling techniques to characterise streambed biogeochemical conditions, including their characteristic spatial and temporal resolutions, and associated advantages and limitations. A field study comparing three commonly-used pore-water sampling techniques (multilevel mini-piezometers, miniature drivepoint samplers and diffusive equilibrium in thin-film gels) was conducted to assess differences in observed nitrate and ammonium concentration profiles. Pore-water nitrate concentrations did not differ significantly between sampling methods (p-value = 0.54) with mean concentrations of 2.53, 4.08 and 4.02 mg l 1 observed with the multilevel mini-piezometers, miniature drivepoint samplers and diffusive equilibrium in thin-film gel samplers, respectively. Pore-water ammonium concentrations, however, were significantly higher in pore-water extracted by multilevel mini-piezometers (3.83 mg l 1) and significantly lower where sampled with miniature drivepoint samplers (1.05 mg l 1, p-values <0.01). Differences in observed pore-water ammonium concentration profiles between active (suction: multilevel mini-piezometers) and passive (equilibrium; diffusive equilibrium in thin-film gels) samplers were further explored under laboratory conditions. Measured pore-water ammonium concentrations were significantly greater when sampled by diffusive equilibrium in thin-film gels than with multilevel mini-piezometers (all p-values ≤0.02). The findings of this study have critical implications for the interpretation of field-based research on hyporheic zone biogeochemical cycling and highlight the need for more systematic testing of sampling protocols. For the first time, the impact of different active and passive pore-water sampling methods is addressed systematically here, highlighting to what degree the choice of pore-water sampling methods affects research outcomes, with relevance for the interpretation of previously published work as well as future studies.


Original languageEnglish
Article number136075
Number of pages19
JournalScience of the Total Environment
Early online date19 Dec 2019
Publication statusPublished - 20 Mar 2020


  • Ammonium, Nitrate, Nutrients, Samplers, Streambed sampling