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Water column contributions to the metabolism and nutrient dynamics of mid-sized rivers

Abstract

Lotic and lentic ecosystems are traditionally viewed as dominated by either benthic or water column processes. However, mid-sized rivers represent a transition zone where both benthic and water column processes may both contribute substantially to ecosystem dynamics. Ecosystem processes such as gross primary production (GPP), ecosystem respiration (ER), or nutrient uptake, and the relative contribution of the water column to these processes at the reach scale, are poorly understood in non-wadeable, mid-sized rivers. To clarify the role of the water column at the reach-scale, and to quantify controls on water column processes, we measured GPP, ER, and uptake of nitrate (NO3), ammonium (NH4+), and soluble reactive phosphorus (SRP) in the water columns of 15 mid-sized rivers (discharge: 13.5–83.3 m3 s−1) spanning nutrient and total suspended solids gradients. We compared water column metabolic and nutrient uptake rates to reach-scale rates to estimate the contribution of the water column to the entire river. Water column metabolism was autotrophic on the day when measured, GPP increased with nutrient availability, and the water column contributed more to whole river GPP than to ER. Water column nutrient uptake increased with GPP across solutes, and there was a positive relationship between human land use and water column uptake of NO3–N and SRP. The water column accounted for a substantial proportion of reach-scale metabolism and nutrient uptake, but this contribution depended on suspended material and nutrient availability. Integrating the water column into theory describing lotic ecosystem function should clarify mechanisms controlling metabolism and nutrient processing and enhance management of non-wadeable rivers.

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Data availability

Data will be made publicly available through the UF Institutional Repository (IR@UF; https://ufdc.ufl.edu/ufir) upon acceptance of the manuscript.

Code availability

All analyses were carried out using established R packages and are referenced in the manuscript. Code used to analyze data and create figures will be made publicly available through the UF Institutional Repository (IR@UF; https://ufdc.ufl.edu/ufir) upon acceptance of the manuscript.

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Acknowledgements

We thank all of the field and lab support who helped with field work for the water column and reach-scale metabolism and nutrient uptake components of this study: N. Anderson, M. Dee, S. Gregory, B. Hanrahan, E. Hotchkiss, C. Johnson, D. Kincaid, U. Mahl, D. Oviedo, J. Reed, T. Royer, C. Ruiz, A. Saville, M. Schroer, A. Shogren, E. Taylor-Salmon, and Z. Volenec. This manuscript was improved by reviews from J. Gardner and an anonymous reviewer. Most of this work was funded by a collaborative grant from NSF Ecosystems, (DEB-09-22118, 09-21598, 09-22153, and 10-7807) and the return trip to measure water column metabolism in 2013 was funded by a grant awarded to JLT and AJR from the University of Wyoming-National Parks Service Research Station.

Funding

This research was funded by a collaborative grant from NSF-Ecosystems (DEB-09-22118, 09-21598, 09-22153, and 10-7807). The return trip in 2013 to measure water column metabolism was funded by a grant awarded to JLT and AJR from the University of Wyoming-National Parks Services Research Station.

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Contributions

Conceptualization: AJR, JLT, ROH, EJR, MAB, LG; Data curation: AJR; Formal analysis: AJR; Funding acquisition: AJR, JLT, ROH, EJR, MAB; Investigation: AJR, LG; Methodology: AJR, JLT, ROH, EJR, MAB, LG; Project administration: AJR, JLT; Resources: JLT, ROH, EJR, MAB; Software: AJR, ROH, LG; Supervision: JLT, ROH, EJR, MAB; Validation: AJR; Visualization: AJR, JLT, ROH, EJR, MAB, LG; Writing original draft: AJR; Writing-reviewing and editing: AJR, JLT, ROH, EJR, MAG, LG.

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Correspondence to Alexander J. Reisinger.

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The authors report no conflicts of interest.

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Reisinger, A.J., Tank, J.L., Hall, R.O. et al. Water column contributions to the metabolism and nutrient dynamics of mid-sized rivers. Biogeochemistry 153, 67–84 (2021). https://doi.org/10.1007/s10533-021-00768-w

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  • DOI: https://doi.org/10.1007/s10533-021-00768-w

Keywords

  • River
  • Water column
  • Gross primary production
  • Ecosystem respiration
  • Metabolism
  • Nutrient uptake