Abstract
Longitudinal changes in the structure and function of river ecosystems have long been recognized, yet our understanding of how such patterns shape elemental cycles remains limited. In particular, while benthic fine particulate organic matter (POM, 0.7–1000 μm) may control many stream nutrient cycles, less is known about longitudinal patterns or controls of benthic POM-associated nutrient uptake. We conducted a survey of benthic POM-associated respiration and nutrient uptake as well as microbial biomass (bacteria and algae) and benthic POM composition in four size classes (0.7–53 μm, 53–106 μm, 106–250 μm, and 250–1000 μm) in six streams in the forested South Fork Eel River watershed (California), encompassing a longitudinal gradient in light availability and primary production. Benthic POM at downstream sites was composed of smaller particles with lower organic matter content that were richer in nitrogen and autotrophic material. Areal respiration and nutrient uptake rates increased 11- to 67-fold with stream size. While microbial activity rates did not increase with stream size, benthic POM-associated microbial biomass increased 20-fold with stream size, and closely tracked a 15-fold increase in light availability, and primary production. Thus, microbial biomass, not activity, determined longitudinal patterns in benthic POM-associated areal nutrient uptake and respiration rates. We attribute longitudinal patterns in microbial biomass to increases in light availability and primary production. Our findings help clarify the role of local (primary production) and upstream processes in shaping ecosystem structure and function.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 2684-2696 |
| Number of pages | 13 |
| Journal | Limnology and Oceanography |
| Volume | 66 |
| Issue number | 7 |
| DOIs | |
| State | Published - Jul 2021 |
Bibliographical note
Funding Information:We thank C. Booth, S. Brovold, T. Devries, B. Gallagher, H. Grun, and T. Moen for assistance in the field or laboratory. D. Glover, M. Limm, R.W. Sterner, and J.R. Welter provided insights that improved this study. A. Conine, B. Hall, A. Huryn, and six anonymous reviewers provided valuable edits. This research was supported by the National Science Foundation via grants to DEB (0315990 and 0543363) and to the Science and Technology Center program through the National Center for Earth-Surface Dynamics (EAR0120914). The research described in this article has also been funded in part by the US Environmental Protection Agency (EPA) under the Science to Achieve Results Graduate Fellowship Program (916870001). The EPA has not officially endorsed this publication, and views expressed herein may not reflect the views of the EPA. The Dayton–Wilkie Fund and a University of Minnesota Thesis Research Grant provided additional support. We are grateful to the Angelo family and the University of California Natural Reserve System for protecting the Angelo Coast Range Reserve. We thank P. Steele for managing the Angelo Reserve and for his work supporting this research.
Funding Information:
We thank C. Booth, S. Brovold, T. Devries, B. Gallagher, H. Grun, and T. Moen for assistance in the field or laboratory. D. Glover, M. Limm, R.W. Sterner, and J.R. Welter provided insights that improved this study. A. Conine, B. Hall, A. Huryn, and six anonymous reviewers provided valuable edits. This research was supported by the National Science Foundation via grants to DEB (0315990 and 0543363) and to the Science and Technology Center program through the National Center for Earth‐Surface Dynamics (EAR0120914). The research described in this article has also been funded in part by the US Environmental Protection Agency (EPA) under the Science to Achieve Results Graduate Fellowship Program (916870001). The EPA has not officially endorsed this publication, and views expressed herein may not reflect the views of the EPA. The Dayton–Wilkie Fund and a University of Minnesota Thesis Research Grant provided additional support. We are grateful to the Angelo family and the University of California Natural Reserve System for protecting the Angelo Coast Range Reserve. We thank P. Steele for managing the Angelo Reserve and for his work supporting this research.
Publisher Copyright:
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