University of Oulu

Jyväsjärvi, J., Rajakallio, M., Brüsecke, J., Huttunen, K-L, Huusko, A., Muotka, T., & Taipale, S. J. (2022). Dark matters: Contrasting responses of stream biofilm to browning and loss of riparian shading. Global Change Biology, 28, 5159– 5171.

Dark matters : contrasting responses of stream biofilm to browning and loss of riparian shading

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Author: Jyväsjärvi, Jussi1; Rajakallio, Maria1; Brüsecke, Joanna1;
Organizations: 1Ecology and Genetics Research Unit, University of Oulu, Oulu, Finland
2Natural Resources Institute Finland (Luke), Paltamo, Finland
3Department of Biological and Environmental Science, University of Jyväskylä, Jyväskylä, Finland
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 1.2 MB)
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Language: English
Published: John Wiley & Sons, 2022
Publish Date: 2022-09-08


Concentrations of terrestrial-derived dissolved organic carbon (DOC) in freshwater ecosystems have increased consistently, causing freshwater browning. The mechanisms behind browning are complex, but in forestry-intensive regions browning is accelerated by land drainage. Forestry actions in streamside riparian forests alter canopy shading, which together with browning is expected to exert a complex and largely unpredictable control over key ecosystem functions. We conducted a stream mesocosm experiment with three levels of browning (ambient vs. moderate vs. high, with 2.7 and 5.5-fold increase, respectively, in absorbance) crossed with two levels of riparian shading (70% light reduction vs. open canopy) to explore the individual and combined effects of browning and loss of shading on the quantity (algal biomass) and nutritional quality (polyunsaturated fatty acid and sterol content) of the periphytic biofilm. We also conducted a field survey of differently colored (4.7 to 26.2 mg DOC L−1) streams to provide a ‘reality check’ for our experimental findings. Browning reduced greatly the algal biomass, suppressed the availability of essential polyunsaturated fatty acids, especially eicosapentaenoic acid (EPA), and sterols, but increased the availability of terrestrial-derived long-chain saturated fatty acids (LSAFA). In contrast, loss of shading increased primary productivity, which resulted in elevated sterol and EPA contents of the biofilm. The field survey largely repeated the same pattern: biofilm nutritional quality decreased significantly with increasing DOC, as indicated particularly by a decrease of the ω-3:ω-6 ratio and increase in LSAFA content. Algal biomass, in contrast, was mainly controlled by dissolved inorganic nitrogen (DIN) concentration, while DOC concentration was of minor importance. The ongoing browning process is inducing a dramatic reduction in the nutritional quality of the stream biofilm. Such degradation of the major high-quality food source available for stream consumers may reduce the trophic transfer efficiency in stream ecosystems, potentially extending across the stream-forest ecotone.

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Series: Global change biology
ISSN: 1354-1013
ISSN-E: 1365-2486
ISSN-L: 1354-1013
Volume: 28
Issue: 17
Pages: 5159 - 5171
DOI: 10.1111/gcb.16279
Type of Publication: A1 Journal article – refereed
Field of Science: 1181 Ecology, evolutionary biology
Funding: Our study was funded by the Academy of Finland (grant no. 318230), the SOurce STream PROtection (SOSTPRO) project organized through the ERA-NET co-funded call Water JPI Waterworks 2015, and the Nordic Centre of Excellence BIOWATER, funded by NordForsk under project no. 82263.
Academy of Finland Grant Number: 318230
Detailed Information: 318230 (Academy of Finland Funding decision)
Copyright information: © 2022 The Authors. Global Change Biology published by John Wiley & Sons Ltd. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.