University of Oulu

Kaisa-Leena Huttunen, Timo Muotka, Satu Maaria Karjalainen, Tiina Laamanen, Jukka Aroviita, Excess of nitrogen reduces temporal variability of stream diatom assemblages, Science of The Total Environment, Volume 713, 2020, 136630, ISSN 0048-9697,

Excess of nitrogen reduces temporal variability of stream diatom assemblages

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Author: Huttunen, Kaisa-Leena1; Muotka, Timo1,2; Karjalainen, Satu Maaria2;
Organizations: 1Department of Ecology and Genetics, University of Oulu, P.O. Box 3000, FI-90014 Oulu, Finland
2Finnish Environment Institute, Freshwater Centre, P.O. Box 413, FI-90014 Oulu, Finland
Format: article
Version: accepted version
Access: embargoed
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Language: English
Published: Elsevier, 2020
Publish Date: 2022-01-10


Nutrient enrichment degrades water quality and threatens aquatic biota. However, our knowledge on (dis)similarities in temporal patterns of biota among sites of varying level of nutrient stress is limited. We addressed this gap by assessing temporal (among seasons) variation in algal biomass, species diversity and composition of diatom assemblages in three streams that differ in nutrient stress, but are otherwise similar and share the same regional species pool. We monitored three riffle sections in each stream bi-weekly from May to October in 2014. Temporal variation in water chemistry and other environmental variables was mainly synchronous among riffles within streams and often also among streams, indicating shared environmental forcing through time. We found significant differences in diatom assemblage composition among streams and, albeit less so, also among riffles within streams. Diatom assemblages in the two nutrient-enriched streams were more similar to each other than to those in the nutrient-poor stream. Taxa richness did not differ consistently among the streams, and did not vary synchronously at any spatial scale. Temporal variation in diatom assemblage composition decreased with increasing DIN:TotP ratio, likely via a negative effect on sensitive taxa while maintaining favorable conditions for certain tolerant taxa, irrespective of season. This relationship weakened but remained significant even after controlling for stochastic effects, suggesting deterministic mechanisms between nutrient levels and diatom assemblage stability. After controlling for stochastic effects temporal variability was best explained by DIN suggesting that excess of nitrogen reduces temporal variability(intra-annual beta diversity) of diatom assemblages. The high temporal variation, and especially the lack of temporal synchrony at the within streams scale, suggests that single sampling at a single site may be insufficient to reliably assess and monitor a complete stream water body. Our results also showed that measures including species identity outperform traditional diversity metrics in detecting nutrient stress in streams.

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Series: Science of the total environment
ISSN: 0048-9697
ISSN-E: 1879-1026
ISSN-L: 0048-9697
Volume: 713
Article number: 136630
DOI: 10.1016/j.scitotenv.2020.136630
Type of Publication: A1 Journal article – refereed
Field of Science: 1172 Environmental sciences
1181 Ecology, evolutionary biology
Funding: This study was partly funded by Ministry of Agriculture and Forestry of Finland as part of the monitoring network MaaMet and BIOWATER Nordic Centre of Excellence funded by NordForsk. Additional funding was obtained from Kvantum Institute of University of Oulu and Academy of Finland.
Copyright information: © 2020 Elsevier B.V. This manuscript version is made available under the CC-BY-NC-ND 4.0 license