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Pelagic food web response to whole lake N fertilization
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. (Arcum)
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Department of Oceanography, University of Hawai'i, Honolulu, USA.
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. (Arcum)
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
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2017 (English)In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 62, no 4, 1498-1511 p.Article in journal (Refereed) Published
Abstract [en]

Anthropogenic activities are increasing inorganic nitrogen (N) loadings to unproductive boreal lakes. In many of these lakes phytoplankton are N limited, consequently N fertilization may affect ecosystem productivity and consumer resource use. Here, we conducted whole lake inorganic N fertilization experiments with six small N limited unproductive boreal lakes (three control and three N enriched) in an area receiving low N deposition with one reference and two impact years. Our aim was to assess the effects of N fertilization on pelagic biomass production and consumer resource use. We found that phytoplankton primary production (PP) and biomass, and the PP: bacterioplankton production ratio increased after fertilization. As expected, the relative contribution of phytoplankton derived resources (autochthony) that supported the crustacean zooplankton community increased. Yet, the response in the consumer community was modest with autochthony only increasing in one of the three major zooplankton groups and with no effect on zooplankton biomass. In conclusion, our findings imply that newly available phytoplankton energy derived from N fertilization was not efficiently transferred up to zooplankton, indicating a mismatch between producer energy supply and consumer energy use with potential accumulation of phytoplankton biomass as the result.

Place, publisher, year, edition, pages
2017. Vol. 62, no 4, 1498-1511 p.
Keyword [en]
autochthony, basal production, boreal, dissolved organic carbon, limitation, nitrate, phytoplankton, zooplankton
National Category
Ecology Environmental Sciences
Research subject
Limnology
Identifiers
URN: urn:nbn:se:umu:diva-130332DOI: 10.1002/lno.10513ISI: 000404993100013OAI: oai:DiVA.org:umu-130332DiVA: diva2:1066121
Funder
Swedish Research Council, 621-2010-4675
Available from: 2017-01-17 Created: 2017-01-17 Last updated: 2017-08-02Bibliographically approved
In thesis
1. Effects of inorganic nitrogen and organic carbon on pelagic food webs in boreal lakes
Open this publication in new window or tab >>Effects of inorganic nitrogen and organic carbon on pelagic food webs in boreal lakes
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
Effekter av oorganiskt kväve och organiskt kol på pelagiska födovävar i boreala sjöar
Abstract [en]

Anthropogenic activities are increasing inorganic nitrogen (N) loadings to lakes in the northern hemisphere. In many boreal lakes phytoplankton are N limited, wherefore enhanced N input may affect the productivity of pelagic food webs. Simultaneously, global change causes increased inflows of terrestrial dissolved organic carbon (DOC) to boreal lakes. Between clear and humic lakes, whole lake primary and consumer production naturally differs. However, research is inconclusive as to what controls pelagic production in these lakes. Further, it is unclear how DOC affects the response of the pelagic food web to enhanced inorganic N availability. The overarching goal of this thesis was to study the effects of inorganic N and organic C for pelagic food webs in boreal lakes. In the thesis, I first identified the main drivers of pelagic production during summer in eight non-manipulated Swedish boreal lakes with naturally low or high DOC. Then I investigated how increased N availability affects the pelagic food chain, and how the response differs with DOC. Therefore, whole lake inorganic N fertilization experiments were conducted in six Swedish boreal lakes across a DOC gradient (low, medium, high) divided into three lake pairs (control, N enriched) with one reference and two impact years. In each lake, I also investigated the response of zooplankton growth using in situ mesocosm experiments excluding planktivores. I found that humic boreal lakes had lower phytoplankton production and biomass than clear water lakes. Further, phytoplankton community composition and food quality differed with DOC. However, high DOC did not reduce pelagic energy mobilization or zooplankton biomass, but promoted a higher dominance of cladoceran relative to copepod species. N addition clearly enhanced phytoplankton biomass and production in the experimental lakes. However, this stimulating N effect decreased with DOC as caused by light limitation. Further, the newly available phytoplankton energy derived from N addition was not efficiently transferred to zooplankton, which indicates a mismatch between producer energy supply and consumer energy use. Indeed, the mesocosm experiment revealed that decreased food quality of phytoplankton in response to N addition resulted in reduced food web performance, especially in clearer lakes. In humic lakes, zooplankton production and food web efficiency were clearly more resilient to N addition. In summary, my thesis suggests that any change in the landscape that enhances inorganic N availability will especially affect pelagic food webs in clear water lakes. In contrast, brownification will result in more lakes being resilient to eutrophication caused by enhanced N deposition.

Place, publisher, year, edition, pages
Umeå: Umeå University, 2017. 33 p.
Keyword
autochthony, basal production, boreal, global change, dissolved organic carbon, food web efficiency, N deposition, phytoplankton, seston stoichiometry, whole lake enrichment, zooplankton
National Category
Ecology Environmental Sciences Physical Geography
Research subject
Limnology
Identifiers
urn:nbn:se:umu:diva-130340 (URN)978-91-7601-640-4 (ISBN)
Public defence
2017-02-10, Älgsalen, Uminova Science Park, Umeå, 09:30 (English)
Opponent
Supervisors
Available from: 2017-01-20 Created: 2017-01-17 Last updated: 2017-02-17Bibliographically approved

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Deininger, AnneFaithfull, Carolyn L.Karlsson, JanKlaus, MarcusBergström, Ann-Kristin
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Citation style
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