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Asymmetrical competition between aquatic primary producers in a warmer and browner world
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Austral Centre for Scientific Research (CADIC-CONICET), 9410 Ushuaia, Tierra del Fuego, Argentina.
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. (EcoChange)
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2016 (English)In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 97, no 10, 2580-2592 p.Article in journal (Refereed) Published
Abstract [en]

In shallow lakes, pelagic and benthic producers engage in spatially asymmetrical resource competition. Pelagic producers intercept the flux of light to the benthic habitat and benthic producers intercept the flux of sediment-derived nutrients to the pelagic habitat. In boreal and subarctic regions, climate change is affecting this interaction both directly through warming and indirectly through increased loading with colored dissolved organic matter (cDOM) from the catchment (brownification). We use a dynamical ecosystem model to explore the consequences of these changing environmental conditions for lake primary production and compare model predictions with the results of an experiment in which we manipulated water temperature and cDOM supply in a 2x2 factorial design. The experiment was performed in field mesocosms large enough to harbor reproducing fish populations and was run over an entire growing season. In agreement with model predictions, benthic algal production and biomass declined and pelagic algal production and biomass increased with browning. Pelagic nutrient concentrations diverged over time between low and high cDOM treatments, suggesting that browning alleviated pelagic algal nutrient limitation by shading benthic competitors and preventing them from intercepting the release of nutrients from the sediment. Warming considerably reduced benthic and pelagic algal production as well as pelagic algalbiomass and total phosphorus. The warming results are only in partial accordance with model expectations, but can be explained by an indirectly inferred, positive response of macrophyte production (which was not included in the model) to warming. Our study suggests that lake ecosystem responses to climate change are mediated by cross-habitat feedbacks between benthic and pelagic producers.

Place, publisher, year, edition, pages
2016. Vol. 97, no 10, 2580-2592 p.
Keyword [en]
asymmetry, benthic, boreal, brownification, pelagic, resource competition, shallow lake, warming
National Category
Ecology
Identifiers
URN: urn:nbn:se:umu:diva-127720DOI: 10.1002/ecy.1487ISI: 000386088000007PubMedID: 27859128OAI: oai:DiVA.org:umu-127720DiVA: diva2:1056526
Available from: 2016-12-15 Created: 2016-11-18 Last updated: 2017-08-30Bibliographically approved
In thesis
1. Effects of warming and browning on benthic and pelagic ecosystem components in shallow lakes
Open this publication in new window or tab >>Effects of warming and browning on benthic and pelagic ecosystem components in shallow lakes
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The majority of lakes on Earth are shallow, unproductive and located at high latitudes. These lakes are experiencing big changes due to climate change, where two environmental drivers operate simultaneously, browning and warming. How they affect lake ecosystems is not well understood. Here, I addressed this issue by using a theoretical and an experimental approach. In particular, I generated model predictions and compared them with the results of a realistic large-scale experiment, where browning and warming were manipulated in a factorial design. In addition, model outcomes were compared with data from 12 unproductive lakes sampled along a gradient of browning. Another novelty of my thesis is that it integrates benthic and pelagic food web components in the model and experimental approaches. I found that browning affected the resources availability for benthic and pelagic producers in the model and in the experiment. With browning, benthic primary producers became increasingly light limited and declined, while pelagic producers became less nutrient limited and increased. Pelagic nutrient limitation was alleviated by two non-exclusive mechanisms. Browning directly enriched the water with nutrients, and browning indirectly increased the nutrient flowing from the sediment to the pelagic habitat via suppression of benthic producers. To tease apart these two mechanisms I applied structural equation modeling (SEM). The indirect evidence by SEM suggests that both mechanisms contributed equally to the pelagic nutrient concentration in the experiment. Interestingly, a model food web with only primary producers shows similar qualitative behavior as a food web with grazers and carnivores included. This happens because carnivorous fish exert strong top-down control in the more productive habitat, which relaxes grazing pressure on primary producers and increases resource limitation in the adjacent habitat. Biomass of benthic and pelagic consumers followed the same pattern as their resources. The lake data were largely congruent with model expectations and supported the findings of the experiment. Furthermore, the model also predicted a negative relationship between total phosphorus and both primary and fish production, which was observed across the 12 lakes. Warming effects were more complex. The model predicts that warming effects should depend on browning and are expected to be strongest in the more productive of the two (benthic and pelagic) habitats. For example, at low levels of browning the biomasses of benthic algae and fish are expected to decline with warming, which was observed in the experiment. In contrast, observed warming effects at high levels of browning deviated from model expectations. The mechanisms by which browning and warming interactively affect lake food webs are still poorly understood. This thesis offers a conceptual foundation for their further study through the integration of within- and between-habitat interactions.

Place, publisher, year, edition, pages
Umeå: Umeå Universitet, 2017. 23 p.
Keyword
benthic, pelagic, algae, consumers, browning, warming, shallow lakes, food web, dissolved organic matter
National Category
Ecology
Identifiers
urn:nbn:se:umu:diva-133327 (URN)978-91-7601-690-9 (ISBN)
Public defence
2017-05-04, KBE301, Lilla Hörsalen (KBC), Umeå Universitet, Umeå, 09:30 (English)
Opponent
Supervisors
Funder
Swedish Research Council, 621-2011-3908Swedish Research Council, 621-2014-5238The Kempe FoundationsKnut and Alice Wallenberg FoundationEcosystem dynamics in the Baltic Sea in a changing climate perspective - ECOCHANGE
Available from: 2017-04-13 Created: 2017-04-05 Last updated: 2017-09-13Bibliographically approved

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