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Resource and consumer control of cross-habitat trophic interactions in shallow lakes
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 Mathematics and Mathematical Statistics.
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
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(English)Manuscript (preprint) (Other academic)
National Category
Ecology
Identifiers
URN: urn:nbn:se:umu:diva-111297OAI: oai:DiVA.org:umu-111297DiVA: diva2:868999
Available from: 2015-11-12 Created: 2015-11-12 Last updated: 2017-04-05
In thesis
1. Biomass patterns in boreal-subarctic lake food webs along gradients of light and nutrients
Open this publication in new window or tab >>Biomass patterns in boreal-subarctic lake food webs along gradients of light and nutrients
2015 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

There is large natural variation in light and nutrient conditions across lakes. In the boreal-subarctic region most lakes are small, shallow and nutrient poor. In such lakes there is often sufficient light to support primary production at the lake bottom. An expectation for the future is that colored dissolved organic matter (cDOM) of terrestrial origin will increase in these lakes. cDOM depresses the underwater light climate but is often associated with elevated pelagic nutrient concentrations.

A dynamical model of a coupled benthic-pelagic food web was explored for how lake ecosystems might respond to altered light and nutrient regimes. The model predicts that mobile carnivores (fish) control grazers and release primary producers from grazing pressure. Primary producers are therefore limited by their resources and cross-habitat interactions are dominated by spatially asymmetric competition for light and nutrients. At high light and low nutrient supply benthic algae out-compete pelagic algae for nutrients diffusing from the sediment, whereas pelagic algae shade out benthic algae at lower light and/or higher nutrient supply. Biomass patterns of benthic and pelagic consumers follow the patterns of primary production. In contrast, habitat coupling through carnivore movement has only a weak impact on biomass patterns in the model food web.

Model predictions were compared with data from boreal-subarctic lakes covering a broad range of cDOM concentrations. In agreement with model expectations the following relationships with increasing light attenuation were observed: benthic primary and secondary production decreased, pelagic primary production showed a unimodal trend, and pelagic nutrient concentrations as well as the proportion of fish feeding in the pelagic habitat increased. As a consequence, both primary and fish production were negatively related to pelagic nutrient concentrations across lakes.

In a comparative study of boreal-subarctic lakes covering a broad range of cDOM concentrations, a similar negative relationship was found between pelagic total nutrient concentrations and the biomass of epilithic algae. This was surprising, because epilithon cannot access nutrients from the sediment. Patterns in epilithon biomass were largely driven by nitrogen fixing cyanobacteria, which in turn were positively related to light supply. The data suggest that nitrogen fixing autotrophs may have a competitive advantage over other epilithic primary producers in low-cDOM, low-nutrient, high-light environments, and that patterns in epilithic biomass, nutrient sequestration and elemental stoichiometry depend upon which functional group is dominant in the epilithic biofilm.

Place, publisher, year, edition, pages
Umeå: Umeå universitet, 2015. 14 p.
Keyword
boreal-subartic lake, cDOM, epilithon, benthic-pelagic coupling, carnivores
National Category
Ecology
Identifiers
urn:nbn:se:umu:diva-111299 (URN)978-91-7601-343-4 (ISBN)
Presentation
2015-10-15, Hörsal N320, Naturvetarhuset, Umeå universitet, Umeå, 10:00 (English)
Opponent
Supervisors
Available from: 2015-11-13 Created: 2015-11-12 Last updated: 2015-11-13Bibliographically approved
2. 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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