Climate Change Impacts on Stoichiometry, Phytoplankton, and Zooplankton in Alpine Lake Food Webs

• Author / Creator

  Weidman, Raymond Paul

• The main hypothesis of this study was that warmer and drier conditions affect fishless alpine lakes by increasing (1) phosphorus (P)-availability, (2) P-limited autotrophs versus mixotrophic phytoflagellates, and (3) fast-growing P-limited cladocerans versus slower-growing nitrogen (N)-rich calanoid copepods. To test this hypothesis, I conducted (1) a spatial survey of 16 mountain lakes along 1016 m of elevation (summer water temperatures: 5–17°C) in Alberta; (2) a temporal survey of an alpine lake over 16 y (summer water temperatures: 3–14°C); and (3) a laboratory experiment using two alpine and montane plankton communities subjected to warming (10°C; 17°C) and increased dissolved organic carbon (DOC; +80%). In the lake survey, higher temperatures and decreased lake depth were inferred using structural equation modeling (SEM) to decrease dissolved N:P, which increased chlorophytes and cyanophytes relative to phytoflagellates. Warming suppressed large-bodied cladocerans (Daphnia middendorffiana) and calanoid copepods (Hesperodiaptomus arcticus) and increased small-bodied zooplankton taxa. Small copepods increased relative to small cladocerans; this decreased particulate C:P via increased P-recycling by copepods. In the temporal investigation, SEM revealed that decreased rain reduced flushing of dissolved P, which increased diatoms relative to phytoflagellates in Pipit Lake. Unlike the lake survey, more moderate warming increased D. middendorffiana, while H. arcticus increased with advanced ice-off. Thus, cladocerans increased relative to copepods, which increased particulate C:P via increased P-retention by zooplankton. In the experiment, warming and DOC additions together increased P-availability, which increased autotrophs and offset the negative direct effects of warming and DOC. Warming increased D. middendorffiana but suppressed H. arcticus. Particulate C:P increased with DOC additions and increased cladocerans relative to copepods. These findings partially supported my main hypothesis. Climate effects increased dissolved P-availability, thereby increasing autotrophs relative to phytoflagellates. Shorter-term warming (temporal survey and experiment) increased cladocerans relative to copepods, whereas longer-term warming (spatial survey) suppressed large-bodied zooplankton and increased small taxa. Particulate C:P varied with changes in cladocerans relative to copepods (via P-recycling) and increases in C-rich terrestrial inputs. Findings suggest climate change will increase primary productivity of alpine lakes over several decades by increasing P-availability, and decreasing grazing efficiency as copepods and smaller-bodied zooplankton supercede cladocerans.

• Subjects / Keywords

  • Phytoplankton
  • Stoichiometry
  • Alpine lakes
  • Zooplankton
  • Food webs
  • Climate change

• Graduation date

  Fall 2013

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3FX7463N

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.