Changes in mixing depth reduce phytoplankton biomass in an Arctic lake: Results from a whole-lake experiment

ABSTRACT

Research has revealed contradictory responses of primary producers in Arctic lakes to increasing temperatures, making it unclear how future warming and climate change will alter lake productivity. We conducted a whole-lake manipulation to examine the effect of altered thermal structure on phytoplankton biomass in a lake in Greenland, one of the most rapidly warming regions of the world. Deepened lake mixing (from 4 to 8 m) in the experimental lake led to significant declines in phytoplankton biomass in the sediment traps despite warmer surface waters, indicating that changes in mixing depth may negate a positive, direct effect of warming on primary producer biomass. Light limitation (induced by deeper mixing) of phytoplankton played a greater role than temperature in structuring these Arctic lake phytoplankton communities. To put the manipulation in context, we surveyed twenty-four lakes across western Greenland to determine the strongest regional predictors of phytoplankton density. Across the landscape, lake chemistry and light attenuation in the epilimnion were the most important predictors of algal assemblages in the survey lakes. Though temperature can directly influence lake ecosystems, multiple factors will affect mixing depths of Arctic lakes, potentially leading to variable effects of warming on phytoplankton biomass and community structure.

KEYWORDS:

• Phytoplankton biomass
• Arctic lakes
• climate change
• Greenland
• whole-lake manipulation

Acknowledgments

We thank Rachel Fowler, Hamish Greig, Steve Juggins, Emily Rice, Kristin Strock, and Kathryn Warner for field assistance, along with our helicopter pilots Gregor Beer and Petrus Nobreus. CH2M Hill Polar Services provided logistical support for this project. We thank Corey Simnioniw of the Medora Corporation for modifying the design of the Solar Bee to meet our requirements. Brian McGill provided assistance with statistical analyses. We also thank the two anonymous reviewers for their helpful critiques, which allowed for the substantial improvement of this article for publication.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the Arctic System Science program of the U.S. National Science Foundation under Grant #1203434 to JES.