Journal cover Journal topic
Biogeosciences An interactive open-access journal of the European Geosciences Union
Biogeosciences, 14, 2865-2875, 2017
https://doi.org/10.5194/bg-14-2865-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
15 Jun 2017
Cyanobacterial carbon concentrating mechanisms facilitate sustained CO2 depletion in eutrophic lakes
Ana M. Morales-Williams1,2,3, Alan D. Wanamaker Jr.4, and John A. Downing1,5 1Department of Ecology, Evolution, and Organismal Biology, Iowa State University, 251 Bessey Hall, Ames, IA 50011, USA
2Department of Ecology, Evolution, and Behavior, University of Minnesota Twin Cities, 1475 Gortner Ave., Saint Paul, MN 55108, USA
3Rubenstein School of Environment and Natural Resources, University of Vermont, 81 Carrigan Drive, Burlington, VT 05405, USA
4Department of Geological and Atmospheric Science, Iowa State University, 253 Science Hall, Ames, IA 50011, USA
5Minnesota Sea Grant, University of Minnesota Duluth, 141 Chester Park, 31 West College St., Duluth, MN 55812, USA
Abstract. Phytoplankton blooms are increasing in frequency, intensity, and duration in aquatic ecosystems worldwide. In many eutrophic lakes, these high levels of primary productivity correspond to periods of CO2 depletion in surface waters. Cyanobacteria and other groups of phytoplankton have the ability to actively transport bicarbonate (HCO3) across their cell membrane when CO2 concentrations are limiting, possibly giving them a competitive advantage over algae not using carbon concentrating mechanisms (CCMs). To investigate whether CCMs can maintain phytoplankton bloom biomass under CO2 depletion, we measured the δ13C signatures of dissolved inorganic carbon (δ13CDIC) and phytoplankton particulate organic carbon (δ13Cphyto) in 16 mesotrophic to hypereutrophic lakes during the ice-free season of 2012. We used mass–balance relationships to determine the dominant inorganic carbon species used by phytoplankton under CO2 stress. We found a significant positive relationship between phytoplankton biomass and phytoplankton δ13C signatures as well as a significant nonlinear negative relationship between water column ρCO2 and isotopic composition of phytoplankton, indicating a shift from diffusive uptake to active uptake by phytoplankton of CO2 or HCO3 during blooms. Calculated photosynthetic fractionation factors indicated that this shift occurs specifically when surface water CO2 drops below atmospheric equilibrium. Our results indicate that active HCO3 uptake via CCMs may be an important mechanism in maintaining phytoplankton blooms when CO2 is depleted. Further increases in anthropogenic pressure, eutrophication, and cyanobacteria blooms are therefore expected to contribute to increased bicarbonate uptake to sustain primary production.

Citation: Morales-Williams, A. M., Wanamaker Jr., A. D., and Downing, J. A.: Cyanobacterial carbon concentrating mechanisms facilitate sustained CO2 depletion in eutrophic lakes, Biogeosciences, 14, 2865-2875, https://doi.org/10.5194/bg-14-2865-2017, 2017.
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Our study investigated the mechanisms sustaining cyanobacteria blooms when CO2 is depleted in lake surface waters. We found that when lake CO2 concentrations drop below those of the atmosphere, cyanobacteria switch on carbon concentrating mechanisms (CCMs), allowing them to actively take up bicarbonate. This may provide bloom-forming cyanobacteria with a competitive advantage over other algae. These results provide insight into the timing and duration of blooms in high-nutrient lakes.
Our study investigated the mechanisms sustaining cyanobacteria blooms when CO2 is depleted in...
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