Paper Reviewed
Hamdan, M., Byström, P., Hotchkiss, E.R., Al-Haidarey, M., Ask, J. and Karlsson, J. 2018. Carbon dioxide stimulates lake primary production. Scientific Reports 8: 10878, DOI:10.1038/s41598-018-29166-3.

Writing as background for their study, Hamdan et al. (2018) state that "the rate at which primary producers fix inorganic carbon controls the supply of organic matter to food webs and influences the biogeochemistry of aquatic ecosystems." Thus, ecosystems with greater gross primary production (GPP) generally sustain larger and higher-order trophic food webs.

The role of temperature, light and/or nutrient supply in driving and sustaining GPP has been extensively studied in aquatic ecosystems. However, much less is known about the role of CO2 on GPP, especially in shallow lake ecosystems. Thus, it was the goal of Hamdan et al. to estimate whole-ecosystem GPP at a series of ponds located at the Umeå University Experimental Ecosystem Facility in northern Sweden over a one-month period during the spring of 2016. The ponds there are home to natural food webs that include "basal producers (algae and bacteria), consumers (insect larvae and zooplankton) and a reproducing top-consumer population (nine-spine Sticklebacks), where benthic GPP constitutes approximately 50% of whole-ecosystem GPP." A novel approach was utilized to alter the CO2 concentration of half of the pond ecosystems by removing a portion of their ice cover (10 and then 50% removal) to decrease their pCO2 while having a limited impact on light, temperature and other key environmental factors. Whole-ecosystem GPP was then estimated from dissolved oxygen time series data.

In reporting their findings, Hamdan et al. say there was "a positive correlation between GPP and CO2 concentration in both control and treatment ponds," which results, they say, "show that the CO2 concentration was a key controlling factor for GPP," while adding that "no other abiotic or biotic factors explain the patterns in GPP over time and between treatments." Indeed, there was no difference in nutrient concentrations, photosynthetically active radiation or water temperature among the control and treatment ponds.

In commenting on their work, the researchers write that "CO2 stimulation of GPP is a common but often overlooked phenomenon" that "needs to be taken into account in food web models for lakes." And this overlooked phenomenon is really quite amazing; it suggests that as the air's CO2 concentration continues to rise, so too will the GPP of the world's aquatic ecosystems, which will enhance the biomass production of lake food webs to support and sustain even greater masses of life.