• Energy Research

AbstractMany inland waters exhibit complete or partial desiccation, or have vanished due to global change, exposing sediments to the atmosphere. Yet, data on carbon dioxide (CO2) emissions from these sediments are too scarce to upscale emissions for global estimates or to understand their fundamental drivers. Here, we present the results of a global survey covering 196 dry inland waters across diverse ecosystem types and climate zones. We show that their CO2 emissions share fundamental drivers and constitute a substantial fraction of the carbon cycled by inland waters. CO2 emissions were consistent across ecosystem types and climate zones, with local characteristics explaining much of the variability. Accounting for such emissions increases global estimates of carbon emissions from inland waters by 6% (~0.12 Pg C y−1). Our results indicate that emissions from dry inland waters represent a significant and likely increasing component of the inland waters carbon cycle.

The freshwater dinoflagellate Borghiella dodgei is adapted to cold temperatures. We investigated the effects of small temperature changes on its galactolipid composition, choosing 3 and 7°C as deviations from its optimal growth temperature (5°C). The galactolipid profile, important for maintenance of membrane fluidity, was determined by liquid chromatography-mass spectrometry and the influence of temperature on galactolipids was investigated by one-way ANOVA. We found 24 different galactolipid species, including novel tri-galactosyldiacylglycerols (TGDGs). The overall amount of mono- (MGDG), di- (DGDG) and tri- (TGDG) galactosyldiacylglycerols remained stable while single galactolipids varied with temperature. Few changes were found from 3 to 5°C, instead 11 galactolipid species changed from 5 to 7°C. Concomitantly with the unsaturation index of MGDGs, the more unsaturated galactolipids decreased at higher temperature, and the less abundant and less unsaturated galactolipids in each lipid class accumulated. Changes in the galactolipid profile of Borghiella underlined its cold-stenothermal nature: it can adapt to relatively 'higher' temperatures by reducing the synthesis of the more unsaturated MGDGs, DGDGs and TGDGs, but remains restricted by its lower growth rate. Based on our results, we predict that with climate change the galactolipid profile of cold-stenothermal algae will change with important repercussions on their consumers.

AbstractTo determine the drivers of phytoplankton biomass, we collected standardized morphometric, physical, and biological data in 230 lakes across the Mediterranean, Continental, and Boreal climatic zones of the European continent. Multilinear regression models tested on this snapshot of mostly eutrophic lakes (median total phosphorus [TP] = 0.06 and total nitrogen [TN] = 0.7 mg L−1), and its subsets (2 depth types and 3 climatic zones), show that light climate and stratification strength were the most significant explanatory variables for chlorophyll a (Chl a) variance. TN was a significant predictor for phytoplankton biomass for shallow and continental lakes, while TP never appeared as an explanatory variable, suggesting that under high TP, light, which partially controls stratification strength, becomes limiting for phytoplankton development. Mediterranean lakes were the warmest yet most weakly stratified and had significantly less Chl a than Boreal lakes, where the temperature anomaly from the long‐term average, during a summer heatwave was the highest (+4°C) and showed a significant, exponential relationship with stratification strength. This European survey represents a summer snapshot of phytoplankton biomass and its drivers, and lends support that light and stratification metrics, which are both affected by climate change, are better predictors for phytoplankton biomass in nutrient‐rich lakes than nutrient concentrations and surface temperature.