CO2 evasion from boreal lakes: Revised estimate, drivers of spatial variability, and future projections.

Lakes (including reservoirs) are an important component of the global carbon (C) cycle, as acknowledged by the fifth assessment report of the IPCC. In the context of lakes, the boreal region is disproportionately important contributing to 27% of the worldwide lake area, despite representing just 14% of global land surface area. In this study, we used a statistical approach to derive a prediction equation for the partial pressure of CO2 (pCO2 ) in lakes as a function of lake area, terrestrial net primary productivity (NPP), and precipitation (r2  = .56), and to create the first high-resolution, circumboreal map (0.5°) of lake pCO2 . The map of pCO2 was combined with lake area from the recently published GLOWABO database and three different estimates of the gas transfer velocity k to produce a resulting map of CO2 evasion (FCO2 ). For the boreal region, we estimate an average, lake area weighted, pCO2 of 966 (678-1,325) µatm and a total FCO2 of 189 (74-347) Tg C year-1 , and evaluate the corresponding uncertainties based on Monte Carlo simulation. Our estimate of FCO2 is approximately twofold greater than previous estimates, as a result of methodological and data source differences. We use our results along with published estimates of the other C fluxes through inland waters to derive a C budget for the boreal region, and find that FCO2 from lakes is the most significant flux of the land-ocean aquatic continuum, and of a similar magnitude as emissions from forest fires. Using the model and applying it to spatially resolved projections of terrestrial NPP and precipitation while keeping everything else constant, we predict a 107% increase in boreal lake FCO2 under emission scenario RCP8.5 by 2100. Our projections are largely driven by increases in terrestrial NPP over the same period, showing the very close connection between the terrestrial and aquatic C cycle.

Treeline displacement may affect lake dissolved organic matter processing at high latitudes and altitudes.

Climate change induced shifts in treeline position, both towards higher altitudes and latitudes induce changes in soil organic matter. Eventually, soil organic matter is transported to alpine and subarctic lakes with yet unknown consequences for dissolved organic matter (DOM) diversity and processing. Here, we experimentally investigate the consequences of treeline shifts by amending subarctic and temperate alpine lake water with soil-derived DOM from above and below the treeline. We use ultra-high resolution mass spectrometry (FT-ICR MS) to track molecular DOM diversity (i.e., chemodiversity), estimate DOM decay and measure bacterial growth efficiency. In both lakes, soil-derived DOM from below the treeline increases lake DOM chemodiversity mainly through the enrichment with polyphenolic and highly unsaturated compounds. These compositional changes are associated with reductions in bulk and compound-level DOM reactivity and reduced bacterial growth efficiency. Our results suggest that treeline advancement has the potential to enrich a large number of lake ecosystems with less biodegradable DOM, affecting bacterial community function and potentially altering the biogeochemical cycling of carbon in lakes at high latitudes and altitudes.

Remote sensing provides new insights on phytoplankton biomass dynamics and black pearl oyster life-history traits in a Pacific Ocean deep atoll.

Thus far, no long-term in situ observation of planktonic biomass have been undertaken to optimize the black-lip pearl oyster aquaculture in the remote Tuamotu atolls. The feasibility of using data from the OLI sensor onboard Landsat-8 satellite to determine chlorophyll a concentrations (Chla) in a deep atoll, Ahe, was then assessed over the 2013-2021 period using 153 images. Validations with in situ observations were satisfactory, while seasonal and spatial patterns in Chla were evidenced within the lagoon. Then, a bioenergetic modelling exercise was undertaken to estimate oyster life-history traits when exposed to the retrieved Chla. The outputs provide spatio-temporal variations in pelagic larval duration (11.1 to 30.6 days), time to reach commercial size (18.8 to 45.3 months) and reproductive outputs (0.5 to 1.7 event year-1). This first study shows the potential of using remote sensing to monitor the trophic status of deep pearl farming lagoons and help aquaculture management.

Organic carbon burial in global lakes and reservoirs.

Burial in sediments removes organic carbon (OC) from the short-term biosphere-atmosphere carbon (C) cycle, and therefore prevents greenhouse gas production in natural systems. Although OC burial in lakes and reservoirs is faster than in the ocean, the magnitude of inland water OC burial is not well constrained. Here we generate the first global-scale and regionally resolved estimate of modern OC burial in lakes and reservoirs, deriving from a comprehensive compilation of literature data. We coupled statistical models to inland water area inventories to estimate a yearly OC burial of 0.15 (range, 0.06-0.25) Pg C, of which ~40% is stored in reservoirs. Relatively higher OC burial rates are predicted for warm and dry regions. While we report lower burial than previously estimated, lake and reservoir OC burial corresponded to ~20% of their C emissions, making them an important C sink that is likely to increase with eutrophication and river damming.