Professor Isaac R Santos

Coastal lagoons are important nutrient filters and carbon sinks but may release large amounts of methane (CH4) to the atmosphere. Here, we hypothesize that eutrophication and population density will turn coastal lagoons into stronger methane emitters. We report benthic fluxes from 187 sediment cores incubated from three of the largest European lagoons suffering persistent eutrophication. Methane fluxes were mainly driven by sediment porosity, organic matter, and dissolved inorganic carbon (DIC) fluxes. Methane was always supersaturated (250–49,000%) in lagoon waters leading to large, variable emissions of 0.04–26 mg CH4 m−2 d−1. Combining our new dataset with earlier estimates revealed a global coastal lagoon emission of 7.9 (1.4–34.7) Tg CH4 yr−1 with median values of 5.4 mg CH4 m−2 d−1. Lagoons with very highly populated catchments released much more methane (223 mg CH4 m−2 d−1). Overall, projected increases in eutrophication, organic loading and population densities will enhance methane fluxes from lagoons worldwide.

Headwater streams play a large role in aquatic greenhouse gas emissions. Carbon dioxide (CO 2 ) and dissolved oxygen in streams often undergo changes through diel cycles. However, methane (CH 4 ) and nitrous oxide (N 2 O) have unknown diel dynamics. Here, we reveal consistent patterns in CO 2 , CH 4 , and N 2 O over diel cycles and during flood events using high‐frequency continuous observations in a subtropical headwater stream. Diel cycles were most pronounced during baseflow. Increased nighttime discharge due to higher groundwater inputs enhanced gas transfer velocities and concentrations. Overall nocturnal emissions were 31%, 68%, and 32% greater than daytime for CO 2 , CH 4 , and N 2 O, respectively. Floods dampened diel signals. If both flood events and diel patterns are neglected, estimates of greenhouse gas emissions from headwaters may be greatly underestimated. Overall, CH 4 and N 2 O emissions from headwater streams may be underestimated by ~ 20–40% due to a lack of observations during nighttime, floods, and in warmer climates.

Wolfe and Roff have presented a response to our analysis of global coral reef calcification and primary productivity rates. Our earlier publication suggested that coral reef ecosystems could become net dissolving worldwide around 2054. Wolfe and Roff argue that global predictions of coral reef dissolution are increasingly important as climate change and anthropogenic activities continue to impact coral reef ecosystems. Broadly, we agree with Wolfe and Roff that refining those estimates and reducing uncertainties is essential. Our meta-analysis and Wolfe and Roff's comments provide a framework to design new field observations and refine predictions into the future.