Dissolved CH<sub>4</sub> coupled to Photosynthetic Picoeukaryotes in Oxic Waters and Cumulative Chlorophyll-a in Anoxia

Abstract

Abstract. CH4 emissions from reservoirs are responsible for the majority of the atmospheric climatic forcing of these aquatic ecosystems, comparable to emissions from paddies or biomass burning. Primarily, CH4 is produced during the anaerobic mineralization of organic carbon in the anoxic sediments by methanogenic archaea. However, the origin of the recurrent and ubiquitous CH4 supersaturation in oxic waters (i.e., methane paradox) is still controversial. Here, we determined the dissolved CH4 concentration in the water column of twelve reservoirs during the summer stratification and the winter mixing. We obtained that the dissolved CH4 concentration varied up to four orders of magnitude (0.02–213.64 μM), and all depths were consistently supersaturated (710–7082234 %) in both periods. Phytoplanktonic sources of carbon appear to determine the concentration of CH4 in the reservoirs. In the anoxic waters, the depth-cumulative chlorophyll-a concentration, a proxy for the total phytoplanktonic biomass exported to sediments, determined the CH4 concentration. In the oxic waters, the photosynthetic picoeukaryotes abundance significantly determined the dissolved CH4 concentration both during the stratification and the mixing. The mean depth of the reservoirs, as a surrogate of the CH4 transport from sediment to the oxic waters, also contributed in shallow systems. Our findings suggest that photosynthetic picoeukaryotes can have a significant role in determining the CH4 concentration in oxic waters and, in comparison to cyanobacteria, have been poorly explored as CH4 sources.

P inputs determine denitrifier abundance explaining dissolved nitrous oxide in reservoirs

“…S1d). We provided more information and detailed maps in León‐Palmero et al (2019, 2020 a , b , c , d ).…”

Spatial Distribution of Dissolved Methane Over Extreme Oceanographic Gradients in the Subtropical Eastern South Pacific (17° to 37°S)

“…In contrast, the subtropical gyre contains warm waters with significantly higher oxygen levels and undetectable nutrient and Chl‐a levels (Lepère et al., 2009; Ras et al., 2008; Troncoso et al., 2018). Given these conditions, it is likely that CH 4 levels will respond to gradients, as it is closely related with microalgal dynamics (Bogard et al., 2014; Leon‐Palmero et al., 2020), as well as with oxygen deficiency as a result of anaerobic methanogenesis, which in turn is fueled by organic matter (Reeburg, 2007).…”

Oxic methane production by cyanobacteria from the Brazilian Pantanal soda lakes

“…The classical methanogenesis performed by archaea in the sediment of lakes uses products generated by organic matter degradation. Thus, cyanobacteria can be regarded as food for the classical methanogenic pathway in the sedimentan indirect association to archaea (Fazi et al, 2021;León-Palmero et al, 2020;Yan et al, 2019;Zhou et al, 2020). Because we have only analyzed water metadata, yet, we cannot say much about this relationship in sediments.…”

“…Moreover, the lakes' dimensions favor the lateral transport from the sediment and vegetation on lakeshore. Lateral transport from the littoral zones is commonly pointed as a relevant source of methane in the epilimnion of some aquatic systems (Bastviken et al, 2010;León-Palmero et al, 2020). Many red flags were brought as well when point to OMP as a major source alone when considering experimental extrapolations as some variables cannot be accounted on calculations (Peeters et al, 2019).…”