Dissolved methane and oxygen depletion in the two coastal lagoons, Red Sea

Abstract

The emission of methane (CH₄), a major greenhouse gas, from polluted lagoons is of scientific interest. Polluted basins are conducive to CH₄ production through microbial activity. This study presents a baseline dataset on dissolved CH₄ from two Red Sea coastal lagoons. These lagoons are extremely polluted, primarily due to extensive sewage dumping. Both the lagoons were experienced severe oxygen depletion. Nitrate deficit value was negative and most of the nitrate were lost through denitrification pathway. The observed ammonia concentration was also high. Methane concentrations in both lagoons were measured, and maximum concentrations were observed at the bottom waters of the lagoons and minimums at the surface. Average surface methane concentrations were 0.16 and 4.09 µM in the Al-Shabab and Al-Arbaeen lagoons, respectively, and those of the bottom were 3.11 and 13.2 µM, respectively. The diffusive flux of methane from the bottom to surface waters in the Al-Arbaeen lagoon was notably high, and significant hydrogen sulfide production was also observed. Methanotrophic bacterial activity occurred in the oxic environment of the water column. Organic matter decomposition led to an oxygen-depleted system which will enhance the different nitrogen transformation processes.