Greenhouse gases fluxes from (sub) tropical blue carbon ecosystems: a review

Abstract

Blue carbon ecosystems are crucial for global carbon cycle. Fluxes of methane (CH4), nitrous oxide (N2O), and carbon dioxide (CO2) from subtropical and tropical coastal wetlands revealed that these ecosystems act as net sources, with mean emission rates of 187 ± 19 mg CO2/m²/h, 7.6 ± 1.0 mg CH4/m²/h, and 0.13 ± 0.05 mg N2O/m²/h. Greenhouse gas emission rates decrease with increasing water salinity and soil pH shifts towards acidic or alkaline values. In subtropical coastal wetlands, lower both soil temperatures and organic matter content during the winter decrease emission rates of carbon dioxide and methane. In subtropical coastal wetlands lower both soil temperatures and organic matter content during the winter decrease emission rates of carbon dioxide and methane. In the tropical zone, high emission of carbon dioxide and nitrous oxide are observed during the dry season, whereas methane emissions peak during the wet season. Coastal wetlands located in tropical monsoon climates exhibit significantly higher carbon dioxide and methane emissions compared to those in tropical rainforest (constantly humid) and tropical savanna (seasonally humid) climate types. Among coastal wetland ecosystems in the tropics and subtropics, freshwater marshes and coastal swamps are characterized by the highest emission rates of climatically active gases.