Abstract
Methanogenesis may represent a key process in the terminal phases of anaerobic organic matter mineralization in sediments of coastal lagoons. The aim of the present work was to study the temporal and spatial dynamics of methanogenic archaea in sediments of tropical coastal lagoons and their relationship with environmental changes in order to determine how these influence methanogenic community. Sediment samples were collected during the dry (February, May, and early June) and rainy seasons (July, October, and November). Microbiological analysis included the quantification of viable methanogenic archaea (MA) with three substrates and the evaluation of kinetic activity from acetate in the presence and absence of sulfate. The environmental variables assessed were temperature, pH, Eh, salinity, sulfate, solids content, organic carbon, and carbohydrates. MA abundance was significantly higher in the rainy season (106–107 cells/g) compared with the dry season (104–106 cells/g), with methanol as an important substrate. At spatial level, MA were detected in the two layers analyzed, and no important variations were observed either in MA abundance or activity. Salinity, sulfate, solids, organic carbon, and Eh were the environmental variables related to methanogenic community. A conceptual model is proposed to explain the dynamics of the MA.
Highlights
Coastal and marine environments, including estuaries and coastal lagoons, are characterized by large amounts of organic matter, which is mineralized primarily in sediments through anaerobic processes, sulfate reduction being the dominant metabolic pathway [1, 2]. These ecosystems are the typical habitat of sulfate-reducing prokaryotes (SRP), methanogenic archaea (MA) and methane production have been detected [3, 4]
In the presence of these electron acceptors, methanogenesis is outcompeted by anaerobic respiration, mainly for thermodynamic reasons [5]
Most of the ecological studies assessing the structure of methanogenic communities in estuarine systems have been performed in temperate latitudes where temperature is one of the major factors regulating ecosystem function. ese investigations have included an evaluation of the MA in the intertidal zone of marshes with the presence of Spartina alterni ora, whose roots provide organic carbon and contribute to create aerobic microhabitats [9, 10]
Summary
Coastal and marine environments, including estuaries and coastal lagoons, are characterized by large amounts of organic matter, which is mineralized primarily in sediments through anaerobic processes, sulfate reduction being the dominant metabolic pathway [1, 2]. These ecosystems are the typical habitat of sulfate-reducing prokaryotes (SRP), methanogenic archaea (MA) and methane production have been detected [3, 4]. Ese organisms are common in anoxic environments in which electron acceptors such as nitrate and sulfate are either absents or present at low concentrations and are usually dominant in freshwater environments. MA abundance has been uanti ed with two or three substrates, of which acetate and hydrogen have been reported as the two most important ones
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