Synonyms

Non-aerial environment

Definition

An anaerobic environment is characterized by the absence of free oxygen but may contain atomic oxygen bound in compounds such as nitrate (NO3), nitrite (NO2), and sulfites (SO3), in contrast to an aerobic environment where free oxygen is available (WKU, 2013).

Description

Some organisms are successfully adapted to anaerobic environments (EPA, 2012). These organisms do not use O2 as their electron acceptors. There are a number of substances that they will use as a substitute for O2, including (among others) nitrate (NO3), ferric iron (Fe3+), manganese (Mn2+), sulfate (SO42−), and carbon dioxide (CO2) (Scharf, 2000). Bacteria use sulfate as an acceptor for electrons in place of oxygen under anaerobic conditions. As the reduced organic tissue is oxidized to CO2, the sulfate is reduced to sulfide (Nietch, 2000).

In bottom waters of stratified estuaries, oxygen consumed primarily by bacteria will exceed oxygen input via atmospheric and photosynthetic reoxygenation. While the anoxia/hypoxia that develops will eliminate almost all estuarine and marine organisms, a large number of bacteria and protists can still remain active in these areas by changing their metabolism to anaerobic respiration (Dang et al., 2008). If oxygen becomes so low that the system becomes anoxic, which occurs frequently in shallow turbid estuaries in the summer time, anaerobic mechanisms for decomposition become important. Carbon turnover occurs continuously in subtidal and intertidal sediments where oxygen is depleted just a few millimeters below the sediment surface. Much of the organic matter undergoes decomposition in an estuarine anaerobic environment via sulfate reduction (Nietch, 2000). Preservation of skeletal remains in these environments appears to be correlated with the abundance of dissolved organic matter rather than with high sedimentation rates (Simon et al., 1994).

Cross-references