BIOTURBATION AND REMINERALIZATION OF SEDIMENTARY ORGANIC-MATTER - EFFECTS OF REDOX OSCILLATION

A variety of field and laboratory observations demonstrate that partic le reworking and irrigation activities of benthic fauna promote the re mineralization of organic matter. Of the many simultaneous factors inv olved, repetitive oscillation of redox conditions may be one of the mo st important. In bioturbated C(org)-rich sediments with restricted O2 penetration, particles constantly cycle between oxic and anoxic zones but typically spend approximately 10-100 X longer under anoxic than ox ic conditions. Cyclic redox patterns are also common within individual burrow structures and are accompanied by rapid switching in dominant metabolic processes. Geometrically and temporally complex redox mosaic s are the rule. Experimental evidence and theoretical considerations i ndicate that even brief, periodic re-exposure to O2 results in more co mplete and sometimes rapid decomposition than is possible under consta nt conditions or unidirectional redox change. Redox oscillation appare ntly results initially in net remineralization of existing microbial b iomass followed by stimulated renewed synthesis (self-priming) in a ma nner similar to many disturbances or grazing effects. Some properties, such as sedimentary P storage, are comparable under fully oxic and os cillating redox conditions but differ under anoxic. The relative frequ ency and duration of redox change are presumably critical properties g overning response. Redox oscillation common in bioturbated sediments o r the terrestrial rhizosphere likely represents a distinct functional environmental state with unique biogeochemical properties. Studies of decomposition and C(org) preservation processes should take this possi bility into account.