Anoxic refers a region having no oxygen present, with nitrite
and nitrate present and taking over the function as the oxidiser
(with the oxidation reduction potential between +50 and -50 mV).
Within a reef system, denitrification (conversion of nitrate to
nitrogen gas) occurs in the anoxic regions (includes interior
regions of liverock, bottom layers of sand bed and inside a
denitrator i.e. surfaces not directly in contact with the
water). The presence of oxygen is referred to as aerobic and the
absence anaerobic. Oxygen will penetrate through approximately
0.5 millimeters of a stationary biofilm. - ↑
(http://dx.doi.org/10.1016/j.bej.2003.10.003): Hibiya, K.,
Nagai, J., Tsuneda, S., and Hirata, A., Simple prediction of
oxygen penetration depth in biofilms for wastewater treatment,
Biochemical Engineering Journal, 19(1), (2004), 61-68.