FIG. 1.

Steady-state oxygen and sulfide profiles in Lake Chiprana microbial mats at different light intensities. (A) Oxygen concentration profiles with 0, 33, 83, 166, and 300 μmol photons m⁻² s⁻¹. The oxygen concentration reaches up to six times the air saturation level at higher light intensities, indicating that CLB in the photic zone have to cope with high and fluctuating oxygen concentrations. (B) Oxygen and sulfide (H₂S) concentration profiles at light intensities of 83 and 300 μmol photons m⁻² s⁻¹. Oxygen and sulfide cooccur in the zone between 1 and 1.5 mm deep, a zone where CLB are able to oxidize sulfide both phototrophically and chemotrophically, in the latter case using oxygen as the electron acceptor. μE, microeinsteins.