AME 21:169-175 (2000)  -  doi:10.3354/ame021169

ABSTRACT: The uptake of urea and dissolved organic nitrogen by a Lyngbya gracialis dominated microbial mat was studied in a double chambered continuous flow-through system in a 12:12 h light:dark cycle experiment and during a prolonged dark incubation. In addition, the fluxes of total inorganic carbon, oxygen, dissolved free amino acids, nitrate and ammonium across the microbial mat were studied. In the 12:12 h light:dark cycle, the microbial mats grew exponentially (0.5 d^-1) with dissolved organic nitrogen as a nitrogen source. Dark urea uptakes were 50 to 85% of the urea uptakes in light. The uptake of urea continued during the 2 wk of prolonged dark incubation. Natural microbial mats may be important regulators of urea dynamics in shallow marine environments, as the microbial mat efficiently took up urea at concentrations somewhat higher than in situ urea concentrations in surface sediments.

KEY WORDS: Cyanobacteria · Fluxes · Flow-through system · Microbial mats · Nitrogen retention