Metabolism As Determinant Of Nutrient Exchange In Organic-Rich Sediments Of A Coastal Lagoon

Some experiments in situ were performed in a typical coastal lagoon in order to evaluate the effects of physico-chemical processes and biotic activities on the nutrient exchange at the sediment-water interface. Evolution of dissolved oxygen, phosphate and ammonium concentrations were monitored under the following different conditions: aerobic, anaerobic, increasing phosphate and ammonium concentrations, and microbial and macrobenthic inhibition. Immediate adsorption under oxic conditions was registered for both ions. Phosphate adsorption continues at low oxygen levels. Stagnation provides conditions for release of P0 sub(4) super(-) and NH sub(4) super(+). Physico-chemical conditions were the main component for nutrient mobility, more than 50% of oxygen consumption was the chemical demand, and 2/3 of biotic consumption was macrobenthic related. Phosphorus movement was more active (15%) by macrobenthic activities. Flow of ammonium was 1/3 by microbial pathways, and 1/4 used up by phytoplankton production. Sediments may release or fix nutrients in high quantities depending on conditions; oxidable organic matter content was less important in the mobility.