THE RELATIVE IMPORTANCE OF BIOLOGICAL AND CHEMICAL PROCESSES IN THE RELEASE OF PHOSPHORUS FROM A HIGHLY ORGANIC SEDIMENT

Bacteria can play an important role in the process of anaerobic phosph orus release: they can act as a direct source of orthophosphates, or a s a catalyst of iron hydroxyde reduction. We studied their influence o n phosphorus release from highly organic sediments of a Canadian shiel d lake. Phosphorus and iron release were measured under aerobic and an aerobic conditions, with or without sterilization, and at different pH . We measured also the abundance and activity of bacteria in sediments . The increased P release after sterilization can be explained by cell lysis. Compared to sterilization, changing oxygen concentrations or a cidification had little or no effect on P release. In these sediments, phosphorus and iron movements were independent. Most of the total dis solved iron seemed to be linked to humic acids, but not phosphorus.