Under aerobic conditions (presence of oxygen), the natural cycles may be more or less in the balance until an excess of nitrate (nitrogen) and/or phosphate enters the system.• Bacteria try to decompose the organic waste, consuming the oxygen, and releasing more phosphatewhich is known as "recycling or internal cycling". Some of the phosphates may be precipitated as iron phosphate and stored in the sediment where it can then be released if anoxic conditions develop.