There are other bacteria that use the ammonium in the water as a nitrogen source and take it up to make organic nitrogen and new bacteria. When they do this and hold the nitrogen inside bacterial cells, it is called

the circled areas are referred to   as sunspots.   the sunspots are cooler than the   surrounding area.

sunspots are temporary phenomena on the photosphere of the sun that appear visibly as dark spots compared to surrounding regions. they correspond to concentrations of magnetic field flux that inhibit convection and result in reduced surface temperature compared to the surrounding photosphere.