Constructed wetlands show different processes to substantially decrease the number of microorganisms of
antropogenic origin. Microorganisms are trapped in the system by filtration, sedimentation and adsorption. In
stabilization ponds UV radiation is an important process. Some wetland plants excrete biocides that are lethal to
microorganisms. Predation by nematodes, protozoa and zooplankton, attack by lytic bacteria and viruses and
natural die-off are other known removal mechanisms.