Tracer and spike tests of constructed wetlands

This paper reviews the types of tracer testing that have been used in treatment wetlands, and summarizes example studies and collections of results. Impulse tests typically produce outlet gamma distributions, characterized by N tanks in series (TIS) and a volumetric efficiency (eV) calculated from the mean tracer detention time. TIS values center on N = 4 for FWS and N = 6 for SSF wetlands; while median eV values are 77% for FWS and 89% for SSF systems. When used in conjunction with inert tracers, reactive material behavior may be better understood via spike additions. Thus dual additions of an inert, such as bromide, accompanied by a spike of a target substance, such as a pathogen, can provide easy interpretation of the removal rate. Sample results from 32P and 15N studies are shown to yield valuable insights into internal processes and their speeds. Wetland sediment storages build slowly, but the progress of accretion can sometimes be followed via radioisotopes such as 137Cs and 210Pb.