Artificial wetland wastewater treatment (AWWT) systems are a complex interaction of microorganisms and higher plants in a submerged environment. Media type and size are an integral part of the whole. The microorganisms are the “heart” of the AWWT system forming a complex living system with the plants and the media, and thus the systems must be studied in their entirety. As such there is a need for improved understanding of the microbial ecosystem within each specific AWWT type, free water surface or submerged bed treatment (SBT) systems. Top Loading Vertical Flow Submerged Bed Treatment Systems (TLVFSBTS, Pat. Pending) are a variant of SBT systems. Little has been published about the performance or design parameters of this type of system. To overcome the paucity of published data, media/microbe samples were removed from a TLVFSBTS wetland treating domestic sewage in Highland, NY. Cores were transported to the laboratory, and allowed to acclimate to incubation temperature for 24 hr prior to addition of 14C-glucose. Labeled samples were incubated for varying times, dependant on temperature of incubation (1-2 hr at 20o C and 12 hr at 4o C). Incubation times were adjusted so that no more than 5% of the substrate was removed in the most dilute solutions. Metabolic activity was stopped in samples and prevented in blanks with the addition of Lugol's acetic acid solution.