Technical Abstract: Wetlands may be constructed to provide several ecosystem functions. A constructed wetland receiving agricultural runoff water was observed prior to, and for more than two years after, establishment. The excavated portion of this wetland was compared to an undisturbed, upland area and to an adjacent, natural reference wetland. After construction the excavated cell was rapidly colonized by wetland plant species, including some exotic invasive weeds. Flourescein diacetate and triphenyl tetrazolium chloride enzyme assays indicated that the soil microbial community was more active in the excavated wetland cell than either of the two reference areas. The soil microbial community of the constructed wetland rapidly decreased in the abundance of fungi and gram-negative bacteria and increased in gram-positive bacteria and overall bacteria, as measured by fatty acid methyl esters. These shifts in the microbial community were consistent with the differences noted between the communities of the upland system and the reference wetland. Measurements of soil nitrogen and carbon did not indicate sequestration of C or N in the constructed wetland.