Macrocosm experiments at various scales have been applied in lake eutrophication management worldwide. This study investigated how artificially created macrocosms affect the physicochemical characteristics of lake water, as well as the density, community structure, and biodiversity of benthic diatoms. First, we found that macrocosms were mesotrophic compared to the eutrophic control lake water from March 2012 to February 2013. Second, 148 diatom taxa were recorded across all study sites; both species richness and the number of dominant diatom taxa were higher in the macrocosms, compared with the control lake water. Mean diatom densities in the macrocosms and the control were 8.4 and 21 x 10(9) cells/m(2), respectively. Across all sites and seasons, Achnanthidium minutissimum was the most abundant species and dominant contributor to total abundance (14%). In the macrocosms, other abundant diatom taxa were Cymbella gracilis, Cymbellaaffinis, Gomphonema truncatum, and Gomphoneis olivaceum, all of which are associated with high water quality. Canonical correspondence analysis indicated that the variation in benthic diatom communities was strongly related to phosphorus and nitrogen concentrations in macrocosms, but related to pH and total nitrogen in the control. This study suggests that macrocosms created to alter water characteristics have a positive effect on ecosystem biodiversity and function.