Wetlands are vital ecosystems vulnerable to threats such as metal contamination. Wetland microorganisms can mediate metal fate and bioavailability; however, the influence of environmental factors, particularly light exposure, on these interactions remains unclear. While previous studies suggest that light affects microbial communities, its consequences for metal dynamics are understudied. In this study, we conducted a microcosm experiment using two wetlands: a constructed wetland designed for metal retention and a natural depressional wetland at the Savannah River Site (Aiken, South Carolina USA). Microcosms were established from water and sediment collected from the two wetlands and incubated for eight days under natural light cycles or constant dark conditions, with copper spiked in at the experiment’s midpoint. Analysis of the water microbial community revealed that light significantly altered microbial alpha diversity illustrating higher species richness and lower Pielou’s evenness compared to communities under dark conditions. Compared to dark conditions, copper retention in the sediments was enhanced with natural light under ambient conditions but decreased after the addition of a copper spike. With the use of predicted microbial functional analysis, this study found that light exposure, particularly under copper-amended conditions, significantly influenced the relative abundances of functional groups including those for sulfur respiration, photosynthesis, and methanogenesis, but there were no significant variations between wetland sources. These results highlight how abiotic factors, such as light, shape microbial processes, informing strategies for wetland conservation and management of metal contamination. More broadly, they emphasize the importance of incorporating landscape-scale features such as vegetation structure, foliage coverage, and light-mediated microbial responses into the design, management, and restoration of constructed wetlands