Algal priming is when light stimulates growth of algae, increasing the release of labile carbon, which influences heterotrophic decomposition and nutrient acquisition. Headwater streams tend to be shaded by canopy cover, which is associated with high rates of organic nutrient inputs as leaf litter, but low rates of photosynthesis. Increasing labile N and P or light can stimulate primary production and alter heterotrophic decomposition. Trace metals like Fe and Zn can be limiting to primary production because of their importance in photosynthetic pathways yet their role in algal priming has not been explored. The effects of metal addition (Zn and Fe) and light on nutrient acquisition and decomposition were tested in 32 mesocosms over a two-week period. An artificial stream system (ExStream) pulled water from a fourth-order, high-nutrient stream (Cuyahoga River, Kent, OH). The decomposition substrates (cotton strips and leaves) were collected and analyzed for C, N, and P and microbial enzymes. Preliminary results show highest mean leucine aminopeptidase (LAP) activity in leaves for the treatment with light and no metals (13.54 µmol/g/hr) while the lowest was in the light and metal addition treatment (10.31 µmol/g/hr). Conversely, the metal addition and shaded treatment exhibited the highest mean alkaline phosphatase (APA) activity in the leaves (12.16 µmol/g/hr), while the light and metal treatment showed the lowest (10.76 µmol/g/hr). Analysis of LAP and APA activity for the cotton strips is still ongoing, as well as N and P concentrations in both substrates. We expect to see enzyme activity in the cotton strips closely resemble that of the leaves. We also predict the highest and N and P concentrations to be in the treatment with light and no metal additions.