The document summarizes a study that investigated the physiological effects of increasing concentrations of nickel chloride hexahydrate on aquatic microbial biofilm. Sweet gum leaf squares were incubated in enriched water for 25 days to develop biofilm. The leaves were then exposed to various concentrations of nickel for 24 hours. Dissolved oxygen levels and microbial respiration were measured. Results showed that microbial respiration initially increased at lower nickel concentrations but then decreased with higher concentrations, supporting the hypothesis. Future work could include more replicates and testing other nickel compounds.