| Summary: | Small ponds constitute a significant number of standing water bodies on earth and may contribute to CO<sub>2</sub> uptake or release into the atmosphere. Despite their importance, few studies have examined ecosystem metabolism in ponds, especially in ponds that may be dominated by floating-leaved macrophytes. In this study, we examined ecosystem metabolism by measuring changes in dissolved oxygen levels every 10 min from late May through late October for four shallow ponds (0.5–1.5 m) in east-central Minnesota, USA. Ponds had varying levels of floating-leaved macrophytes from sparse (<1% coverage) to abundant (61% coverage). We found significant differences in a number of physical/chemical factors including P, N, DOC, water temperature and light penetration. We also found significant difference in gross primary production (GPP—average ranged from 2.2 to 5.5 mg O<sub>2</sub>/L/day), respiration (R—average ranged from −6.8 to −3.6 mg O<sub>2</sub>/L/day) and net ecosystem production (NEP—average ranged from −1.5 to −0.1 mg O<sub>2</sub>/L/day) among the ponds. On average, all of the ponds were heterotrophic (R > GPP). While it appeared that floating-leaved macrophytes provided a significant impact on ecosystem metabolism, there was not a one-to-one correspondence between the amount of macrophytes and the level of ecosystem metabolism.
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