To clarify the relationship between climate and cellulose isotopic compositions, samples of mosses, pond water, and groundwater were collected in three locations (Au Train, Grand Traverse, and Ontonagon) along with southern shoreline of Lake Superior throughout the 2003 and 2004 growing seasons. Isotope data of water samples show that the studied ponds experience different hydrology. Whereas groundwater inflow dominates the hydrological balance of the ponds located in Grand Traverse and Ontonagon, groundwater and meteoric precipitation equally influence the hydrology of the pond located in Au Train. None of the investigated ponds show clear evidence of evaporative enrichment. Isotopic results of the Sphagnum samples collected in Au Train exhibit a small variability of cellulose [Delta]18O values compared to pond water [Delta]18O values. Whereas the range in pond water [Delta]18O values is 4.4%0(from -11.14%0 to -6.7%0), moss cellulose exhibits a range of only 2.2%0 (from 17.2%0 to 19.42%0). Given the fairly invariable ecology and phenology of the sampled mosses, it is concluded that the reduced variability in cellulose [Delta]18O values is caused by the continuous, water-unlimited growth of mosses throughout the entire growing seasons. In fact, moss cellulose at Au Train reflects the average isotopic composition of pond water during the growing season. Isotope data for the moss samples collected in Grand Traverse and Ontonagon show a higher variability in cellulose [Delta]18O values relative to the Au Train samples. In addition, it was found that ecology and phenology affect the cellulose [Delta]18O values of the studied samples. For example, at Grand Traverse, the average cellulose [Delta]18O value of Sphagnum cuspidatum (16.4%0) is 3.2%0 lower than the average cellulose [Delta]18O value of Drepanocladus fluitans (19.62%0). Evaporation of leaf water likely causes the enrichment of 18O in Drepanocladus flutans with respect to Sphagnum cuspidatum-cellulose. Because of the presence of species with different ecology in the three sites and because of the different hydrology of the ponds, it is concluded that any peat-based paleoclimatic investigation of the area has to be strictly site-specific and has to be conducted at the species level.