Understanding the environmental and climate influence on the Holocene stable isotope record in peat is essential for applying the proxies in the paleoenvironmental reconstruction of lake and bog ecosystems. Here, we report total organic carbon (TOC), TOC to total nitrogen (N) ratio (C/N), and stable isotope ratios of organic carbon (S13C) and nitrogen (S15N) of bulk sediment and peat organic matter (OM) from a radiocarbon-dated core collected from Stavs & aring;kra bog in southern Sweden. Changes in the TOC, C/N, S13C and S15N between 12 ka and 10.4 ka BP represent shifts in the OM source from aquatic primary producers to terrestrial swamp vegetation and pinpoint the transition of a highly productive water body into a reed swamp. The variation in S13C values and increase in peat accumulation rate (AR) from 10.8 ka BP imply a rapid transition of the aquatic body into a peatforming swamp and a shift from aquatic to atmospheric CO2 as the source of carbon (C) to the vegetation at the site. A sharp drop in N and S15N in the reed swamp peat may indicate fixed-N in the soil as the source of N to the growing vegetation. Heavier S13C and higher C/N ratio at the bottom of wood carr peat may reflect fire events. The rapid increase in peat AR between 7 ka and 6.5 ka BP suggests increased peat deposition under warmer and drier conditions. Lighter S15N and S13C, lower N, and TOC concentrations between 1.1 ka and 0.8 ka BP likely suggest warmer conditions related to the 'Medieval Climate Anomaly'. The research demonstrates the successful application of stable C and N isotope ratios of bulk peat in palaeoenvironment and palaeoecological interpretations.