This study evaluated the role that carbon source and character have on processes driving organic carbon (OC) burial in a eutrophic lake, Rostherne Mere, UK. Novel methods identified anthropogenic impacts such as nutrient loading from sewage treatment input, subsequent lake restoration efforts, and changes in algal communities and climate. Stepped combustion radiocarbon analysis was used to identify carbon sources in a sediment core spanning the last ~100 years, and in contemporary lake carbon pools. Samples combusted at low and high temperatures split labile (readily decayed) and detrital (recalcitrant) OC fractions, which were then attributed to terrestrial (allochthonous) or in-lake (autochthonous) sources through radiocarbon analysis. Historical production rates and phytoplankton community structure were examined in the sediment core from diatom assemblage composition, abundance and biogenic silica accumulation, and high performance liquid chromatography pigment analysis. Fluctuations in production rates and abundances of diatom and algal pigments, were linked with carbon source/character and used to determine the primary processes driving carbon sequestration in the lake. This combined approach characterised OC accumulation in Rostherne Mere, and initial results indicate that the relative importance of allochthonous and autochthonous carbon has varied over the last century, which in turn has had significant impacts on burial rate.