Carbon cycling in freshwater is a large flux linking land to the sea and atmosphere, and better understanding some of the biogeochemical processes that occur in rivers is essential in our knowledge of nutrient cycling in aquatic systems, and the impact of CO2 output of rivers as a whole. Much dissolved organic carbon occurs naturally and moves into rivers. A significant portion of this carbon is recalcitrant, and the processing of how it breaks down is not yet well understood. One hypothesis is the positive priming effect. Biologically available, or labile, carbon is believed by many to produce positive priming effects on the microbial breakdown of other, hard-to-break-down carbon forms, creating a greater CO2 output via microbial respiration. We find that a better understanding of this aquatic priming effect is necessary, and seek to measure and observe this priming effect using traceable, labeled, recalcitrant 13C. We tested the effects of sugar and nutrients on the breakdown of 13C labeled recalcitrant carbon using experimental bioassays. We simplified the study of priming by directly testing the mineralization rate of aged, recalcitrant carbon. Across the treatments with sugar and nutrients, we observed evidence of positive priming effects. Increased CO2 concentrations among the sugar and nutrient treatments from time zero indicate that the microbes are mineralizing carbon and respiring more than in the treatment without the added nutrients and carbon. Furthermore, an observed increase in the production of 13C CO2 indicates that much of this CO2 came from the breakdown of our recalcitrant carbon: recalcitrant, labeled 13C leachate. Using this recalcitrant labeled 13C gives us a way to more easily observe and calculate the respiration of the microbes breaking down the recalcitrant carbon. Because of this direct measurement, we observe clear evidence of the priming effect in an aquatic system. A better understanding of this process in aquatic systems is crucial in bettering our understanding of carbon cycling and CO2 fluxes in our river systems.