Streams are a consistent source of carbon dioxide to the atmosphere, with some estimates placing emissions at over 5.5 petagrams per year. Yet, there is significant uncertainty in quantitative estimates of contributions to stream carbon from sources such as groundwater. This study aims to assess groundwater contributions to stream carbon from a localized perspective by examining carbon dioxide fluxes from headwater streams at Harvard Forest in Petersham, Massachusetts. I hypothesize that CO2 values from groundwater will be much higher than those at the surface; with this in mind, I also expect groundwater carbon contributions to correlate with stream emissions.

To quantify carbon emissions, we measured CO2 and critical chemical variables, including cation and anion concentrations, pH, temperature, and dissolved oxygen throughout Fall 2025. We tracked these variables along a stream reach and groundwater wells adjacent to the stream sites to develop a spatial map of CO2 flux across sites upstream and downstream of the Harvard Forest waters. Additionally, we calculated carbon fluxes using a model that incorporates pCO2 values alongside gas transfer velocities (kCO2). Finally, we created a Piper diagram of the ionic composition of the streams, which we use to estimate quantitative groundwater input rates. 

A spatial representation of carbon flux is critical for understanding the physical and chemical processes that shape local gas transfer and the impact of groundwater discharge on the carbon budget. These results provide insights into the mechanisms governing stream carbon fluxes at the local scale and contribute to a better understanding of watershed-level carbon budgets.