The forested watersheds of the Pacific Northwest can sequester a significant amount of atmospheric carbon dioxide (CO2), making them valuable carbon sinks for offsetting the carbon emissions that are contributing to global changes in the climate. However, as trees are storing carbon, water is leaching it from the soil. Some of the carbon is captured by microbial communities living in the stream’s hyporheic zone, a region within the streambed, where it is turned back into CO2. Gas exchanges between water and air release this CO2 back into the atmosphere. These carbon fluxes previously have not been well quantified, which could affect carbon budgets developed for national forests.
Researchers with the U.S. Forest Service Pacific Northwest Research Station and Oregon State University analyzed 10 years of data from a headwater stream located in the H.J. Andrews Experimental Forest in western Oregon to calculate the watershed’s annual carbon budget. They measured the concentrations of dissolved organic carbon, dissolved inorganic carbon, and particulate organic carbon in the stream and hyporheic zone and estimated the CO2 flux from the stream surface.
Their calculations revealed that the watershed annually exported 6 percent of the estimated amount of carbon sequestered by the forest, or 33,476 lbs, equal to the carbon contained in 32 cords of wood.
Watts, Andrea; Wondzell, Steve; Johnson, Sherri; Argerich, Alba. 2018. Counting carbon: Calculating how headwater streams contribute to the carbon cycle. Science Findings 212. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 5 p.