Subsurface Dynamics Play Crucial Role in Carbon Cycling in Vermont's Sleepers River

In the Sleepers River headwater catchment in Vermont, United States, a comprehensive study using the BioRT-HBV reactive transport model has provided valuable insights into the subsurface processes influencing dissolved organic and inorganic carbon (DOC and DIC) dynamics. This research is crucial for understanding factors that affect water quality and ecosystem health.

To comprehend the study's findings, it's essential to understand the subsurface, which refers to the area beneath the Earth's surface where various hydrological and biogeochemical processes occur. This subsurface is divided into shallow and deep zones, each playing distinct roles in the carbon cycle. Discharge dynamics refer to the movement of water and dissolved substances from these subsurface areas into streams and rivers.

DOC, which includes carbon from sources like decaying vegetation and microbial activity, showed distinct behaviors in the shallow and deep subsurface areas of Sleepers River. In the shallow subsurface, DOC was produced at an average rate of 4.8 g/m2/yr, a quantity comparable to scattering about five teaspoons of sugar over a square meter annually. However, in the deeper subsurface, DOC was consumed, averaging -2.7 g/m2/yr, indicating a net loss of carbon in this zone. Regarding export, more DOC flowed from the shallow subsurface (1.5 g/m2/yr) than from the deep subsurface (0.7 g/m2/yr).

DIC, which can originate from the breakdown of rocks and soil minerals, was produced in both shallow and deep subsurface zones. In the shallow zone, DIC production was 6.2 g/m2/yr, similar to placing six and a half sugar cubes on a square meter each year. In the deep subsurface, the production rate was 3.2 g/m2/yr. However, DIC export was significantly higher from the deeper subsurface (7.9 g/m2/yr) than from the shallow subsurface (1.9 g/m2/yr).

These findings underscore the varied roles of the shallow and deep subsurface in the production and export of DOC and DIC. They highlight the intricacies of subsurface processes in carbon cycling, with DOC being more influenced by shallow subsurface activities (like organic matter decomposition), and DIC being significantly affected by deeper subsurface activities (such as mineral dissolution).

The research also suggests potential impacts of climate change on these processes. Alterations in temperature and precipitation patterns could change the production and export rates of DOC and DIC, impacting water quality and stream ecosystem carbon cycling. This study emphasizes the importance of understanding subsurface processes for effective prediction and management of environmental changes.

“Differential Production and Export of Dissolved Carbon from Shallow and Deep Subsurface (Invited)” was presented as part of “Surface Water Chemistry as an Integrated Signal of Ecosystem Vectors and Critical Zone Reactors" on December 14, 2023 during the American Geophysical Union Annual Fall Meeting

1. Bryn Stewart, Pennsylvania State University Main Campus
2. James B Shanley, United States Geological Survey
3. Serena Matt, USGS
4. Erin Cedar Seybold, University of Kansas
5. Dustin W Kincaid, University of Vermont
6. Andrew Vierbicher, Pennsylvania State University Main Campus
7. Bren Cable, University of Vermont
8. Niara Hicks, University of Vermont
9. Julia N Perdrial, University of Vermon
10. Li Li, Pennsylvania State University Main Campus