Winter Carbon Dioxide Efflux in Sierra Nevada Meadows: Contributions to Annual Carbon Budgets, Influence of Snowpack, and Subnivean Conditions

Meadows in the Sierra Nevada contain a disproportionate share of regional soil carbon and can display high levels of carbon dioxide (CO2) efflux during the growing season. Yet wintertime instantaneous CO2 efflux rates from these systems, along with further understanding of what ecological mechanisms are affecting CO2 efflux remains poorly constrained due to limited site access and hazardous winter conditions. Wintertime CO2 efflux may represent a substantial amount of the annual carbon budget because low but persistent fluxes can continue occurring beneath snowpack for several months. We quantified instantaneous wintertime CO2 efflux rates across two Sierra Nevada meadows. We measured Van Norden meadow in the winters of 2023-2024 and 2024-2025 and Martis meadow, during the winter of 2024-2025. We collected more than 300 instantaneous CO2 efflux measurements across both snow surface and subnivean environment (including soil, water, and ice). Mean winter CO2 efflux rates among both meadows, all collection dates and all surface types (snow, soil, ice and water) was ~1.5 μmol m⁻² s⁻¹. When comparing both sites in the winter of 2024-2025, CO2 efflux was highest in Van Norden at the soil surface, whereas CO2 efflux was lowest at the snow surface in Martis. CO2 efflux was similar when comparing soil surface efflux rates at Martis and snow surface efflux rates at Van Norden. CO2 efflux was significantly different between the meadows, between surfaces (snow surface and pit surfaces), and there was a significant meadow by surface type interaction. Snow depth did not significantly influence CO2 efflux at the snow surface in either meadow, whereas increasing subnivean water depth was associated with reduced rates of CO2 efflux in Van Norden meadow. Our sensitivity analysis indicated that while cumulative winter CO2 efflux estimates were sensitive to changes in instantaneous flux rates, these changes had relatively minor influence on cumulative annual CO2 efflux estimates. Together, these results demonstrate that wintertime CO2 efflux rates from Sierra Nevada meadows is substantial, influenced by site-specific and subnivean conditions, and sensitive to measurement location, emphasizing the importance of wintertime sampling approaches for improving annual carbon flux estimates.

Level thesis:degree_level

Master's Degree

Year dc:date.issued

2025

Author dc:creator

• Harris, Julia

Advisor dc:contributor.advisor

• Sullivan, Benjamin W.

Committee members dc:contributor.committeemember

• Reed, Cody C.
• Loisel, Julie

Language dc:language.iso

en_US, English

Repository record dc:identifier.uri

https://scholarwolf.unr.edu/handle/11714/11761

OAI identifier oai:identifier

oai:scholarwolf.unr.edu:11714/11761