The Agricultural Contribution to the Land Carbon Sink in Northern New England: the Role of Deep Soil, Soil Fractions, and Carbon Flux

Author

Erin D. Lane, Dartmouth CollegeFollow

Author ORCID Identifier

https://orcid.org/0000-0002-9717-3797

Date of Award

Summer 6-6-2025

Document Type

Thesis (Ph.D.)

Department or Program

Ecology, Evolution, Environment and Society

First Advisor

Caitlin Hicks Pries

Abstract

Agricultural lands and managed grasslands cover a large portion of the Earth's surface and serve as a critical interface between climate mitigation and food production. This dissertation investigates how farms in northern New England contribute to the terrestrial carbon sink by examining deep soil carbon stocks, carbon fractions, and carbon fluxes, across croplands and pastures. Using a combination of deep soil sampling, fractionation analyses, and eddy covariance measurements, we assessed how management and environmental factors influence carbon storage and persistence. First, measuring soil organic carbon (SOC) stocks to one meter soil depth across 12 Vermont pastures revealed that deep soils (below 30 cm) contained 30–50% of total SOC, emphasizing the importance of sampling beyond the surface. Surface SOC was a poor predictor of deeper carbon stocks, and accurate quantification required accounting for site-specific factors such as depth to bedrock, bulk density, and inorganic carbon—underscoring the need for direct, deep soil measurements. Second, soil fractionations from 196 agricultural fields across Vermont showed that improved soil health and perennial land use was positively correlated with both particulate and mineral-associated organic carbon (MAOC), with MAOC particularly responsive to management in certain soil textures. This demonstrates the potential to enhance persistent carbon sequestration through soil health practices. Third, establishing and using an eddy covariance tower on a rotationally grazed pasture in southern Maine, we quantified carbon fluxes while monitoring weather and grazing of cows. The pasture was a modest net carbon source for two years, with carbon uptake highest during moderate weather conditions and with carbon release directly after grazing. These results underscore the need for context-specific strategies to balance carbon and productivity goals. Overall, the findings of this dissertation suggest that climate mitigation and agricultural productivity can be mutually supportive, and that maintaining photosynthetically active agricultural landscapes can support both goals.

Recommended Citation

Lane, Erin D., "The Agricultural Contribution to the Land Carbon Sink in Northern New England: the Role of Deep Soil, Soil Fractions, and Carbon Flux" (2025). Dartmouth College Ph.D Dissertations. 365.
https://digitalcommons.dartmouth.edu/dissertations/365