Doctoral Dissertation Research: Spatio-Temporal Patterns of Soil Respiration and Age of Respired Carbon from High-Elevation Alpine Tundra

University Of Colorado At Boulder, Boulder CO

Investigators

Abstract

Carbon dioxide is increasing in the contemporary atmosphere as a result of an imbalance between the rates of human-related and natural carbon dioxide emission and biospheric and oceanic carbon dioxide assimilation. These circumstances are augmenting the natural greenhouse effect. Resultant climate warming has been linked to flooding, hurricanes, and the loss of sea-ice, glaciers, and permafrost. Alpine tundra is an underrepresented ecosystem in global environmental databases due to its inherently remote nature and the difficulties associated with working in steep, mountainous terrain. Recent research suggests that carbon dioxide emissions from alpine tundra may be far greater than previously estimated. Toward a process-based reconciliation of net annual carbon loss from high-elevation alpine tundra, this doctoral dissertation research project will evaluate soil respiration and net ecosystem exchange through space and time at Niwot Ridge, Colorado, using a distinctive suite of measurement techniques in combination with radiocarbon isotopic analysis. The doctoral student will use a multi scale approach to (1) substantiate previous data through the use of independent sampling designs including chamber, gradient, and eddy covariance techniques; (2) investigate the relationship between soil properties, climate, and carbon dioxide flux; (3) model the differential response of carbon dioxide flux by soil type; and (4) constrain the age, mechanism for, magnitude, and trend of atmospheric carbon loss through the application of radiocarbon dating techniques. These methods will be used to test the hypothesis that an imbalanced carbon cycle suggested by previous research represents metabolism of paleocarbon by an unexpectedly active microbial community. Confirmation of this hypothesis would demonstrate that directional climate change has already begun to affect alpine regions while also providing an early indication of potentially more-widespread carbon cycling patterns in the future. This project addresses expansion of the current network of carbon dioxide flux measurements into understudied ecosystems and will refine the magnitude and spatio-temporal variability of carbon dioxide flux from alpine tundra. By coupling top-down monitoring techniques to bottom-up mechanistic analyses, this project will investigate both the causes and effects of observed alpine carbon dioxide loss. To promote application of specific results to other alpine systems, conceptual and empirical models will be developed to describe both plot- and ecosystem-scale fluxes. These models will directly contribute to knowledge about the global carbon cycle. A comprehensive understanding of the natural carbon cycle is crucial to accurately assess the future ramifications of present-day carbon dioxide emissions, policy decisions, and climate-forcing scenarios. To that end, the results of this work will help constrain the probable effects of proposed policies and regulations. As a Doctoral Dissertation Research Improvement award, this award also will provide support to enable a promising student to establish a strong independent research career.