ARCUS | Arctic Research Consortium of the United States

7th Annual ARCUS Award for Arctic Research Excellence

Submitted by		Hyojung Kwon
Authors		Hyojung Kwon, W. C. Oechel, R. C. Zulueta, and S. J. Hastings
Category		Physical Science
Title		Seasonal and Spatial Variability in Net Ecosystem CO₂ Exchange Over Arctic Tundra Ecosystems
Affiliation		Biology, San Diego State University, San Diego, CA, USA

Abstract

Temporal and spatial variability is an under-rated characteristic of the arctic tundra region. This variability induces considerable uncertainty in the estimation of the carbon budget of the Arctic ecosystem response to climate change. There is a lack of representative measurements available for land-surface parameterization for the arctic tundra in regional and global climate models. Very few measurements of net ecosystem CO₂ exchange have been conducted in moist sandy tussock tundra, which is one of three main tundra categories of the Arctic slope. In this study, eddy covariance was used to measure net ecosystem CO₂ exchange of Alaskan wet coastal sedge tundra and moist sandy tussock tundra ecosystems during the 2000 growing season. The objective of this study were to quantify the seasonal and spatial net ecosystem CO₂ exchange and to determine control mechanisms on net ecosystem CO₂ exchange in the Arctic tundra ecosystems. On average during the 2000 growing season, the general climate condition showed that the moist sandy tussock tundra was warmer and drier than the wet coastal sedge tundra. The average daily net CO₂ flux in the wet coastal sedge tundra was -0.6 gC m^-2 d^-1 (carbon sink), while the average daily net CO₂ flux in the moist sandy tussock tundra was 0.6 gC m^-2 d^-1 (carbon source). The wet coastal sedge tundra ecosystem accumulated ~ 60 gC m^-2 season^-1, while the moist sandy tussock tundra lost ~ 63 gC m^-2 season^-1 to the atmosphere during the growing season. This contrasting pattern of net ecosystem CO₂ exchange resulted from the warmer and drier local climate in the moist sandy tussock tundra compared to the wet coastal sedge tundra. Warming and drying increased ecosystem respiration (e.g. heterotrophic and autotrohpic respiration) in the moist sandy tussock tundra causing a net loss of carbon during the growing season. These results suggest that a reduction in soil moisture and an increase in air temperature will play a predominant role in controlling ecosystem respiration and likely result in net ecosystem carbon loss. Estimation of landscape and regional carbon balance over the Arctic region will require taking into account the spatial variability in net ecosystem CO₂ exchange in order to improve our ability to predict the current and future carbon balance of the Arctic.