Variability in Trends and Meteorological Drivers of Carbon Dioxide Exchange across Arctic Wetlands.

AMANATIDES, MEGAN MICHELLE. Variability in Trends and Meteorological Drivers of Carbon Dioxide Exchange across Arctic Wetlands. (Under the direction of Dr. Erin Lee Hestir.) Arctic ecosystems are particularly vulnerable to future projections in climate variability and climate change. Wetlands make up nearly 10% of all Arctic ecosystems which, historically, have acted as sinks for atmospheric carbon dioxide (CO2); however, the future CO2 balance of Arctic wetlands will be dependent on the balance between CO2 taken up through plant productivity and CO2 lost through microbial respiration. This study analyzes in situ measurements of net ecosystem exchange of CO2 (NEE) from June-August at four wetland sites across the Arctic to investigate changes in CO2 balance over time as well as to identify the meteorological drivers of CO2 exchange. Satellite data was also analyzed to account for changes in vegetation cover. Prior to analysis, the CO2 balance of each site was determined and each site was found to be a sink for atmospheric CO2. Then, a nonparametric test for trend was performed on data at each site to consider how CO2 exchange, meteorological conditions, and vegetation cover may have changed over time. Results indicate contrasting trends in CO2 exchange across these ecosystems. At US-Brw, NEE was significantly decreasing over time meaning that the site became a stronger sink for atmospheric CO2 while at FI-Kaa, NEE was significantly increasing over time meaning that the site shifted from a sink towards a source of atmospheric CO2. At US-ICs and DK-NuF, NEE did not significantly change. Vegetation cover and most meteorological factors showed little evidence of statistically significant changes likely due to the relatively short time series considered. However, air temperature increased at US-Brw, evapotranspiration decreased at US-ICs, and vegetation cover increased at FI-Kaa Then, to explore which meteorological factors have the largest influence on CO2 exchange, a conditional Random Forest regression algorithm was applied to each dataset and variable importance was assessed. Results suggest large site-to-site variability. However, air temperature frequently demonstrated high variable importance meaning that air temperature is important in predicting CO2 exchange – including both plant productivity and microbial respiration – in these ecosystems. Thus, it is expected that projected increases in air temperature have the potential to alter all aspects of CO2 exchange in Arctic wetlands. Additionally, spatial and interannual variability among sites highlights the need for increased spatial and temporal coverage across varying wetland ecosystems and climatic gradients. Future efforts should be made to increase both temporal and spatial coverage of in situ measurements of CO2 exchange across Arctic wetlands. Variability in Trends and Meteorological Drivers of Carbon Dioxide Exchange across Arctic Wetlands by Megan Michelle Amanatides A thesis submitted to the Graduate Faculty of North Carolina State University in partial fulfillment of the requirements for the degree of Master of Science Marine, Earth and Atmospheric Science Raleigh, North Carolina 2017