Date of Award

Summer 8-16-2024

Level of Access Assigned by Author

Open-Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Ecology and Environmental Sciences

Advisor

Jasmine Saros

Second Committee Member

Brian McGill

Third Committee Member

Michael Kinnison

Additional Committee Members

Hamish Greig

Suzanne McGowan

Abstract

With amplified warming and predicted intensification of the hydrological cycle in the circumpolar North, the linkages between terrestrial and aquatic environments are changing. Yet, the impact of these alterations on Arctic terrestrial ecosystems and their functions remains uncertain. While it is evident that air temperature and precipitation do not change consistently throughout the annual cycle, ecosystem ramifications are not always examined in the context of relevant seasonal variations.

Lakes are ubiquitous across the Arctic and research over the past three decades has demonstrated their pivotal role in the Arctic carbon cycle, emphasizing their contributions as carbon sources to the atmosphere. Recent work focusing on arid Arctic landscapes challenges the conventional view of Arctic lakes as strong emitters of carbon dioxide fueled by inputs of external, terrestrial carbon. As the hydrological cycle intensifies, tightening the connections between lakes and their watersheds, aquatic carbon cycling dynamics are poised to undergo notable shifts.

Focusing on a suite of lakes in West Greenland—an arid Arctic landscape experiencing abrupt, ecosystem transformations, I address how lakes respond to seasonal and interannual variability in climate forcing. I show that Arctic lakes have pronounced seasonality, and that the transitional period between icecovered and open-water conditions has a disproportionate effect on lake physics, biogeochemistry, and biology.

As rapidly rising air temperatures in early spring bring about earlier melt of lake ice, the propensity of lake water to mixing increases, with important consequences for oxygen dynamics and lake biogeochemistry (Chapter 3). Despite limited inputs of terrestrial carbon, lakes in West Greenland are broadly heterotrophic with high ecosystem respiration and carbon dioxide emission rates at ice-out regardless of peak phytoplankton growth at that time (Chapter 2, 4). Heterotrophy and carbon dioxide emissions were augmented after an extreme autumnal precipitation event that altered hydrological connections between the lakes and their watersheds (Chapter 4). Synthesizing carbon dioxide fluxes across the Arctic, I provide strong evidence that while lakes in arid Arctic regions are hotspots of internal carbon processing, their annual carbon dioxide fluxes vary strongly, from the lowest to the highest recorded fluxes (Chapter 5).

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