Southwest Greenland is one of the most rapidly-changing parts of the Arctic, which has led to a variety of consequences for both aquatic and terrestrial ecosystems. Lack of significant hydrologic connection between lakes and tundra, except during snowmelt, result in aquatic systems that serve as bioreactors embedded in a changing terrestrial landscape. Consequently, carbon cycling has been altered in lakes, such that DOC has shown significant declines since the early 2000's and methane is being generated across the landscape. The mechanisms behind the loss of DOC are less clear, and provide important questions as to the controls of carbon loss and reactivity in these lake systems. Additionally, rapid warming of lakes may have consequences for lake productivity as a result of changing pelagic thermal structure. Over the past 4 years, we have conducted a series of experiments in lakes across Greenland to investigate changes to carbon cycling, nutrient availability, and lake productivity in the region.
Results/Conclusions
Our experiments demonstrate a strong influence of light on DOC quality, such that even small changes may result in changes to in-lake productivity and feedbacks to warming in the region. Our data also suggest different patterns of nutrient limitation in lakes, leading to differences in the ability of bacteria to acquire and use nutrients to sustain their growth. Specifically, DOC concentration is positively related to microbial P limitation in southwest Greenland lakes. DOC decline may therefore alter lake nutrient limitation dynamics. Our experimental manipulations of lake thermal structure led to altered light availability in the water column, resulting in significant declines in phytoplankton biomass and shifts in phytoplankton taxa. Taken together, these changes in nutrients, carbon, and autotrophic biomass suggest that arctic lakes are integral components of the landscape, and serve as sentinels for current and future climate change in the region.