Northern Delta Lakes as Summertime CO<sub>2sub> Absorbers Within the Arctic Landscape

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• 作者：Suzanne E. Tank ; Lance F. W. Lesack and Raymond H. Hesslein
• 关键词：CO2 flux ; arctic lakes ; arctic deltas ; permafrost melting ; dissolved organic carbon ; lake ; landscape connectivity ; shallow productive lakes ; climate change
• 刊名：Ecosystems
• 出版年：2009
• 出版时间：February, 2009
• 年：2009
• 卷：12
• 期：1
• 页码：144-157
• 全文大小：583.1 KB

文摘

The vast majority of lakes examined worldwide emit CO<sub>2sub> to the overlying atmosphere, through a process by which catchment-derived subsidies of terrigenous C, often in the form of dissolved organic carbon (DOC), augment within-lake CO<sub>2sub> production above the level consumed via photosynthesis. We show that shallow, macrophyte-rich lakes of the Mackenzie Delta, western Canadian Arctic, do not follow this pattern. These lakes are strong summertime CO<sub>2sub> absorbers, despite DOC concentrations at or above levels commonly shown to produce CO<sub>2sub> emission. Paradoxically, CO<sub>2sub> levels were lowest where DOC was greatest, in lakes which appear to be annual net CO<sub>2sub> absorbers, and have poor hydrologic connection to the terrestrial landscape. CO<sub>2sub> in these lakes is depleted by high macrophyte productivity, and although catchment-derived C subsidies are low, within-lake DOC generation appears to occur as a byproduct of macrophyte photosynthesis and evapoconcentration. Additionally, after accounting for DOC and macrophytes, lakes that were least connected to the larger terrestrial landscape remained weaker CO<sub>2sub> absorbers, suggesting that CO<sub>2sub> balance may also be affected by DOC quality, foodweb structure, or inputs of pCO<sub>2sub>-rich riverwater to connected lakes. In contrast, a small subset of Delta lakes that were strongly affected by permafrost melting were CO<sub>2sub> emitters, suggesting future permafrost degradation could engender a change in the overall CO<sub>2sub> balance of these lakes from near-CO<sub>2sub> neutral over the ice-free season, to clear CO<sub>2sub> emission. Our work suggests that the current paradigm of lakewater CO<sub>2sub> regulation may need to specifically incorporate shallow, productive lakes, and those that are poorly connected to their surrounding landscape.