YEAR-ROUND DETERMINATION OF METHANE (CH4) SOURCES AND SINKS IN ARCTIC LAKES USING CONTINUOUS AND AUTONOMOUS SAMPLING

• Main Author: McIntosh Marcek, Hadley
• Other Authors: Lapham, Laura L, Digital Repository at the University of Maryland, University of Maryland (College Park, Md.), Marine-Estuarine-Environmental Sciences
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: 2020
• Subjects: Geochemistry; Chemical oceanography; Diffusion; Lakes; Mackenzie Delta; Methane; OsmoSampler; Radiocarbon; Arctic
• Online Access: http://hdl.handle.net/1903/26266; https://doi.org/10.13016/luol-c9hv

Methane (CH4) is a potent greenhouse gas and its concentration has been increasing in the atmosphere. While natural emissions from inland water bodies are known to be important, there is large uncertainty in the amount of methane released from lakes to the atmosphere, especially from Northern latitudes. Part of this is due to limited sampling in these systems during dynamic periods, such as ice-over and ice-melt. To better understand these temporal dynamics, I used autonomous, continuous samplers (OsmoSamplers) to collect lake water year-round over two years (2015-2017). Lake water was collected at a fine temporal resolution to provide time-integrated (~1 week) samples from multiple Arctic lakes within the Mackenzie Delta. The Mackenzie Delta is a lake-rich, productive environment that is expected to be a significant source of methane to the atmosphere. Lakes spanning the central delta and outer delta were sampled for methane concentration and stable carbon isotope ratio (δ13C-CH4) changes, ion concentrations, and water column characteristics were measured with continuous sensor data (temperature, water pressure, conductivity, light, and dissolved oxygen). These unique time-series datasets show lakes exhibit a close coupling of dissolved oxygen, and other electron acceptors, with the timing of methane increasing during ice-cover. The increase in methane concentrations is primarily from diffusion out of sediments and possibly water-column methanogenesis. One lake in the outer delta exhibited thermogenic gas bubble dissolution that contributed to under-ice methane concentration increases. Following ice-melt, lake depth appears to impact methane release to the atmosphere. Shallower lakes exhibit rapid fluxes followed by significant microbial methanotrophy. Deeper lakes in the central delta are connected to groundwater, though it does not appear groundwater transports methane. This is the first study of dissolved methane and gas bubble 14C-age in the Mackenzie Delta and shows that dissolved methane is produced ...