Contrasting Patterns of CO2 Flux from Ponds, Rivers and Lakes of the Arctic Coastal Tundra.

Abstract:

Multiple lines of evidence indicate that small coastal watersheds in the Arctic are changing dramatically and may be substantial sources of carbon to the atmosphere and coastal waters. Recent findings have shown that small ponds and rivers in the Arctic Coastal Plain are substantial sources of CO₂ to the atmosphere, and that temperature and precipitation may drive CO₂ release from tundra ponds. However, it remains unknown whether these drivers are consistent across habitats and how the expansion of thermokarst ponds in permafrost regions may influence CO₂ balance. This study compares patterns and drivers of pCO₂ flux among low-gradient rivers, lakes, tundra ponds (formed through the seasonal thaw of the active layer within low-centered polygons), and thermokarst ponds (caused by abrupt thawing of ice-rich permafrost, and subsequent land subsidence and slumping). We present data from 2 lakes, 4 rivers, 1 pond and 1 thermokarst pond near Utqiaġvik, AK where CO₂ was monitored on a diel basis for at least 2 weeks during late summer of 2015-2019. We recorded substantial difference in pCO₂ among these 2 ecosystems, ranging from the lowest concentrations in lakes (368 ± 220 µatm), to rivers (1139 ± 147 µatm) and tundra ponds (1596 ± 911 µatm), and the highest concentrations in thermokarst ponds (8111 ± 213 µatm). While temperature appeared to have a positive effect on CO₂ concentration in ponds and lakes, rivers were more likely to see CO₂ decline with increased temperature. At lake and river sites, marked diurnal patterns of pCO₂ were observed with pCO₂ generally increasing as darkness falls and temperature declines; however, these trends were less strongly coupled for ponds, especially during mid-day, where the generalized pattern of uptake of CO2 during the day appears to be counterbalanced by some combination of factors resulting in CO2 production. This may include microbial respiration in the sediment, or some form of mineralization. Quantifying patterns and drivers ofCO₂ flux from these abundant aquatic ecosystems on the Arctic coastal tundra and elsewhere in the high northern latitudes will likely have important implications for furthering understanding of landscape-level and nearshore carbon dynamics in the Arctic.