Implications of river intrusion and convective mixing on the spatial and temporal variability of under-ice CO2

• Published in: Inland waters (Print) 2019-04, Vol.9 (2), p.162-176
• Main Authors: Pasche, Natacha, Hofmann, Hilmar, Bouffard, Damien, Schubert, Carsten J., Lozovik, Petr A., Sobek, Sebastian
• Format: Article
• Language: English
• Subjects: Carbon dioxide; convective mixing; Freshwater; Greenhouse effect; humic lake; Ice conditions; Ice cover; Ice thickness; Ice-water interface; Lakes; Physical limnology; river intrusion; spatial distribution; under-ice
• ISSN: 2044-2041; 2044-205X
• DOI: 10.1080/20442041.2019.1568073

Ice-covered periods might significantly contribute to lake emissions at ice-melt, yet a comprehensive understanding of under-ice carbon dioxide (CO 2 ) dynamics is still lacking. This study investigated the processes driving spatiotemporal patterns of under-ice CO 2 in large Lake Onego. In March 2015 and 2016, under-ice CO 2 , dissolved inorganic carbon (DIC), and dissolved organic carbon (DOC) distributions were measured along a river to an open-lake transect. CO 2 decreased from 120/129 μmol L −1 in the river to 51/98 μmol L −1 in the bay, and 34/36 μmol L −1 in the open lake, while DOC decreased from 1.18/1.55 mmol L −1 in the river to 0.67/1.04 mmol L −1 in the bay in 2015 and 2016, respectively. These decreases in concentrations with increasing distance from the river mouth indicate that river discharge modulates spatial patterns of under-ice CO 2 . The variability between the 2 years was mainly driven by river discharge and ice transparency affecting the extent of under-ice convection. Higher discharge during winter 2016 resulted in higher CO 2 concentrations in the bay. By contrast, intensive under-ice convection led to lower, more homogeneously distributed CO 2 in 2015. In conclusion, the river-to-bay transition zone is characterized by strong CO 2 variability and is therefore an important zone to consider when assessing the CO 2 budget of large lakes.