Epsilon Archive for Student Projects

Abstract

Though there is an innumerable amount of freshwater systems, they cover just a small fraction of the Earth's surface area and have been mostly disregarded as an important quantitative element in the carbon cycle on regional or global scales. Recently several studies showed the importance of freshwater systems as a significant source of carbon dioxide (CO2) emissions. Global estimates show that the amount of carbon (C) exported from terrestrial environments to aquatic systems is on par with the terrestrial uptake of CO2 via photosynthesis. About half of this C that is exported to aquatic inland ecosys-tems is transferred back to the atmosphere via outgassing. Most studies have been fo-cused on either lentic or lotic ecosystems and disregarded the connectivity between streams and lakes. This study aims to quantify carbon emissions from a small boreal catchment area in central Sweden. Automatic floating chambers were placed on lake Gäddtjärn, and its connecting streams to measure the CO2 flux rates. Furthermore the small scale spatial variability of the partial pressure of CO2 (pCO2) and CO2 emission rates along the streams were analysed, results of the lake and its connecting streams have been compared, and the suitability of automatic chambers for CO2 flux measurements and data reproducibility was tested.
The results showed that all sampling sites across the lake and along the streams were supersaturated in pCO2 with respect to the atmosphere. Stream pCO2 was largely influ-enced by the processes in the lake Gäddtjärn and an upstream wetland. However, the high pCO2 decreased over a small distance due to the fast process of CO2 outgassing. Spatial variability of stream CO2 emission rates was highly controlled by the gas transfer veloci-ties which were positively correlated to the turbulence conditions. Average pCO2 was similar for lake and streams and in agreement with findings from other studies. Lake CO2 emission rates were usually lower than stream CO2 emission rates as a consequence of lower gas transfer velocities.
Findings of this study show that automatic floating chambers are suitable for analyzing CO2 emissions on lakes, but stream CO2 emissions seem to be underestimated as a reason of technical (sensor response time) and practical (placement of chambers in turbulent conditions) limitations.