Effect of macrophyte removal on CO2 emissions in the river Otra, Norway

Abstract

The main goal of this study is to examine how macrophyte removal affects CO2 emissions in rivers with a secondary aim of quantifying CO2 concentrations and emissions in the river over the course of 24 hours. The study was performed in river Otra in Norway which flows through the valley of Setesdalen. CO2 emissions were measured by floating chambers with infrared gas analyzers (IRGA) with logging abilities. The study uses before and after control impact (BACI) design. Large amounts of macrophytes (submerged growth of Juncus bulbosus) were removed between the 15th and 22nd of June 2020 from the impact site, but not from the control site. CO2 emissions and other measurements were done in both the control and the impact site before, during and after macrophyte removal. There were no significant differences in CO2 emissions between the Control and Impact site. Neither before, during nor after macrophyte removal. Even though there was a slight CO2 emission increase after removal it was probably due to factors like water-level, -velocity, and -temperature fluctuations. As secondary studies we also 1) measured CO2 emissions in the river every 2 hours for 24 hours, 2) measured the gas transfer velocity in the river. These studies helped us better understand the fluxes in the river.