Browsing by Subject "kammiomittausmenetelmä"

Large amounts of carbon is stored in the soil and vegetation of the tundra ecosystem. Carbon dioxide is stored in the vegetation in photosynthesis and is released into atmosphere from the soil and vegetation in ecosystem respiration. Rising temperatures can cause considerable changes to the delicate tundra ecosystem and create new potential feedbacks to global warming as the environment changes. There are several factors regulating carbon dioxide fluxes and their interactions and temporal changes are not yet fully known. Understanding carbon dioxide fluxes and the factors contributing to them is important in order to study and predict temporal and local changes. This research focuses on describing changes in net ecosystem exchange, primary production, and ecosystem respiration in the tundra as well as the factors contributing to them. The measurements were made with the chamber method in Saana fell, Kilpisjärvi in Finnish Lapland. This study includes 14 nivations with a total of 84 study points that were measured three times during the growing season in the summer of 2019. In addition to flux the measurements, information about controlling environmental variables were collected. These included vegetation, air temperature, soil moisture and soil temperature. The impact of the explanatory variables on fluxes at different times in the growing season was studied using mixed effects model and an estimated carbon budget was calculated for the region. The largest fluxes were measured mid-July during the peak growing season. Ecosystem respiration and primary production declined from the peak of the growing season in August towards the end of the growing season, but net ecosystem exchange increased slightly due to imbalances in the other two fluxes. Vegetation was an important explanatory variable (p ≤ 0,001) in every flux and during different times of the growing season. Air temperature had the greatest impact on net ecosystem exchange and ecosystem respiration, but the intensity of its response varied during different periods of the growing season. In both of these fluxes, higher temperatures increased the flux into the atmosphere. In primary production, the response changed in the middle of the growing season from positive to negative due to high temperatures. Soil moisture had a positive effect especially on ecosystem respiration, but its significance varied during the growing season (p = 0,0012; 0,02; < 0,001) and the response increased towards the end of the growing season. Also in primary production, response intensity and significance (p = 0,02) increased at the end of the growing season and in net ecosystem exchange the response changed from negative to positive at the end of the growing season. The response of soil temperature increased with all fluxes from the beginning of the growing season and decreased with ecosystem respiration and net ecosystem exchange towards the end of the growing season. Soil temperature was only significant in the second measurement campaign for net ecosystem exchange (p = 0,01) and ecosystem respiration (p = 0,005). During the growing season, carbon dioxide fluxes changed considerably and their explanatory factors also varied in time. The responses to soil moisture and air temperatures also turned negative or positive during the growing season. These changes and studying them is very important to understanding the processes behind different fluxes. The change in carbon dioxide fluxes and the variables that affect them in the tundra environment affects the region's carbon budget.