Utvärdering av koldioxidmätaren Vaisala GMP343 samt sambandet mellan grundvattennivå och koldioxidavgång från torvjordar

Abstract: The research group Soil and Water Management at the department of Soil and Environment at theSwedish University of Agricultural Sciences in Uppsala are studying greenhouse gas emissions fromcultivated peat soils. To measure carbon dioxide emissions from peat soils in the field the researchgroup are now using two portable carbon dioxide meters (Vaisala GMP343). For practical reasons,they plan to acquire a new type of automated field meter. The aim of this study is to evaluate thepresent meters to see how environmental conditions and instrument settings affect the results,which is meant to facilitate the introduction of the new field meter when the meters needs to becompared. As a part of the study the relationship between groundwater level and carbon dioxideemissions from peat soils will be investigated.The evaluation of the two carbon dioxide meters was made by connecting them to one single airtightsystem, with the aim of creating identical measurement environments. Various factors such aswarm-up time and flow rate was tested to see how they affect the results, and to see if there are anydisparities between the meters. The relationship between groundwater level and carbon dioxideemission was investigated by adjusting the groundwater level in three different peat soil profilesfrom Örke in Sweden (60 ° N, 17 ° E) in a temperature regulated laboratory. The carbon dioxideemissions from the profiles were measured using a Vaisala GMP343 carbon dioxide meter atgroundwater levels 0, -5, -20, -30 and -40 cm.The results from the evaluation of the carbon dioxide emission meters show that there are somedifferences between the meters that needs to be taken into account when measurements are made.The most important discovery is that the two meters registers different carbon dioxideconcentrations, and that the difference between them is not constant at different concentrations.The observed difference can introduce systematic errors when both meters are used in the sameexperiment, errors that may result in erroneous conclusions when the research group investigatehow different treatments of peat soils affects carbon dioxide emissions. The results frominvestigating the relationship between groundwater level and carbon dioxide emission show thatthere is an obvious positive correlation between the two. Carbon dioxide emissions was largest atthe groundwater level of -40 cm and then declined to an average of 43% and 12% at levels of -20 and-5 cm respectively. The optimal groundwater level to minimize carbon dioxide emissions was 0 and -5 cm.