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IDAS – GHG (Instrumental and Data-driven Approaches to Source-Partitioning of Greenhouse Gas Fluxes)

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Instrumental and Data-driven Approaches to Source-Partitioning of Greenhouse Gas Fluxes: Comparison, Combination, Advancement

The increase in global atmospheric CO2 concentration is caused by mankind’s burning of fossil fuels. The strength of this increase, however, cannot be directly derived from our annual CO2 emissions, and so neither its effect on climate. This is due to biosphere-atmosphere-interactions: With environmental conditions changed by mankind, plants and soils change the way they absorb, store and emit carbon. For example, increased CO2 concentration acts as a fertilizer for green plants in the presence of sufficient sunlight and other resources: Through accelerated growth, they withdraw more CO2 from the atmosphere than before, a process which has slowed down net CO2 increase considerably. Other compartments of vegetation, and the soils with their content of organic carbon and microorganisms feeding on it, however, emit more CO2 in a globally warmed atmosphere due to accelerated respiration. In order to understand these changes and predict the further development of the resulting net exchange, robust and simple means are required to quantify the simultaneous photosynthesis and respiration in different parts of a single ecosystem.

The project IDAS-GHG, funded by the German Federal Ministry of Education and Research (BMBF) and hosted at the Research Centre Jülich, aims at improving and facilitating the partitioning of existing greenhouse gas net exchange measurements on agricultural areas, forests and other ecosystems into different source and sink processes. Beyond CO2 exchange, this is also of interest in the context of evapotranspiration, which controls atmospheric concentrations of the greenhouse gas water vapour, and of the potent greenhouse gas nitrous oxide (N2O). Starting point of the project is a comparison between existing methods on common measurement sites. This includes amending stations with additional measurement instruments as well as testing methods for the analytical partitioning of already existing net exchange time series. Based on this, innovations of the most promising methods will be tested. Finally, the improved methodology will be used to assess the robustness of land use adaptations to climate change and their potential to mitigate this same climate change. Among more agriculture-focused experiments, this will include studying transient processes when coniferous is transformed to deciduous forest.

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The concentration (indicated by bubble size), correlation and isotopic signature of CO2 and water vapour at each height in the atmosphere are controlled by local sources and sinks (block arrows) as well as by turbulent exchange between heights (thin arrows). The latter provides evidence for these sources and sinks that can be detected by the sensors of an eddy-covariance station (EC), which is primarily intended for the measurement of land surface – atmosphere net exchange. This is one of the effects IDAS-GHG aims at utilizing. Further information can be acquired from chamber measurements, profile measurements at a high temporal resolution (P) and direct measurements of controlling environmental factors such as solar irradiation. (T: transpiration, E: evaporation, PP: primary production, R: respiration.

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Chamber (foreground) and Eddy-Covariance (background) measurements of net CO2 exchange and evapotranspiration in a wheat stand. In IDAS-GHG, such measurements will be analyzed, modified and extended towards a more accurate estimation of the contributions by soil and plants. These contributions to the net flux depend differently on environmental factors; knowledge on them is important to improve predictions of the net flux in future climates and CO2 concentrations. The project also intends to test management strategies that could improve the greenhouse gas balance, sustainability and climate tolerance of agriculture.

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Measuring next to each other on differently managed ecosystems having similar soils can help to compare the CO2 balance and climate effect of managements under well monitored conditions. Biosphere-atmosphere interactions of a spruce monoculture are assessed on the tower in the background. In the foreground, a station with identical equipment can be seen on an area where all conifers were cut and new deciduous trees are expected to grow between scattered existing ones. In the past, the focus on environmental impacts of such management was on biodiversity and water protection. Analyzing CO2 sinks and sources could help to include climate effects into their assessment and planning.



Contact:

Dr. Alexander Graf

Phone: +49-2461-618676

Fax: +49-2461-612518

E-mail: a.graf@fz-juelich.de


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