Theme 1: Understanding the dynamic processes determining the interaction between land, ecosystem and atmosphere in the human-Earth system

Theme 1 contains the different categories of processes involved in the land – ecosystem –atmosphere interaction which can be summarized in two foci of which the first focus is on distribution, sources and sinks and the second on processes, observations and models.

The land-atmosphere exchange, its distribution, sources and sinks, includes the exchange of greenhouse gases, oxidants and aerosol particles and its precursors between land, ecosystems and atmosphere influencing the atmospheric composition. This component feedback influencing the ecosystems directly and indirectly through climate. Industrial and urban emissions have reached such amounts that it actually changed the atmospheric global burden, e.g. the atmospheric fine aerosol mass has increased by about 50% (Andreae and Rosenfeld, 2008). Biomass combustion alone contributes with about 10% of this increase. These strong changes in emissions affect the chemistry of the atmosphere, its oxidation capacity, its ability to process the emitted substances. That means that the biogeochemical cycle of many critical elements (such as N, C, P and others) are significantly affected.

Observations of the ecosystem-atmosphere exchange, in the laboratory and field, is crucial in developing theory and models. The exchange is depending on the characteristics and processes in the ecosystem and the atmosphere, respectively, thus modeling the exchange is quite complex and still it is just a part of the Earth System forming an even more complex structure of processes and properties. To facilitate an as thorough evaluation as possible of a model securing a correct understanding of the key processes the observations has to be on many of the levels in the hierarchy of processes of which the models are built. This calls for comprehensive long term measurements including ecosystem parameters, meteorology, gas and particle components, clouds and boundary layer processes (Figure 1). To this should be added the influence of anthropogenic emissions influencing the atmospheric composition and properties that in turn affect the land ecosystem, e.g. ozone induced changes in photosynthesis.

Figure 1. Schematic of land ecosystem – atmosphere interactions and hierarchical observation levels that include basic, advanced and comprehensive measurements at flagship sites. Adapted from Guenther et al., 2011.


iLEAPS foci, activities, and top priorities for Theme 1