What are the Major Bottlenecks in the Understanding of the Freshwater-atmosphere Interactions ?

Abstract:

In the boreal zone lakes cover on average 7 % of land area, and furthermore in some parts in Finland and northern Canada they occupy up to 20 % and 30 % of the landscape. Many of the water bodies are small. The arctic tundra is similarly occupied by numerous small ponds, the response of which to high-latitude warming and the resulting changes in CO₂ and CH₄ effluxes is very uncertain. The present outgassing estimates are still provisional and probably underestimated. The eddy covariance (EC) technique would be an indispensable tool for directly assessing the fluxes from lakes, rather than using chambers, although there is the expectation that agreement between methods can be found with appropriate chamber design.

The influence of energy and mass fluxes from lakes and other water bodies on atmospheric circulation and climate may be considered as a three-step chain of processes. First, coupled thermo-, hydrodynamics and biogeochemistry of “lake-sediments” system produces energy source/sink and a source of greenhouse gases for the atmosphere. Second, the structure and dynamics of Atmospheric Boundary-Layer (ABL) creates conditions for the rate of energy and mass transfer between the hydrologically heterogeneous surface and the atmosphere. Finally, the mesoscale dynamics of atmosphere is likely to cause upscale propagation of energy and tracers emitted from the heterogeneous surface towards synoptic scales. The interaction of these scales is still poorly understood, and modelling approach involving high resolution spatial grids and process-based formulations can give much insight in the problem and bring a new knowledge of the physical mechanisms involved.

The crucial questions are the following: What are the ultimate processes determining the gas exchange between lakes and rivers and the atmosphere? What are the site specific factors and do small lakes differ from large lakes? To what extent the gas exchange on rivers is similar to lakes? How much information we can deduce from flux measurements above the surface and what is the crucial information required from the water-side? What are the major features and how to assess multiscale gas and energy transfer in the ABL over hydrologically heterogeneous land?