Land-atmosphere exchange

Table 4 Primary processes controlling land-atmosphere exchange of gases...

Primary processes regulating land-atmosphere exchange (secondary) Availability of data and including models to calculate annual fluxes ... 

Land-atmosphere exchange processes include the evaporation of soil moisture, from the leaf surface, stems, and trunks of plants, as well as transpiration, precipitation, and evaporation olf the surface of unstable water accumulations low in the ground (Figure 4.11). The water flow from the soil through the plant is the least studied link in this chain. The importance of the process of transpiration in the global water cycle cam be judged from available estimates, according to which the process of... 

Bonan, G. B. (1995a). Land-atmosphere CO2 exchange simulated by a land surface process model coupled to an atmospheric general circulation model, j. Geophys. Res. 100,2817-2831. 

Biotic regulation in atmosphere-land C02 exchange in tropical rainforests that demonstrate a vast biodiversity of species is still poorly studied (Bampfylde et al., 2005). 

The surface s role in land-atmosphere water exchange deals with the subdivision of the phase space into at least two levels soil and ground water. The soil level plays the role of a buffer zone between precipitation and ground water. The simplest parameterization of fluxes between these levels is reduced to their linear dependences WsH(t,i,j) = XijWs(t,iJ) and wHS(t,i,j) = However, a more strict... 

Well, actually a lot is known about them, but they behave in a complicated way. Particulates over the ocean increase the albedos because the albedo of the ocean is only about 5%. Particulates over the land lead to warmth, because they in fact absorb and re-radiate radiation, and they reduce the albedo, they are less reflective than the land surface itself. So it is not by any means obvious that they would actually reduce the temperature. The other question about the airborne fraction, that depends on the rate of emission of CO2 and the airborne fraction of 0.4, or rather the amount going into the ocean is about 40%. Remember I said that the entire atmosphere exchanges with the ocean in about 7 or 8 years. 

Land net exchange of carbon between terrestrial ecosystems and the atmosphere... 

Box (1981) classified all of the different plant species into 16 different structural types (trees, small trees, etc.) and in turn into a total of 77 plant forms (e.g., evergreen tropical rainforest trees, mediterranean dwarf shrubs, etc.). This latter classification combines form, geographical distribution, and to a certain extent function (evergreen, deciduous, ephemeral). So fundamentally there are not too many different structural types of plants, as Theophrastus noted several millennia ago. These basic forms, when coalesced into communities, certainly have an influence on land surface/atmospheric models through turbulent transfer and boundary-layer effects that are often incorporated into atmospheric exchange models. 

The carbon cycle in seas involves the assimilation of carbon dioxide dissolved in sea water by the phytoplankton with a simultaneous oxygen release. Zooplankton and fish use this oxygen for the respiration. During the organic matter decomposition, CO2 is supplied into the atmosphere. On land, the exchange of carbon dioxide with the atmosphere is accomplished by respiration, photosynthesis and by the combustion of fossil fuels. 

The amount presented in the cycle has been rounded oflF to 30 tons/day. The rainwater running over land surface exchanges its mercury with that in soil and establishes an equilibrium before draining into creeks and rivers. About 20 tons/day in immediate runoff is considered adsorbed on suspended particles whereas 10 tons/day can be considered as dissolved (section on Alluvium and Internal Waterways). The immediate runoff partially evaporates, percolates, and exchanges its mercury with alluvium and atmospheric air. Any input of mercury into the internal waterways will be subject to the same line of action. The final... 

Fluvial and atmospheric transport links the coastal zone to the land gas exchange and deposition are its links with the atmosphere net advective transport of water, dissolved solids and particles, and coastal upwelling connect it with the open ocean. In addition, coastal marine sediments are repositories for much of the material delivered to the coastal zone. In the last several centuries, human activities on land have become a geologically important agent affecting the land-sea exchange of materials. In particular, river and groundwater flows and atmospheric... 

The cycles of carbon and the other main plant nutrients are coupled in a fundamental way by the involvement of these elements in photosynthetic assimilation and plant growth. Redfield (1934) and several others have shown that there are approximately constant proportions of C, N, S, and P in marine plankton and land plants ("Redfield ratios") see Chapter 10. This implies that the exchange flux of one of these elements between the biota reservoir and the atmosphere - or ocean - must be strongly influenced by the flux of the others. 

Rainwater and snowmelt water are primary factors determining the very nature of the terrestrial carbon cycle, with photosynthesis acting as the primary exchange mechanism from the atmosphere. Bicarbonate is the most prevalent ion in natural surface waters (rivers and lakes), which are extremely important in the carbon cycle, accoxmting for 90% of the carbon flux between the land surface and oceans (Holmen, Chapter 11). In addition, bicarbonate is a major component of soil water and a contributor to its natural acid-base balance. The carbonate equilibrium controls the pH of most natural waters, and high concentrations of bicarbonate provide a pH buffer in many systems. Other acid-base reactions (discussed in Chapter 16), particularly in the atmosphere, also influence pH (in both natural and polluted systems) but are generally less important than the carbonate system on a global basis. 

Large amounts of carbon are found in the terrestrial ecosystems and there is a rapid exchange of carbon between the atmosphere, terrestrial biota, and soils. The complexity of the terrestrial ecosystems makes any description of their role in the carbon cycle a crude simplification and we shall only review some of the most important aspects of organic carbon on land. Inventories of the total biomass of terrestrial ecosystems have been made by several researchers, a survey of these is given by Ajtay etal.(1979). 

Denning, A. S., Fung, I. Y. and Randall, D. A. (1995). Latitudinal gradient of atmospheric CO2 due to seasonal exchange with land biota. Nature 376, 240-243. 

Keeling, C. D. (1973a). The carbon dioxide cycle. Reservoir models to depict the exchange of atmospheric carbon dioxide with the oceans and land plants. In "Chemistry of the Lower Atmosphere" (S. Rasool, ed.), pp. 251-329. Plenum Press, New York. 

Knorr, W. and Heimann, M. (1995). Impact of drought stress and other factors on seasonal land biosphere CO2 exchange studied through an atmospheric tracer transport model, Tellus, Ser. B, 47, 471-489. 

Nemry, B., Francois, L., Warnant, P., Robinet, R. and Gerard, J.-C. (1996). The seasonality of the CO2 exchange between the atmosphere and the land biosphere A study with a global mechanistic vegetation model, /. Geophys. Res. 101, 7111-7125. 

Exchange rates of mercury between the atmosphere and the land and between the atmosphere and the ocean are much greater... 

While the natural exchange of mercury between the land and atmosphere and the atmosphere and oceans is balanced, human activity has tipped this balance. There is now about three times more mercury in the atmosphere and fluxes of more than four times to and from the atmosphere. 

The major function of cutin is to serve as the structural component of the outer barrier of plants. As the major component of the cuticle it plays a major role in the interaction of the plant with its environment. Development of the cuticle is thought to be responsible for the ability of plants to move onto land where the cuticle limits diffusion of moisture and thus prevents desiccation [141]. The plant cuticle controls the exchange of matter between leaf and atmosphere. The transport properties of the cuticle strongly influences the loss of water and solutes from the leaf interior as well as uptake of nonvolatile chemicals from the atmosphere to the leaf surface. In the absence of stomata the cuticle controls gas exchange. The cuticle as a transport-limiting barrier is important in its physiological and ecological functions. The diffusion across plant cuticle follows basic laws of passive diffusion across lipophylic membranes [142]. Isolated cuticular membranes have been used to study this permeability and the results obtained appear to be valid... 

The study of the low atmosphere (including land and ocean exchanges with or through the atmosphere) which is the supply of most material found in the stratosphere. 

Unfortunately, due to the global and poorly studied character of correlation between climate change and vegetation cover behavior (forest ecosystems, in particular), at present there are no reliable estimates of the climate change consequences for their productivity. The problems arising here are just beginning to be studied. This especially refers to the boreal forests that cover 15% of the land area (75% of them are in Eurasia, mainly in Russia). It is in these forests that the intensive gas and heat exchange with the atmosphere takes place. 

The complex of feedbacks controls interactive exchange with energy, water, and carbon between the atmosphere and the Earth s surface causing a response of these fluxes to disturbances such as transformation of land cover or pollution of the World Ocean with oil. Substantial feedbacks are physiological responses of vegetation communities to changes in temperature and humidity of the atmosphere and soil. 

---