Exchange between Atmosphere and Biota

This flow, SAB, is a sum of the following flows:

1. entropy flow caused by diffusion of CO2 through stomata into leaves, SAB(CO2);

2. entropy flow caused by diffusion of O2 through stomata into the atmosphere, SBA(O2); and

3. entropy flow caused by the transpiration of water, Sba(H2O).

The first and second flows are defined as S_ab(CO)2) = s(CO2)ab ? MCO2) and Sba(O2) = -s(O2)-?ba(O2), where ?ab(CO2) = NPP[gC] • (44/ 12) = (6.6 x 1016gC)(44/12) = 2.42 x 1017gCO2yr-1 and qBA(O2) = -(6.6 x 1016gC)(32/12) = -1.76 x 1017gO2yr-1 are the rates of consumption and release of carbon dioxide and oxygen by plants in the process of photosynthesis. The specific entropies are: s(CO2) = 4.86J K- g-and s(O2) = 6.41 J K-1 g-1. Then SAB(CO2) = 1.18 x 1018J K-1 yr-1 and SBA(O2) = -1.13 x 1018JK-1 yr-1. The summation of these flows gives SAB(CO2) + S_BA(O2) = (1.18 - 1.13) x 1018 = 5 x 1016J K-1 yr-1, that is, the exchange flows of entropy related to CO2 and O2 are almost balanced by each other, so that their sum is reduced by two orders of magnitude.

The entropy flow SBA(H2O) = s(WV) • qBA(H2O), where qBA(H2O) = -qHB(H2O) = -4.8 x 1019g H2Oyr-1 is the annual transpiration through stomata (we assume that all consumed water is transpired), and s(WV) is the specific entropy of water vapor at TB = 288 K and 1 atm. We see that maximal entropy flows are associated with water in liquid and vapor forms, that is, with the global water cycle. Their total balance

¿(H2O) = ¿hb + ¿ba(H2O)= ?ba(^OH^/TO, where hev = 2462 J per g H2O is the specific enthalpy of evaporation, and is equal to a jump of entropy caused by the phase transition 'liquid water! water vapor', ¿(H2O) = -4.1 x 1020JK-1yr-1.

The internal production of entropy, SB, can be represented as a sum of two terms: ¿B = ¿DOM + ¿Work. The first is mainly connected with chemical reactions forming structural molecules of biomass (cellulose, proteins, carbohydrates, lipids, etc.). Organic compounds containing phosphorus take an active part in such type of reactions. All these processes are associated mainly with the carbon, nitrogen, and phosphorus biochemical cycles, the entropy flows of which are less than in the water cycle approximately by two (and less) orders of magnitude. Certainly, knowing the chemical composition of living matter, we can calculate its chemical entropy as a sum of corresponding specific entropies weighted proportionally to their percentages. However, since the dead matter has the same composition, then the specific chemical entropies of living and dead matter do not differ from each other. Hence, we can assume that the processes of forming of the new biomass and falling off the DOM with respect to their chemical composition are mutually reversible, that is,

The second term, ¿W°rk, is the entropy produced by the biota during its working cycle (see details below).

By summing all these flows, we get d^s/dz « [(0.53-4.11) x 1020

that is, from the thermodynamic point of view, biota is a strongly nonequilibrium system. The structure of the exchange entropic flows for the biota is shown in Figure 2.

If we compare deSB/dt 3.57 x 10 JK- yr- and deSc/dt9.41 x 1021J K-1yr-1, then it is easy to see that these values differ by 26 times. Even if we take into account that in the case of biota we deal with the land area

(covered by vegetation), which is less by almost fivefolds than the globe area, then we have almost five-multiple excess. Nevertheless, if we now compare the biota and the Earth's surface with respect to the energy obtained (the first obtains less than 1% in comparison with the second), then we can conclude that the biota is one of the main actors on the entropic scene.

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