THERMODYNAMIC ANALYSIS OF BOREAL ECOSYSTEM
R. Sandlerskiy, Yu.G.Puzachenko
A.N. Severtsov Institute of Ecology and Evolution RAS
119071, Moscow, Leninsky prospect 33, Russia
e-mail: [email protected], [email protected]
Transformation of matter and energy in plant associations and their relationship with other
parts of the ecosystem are being determined by the physiological processes in plants. Accordingly,
to identify general patterns of ecosystem energy transformation, assessment of an energy balance
components reflecting the nature of physiological processes: photosynthesis, transpiration (of which
carbon balance is evaluated), water and minerals exchange, is required.
Assessment of the main energy variables for ecosystems is possible on the basis of
information-thermodynamic approach in which the ecosystem – is an open system, producing yield
for self-maintenance on its structure through the conversion of solar energy. In doing so, the
distribution of energy absorbed by balance components depends on the structure of the system that
determines the nonequilibrium energy conversion. In the information -thermodynamic approach
essential component in the transformation of solar energy is exergy - the maximum work that a
thermodynamic system may commit during its transition from the current state to the state of
equilibrium with the environment (Jorgensen, Svirezhev, 2004). Exergy sometimes called system
yield, it is the function of the distance between the current state of the system and thermodynamic
equilibrium. Relating to ecosystems, exergy – part of absorbed solar energy, spend on biological
productivity and evapotranspiration. The rest goes into the bound energy – energy transition in the
heat flow and entropy, and in increment of internal energy – system energy accumulation wich in its
turn spend on maintenance of intercomponent and interspecific interactions, local cycles.
Get estimation of energy balance for the entire set of ecosystems based on ground-based
measurements is virtually impossible. Such assessments are possible on the basis of remote sensing
data, which show the energetic state of the Earth's surface at the time of shooting in different
spectral bands. Satellite measurements of reflected solar energy in relation to the solar constant
allow the calculation of solar radiation absorbed per unit surface. Heat channel allows to calculate
the heat flow from the surface and its temperature. The development of remote sensing and
instrument base allows to measure a wide range of ecosystems characteristics: measurements are
preformed directly in the field on transects with the regular testing step, and through remote sensing
and digital models of different relief. Ultimately, the combination of complex ground and remote
measurements in the study of energy balance should promote understanding of the interaction
mechanism between relief, soil, vegetation and atmosphere at various hierarchical levels of the
landscape cover and create a basis for the development of models describing mesoclimate, as a
result of landscape functioning and self-evolution.
The presented approach and implemented a set of measurements for the territory of Central
Forest Biosphere Reserve and its conservation zone – 32° 53 'E, 56° 46' N latitude. The landscape
properties are in many respects unique (moraine ridge height with boreal spruce and complex
spruce forest in a combination with bogs, windfalls, cutover patches and fields), create a basis for
comparison of properties of various types of a surface and their territorial combinations.
The method of reflected solar energy estimation through Landsat satellite is described in the
relevant manuals (Landsat 7 Science Data Users Handbook): values of this band are recalculated in
reflected energy (watt/m2) flow, energy absorption value is the difference between inbound and
reflected energy. On the basis of 6th band the heat flow is calculated (watt/m2) and active surface
temperature (C). Calculation of energy characteristics of the territory conducted by the method
proposed by S. E. Jorgensen and Y. M. Svirezhev (2004). Measurement of exergy on the basis of
remote sensing data carried out through assessment of distance between the real distribution of
energy absorption of solar energy and equilibrium state, with a hypothetical absorption of solar
energy in proportion to the distribution of energy in the spectrum of solar constant. The degree of
reality deviation from the equilibrium absorption spectrum is evaluated as Kulbak’s entropy (a
measure of differences of two distributions and the parameter of open nonequilibrium
thermodynamic systems). Bound energy is calculated as the product of heat flow and entropy of
reflected solar energy. Internal energy is estimated as absorbed energy minus exergy and bound
energy. To assess the expenditure of energy used on biological production NDVI index was used.
Thus for the studied territory through Landsat data with a spatial resolution of 28.5 m, for the five
dates (March, April, May, June, September) computed following energy characteristics: the
incoming solar energy, reflected solar energy, absorbed energy (radiation balance), albedo, entropy,
exergy, entropy of reflected solar energy, heat flow and temperature of active surface, bound
energy, internal energy delta, the index of productivity. For the analysis of the spatial variation of
energy parameters their average values was calculated for flowing generalized landcover types:
coniferous forests, deciduous forests, windfalls, meadows and agricultural land, high moors, and
small man-made ponds (benchmarks maximum of solar energy absorption).
In general, analysis of the thermodynamic variables for different types of ecosystems shows
that the flow of energy absorbed by surface, is redistributed to several different mechanisms and
this redeployment depends on the structure of the system, which expressed through nonequilibrium. A nonequilibrium conversion of solar energy in the first place determines the
expenditure of energy on the biological production and has a little impact on exergy – the cost of
energy for evaporation.
Based on the method of principal components invariance of energy conversion by a landscape
in general and generalized types of ecosystems is evaluated. Revealed energy variables with
minimal variation in time, the maintenance of which can be defined as a target function of
ecosystem energy conversion, for studied territory they are: energy absorption, exergy and heat
flow. The ability to maintain basic invariants forms a regular range, which repeat the succession:
"meadows – windfalls – deciduous forests – coniferous forests". Man-made objects – resident lands
and roads have the lowest autoregulation ability. In contrast to the forest and grassland complexes,
for the high moors internal and bound energy, heat flow and biological production are the most
invariant. Bogs in contrast to the forest, carrying out moisture transportation from the soil into the
atmosphere, holding the high-heating level and conserve precipitation in a groundwater, while
maintaining the level of biological production, comparable to coniferous forests. Thus the nature
and efficiency of energy conversion by a landscape cover is determined by its internal structure
changing in the course of it self-development and succession shifts. On average invariant value
assessed scale of regulation of heat flow through energy expenditure on evaporation, almost
proportional to exergy in the vegetation season. Coniferous Forest in comparison to pravifoliate
decrease temperature by 1°C, relative to windfalls- nearly 2oC, and in relation to the treeless spaces
– at 4oC, marshes are warmer than coniferous forests at an average of 4.8oC.
Thus, the analysis of satellite imagery on the basis of thermodynamic approach allows
evaluating of the main features of a landscape thermodynamic variables spatial and temporal
variation and their functional relationship, depended on the individual properties of the ecosystem.
Research performed with financial support RFBR – projects № 06-05-64937, № 07-05-12021,
as well as in the program of fundamental research, Russian Academy of Sciences "Biodiversity and
the dynamics of gene pools", subprogram "Biodiversity "(№ 5.1.2).
References
1. Jorgensen S.E., Svirezhev Y.M. 2004. Towards a Thermodynamic Theory for Ecological
Systems. Langford Lane Kidlington. Oxford. Elsevier. 369 p
2. Landsat 7 Science Data Users Handbook / / http://ltpwww.gsfc.nasa.gov
3. Vernadsky V.I. 2004. Biosphere and Noosfere. Metro: Iris Press. 576 p. (in russian)
4. Sukachev V.N., Dylis N.V. 1964. Fundamentals of forest biogeocenology. Moscow:
Science. 574 p. (in russian)