lost work in an ecosystem used as an environmental impact index

ESDA2008-59441

Lost Work in an Ecosystem Used as an Environmental Impact Index

Sosimo E. Diaz-Mendez [email protected]

Mechanical Engineering Department Universidad de Guanajuato

Tampico 912, Col. Bellavista, C.P. 36730, Salamanca, Guanajuato, Mexico

Jose Maria Rodriguez-Lelis [email protected]

Mechanical Engineering Department Centro Nacional de Investigacion y Desarrollo Tecnologico

Interior Internado Palmira S/N, C.P. 62490, Cuernavaca, Morelos, Mexico

Abel Hernandez-Guerrero [email protected]

Mechanical Engineering Department Universidad de Guanajuato

Tampico 912, Col. Bellavista, C.P. 36730, Salamanca, Guanajuato, Mexico

Rosa Hilda Chavez [email protected]

Gerencia de Ciencias Ambientales Instituto Nacional de Investigaciones Nucleares

Carretera México – Toluca S/N, C.P. 52750, La Marquesa, Ocoyoacac, Salazar, Estado de México, México

Proceedings of the 9th Biennial ASME Conference on Engineering Systems Design and Analysis ESDA2008

July 7-9, 2008, Haifa, Israel

ABSTRACT

The work that an ecosystem can carry out decreases as a function of lost work, when some natural or anthropogenic alterations exist; the extinction of the ecosystem depends on how much lost work it can support. Lost work assessment in an ecosystem can be determined and then used as an indicator of the environmental impact. If the ecosystem is divided in subsystems and each subsystem is interrelated with the other ones, an ideal work can be obtained to revoke all the damage from each alteration in the ecosystem (being the subsystems the water, the soil, the atmosphere, the organisms and the society). Thus, the global index could be determined by adding the partial indexing of each subsystem, and could be used to determine the trend that an ecosystem will follow due to alterations.

1. INTRODUCTION

The resources in the environment are important for the organisms inside an ecosystem, because they offer wellbeing those are important for the life in the planet [1]; they also offer services that are linked to the regulation of the conditions of the environment.

The maximum exergy principle [2], the maximum power principle [3] and the maximum ascendency principle [4] are used to explain the thermodynamic behavior of the ecosystem and the interdependence between organisms. In an ecosystem in pristine state, the matter and energy that flows between each entity remain almost in a balance state, stable or in harmony,

1

and also the entropy generation does not vary drastically in a large period.

The entropy generation, the matter and energy flows vary quickly when man breaks up the harmony of the ecosystem with his excessive industrial activity and loose control [5-6]. The ecosystems have a limit of adaptation to assimilate lost work; this limit of adaptation can end up being surpassed with an abrupt change. If with time the lost work increases, then the overall damages on the ecosystem place all the organisms inside this ecosystem in extinction danger, this is because a strong interdependence exists between the organisms that compose an ecosystem like Salomonsen [7], Jørgensen [8-9] and Vallino [10] show.

The Pollution Potential [11-12], Environment Negative Effect, ENE [13], Environment Negative Effect Factor, ENEF [14], and Exergy Destruction [15], are works based in exergy that are used to determine the impact that society has on the ecosystems. These works are a good approach to estimate the quantity of energy resources, at least ideally, that is needed to revoke a change in the ecosystem and to return it to its pristine state, but most of these works are only applied to one part of the ecosystems and they do not relate the other parts that exist in the ecosystem (being the parts of an ecosystem dilutes, floor, air, biota and society [16].)

In this work it is believed that the exergy destruction can be referred to the lost work as it is defined by the theorem of Gouy-Stodola [17], because the exergy destruction should vary in function of the dead state. Thus, each part of an ecosystem tries to process the pollutants and to absorb them,

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but its capacity to carry out work decreases and it is transmitted to the following parts of the ecosystem or of another ecosystem, thus increasing the entropy generation to the inherent entropy already produced by the pollutants emitted. At the end, with reference to the dead state and according to the interrelation between species [7-9], the quantity of available energy and resources that the organisms can use are destroyed when the lost work from a part of an ecosystem to other or between ecosystems is added.

Thus, from the emission of pollutants from the society towards an ecosystem, the way in how the available energy decreases it can be studied. Next the procedure is shown. 2. INTERRELATIONS IN AN ECOSYSTEM

The polluting emissions that correspond to the emission from society can perturb a group of ecosystems interrelated between them, due to the fact that all elements on Earth have a strong interrelation with each other. Thus the damage of an element reflects in the whole ecosystem, but a true relationship explaining how every element affects the others, and vice versa, is not fully understood.

Figure 1. Ecosystem parts in mutual interactions. Wall [18] divides the biosphere in five different spheres,

and describes systems involving many kinds of matter in a complex pattern. Energy and matter permanently flow through different systems on the earth’s surface.

Following Wall’s work, Figure 1 it presented as a proposal of the interactions between the parts of an ecosystem on earth.

In Figure 1 S represent society, A the surrounding atmosphere, L the soil, B the organisms, H represent the water and each arrow represents flows of matter and energy.

Using Figure 1, as an example, fossil fuels are extracted then used by the society in different application mainly in combustion. Part of flue gases emitted to the surrounding can be processed by the atmosphere, the rest is sent to other parts of the ecosystem, each part carrying out the same process having always an intrinsic interaction.

Therefore, to determine if the pollutants emitted the society perturb or damage the surroundings, it is necessary to have an indicator of the environmental impact for each part of the ecosystem.

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3. THE ENVIRONMENTAL IMPACT INDEX BASED ON LOST WORK. 3.1 The extended lost work and the environment

The ecosystem in the pristine state has a useful work, Wu,e, which is important for the organism, i.e. clean water, clear air, oxygen, etc. It can be expressed as:

egereveu STWW

,00,, ⎟

⎠⎞

⎜⎝⎛−=

•

(1)

at that time the lost work is:

egelost STW

,00, ⎟

⎠⎞

⎜⎝⎛=

•

(2)

When human activity takes place and it is not in harmony

with the ecosystem, it modifies the ecosystem’s condition. The amount of total useful work changes as,

eg

egereveu STSTWW

,10

,00,, ⎟

⎠⎞

⎜⎝⎛−⎟

⎠⎞

⎜⎝⎛−=

••

(3)

and

eg

egelost STSTW

,10

,00, ⎟

⎠⎞

⎜⎝⎛+⎟

⎠⎞

⎜⎝⎛=

••

For the following cycles there is not a machine or system that removes the lost work then the lost work increases for the following cycles and the work will be:

(4)

eg

eg

egereveu

ST

STSTWW

,20

,10

,00,,

...

...

⎟⎠⎞

⎜⎝⎛

−⎟⎠⎞

⎜⎝⎛−⎟

⎠⎞

⎜⎝⎛−=

•

••

(5)

Thus for n cycles Eq. (5) may be written as:

eig

n

iegereveu STSTWW

,0

1,00,, ⎟

⎠⎞

⎜⎝⎛∑−⎟

⎠⎞

⎜⎝⎛−=

•

=

•

(6)

It is seen from Eq. (6), that the work decreases as the lost

work increases:

eip

n

iepelost STSTW

,0

1,00, ⎟

⎠⎞

⎜⎝⎛∑+⎟

⎠⎞

⎜⎝⎛=

•

=

•

(7)

The total work in the environment can be seen as the sum

of the partial work that each part of the ecosystem carries out. The water, the soil, the atmosphere, the organisms and the society are the parts of the ecosystem. The total work can be expressed as:


SuLuBuHuAueu WWWWWW ,,,,,, ++++= (8)

For the atmosphere, A, has its own useful work, and its

entropy generation is expressed as:

Aig

n

iAgArevAu STSTWW

,0

1,00,, ⎟

⎠⎞

⎜⎝⎛∑−⎟

⎠⎞

⎜⎝⎛−=

•

=

•

(9)

and

Aip

n

iApAlost STSTW

,0

1,00, ⎟

⎠⎞

⎜⎝⎛∑+⎟

⎠⎞

⎜⎝⎛=

•

=

•

(10)

In the same way one equation can represent the useful

work for the other parts in the ecosystem. Referring to an ecosystem in the former discussion and

from the point of view of the society, part of the lost work from society will go through natural machines that can revert partially the pollutant’s effects. However, they also produce some entropy and the sum of the lost work for each natural machine will be transmitted to each other and decrease the ability of the ecosystem to produce work. In this form the ecosystem is unsustainable.

3.1 Environmental impact index

Starting from the concept of exergy of mixing [11, 17], the minimum ideal thermodynamic work per mole, required for complete separation or combination of a component in a mix, on the other hand, the potential environmental consequence associated to release any pollutant is proportional to the degree of chemical change generated in the environment, as measured by the change in configurational entropy per mole of the affected species in the environment of interest [11, 12]:

( )iimix yRTE ,00, ln−=•

(11)

The ideal thermodynamic work per mole, required to

instantaneously return the polluted environment to its pristine estate is expressed as follow:

∑=

•

⎟⎟⎠

⎞⎜⎜⎝

⎛−=

n

i i

iPE

yyRTW

1 ,00 ln (12)

on the other hand

PSPLPBPHPAPE WWWWWW••••••

++++= (13)

The above equation can be seen as the lost work in the

environment, also representing the sum of the lost work in each part forming an ecosystem.

Then, the hydrosphere’s ideal work to revoke damage from each element is:

3

⎟⎟⎠

⎞⎜⎜⎝

⎛−=

•

i

iuiPH

yyTRW

,00, ln

(14)

Similar expressions can be obtained for the other parts of

an ecosystem. Using the concept of dimensionless irreversibility as

described in [19], an environmental impact index for the hydrosphere can be written as:

∑=

•

•

=n

i imix

iPHH

E

WEII1 ,

, (15)

Its value depends on the reference state. The same

expressions can be obtained for the other parts of the ecosystem.

4. ENVIRONMENT IMPACT ON LAKES 4.1 Eutrophication of lakes

The eutrophication of a river or lake is common in many regions in the world; it refers to excessive rate of addition of nutrients; it is a natural process, but it is drastically accelerated when human activities take place [20]. Nutrients addition result in the excessive growth of plants and phytoplankton in natural waters. The process has some negatives effects on water quality like green color by algae growth, loss of dissolved oxygen, odors problems and loss of diversity, mainly loss of fishery that is important for organisms including the human being.

Data from Salomonsen [7] shows the conditions for an oligotrophic and eutrophic lake. Two steady-state carbon-flow models are shown, each one illustrates the change in carbon metabolism, and the distribution of species is considered homogeneous. The data for models is used as reference in this work to demonstrate the environment impact of the lost work on ecosystem due to a change in the concentration of phosphorus in the water (see Tables).

Table 1. Two steady-state carbon-flow models in a lake [7].

Data Oligotrophic gr C/m3 Eutrophic gr C/m3

Phytoplankton 0.1 1.5

Fish 0.1 1.0 Macro-Zooplankton 0.06 0.16 Micro-Zooplankton 0.015 0.030

Bacteria 0.02 0.1

The chemical formula for algae protoplasm (representing

the ratios of element in algae cells) can be taken as C106H263O110N16P1. This chemical formula helps to determine the ratios at which the phosphorus is assimilated during primary production.

The value obtained will be taken in this work as the quantity of nutrients incoming to a lake from the society. Thus, the quantity of phosphorous in the phytoplankton for both models was calculated in this work, and it is shown in Table 2.


Table 2. Phosphorous concentration in a lake. Oligotrophic µgr P/litre Eutrophic µgr P/litre

2.432 36.492

The algal bloom in turn decreases the concentration of

dissolved oxygen due to bacterial growth and end of life of organism in the water. Values of oxygen concentrations for Oligotrophic and Eutrophic lakes can obtained from Claude [21]. From his work the quantity of oxygen dissolved for both models as shown in Table 3, is taken and used in the present analysis.

Table 3. Concentration of dissolved oxygen in a lake.

Oligotrophic mgr O2/litre Eutrophic mgr O2/litre

8.26 5.32

Eventually a process that would have occurred over a

geological time scale is accelerated by the human beings, and the lake becomes excessively productive. From Table 1 it is seen that the quantity of phytoplankton increases and the quantity of fish too. Table 2 shows the phosphorous concentration increase by anthropogenic activities; bacteria also growths greatly due to organism’s end of life; both reduce the concentration of dissolved oxygen in the water lake, as shown in Table 3. The oligotrophic condition puts all organisms that are important for a healthy ecosystem near to extinction. If the emission of phosphorous is not reduced the time is running out, because the concentration of oxygen dissolved is reduced and the ecosystem has a risk of disappearing. The minimum concentration of oxygen dissolved in water lake to support life is 2 mgr/liter. (At this point most of the organism will be dead, mainly fish, macro-zooplankton and micro-zooplankton).

4.2 Lost work in the ecosystem

Taking into account only the changes in the hydrosphere, biosphere and sociosphere, and using Equation (14) and Tables 1 to 3, the ideal thermodynamic work per mole, required to instantaneously return the polluted environment to its pristine estate and to avoid organisms extinction is 6.7 kJ/mol for phosphorous, 1.3 kJ/mol for oxygen and 688.8 kJ/mol for organisms.

Then, applying Equation (15) the environmental impact indexes for the hydrosphere and biosphere are obtained, and shown in Table 4.

Table 4. Environmental impact indexes in a lake.

Part of the ecosystem Value

Hydrosphere 0.1818

Biosphere 8.6057

It is interesting to see that whereas for the water content in the lake the impact is somehow low, the opposite occurs for the microorganisms/fish, etc living in the lake, that is, the impact index calculated in this work for the biosphere is 47.33 times greater than that of the water. This is clearly due to the excessive increase in living microorganisms in the lake.

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It is important to remember that the impact index on the biosphere is the work needed to revoke the damage done on the biosphere by society.

From Table 1 the amount of exergy that the lake has, it was obtained by using Equation (16) from Jorgensen [8]. Table 5 shows those values for both an oligotrophic (one that has low nutrients concentration) and for an eutrophic (one that has a high nutrients concentration) lake:

∑=

⎟⎟⎠

⎞⎜⎜⎝

⎛−=

n

i i

iiu C

CCTREx0 ,0

ln (16)

Table 5. Exergy contents in whole lake.

Oligotrophic kJ/mol Eutrophic kJ/mol

80.04 768.84

From Table 5 it could be seen that the amount of exergy

difference between them is of the order of 9 times, that is, a lake with high nutrients concentrations (an eutrophic lake) will require about 9 times the original exergy to revoke the damage and return the lake to its pristine state (an oligotrophic lake). The increment of more microorganisms in the lake produces a decrement of the available oxygen and some microorganism will die. Clearly all this changes are produced by society to the hydrosphere, sending phosphorous into the lake, this in turn increases the lost work.

5. CONCLUSIONS

Applying the methodology presented here an index of environmental impact was developed, not in a subjective way, but based on energy calculations. An index of environmental impact based on quantitative terms that enable to evaluate in a very clear way the harmful effects of industrial operations, such as the phenomenon of contamination of the environment.

The examples above show that available work decreases as a function of the lost work from one part of an ecosystem to another. Its depletion depends on the number of cycles and the ecosystem capacities to transform contaminants, due to exergy consumption as entropy is produced. This indicates that exergy loss may be used as a measure of reduction and excessive consumption of resources. This work has presented results that confirm this.

Also, combining systems is only good if the systems works in harmony in the new combined system, thus there is little or no exergy destruction on an ecosystem. From tables can be seen that the emission from the society to the water lake is big compared to the pristine state.

Energy is conserved but exergy is not; or on the other hand combining two systems that are at a different state results in a system with large energy content, but after the extinction of some organism the exergy content in the lake is smaller. To avoid lost work, society should be operated separately.

There is still much to be done to clearly identify all necessary indexes that will account for all type of situations, equipments, ecosystem and reactive systems.

The example presented in this paper is a good approximation; it was applied to simple components like phosphorous and oxygen, but the different interaction that they could have with other elements is not taken into account. To


have better approximation about the lost work in the ecosystem, it is necessary to complete the model with some chemodynamics information about the elements, it is important to know how elements can move by different paths inside the parts of the ecosystem and this way predict much better the behavior and tendencies of the ecosystem.

NOMENCLATURE

A Exergy [kJ/mol] C Concentration of the ith component EII Environment impact index R Ideal gas constant = 8.314 J/K mol S Entropy [kJ/mol] T Absolute temperature y Molar concentration W Work

Subscripts

0 Reference state A Atmosphere B Biosphere e Environment g Generate H Hydrosphere L Lithosphere lost Lost mix Mix P Polluted rev Reversible S Society u Useful

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Earth System Processes”, Springer Verlag, 2004. [2] Jørgensen, S.E., Exergy and buffering capacity in

ecological systems. In: W. Mitsch, R. Ragade, R. Bosserman and J. Dillon (Editors), Energetics and Systems. Ann Arbor Science Publishers, Ann Arbor, MI, (1982) 61-72.

[3] Odum, H.T., Ecological potential and analogue circuits for the ecosystem. Am. Sci. 48 (1960) 1-8.

[4] Ulanowicz, R.E., Growth and Development. Ecosystems Phenomenology. Springer, New York, (1960).

[5] Raghbendra, J., “Consumption Based Human Development Index and the Global Environmental Kuznets Curve”, Australia South Asia Research Centre Division of Economics. 2004.

[6] Wall, G., “Engineering Sustainability”, Inaugural presentation, 8th Liège Conference, Belgium, 2006.

[7] Salomonsen, J., Examination of properties of exergy, power and ascendency along a eutrophication gradient. Ecol. Modeling 62 (1992) 171-181.

[8] Jørgensen S.E., Thermodynamics and ecological modeling, Lewis Publishers, (2001).

[9] Jørgensen S.E., Integration of ecosystem theories: A pattern, Cluver Academic Publishers, (2002).

[10] Vallino J.J., Modeling microbial consortiums as distribuided metabolic networks, The Biological Bulletin, 2003, 204, 174-179.

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[11] Seager T.P., Theis T.L., Exergetic pollution potential: Estimating the revocability of chemical pollution, Exergy, An International Journal 2 (2002) 273-282.

[12] Seager T.P., Theis T.L., A thermodynamic basis for evaluating environmental policy trade-offs, Journal Clean Technologies and Environmental Policy 4 (2003) 217-226.

[13] Stavropoulos, G.G. and Skodras, G.,”The Use of Exergy for Evaluating Environmental Impact of Processes, OPET Network, 2003.

[14] Yang, L. et al., “Exergy analysis on eco-industrial systems”, Science in China: Series B Chemistry, Vol. 49 No.3, 281-288, 2006.

[15] Scciuba, E., “Exergy Destruction as an Ecological Indicator: Merits and Limits” Panel ECOS 2006, Grecian, 2006.

[16] Wall, G., and Gong, M., “On Exergy and Sustainable Development, Part I: Conditions and Concepts”, Exergy an International Journal Vol. 1, No. 3, 2001.

[17] Bejan, A., Tsatsaronis, G., and Moran, M., “Thermal Design and Optimization”, John Wiley and Sons Inc., 56-64, New York, 1997.

[18] Wall G., Exergy a Useful Concept Within Resource Accounting, Report no. 77-42, Institute of Theoretical Physics, Chalmers University of Technology and University of Göteborg, Göteborg, Sweden, 1977.

[19] M. Yilmaz et al, “Performance Evaluation Criteria for Heat Exchangers Based on Second Law Analysis”, Exergy, an International Journal, 1(4), 2001, 273-282.

[20] Schnoor J.L., Environmental modeling: fate and transport of pollutants in water, air and soil, John Wiley & Sons, (1996).

[21] Claude E.Z., Some factors which influence oxygen consumption by bacteria in lake water, The Biological Bulletin, 1940, 78, 388-402.


lost work in an ecosystem used as an environmental impact index

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