Closed System Thermodynamics

• 1st Law of Thermodynamics– Irreversible processes result in spontaneous

conversion of internal energy to heat and work

– At equilibrium a state of minimum internal energy is attained

– Enthalpy

Closed System Thermodynamics

• 2nd Law of Thermodynamics– All isolated systems will spontaneously

approach a state of equilibrium– Entropy

Open System Thermodynamics

• Natural setting – only closed system is the entire universe

• Most natural bodies/systems are open –allowing energy/material to flow into and out of them

• Natural systems – highly ordered and energy rich – goes against idea of increasing entropy and decreasing enthalpy

Equilibrium versus Steady State

• Closed systems – move towards equilibrium – time invariant state with entropy maximization

• Open systems – move towards steady-state and entropy minimization

Energy SinkEnergy Source Energy Flow

Eppt

Enpp

Soil System

Ordering Processes

• Humus Accumulation

• Structure Formation

• Horizonation

• Illuviation – Eluviation

• 2º Mineral Formation

Dissipative Processes

• Respiration

• Humus Decomposition

• Mineral Weathering

• Leaching

• Erosion

Pedogenic Trajectory

• Rasmussen et al. (2005)

Testing hypothesis that if soils are open systems, one should be able to quantify soil forming environment and soil development based on energy flux into the soil system

Energy SinkEnergy Source Energy Flow

Eppt

Enpp

Soil System

Ordering Processes

• Humus Accumulation

• Structure Formation

• Horizonation

• Illuviation – Eluviation

• 2º Mineral Formation

Dissipative Processes

• Respiration

• Humus Decomposition

• Mineral Weathering

• Leaching

• Erosion

• How to quantify energy flux?

– Effective precipitation

– Biologic production

• Water balance• Timing of precipitation

0

50000

100000

150000

200000

250000

300000

0

510

1520

25

100200

300400

500600

700

Ein (k

J m

-2 y

r-1)

MAAT (o C)

MAP (cm)

Jenny 1941 Idealized Model

Quantitative data from White and Blum 1995

Ein (kJ m-2 yr-1)

0 5000 10000 15000 20000 25000 30000

Si F

lux

(mol

m-2

yr-1

)

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

Calculated energy flux versus quantitative Si flux data from White and Blum

Arid MollAnd Ent Alf

InceptSpod Ult

Ener

gy T

ype

Dis

tribu

tion

(%)

0

20

40

60

80

100

Arid Moll EntAnd Alf

InceptSpod Ult

Ein (k

J m

-2 y

r-1)

0

5000

10000

15000

20000

25000

30000

35000

ab

c

de

fg

h

Pedogenic Trajectory

†Average of map unit slope from STATSGO‡Values in parentheses are standard errors of the mean. Pairwise comparison done with Tamhane post-hoc test (95% confidence interval). Slopes followed by the same lowercase letter are not significantly different.

9 (1.9) cdeAridisol

10 (0.5) eUltisol

10 (0.7) deAlfisol

12 (0.5) cdMollisol

15 (1.1) bcEntisol

26 (3.4) abSpodosol

26 (1.2) aInceptisol

26 (2.1) aAndisol

Slope %‡Soil Order

Table 3. Average slope for soil orders†

High slope and landscape stability

Impacts on pedogenic trajectory and degree of soil development

Ein (kJ m-2 yr-1)High : 162,260

Low : 0

Figure 1. EIN for the continental U.S. Calculated using the PRISM dataset (30 yr average MAP and MAT, 1971-2000)