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)
