Environmental Engineering Reference
In-Depth Information
decomposition (Chapter 4), or mineralization (Chapter 7) over time or space, or the accu-
mulation of some element of interest can be indicators of ecosystem function. Ecosystem
development is often described by changes in structure, function, and their relationship
over time (e.g., linked changes in soil and vegetation over millennia;
Ewing 2002
).
Many, if not most, of our measurements of ecosystem function are indirect. Sometimes
we can measure function directly, such as measurement of gas exchange, but these mea-
surements are almost inevitably made on a tiny fraction of the ecosystem (e.g., individual
leaves within a grassland or bottle of water from a lake). To estimate a flux over a larger
area of a grassland, for example, an ecosystem scientist might deploy eddy covariance
instruments that measure carbon dioxide, water, temperature, and wind speed and direc-
tion continuously at a place within the grassland. From these measures, a model can be
used to infer carbon dioxide flux into or out of the ecosystem.
Land
management,
natural
disturbance
Atmospheric Deposition
Cations and Anions
Atmospheric CO
2
SUBLIMATION
TRANSLOCATION
Snowpack
CO
2
N
2
O
LITTERFALL
INFILTRATION
NO
x
ET
RUNOFF
PHREEQC soil reactions
SOM DECOMP.
MINERALIZATION
NITRIF./DENITRIF.
UPTAKE
Cation Exchange
Aqueous reactions
Mineral denudation
CO
2
dissolution
Soil Organic
C,N,P,S
NO
3
-
NH
4
+
CO
2
DOC, Cations, Anions, CEC
ANC, pH, BC, Cl, Al, SO
4
2-
LEACHING
Aquifer
PHREEQC stream reactions
BASEFLOW
Aqueous reactions
Mineral denudation
CO
2
dissolution
Stream Flow
CO
2
FIGURE 1.4
DayCent-Chem model processes. DayCent-Chem was developed to address ecosystem responses
to combined atmospheric nitrogen and sulfur deposition. DayCent-Chem operates on a daily time step and com-
putes atmospheric deposition, soil water fluxes, snowpack and stream dynamics, plant production and uptake,
soil organic matter decomposition, mineralization, nitrification, and denitrification (left side of figure) while utiliz-
ing PHREEQC's (an aqueous geochemical equilibrium model) low-temperature aqueous geochemical equilibrium
calculations, including CO
2
dissolution, mineral denudation, and cation exchange, to compute soil water and stream
chemistry (right side of figure). ET
evapotranspiration; DOC
dissolved organic carbon; CEC
cation exchange
5
5
5
capacity; ANC
base cations (Ca, Mg, K, Na). The model requires considerable site-
specific environmental data to run. (From
Hartman et al. 2009
,
Figure 1.3
.)
acid neutralizing capacity; BC
5
5
