Environmental Engineering Reference
In-Depth Information
TABLE 19.2 Vegetation and land-use categories generated by grouping the National Land Cover Dataset/Database (NLCD)
land-cover/land-use classification (Vogelmann et al ., 2001; Homer et al ., 2007).
ε g (g C MJ −1 )
Vegetation and land-use category
This study
NLCD 1992
NLCD 2001
1: Deciduous Forest
Deciduous forest (41)
Deciduous forest (41)
1.56
2: Coniferous Forest
Evergreen forest (42)
Evergreen forest (42)
1.02
3: Mixed Forest
Mixed forest (43)
Mixed forest (43)
1.31
4: Shrubland
Shrubland (51)
Shrub and scrub (52)
0.79
Orchards, vineyards and other (61)
5: Grassland
Herbaceous grassland (71)
Herbaceous grassland (71)
0.86
6: Agriculture
Pasture and hay (81)
Pasture and hay (81)
1.47
Row crops (82)
Cultivated crops (82)
Small grains (83)
Fallow (84)
Urban and recreational grasses
(85)
0.51
7: Built-up
Low intensity residential (21)
Developed, open space (21)
High intensity residential (22)
Developed, low density (22)
Commercial, industrial and
transportation (23)
Developed, medium density (23)
Developed, high density (24)
8: Wetland
Woody wetlands (91)
Woody wetlands (90)
1.11*
Emergent herbaceous wetlands
(92)
Emergent herbaceous wetland
(95)
9: Bare
Bare rock, sand and clay (31)
Barren land (31)
n/a
Quarries, strip mines and gravel
pits (32)
Traditional barren (33)
10: Water
Open water (11)
Open water (11)
n/a
Perennial ice and snow (12)
Perennial ice and snow (12)
The corresponding light-use efficiency ( ε g ) came from Yang et al . (2007), except for the Built-up and Wetland types. ε g of Built-up was estimated as the
weighted average of ε g for deciduous and coniferous forests (1.29 g C MJ −1 ; 20.3%), grassland (0.86 g C MJ −1 ; 29.1%), and impervious surface or water (0;
50.6%); refer to the text for detailed explanation. ε g of Wetland was estimated as the average of ε g for Deciduous Forest, Coniferous FOREST, Mixed Forest,
Shurbland, and Grassland.
Estimated.
In the process of estimating GPP, temperature scalars were
applied to ε g , given that environmental constraints such as
temperature, moisture, and nutrient availability influence the
actual production of carbohydrate (Prince and Goward, 1995;
Running et al ., 2000). The rationale is that, when temperature
drops below certain thresholds, plants would be less efficient
in converting CO 2 to carbohydrate or completely shut down
photosynthesis. The temperature scalar, ranging between 0 and
1, was determined by examining the minimumdaily temperature
( T min ). Its value is 0 for T min below - 8 C, 1 for T min above the
threshold temperature depending on types of vegetation and
land uses, and linear function between 0 and 1 for T min in
between (Heinsch et al ., 2003). The temperature data came from
the monthly average climate forcing data based on the NOAH
land-surface model (Rodell et al ., 2004).
Changes in GPP were derived by subtracting the pixel-wise
estimate in 1992 from the GPP estimate in 2001. Positive value
indicates an increase in GPP at the later date, and negative value
corresponds to the decline of GPP in 2001. These changes in GPP
were associated with different types of urban growth (identified
based on changes in Census HUD) throughout the South Atlantic
study area.
19.4 Results
According to Census HUD, Rural densities (44.1%) predomi-
nated in the South Atlantic division by area in 1990, followed by
the Exurban (39%), Suburban (14.9%), andUrban (2%) densities
(Table 19.3; Fig. 19.3). By 2000, Exurban densities exceeded Rural
densities by area and accounted for 42.7% of the total study area.
The area of Urban densities increased by approximately 21%
during the 1990-2000 period. Suburban densities grew at a
higher rate (approximately 27%) than Urban densities. The area
of Exurban densities also expanded (by approximately 9%) dur-
ing the same time period. The growth of Urban, Suburban, and
Exurban densities resulted in the loss of area at Rural densities,
which dropped by approximately 19% between 1990 and 2000.
GPP was estimated in 1992 to be 4.11 g C m 2 day 1 and in
2001 to be 5.81 g C m 2 day 1 for the South Atlantic division as
a whole. In both years, Exurban densities were found to be the
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