Environmental Engineering Reference
In-Depth Information
1998
1999
2000
4
2
0
- 2
- 4
0
- 2
- 4
- 6
- 8
4
3
2
1
0
31
91
151
211
271
331
31
91
151
211
271
331
31
91
151
211
271
331
Time, day of year
FIGURE 6.7
Net ecosystem gas exchange (upper; NEE
5
NEP
5
GPP
2
R); GPP (middle) and ecosystem respira-
tion (R; lower) in a temperate grassland in Alberta, Canada. Shown are three years of data based on eddy flux
towers. Negative values represent the uptake of CO
2
by the system; positive values represent the net release of CO
2
.
In this system GPP is almost always larger than R, leading to negative values (net uptake) of CO
2
for the system as
a whole (NEE) during the growing season. (Data from
Flanagan et al. 2002
.)
concentrations of the dissolved gases (CO
2
and O
2
) directly and continuously, and model
the gas flux across the air
water interface (see Chapter 2). From these measurements we
can calculate whole-system GPP, R, and NEP. Paul, Peter, and Tuesday Lakes in the
Upper Peninsula of Michigan, near Land O'Lakes, Wisconsin, are typical of the small (1 to
