Italy - The Lagoon of Venice
351
lagoon was underestimated until the end of the 1970s. The standardized
O 2 and 14C methods, which were then used to evaluate phytoplankton
production, were not adequate, because of the huge macroalgal biomass
(up to 20 kg m -2, wet weight) and its stratification. In fact, both O 2 and
14C measurements require low biomasses (0.5-5 g wet weight) to be
reliable and the results of these methods are difficult to extrapolate to the
total biomass. In addition, the oxygen method cannot be applied, since
the lagoon waters were mostly air-oversaturated (up to 360%; Sfriso et al.
1988a). Under these conditions, O 2 is very often directly released in the
form of gas bubbles. Bidwell and McLachlan (1985) reported that at high
O 2 and low CO 2 concentrations in macroalgae photo respiration may
occur producing CO 2 and consuming O 2 , These gases compete for the
active site of ribulose biphosphate carboxylase/oxygenase and produce
glycolate by oxygenase activity during photosynthesis (Bidwell 1983).
Under photo respiration, the photosynthetic quotient is very different
from that normally used in the production calculations (1-1.2) changing
from 0.1 to 1, depending on CO 2 and O 2 concentrations. In view
of the limitation of the O 2 and 14C methods, measurement of biomass
variations with a frequency depending on the seasonal macro algal
growth rate (3-20 days) appeared the most suitable method for the
evaluation of macro algal primary production (Sfriso et al. 1988b, 1991).
For this purpose, an accurate and precise procedure was developed to
correctly measure the standing crop of shallow sampling sites populated
by macro algae with different densities and varying distributions (Sfriso
et al. 1991). An accuracy within 10% was obtained after only three
measurements of the different macroalgal distributions (Fig. 15.3). To
reach a higher accuracy within 5%, 4-14 sub samples are needed
depending on the different macroalgal dispersions.
U sing this procedure, we have sampled over several years, weekly
during spring/summer and twice a month during autumn/winter, three
~ 30
i' 25
W
III 20
i 15
CI} 10
::iii
w
III
Per cent deviation from the BEM
5
7
11
13
15
17
19
Sub-samples
Fig. 15.3. Number of sub samples needed to obtain an SM within a sampling accuracy of
5 and 10%. BEM Best estimated mean; SM sampling mean
351
lagoon was underestimated until the end of the 1970s. The standardized
O 2 and 14C methods, which were then used to evaluate phytoplankton
production, were not adequate, because of the huge macroalgal biomass
(up to 20 kg m -2, wet weight) and its stratification. In fact, both O 2 and
14C measurements require low biomasses (0.5-5 g wet weight) to be
reliable and the results of these methods are difficult to extrapolate to the
total biomass. In addition, the oxygen method cannot be applied, since
the lagoon waters were mostly air-oversaturated (up to 360%; Sfriso et al.
1988a). Under these conditions, O 2 is very often directly released in the
form of gas bubbles. Bidwell and McLachlan (1985) reported that at high
O 2 and low CO 2 concentrations in macroalgae photo respiration may
occur producing CO 2 and consuming O 2 , These gases compete for the
active site of ribulose biphosphate carboxylase/oxygenase and produce
glycolate by oxygenase activity during photosynthesis (Bidwell 1983).
Under photo respiration, the photosynthetic quotient is very different
from that normally used in the production calculations (1-1.2) changing
from 0.1 to 1, depending on CO 2 and O 2 concentrations. In view
of the limitation of the O 2 and 14C methods, measurement of biomass
variations with a frequency depending on the seasonal macro algal
growth rate (3-20 days) appeared the most suitable method for the
evaluation of macro algal primary production (Sfriso et al. 1988b, 1991).
For this purpose, an accurate and precise procedure was developed to
correctly measure the standing crop of shallow sampling sites populated
by macro algae with different densities and varying distributions (Sfriso
et al. 1991). An accuracy within 10% was obtained after only three
measurements of the different macroalgal distributions (Fig. 15.3). To
reach a higher accuracy within 5%, 4-14 sub samples are needed
depending on the different macroalgal dispersions.
U sing this procedure, we have sampled over several years, weekly
during spring/summer and twice a month during autumn/winter, three
~ 30
i' 25
W
III 20
i 15
CI} 10
::iii
w
III
Per cent deviation from the BEM
5
7
11
13
15
17
19
Sub-samples
Fig. 15.3. Number of sub samples needed to obtain an SM within a sampling accuracy of
5 and 10%. BEM Best estimated mean; SM sampling mean