Energy Flow in Benthic Assemblages: Portugal and North Sea Tidal Basins
241
2. Insolation in the Ria Formosa lagoon is in December about ten times
higher caused by the higher angle of the sun with the horizon and longer
day time. Although in June day length is shorter than in the Sylt -R0m0 Bay,
insolation is still twice as high, caused by lower cloudiness.
3. Both systems show a different share of subtidal and intertidal subsystems.
At mean low tide two-thirds of the Ria Formosa lagoon is intertidal
whereas only one-third of the Sylt-R0m0 Bay is uncovered.
4. Although both systems are mesotidal, differences between neap and spring
tide are more pronounced in the Ria Formosa. This is probably one reason
for the extended Ria Formosa salt marshes, which occupy the fringe between neap and spring high tide. In the lower part Spartina maritima
dominates, in the upper part shrub-like plants such as Arthrocnemum spp.,
Suaeda vera or Halimione portulacoides. Originally salt marshes also
fringed a considerable part of the Sylt/R0m0 Bay but these have been
largely reduced by embankments (Reise 1998).
5. Nutrient concentrations in the water column are distinctly lower in the Ria
Formosa lagoon. This can be attributed to the shorter residence time of
the water and the proximity of the continental shelf. The lagoon water is
potentially mixed with a much larger water volume as at the North Sea site
during each tide. In the Sylt-R0m0 Bay the tidal exchange (with eutrophicated coastal North Sea water!) is lower and keeps nutrient levels high
inside the bay.
11.3 Material and Methods
11.3.1 Primary Production
Salt Marsh Plants. Spartina maritima above-ground production has been
estimated monthly during an annual cycle by the increment of individually
marked shoots at two sites of the Ria Formosa. This production estimate has
been assumed representative for the whole salt marsh area.
Microphytobenthos. Production of microphytobenthos has been recorded by
the oxygen method in dark and transparent bell jars at monthly intervals at
different intertidal sites. This method is described in Asmus and Asmus (1985).
For the Sylt-R0m0 site additional laboratory experiments with sediment
cores were carried out under in situ conditions (Kristensen et al.I997).
Seagrasses. In the Sylt-R0m0 Bay spatial distribution of seagrasses was
mapped by true colour remote sensing from air planes (Asmus et al. 1998).
241
2. Insolation in the Ria Formosa lagoon is in December about ten times
higher caused by the higher angle of the sun with the horizon and longer
day time. Although in June day length is shorter than in the Sylt -R0m0 Bay,
insolation is still twice as high, caused by lower cloudiness.
3. Both systems show a different share of subtidal and intertidal subsystems.
At mean low tide two-thirds of the Ria Formosa lagoon is intertidal
whereas only one-third of the Sylt-R0m0 Bay is uncovered.
4. Although both systems are mesotidal, differences between neap and spring
tide are more pronounced in the Ria Formosa. This is probably one reason
for the extended Ria Formosa salt marshes, which occupy the fringe between neap and spring high tide. In the lower part Spartina maritima
dominates, in the upper part shrub-like plants such as Arthrocnemum spp.,
Suaeda vera or Halimione portulacoides. Originally salt marshes also
fringed a considerable part of the Sylt/R0m0 Bay but these have been
largely reduced by embankments (Reise 1998).
5. Nutrient concentrations in the water column are distinctly lower in the Ria
Formosa lagoon. This can be attributed to the shorter residence time of
the water and the proximity of the continental shelf. The lagoon water is
potentially mixed with a much larger water volume as at the North Sea site
during each tide. In the Sylt-R0m0 Bay the tidal exchange (with eutrophicated coastal North Sea water!) is lower and keeps nutrient levels high
inside the bay.
11.3 Material and Methods
11.3.1 Primary Production
Salt Marsh Plants. Spartina maritima above-ground production has been
estimated monthly during an annual cycle by the increment of individually
marked shoots at two sites of the Ria Formosa. This production estimate has
been assumed representative for the whole salt marsh area.
Microphytobenthos. Production of microphytobenthos has been recorded by
the oxygen method in dark and transparent bell jars at monthly intervals at
different intertidal sites. This method is described in Asmus and Asmus (1985).
For the Sylt-R0m0 site additional laboratory experiments with sediment
cores were carried out under in situ conditions (Kristensen et al.I997).
Seagrasses. In the Sylt-R0m0 Bay spatial distribution of seagrasses was
mapped by true colour remote sensing from air planes (Asmus et al. 1998).