Coastal Eutrophication and Marine Benthic Vegetation
103
lactuca was found to adapt to very low nutrient concentrations (Cohen
and Neori 1991) and light conditions (Vermaat and Sand-Jensen 1987).
The growth of primary producers can be limited by nutrients or by
other factors. If the growth of macroalgae is limited by nitrogen, the
frequency at which pulses of dissolved nitrogen occur in the surface
water may affect the species composition of a mixed algal assemblage
containing species which differ in uptake rate and storage capacity
(Fujita 1985). The nitrogen storage capacity of macroalgae is expected to
favour its competitive abilities over phytoplankton in environments with
episodic nitrogen availability, compared to environments with a more
regular nitrogen supply.
During winter in temperate regions, growth is often limited by climatic conditions, e.g. light and temperature. The rapid spring growth of
macro algae could be enhanced by the presence of macroalgal biomass
that survived this unfavourable period. It is hypothesized that this
survival during winter may give macroalgae a particularly strong competitive advantage over phytoplankton in areas with a strongly seasonal
light regime (Mann and Chapman 1975).
These principles are in agreement with findings on the timing and
character of the blooms of the main primary producers in the three
lagoons under consideration {Fig. 3.13). All systems receive additional
nitrogen originating from external sources during winter and early
spring. These nutrients cannot immediately be used for new production
due to restricted climatic conditions.
No substantial biomass of phytoplankton nor aboveground biomass of
macrophytes is present during the winter in Lake Grevelingen. The
nutrients which were accumulated during winter are used to support the
spring bloom of phytoplankton, due to their competitive advantage over
macrophytes by their high PIB ratio. Microphytobenthos also contributes significantly to nutrient depletion, especially silicate, during
spring (De Vries and Hopstaken 1984). This new production of phytoplankton and microphytobenthos in spring is followed by a high regenerated production of phytoplankton with a low biomass in summer and
autumn. Aboveground biomass of eelgrass develops after the depletion
of nutrients in the water column by the spring bloom. Initial eelgrass
growth is supported by reserve material stored in overwintering underground biomass. Further eelgrass growth depends mainly on nutrients
from the pore water (Verhagen and Nienhuis 1983).
Macroalgae in Lake Veere are not able to survive the winter as a result
of the restrictive climatic conditions at this latitude. The relatively high
PIB ratio of phytoplankton and the absence of macroalgae biomass in
spring, results in nutrients accumulated during winter being used for the
103
lactuca was found to adapt to very low nutrient concentrations (Cohen
and Neori 1991) and light conditions (Vermaat and Sand-Jensen 1987).
The growth of primary producers can be limited by nutrients or by
other factors. If the growth of macroalgae is limited by nitrogen, the
frequency at which pulses of dissolved nitrogen occur in the surface
water may affect the species composition of a mixed algal assemblage
containing species which differ in uptake rate and storage capacity
(Fujita 1985). The nitrogen storage capacity of macroalgae is expected to
favour its competitive abilities over phytoplankton in environments with
episodic nitrogen availability, compared to environments with a more
regular nitrogen supply.
During winter in temperate regions, growth is often limited by climatic conditions, e.g. light and temperature. The rapid spring growth of
macro algae could be enhanced by the presence of macroalgal biomass
that survived this unfavourable period. It is hypothesized that this
survival during winter may give macroalgae a particularly strong competitive advantage over phytoplankton in areas with a strongly seasonal
light regime (Mann and Chapman 1975).
These principles are in agreement with findings on the timing and
character of the blooms of the main primary producers in the three
lagoons under consideration {Fig. 3.13). All systems receive additional
nitrogen originating from external sources during winter and early
spring. These nutrients cannot immediately be used for new production
due to restricted climatic conditions.
No substantial biomass of phytoplankton nor aboveground biomass of
macrophytes is present during the winter in Lake Grevelingen. The
nutrients which were accumulated during winter are used to support the
spring bloom of phytoplankton, due to their competitive advantage over
macrophytes by their high PIB ratio. Microphytobenthos also contributes significantly to nutrient depletion, especially silicate, during
spring (De Vries and Hopstaken 1984). This new production of phytoplankton and microphytobenthos in spring is followed by a high regenerated production of phytoplankton with a low biomass in summer and
autumn. Aboveground biomass of eelgrass develops after the depletion
of nutrients in the water column by the spring bloom. Initial eelgrass
growth is supported by reserve material stored in overwintering underground biomass. Further eelgrass growth depends mainly on nutrients
from the pore water (Verhagen and Nienhuis 1983).
Macroalgae in Lake Veere are not able to survive the winter as a result
of the restrictive climatic conditions at this latitude. The relatively high
PIB ratio of phytoplankton and the absence of macroalgae biomass in
spring, results in nutrients accumulated during winter being used for the