Chapter 10 . Aigal Species Succession in Rivers
207
10.4.3.1
Microcystis aeruginosa
Shapiro (1990) presented several hypotheses to explain dominance of blue-greens
in the phytoplankton of north temperate lakes. These inc1uded positive responses
to high water temperature, low
light, low NIP ratios, buoyancy, zooplankton grazing, and the CO 2 -pH complex.
The results of SWD analysis (Fig. 10.4) revealed relationships between M.
aeruginosa, water temperature and pH consistent with this hypothesis. As stated
by Shapiro (1990), blue-green algae are most competitive at temperatures
exceeding 20°C. Results of the SWD indicated that M. aeruginosa starts to grow at
20°C and then explosively augments the phytoplankton at temperatures in excess
of 30°C in the lower Nakdong River.
Changes in pH and CO 2 concentration are important factors controlling
cyanobacteria dominance (Harris, 1986). At pH values greater than 8.5,
exponential growth occurs. King (1970) and Shapiro (1984) suggested that
physiological adaptations of blue greens enable them to out-compete eukaryotic
algae at high pH and/or low CO 2 • Reynolds (1986) documented that this
phenomenon held true for both M. aeruginosa and Anabaena jlos-aquae. In the
case of the lower Nakdong River, Ha et al. (1999) reported that seasonal changes
of pH are important for the middle phase of proliferation of blue-greens, rather
than stimulating their initial growth. Results of the SWD on the validated RNN
model indicate a strong correlation between increasing dominance of M.
aeruginosa in the lower Nakdong River and increased pH, consistent with field
observations (Talling 1976) and controlled experiments (Shapiro 1984) on other
freshwater systems.
Another factor found by SWD to be strongly correlated with the proliferation of
M. aeruginosa was evaporation, wh ich is a function of the river's heat budget and
therefore its water temperature (Yoon 1998). Severe evaporation during a drought
can be linked to a dec1ine of water flow, which causes high water stagnation in the
lower Nakdong River. Jeong et al. (2001a) documented a similar influence of
evaporation on the changes of chI a concentrations through time-series ANN
model application.
Complex interactions among environmental parameters appear to be
responsible for the severe bloom events in the lower Nakdong River. With
elevated water temperatures, low discharge rates, and high irradiance, blooms of
Microcystis spp. are stimulated in this river. In addition, high nutrient
concentrations are a necessary pre-requisite for out-breaks of blue green algal
blooms (Ha et al. 1999). After the initial phase of algal proliferation, pH is
important for selecting the dominant species.
207
10.4.3.1
Microcystis aeruginosa
Shapiro (1990) presented several hypotheses to explain dominance of blue-greens
in the phytoplankton of north temperate lakes. These inc1uded positive responses
to high water temperature, low
light, low NIP ratios, buoyancy, zooplankton grazing, and the CO 2 -pH complex.
The results of SWD analysis (Fig. 10.4) revealed relationships between M.
aeruginosa, water temperature and pH consistent with this hypothesis. As stated
by Shapiro (1990), blue-green algae are most competitive at temperatures
exceeding 20°C. Results of the SWD indicated that M. aeruginosa starts to grow at
20°C and then explosively augments the phytoplankton at temperatures in excess
of 30°C in the lower Nakdong River.
Changes in pH and CO 2 concentration are important factors controlling
cyanobacteria dominance (Harris, 1986). At pH values greater than 8.5,
exponential growth occurs. King (1970) and Shapiro (1984) suggested that
physiological adaptations of blue greens enable them to out-compete eukaryotic
algae at high pH and/or low CO 2 • Reynolds (1986) documented that this
phenomenon held true for both M. aeruginosa and Anabaena jlos-aquae. In the
case of the lower Nakdong River, Ha et al. (1999) reported that seasonal changes
of pH are important for the middle phase of proliferation of blue-greens, rather
than stimulating their initial growth. Results of the SWD on the validated RNN
model indicate a strong correlation between increasing dominance of M.
aeruginosa in the lower Nakdong River and increased pH, consistent with field
observations (Talling 1976) and controlled experiments (Shapiro 1984) on other
freshwater systems.
Another factor found by SWD to be strongly correlated with the proliferation of
M. aeruginosa was evaporation, wh ich is a function of the river's heat budget and
therefore its water temperature (Yoon 1998). Severe evaporation during a drought
can be linked to a dec1ine of water flow, which causes high water stagnation in the
lower Nakdong River. Jeong et al. (2001a) documented a similar influence of
evaporation on the changes of chI a concentrations through time-series ANN
model application.
Complex interactions among environmental parameters appear to be
responsible for the severe bloom events in the lower Nakdong River. With
elevated water temperatures, low discharge rates, and high irradiance, blooms of
Microcystis spp. are stimulated in this river. In addition, high nutrient
concentrations are a necessary pre-requisite for out-breaks of blue green algal
blooms (Ha et al. 1999). After the initial phase of algal proliferation, pH is
important for selecting the dominant species.