196
K.-S. Jeong . F. Recknagel . G.-J. Joo
Reynolds 1984; Sommer et al., 1986; Kromcamp and Walsby 1990) and much has
been achieved in understanding the ecology of this community. However,
Recknagel (1997) and Jeong et al. (2001a) demonstrated that inductive modelling
of phytoplankton dynamics by means of ANN can result in more realistic, holistic
models by exploring the information content and complexity of aquatic time
series. Jeong et al. (2001a) successfully applied recurrent neural networks (RNN)
for modelling phytoplankton dynamics in the Nakdong River ecosystem of Korea.
Phytoplankton becomes a concern to the society when it forms a dense growth
at the water surface, known as an algal bloom. Blooms frequently are observed in
lowland rivers throughout the world. However, studies on mechanisms of algal
bloom formation in rivers have received less attention than in lakes and reservoirs.
Serious water quality problems in the Nakdong River are associated with blooms
of Microcystis aeruginosa during hot summers, and of Stephanodiscus hantzschii
from winter to early spring (Ha 1999). In this study, annual dynamics of these two
algal species in the lower Nakdong River were modeled by RNN. Results of the
study improved our understanding of factors controlling formation of algal blooms
in regulated river systems.
10.2
Description of the Study Site
The Nakdong River basin is situated in the southeastern part of South Korea (35
0
to 37 0 N, 127 0 to 129 0 E) (Fig. 10.1). South Korea experiences four distinct
seasons, and is characterized by heavy rainfall during the monsoon season and
several typhoon events. The annual mean precipitation across the river basin is
about 1,200 mm, but more than 50% of the annual rainfall is concentrated during
summer (June-August). The annual mean water temperature at the study site was
13.7°C. The mean water temperature was 2.2°C during the coldest month
(January), and 25.9°C in August, the warrnest month.
The main channel of the river is 526 km long, and the catchment area occupies
about 25% of the whole country, covering an area of 23,817 km 2 • The Mulgum
station of the Nakdong River, from which data for the model were collected, is
situated 27.4 km upstream of the estuarine dam at the river mouth, and has a
maximum water depth of -11 m, a mean depth of -4 m, and a river width of 250300m.
Over 10 million people depend on the river for their drinking, agricultural, and
industrial water supply. The Nakdong River has 4 multi-purpose dams and an
estuarine dam. Physical alterations, industrialization, and urbanization have
accelerated eutrophication of the lower part of the river (Kim et al. 1998).
K.-S. Jeong . F. Recknagel . G.-J. Joo
Reynolds 1984; Sommer et al., 1986; Kromcamp and Walsby 1990) and much has
been achieved in understanding the ecology of this community. However,
Recknagel (1997) and Jeong et al. (2001a) demonstrated that inductive modelling
of phytoplankton dynamics by means of ANN can result in more realistic, holistic
models by exploring the information content and complexity of aquatic time
series. Jeong et al. (2001a) successfully applied recurrent neural networks (RNN)
for modelling phytoplankton dynamics in the Nakdong River ecosystem of Korea.
Phytoplankton becomes a concern to the society when it forms a dense growth
at the water surface, known as an algal bloom. Blooms frequently are observed in
lowland rivers throughout the world. However, studies on mechanisms of algal
bloom formation in rivers have received less attention than in lakes and reservoirs.
Serious water quality problems in the Nakdong River are associated with blooms
of Microcystis aeruginosa during hot summers, and of Stephanodiscus hantzschii
from winter to early spring (Ha 1999). In this study, annual dynamics of these two
algal species in the lower Nakdong River were modeled by RNN. Results of the
study improved our understanding of factors controlling formation of algal blooms
in regulated river systems.
10.2
Description of the Study Site
The Nakdong River basin is situated in the southeastern part of South Korea (35
0
to 37 0 N, 127 0 to 129 0 E) (Fig. 10.1). South Korea experiences four distinct
seasons, and is characterized by heavy rainfall during the monsoon season and
several typhoon events. The annual mean precipitation across the river basin is
about 1,200 mm, but more than 50% of the annual rainfall is concentrated during
summer (June-August). The annual mean water temperature at the study site was
13.7°C. The mean water temperature was 2.2°C during the coldest month
(January), and 25.9°C in August, the warrnest month.
The main channel of the river is 526 km long, and the catchment area occupies
about 25% of the whole country, covering an area of 23,817 km 2 • The Mulgum
station of the Nakdong River, from which data for the model were collected, is
situated 27.4 km upstream of the estuarine dam at the river mouth, and has a
maximum water depth of -11 m, a mean depth of -4 m, and a river width of 250300m.
Over 10 million people depend on the river for their drinking, agricultural, and
industrial water supply. The Nakdong River has 4 multi-purpose dams and an
estuarine dam. Physical alterations, industrialization, and urbanization have
accelerated eutrophication of the lower part of the river (Kim et al. 1998).