IKEDA-KO (LAKE IKEDA)

A lake view with Mt. Kaimon in the background

Photo.
Photo: A. Kurata


A. LOCATION

  • Kagoshima Prefecture, Japan.

  • 31:14N, 130:34E; 88 m above sea level.


B. DESCRIPTION

    Lake Ikeda is a caldera lake, located 40 km south of Kagoshima city. It has a surface area of 11 km2 and a shoreline length of 15 km. The maximum depth amounts to 233 m. Together with Mt. Kaimon on its south side, it forms one of the most scenic spots of Southern Kyushu tourist zone, Kirishima-Yaku National Park.
    The lake water quality was excellent until some years ago, but has been deteriorated due to the development of the surrounding areas since around 1955. The transparency of the lake measured 26.8 m in 1929, but decreased to about 5 m in recent years. Freshwater red tides have also been observed. There are resort facilities in the northeastern part of the lake, which attract 2.8 million tourists annually. The lake also serves for fish culture and irrigation. An irrigation project for 6,000 ha of agricultural field and 10,000 households was initiated in 1965 and the courses of three nearby rivers were diverted into the lake. The irrigation system has been in operation since 1982, resulting in a considerable amelioration of the lake water quality (Q).


C. PHYSICAL DIMENSIONS (1)

    Surface area [km2] 11
    Volume [km3] 1.47
    Maximum depth [m] 233
    Mean depth [m] 135
    Water level Regulated
    Normal range of annual water
    - level fluctuation [m] 4
    Length of shoreline [km] 15.1
    Residence time [yr] 1.7
    Catchment area [km2] 41

D. PHYSIOGRAPHIC FEATURES

D1 GEOGRAPHICAL (Q)
  • Bathymetric map: Fig. ASI-30-01.

  • Names of main islands: None.

  • Number of outflowing rivers and channels (name): 1 (Shin R.).

D2 CLIMATIC
  • Climatic data at Ibusuki, 1971-1980 (2)

    Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Ann.
    Mean temp. [deg C] 8.7 9.4 12.1 16.6 20.0 23.7 27.3 27.8 24.9 20.4 15.3 10.5 18.1
    Precipitation [mm] 98 134 179 249 291 459 243 182 244 128 77 114 2,439
  • Number of hours of bright sunshine: 2,411 hr yr-1.

    Fig. ASI-30-01
    Bathymetric map (Q).

  • Water temperature [deg C](3, 4)

    Station 1, 1986
    Depth [m] Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    0.5 - 10.4 - 15.6 - 23.0 - - 29.3 23.3 - 14.2
    15 - 10.2 - 13.0 - 13.9 - - 22.9 22.9 - 14.2
    30 - 10.2 - 10.8 - 11.0 - - 11.5 11.5 - 11.0
    100 - 10.2 - 10.1 - 10.2 - - 10.4 10.2 - 10.3
    200 - 10.2 - 10.1 - 10.2 - - 10.4 10.2 - 10.3
  • Freezing period: None (Q).

  • Mixing type: Monomictic (Q).

  • Notes on water mixing and thermocline formation
    The lake is thermally stratified between April and December. The stratification is especially remarkable between June and November. The thermocline is situated at 10-20 m depth (Q).

E. LAKE WATER QUALITY (3, 4)

E1 TRANSPARENCY [m]
    Station 1, 1985
    Depth [m] Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    - 8.6 - 7.0 - 4.3 - 8.2 - 7.3 - 9.4
E2 pH
    Station 1, 1986
    Depth [m] Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    0.5 - 7.2 - 7.9 - 8.8 - - 8.6 8.1 - 7.4
    15 - 7.2 - 7.8 - 7.6 - - 7.8 8.0 - 7.3
    30 - 7.2 - 7.4 - 7.1 - - 7.0 7.1 - 6.8
    100 - 7.2 - 7.2 - 7.1 - - 7.0 7.1 - 6.9
    200 - 7.3 - 7.1 - 7.1 - - 7.0 7.1 - 6.8
E3 SS [mg l-1]
    Station 1, 1986
    Depth [m] Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    0.5 - <1 - 1 - 2 - - <1 1 - <1
    15 - <1 - 1 - 2 - - 1 1 - 1
    30 - <1 - <1 - <1 - - <1 <1 - <1
    100 - <1 - <1 - <1 - - <1 <1 - <1
    200 - <1 - <1 - <1 - - <1 <1 - <1
E4 DO [mg l-1]
    Station 1, 1986
    Depth [m] Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    0.5 - 7.7 - - - 9.0 - - 7.8 8.9 - 9.7
    15 - 7.3 - 10.8 - 10.4 - - 6.9 8.9 - 9.7
    30 - 7.0 - 10.5 - 7.7 - - 6.7 6.0 - 4.7
    100 - 7.6 - 8.6 - 7.4 - - 7.2 7.8 - 6.5
    200 - 6.8 - 7.6 - 7.1 - - 6.6 6.2 - 5.8
E5 COD [mg l-1]
    Determined by KMnO4 method.
    Station 1, 1986
    Depth [m] Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    0.5 - 1.1 - 1.9 - 2.7 - - 2.5 2.8 - 2.2
    15 - 1.2 - 1.3 - 2.6 - - 2.9 2.7 - 2.4
    30 - 1.2 - 1.0 - 0.9 - - 1.0 0.9 - 1.2
    100 - 1.2 - 0.9 - 0.8 - - 0.8 0.9 - 0.8
    200 - 1.1 - 0.8 - 0.8 - - 0.8 0.7 - 0.8
E6 CHLOROPHYLL CONCENTRATION [micro l-1]
    Station 1, 1986
    Depth [m] Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    0.5 - 1.7 - 3.6 - 2.4 - - 0.5 2.6 - 2.7
    15 - 2.0 - 1.9 - 11.0 - - 2.2 2.7 - 2.2
    30 - 2.4 - 0.9 - 0.5 - - 1.1 1.0 - 1.9
    100 - - - 0.2 - 0.1 - - 0.1 0.1 - 0.1
    200 - 1.8 - 0.3 - 0.0 - - 0.2 0.1 - 0.1
E7 NITROGEN CONCENTRATION
  • Total-N [mg l-1]

    Station 1, 1986
    Depth [m] Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    0.5 - 0.22 - 0.25 - 0.25 - - 0.38 0.36 - 0.33
    15 - 0.23 - 0.22 - 0.35 - - 0.55 0.35 - 0.32
    30 - 0.23 - 0.22 - 0.23 - - 0.26 0.26 - 0.30
    100 - 0.23 - 0.23 - 0.24 - - 0.26 0.23 - 0.24
    200 - 0.24 - 0.24 - 0.26 - - 0.27 0.26 - 0.26
E8 PHOSPHORUS CONCENTRATION
  • Total-P [mg l-1]

    Station 1, 1986
    Depth [m] Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    0.5 - .004 - .007 - .008 - - .003 .005 - .006
    15 - .004 - .005 - .007 - - .008 .005 - .007
    30 - .004 - .003 - .002 - - .002 .002 - .003
    100 - .004 - .002 - .002 - - .003 .002 - .002
    200 - .003 - .003 - .002 - - .003 .003 - .003
E9 CHLORIDE CONCENTRATION [mg l-1]
    Station 1, 1986
    Depth [m] Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    0.5 - 8.7 - 7.9 - 7.9 - - 7.8 8.1 - 7.9
    15 - 8.7 - 7.9 - 8.0 - - 7.9 8.0 - 7.9
    30 - 8.8 - 7.9 - 7.9 - - 7.8 8.0 - 7.9
    100 - 8.7 - 7.9 - 7.9 - - 7.8 8.1 - 7.9
    200 - 8.8 - 7.8 - 7.9 - - 8.0 8.0 - 7.9
E10 PAST TRENDS: Fig. ASI-30-02, 03 and 04.

    Fig. ASI-30-02
    Past trend of COD.

    Fig. ASI-30-03
    Past trend of T-N concentration.

    Fig. ASI-30-04
    Past trend of T-P concentration.


F. BIOLOGICAL FEATURES (1)

F1 FLORA
  • Phytoplankton
    Spring: Cyciotella sp., Synedra sp. Summer: Cyclotella sp., Mougeotia sp. Autumn: Anabaena sp. Winter: Anabaena sp., Microcystis sp.
F2 FAUNA
  • Zooplankton
    Spring: Bosmina longirostris, Bosminopsis deitersi. Summer: Conochilus hippocrepis. Autumn: C. hippocrepis, B. longirostris. Winter: B. longirostris, Nauplius.
  • Benthos: Palaemon paucidens, Pisidium parvum, Prochladius sp.

  • Fish
    Anguilla marmorata, A. Japonica*, Cyprinus carpio*, Hypomesus transpacificus nipponensis, Plecoglossus altivelis. * Economically important.
F5 FISHERY PRODUCTS (Q)
  • Annual fish catch [metric tons]
    1980: 379.

G. SOCIO-ECONOMIC CONDITIONS

G1 LAND USE IN THE CATCHMENT AREA (6)
    1980
    Original basin Area [km2] [%] Newly added basin Area [km2] [%]
    Natural landscape 8.95 72.5 19.51 68.7
    Agricultural land 1.36 11.0 5.59 19.7
    Residential area 0.44 3.6 0.37 1.3
    Others 1.59 12.9 2.92 10.3
    Total 12.34 100 28.39 100
  • Main types of woody vegetation (5)
    Evergreen broadleaf forest (Pasania edulis, Castanopsis cuspidata), pine forest (Pinus thunbergii), pine plantation (P. thunbergii).
  • Main types of herbaceous vegetation: Grassland and weeds (5).

  • Main kinds of crops: Rice, sweet potato, radish and tea (5).

G2 INDUSTRIES IN THE CATCHMENT AREA AND THE LAKE (Q)
    1980
    Gross product per year [mill. yen]* No.of persons engaged
    Primary industry 8,900 8,127
    Secondary industry 10,100 4,457
    Tertiary industry 40,300 13,613
    * Data compiled from the statistics of the municipalities in the catchment area.
  • Numbers of domestic animals in the catchment area
    Cattle 2,015, swine 947 and poultry 913,100.
G3 POPULATION IN THE CATCHMENT AREA (Q)
    1980
    Population Population density [km-2] Major cities (population)
    Total 3,434 84.3 None

H. LAKE UTILIZATION

H1 LAKE UTILIZATION (6)
    Source of water, sightseeing and tourism (no. of visitors in 1980: 2,870,000), recreation (sport-fishing) and fisheries.

H2 THE LAKE AS WATER RESOURCE (6)
    Use rate [m3 sec-1]
    Irrigation 0.22

I. DETERIORATION OF LAKE ENVIRONMENT AND HAZARDS (Q)

I2 TOXIC CONTAMINATION
  • Present status: None.

I3 EUTROPHICATION
  • Nuisance caused by eutrophication
    Unusual algal bloom: Peridinium sp.
  • Nitrogen and phosphorus loadings to the lake [t yr-1]

    1983
    Sources Industrial Domestic Agricultural Natural Fisheries Total
    T-N 6.6 5.1 17.9