AKAN-KO (LAKE AKAN)

Near the southeastern end of the lake

Photo.
Photo: T. Kira


A. LOCATION

  • Hokkaido, Japan.

  • 43:27N, 144:06E; 420 m above sea level.


B. DESCRIPTION

    Lake Akan in eastern Hokkaido is a dammed lake formed approximately 6,000 years ago by volcanic activity in a caldera depression that dates back to the middle Pleistocene. Its complicated shoreline is characteristic of dammed lakes. The lake is famous as the only native habitat of "Marimo" or fine ball-like masses of the alga, Aegagropila sauteri, 2-15 cm in diameter. It is believed that the globular shape is formed by the aggregation of filamentous alga and the rotary motion due to water turbulence. Similar kinds of spherical algal mass are observed in a few other lakes of Japan, but they are more irregular in shape. L. Akan is also known as the original home of kokanee salmon (Oncorhynchus nerka).
    Transparency in the early 1930's was 8-9 m throughout the year, but the lake has recently been eutrophicated to a considerable extent owing to the inflowing waste water from the hot-spring town on the coast in spite of its cool and deep water. The eutrophication exerted a profound influence on the benthic fauna, which had once consisted of Chironomidae, Tubificidae, Chaoborus and Pisidium in its deepest bottom. According to the result of a general limnological survey made in 1973, however, the dissolved oxygen concentration in bottom water was only around 5% of saturation and no organisms were observed beyond a depth of 30 m (1, 2, 3).


C. PHYSICAL DIMENSIONS (Q, 4, 5)

    Surface area [km2] 13
    Volume [km3] ca. 0.23
    Maximum depth [m] 44.8
    Mean depth [m] 17.8
    Length of shoreline [km] 25.9
    Catchment area [km2] 148

D. PHYSIOGRAPHIC FEATURES

D1 GEOGRAPHICAL
  • Bathymetric map: ASI-21-01.

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

D2 CLIMATIC
  • Climatic data on the shore, 1982-1983

    Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Ann.
    Mean temp. [deg C] -10.4 -12.2 -5.4 3.2 8.9 9.7 14.8 18.0 12.7 6.5 0.6 -6.1 3.4
    Precipitation [mm] 57 11 73 82 70 100 69 166 106 138 95 47 1,014
  • Number of hours of bright sunshine (L. Akan): 2,218 hr yr-1.

    Fig. ASI-21-01
    Bathymetric map (4).

  • Water temperature [deg C](Q)

    Station 1, 1981-1983
    Depth [m] Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    0 - - - - 8.4 12.6 18.5 19.3 18.1 12.9 - -
    5 - - - - 8.8 12.5 17.3 18.7 17.9 12.7 - -
  • Freezing period: December-April.

  • Mixing type: Dimictic.


E. LAKE WATER QUALITY (Q)

E1 TRANSPARENCY [m]
    Station 1, 1981-1983
    Depth [m] Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    - - - - 3.4 4.4 3.5 3.8 3.1 2.4 - -
E2 pH
    Station 1, 1981-1983
    Depth [m] Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    0 - - - - 7.7 7.9 8.3 8.2 8.0 7.7 - -
    5 - - - - 7.8 7.9 8.2 8.2 8.1 7.7 - -
E3 SS [mg l-1]
    Station 1, 1981-1983
    Depth [m] Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    0 - - - - 1 1 2 1 1 3 - -
    5 - - - - 2 1 2 1 1 3 - -
E4 DO [mg l-1]
    Station 1, 1981-1983
    Depth [m] Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    0 - - - - 9.9 8.8 9.3 8.1 9.1 8.2 - -
    5 - - - - 9.4 8.7 9.0 7.9 8.3 8.1 - -
E5 COD [mg l-1]
    Station 1, 1981-1983
    Depth [m] Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    0 - - - - 2.1 2.3 3.0 2.8 2.9 3.0 - -
    5 - - - - 2.4 2.3 3.0 2.7 3.4 3.1 - -
E7 NITROGEN CONCENTRATION
  • Total-N [mg l-1]

    Station 1 1981-1983
    Depth [m] Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    0 - - - - 0.14 0.13 0.14 0.17 0.15 0.38 - -
    5 - - - - 0.12 0.18 0.15 0.31 0.15 0.44 - -
E8 PHOSPHORUS CONCENTRATION
  • Total-P [mg l-1]

    Station 1, 1981-1983
    Depth [m] Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    0 - - - - 0.036 0.024 0.025 0.035 0.054 0.049 - -
    5 - - - - 0.041 0.029 0.015 0.032 0.035 0.052 - -
E10 PAST TRENDS: Fig. ASI-21-2.

    Fig. ASI-21-2
    Trend of transparency at the lake centre (7).


F. BIOLOGICAL FEATURES (Q)

F1 FLORA
  • Emerged macrophytes: Phragmiltes communis.

  • Floating macrophytes: Nuphar sp.

  • Submerged macrophytes
    Potamogeton crispus, Hydrilla verticillata, Myriophyllum verticillatum, Vallisneria gigantea.
  • Phytoplankton: Melosira italica, Asterionella formosa, Synedra sp.

F2 FAUNA
  • Zooplankton: Daphnia longiremis, Bosmina coregoni, Eurytemora affinis.

  • Benthos: Chironomus plumosus, Tubificidae.

  • Fish
    Oncorhynchus nerka, Cyprinus carpio, Carassius sp., Hypomesus olidus, Leuciscus hakonensis.
F5 FISHERY PRODUCTS (Q)
  • Annual fish catch [metric tons]

    • 1979: 139.

G. SOCIO-ECONOMIC CONDITIONS (Q)

G1 LAND USE IN THE CATCHMENT AREA
    Area [km2] [%]
    Natural landscape
    - Woody vegetation 147 99.3
    Residential area 1 0.7
    Total 148 100.0
  • Main types of woody vegetation (8)
    Deciduous broadleaf forest (Betula ermanii, Quercus mongolica var. grosseserrata, Acer mono, Cercidiphyllum japonicum); evergreen conifer forest (Picea jezoensis, Abies sachalinensis).
G2 INDUSTRIES IN THE CATCHMENT AREA AND THE LAKE (Q)
    No.of establishments Main products or major industries
    Primary industry
    Fisheries - Kokanee salmon, smelt and carp
    Tertiary industry Several facilities for tourists
G3 POPULATION IN THE CATCHMENT AREA (Q)
    1982
    Population Population density [km-2] Major cities (population)
    Rural 2,100 -
    Total 2,100 14.4

H. LAKE UTILIZATION

H1 LAKE UTILIZATION
    Tourism, recreation (sport-fishing, yachting) and fisheries.

M. LEGISLATIVE AND INSTITUTIONAL MEASURES FOR UPGRADING LAKE ENVIRONMENTS

M1 NATIONAL AND LOCAL LAWS CONCERNED
    For national laws see "Biwa-ko".

N. SOURCES OF DATA

  1. Questionnaire filled by the Prefectural Government of Hokkaido.
  2. Imada, K., Ito, T., Yoshizumi, Y. & amp;Yonekawa, T. (1981) Fluctuations of transparency, COD and several dissolved ions in Lake Akan (1973-1980). Sci. Rep. Hokkaido Fish Hatchery, 36: 33-50.*
  3. Miyadi, D. (1932) Studies on the bottom fauna of Japanese Lakes VII. Lakes of Hokkaido. Jap. J. Zool., 4: 223-252.
  4. Kitagawa, N. (1976) Studies on the benthos fauna of four lakes (Kussharo, Akan, Toro, Shikaribetsu) in the eastern part of Hokkaido. Jap. J. Limnol., 37: 37-41.*
  5. Japan Map Centre, (ed.)(1982) Collection of Maps on Japanese Lakes (Technical Data of National Geographical Institute, D 1-No.221). National Geographical Institute, Tsukuba.*
  6. Horie, M. (1956) Morphometry of Japanese lakes. Jap. J. Limnol., 18: 1 28.
  7. Uchida, E., Asakura, T. & Kawamura, T., (ed.)(1983) Meteorological Data of Japan. 1060 pp. Toyo-keizaishinpo-sha, Tokyo.*
  8. Yoshizumi, Y., Ito, T., Imada, K., Awakura, T. & Okamoto, M. (1976) Water quality of Lake Akan and inflowing rivers (1972-1976). Sci. Rep. Hokkaido Fish Hatchery, 31: 113-154.*

    9. * Printed in Japanese. The titles are tentatively translated into English.