SHINJI-KO (LAKE SHINJI)

A view from the eastern lakeshore


Photo: A.Kurata

A. LOCATION

• Shimane Prefecture, Japan.


• 35:27N, 132:57E; 0.30 m above sea level.

B. DESCRIPTION

The Shimane Peninsula, which now separates the two sister lakes, Lake Shinji and Lake Naka-umi, from the Japan Sea, was a hilly island during the post- glacial hypsithermal period, but was reconnected with the mainland (Honshu) a few thousand years B. C., due to the retrogression of the sea and the alluvial deposits of rivers. The water body, thus isolated from the sea by a sand bar (Yumigahama) at the eastern end and an alluvial plain (Izumo Plain) at the western end, was further split into the two sister lakes during the medieval age by the formation of the Matsue Plain. The Hii River, which once entered the Japan Sea directly, was deflected into the western end of Lake Shinji due to marine drift during the Edo Era (1600-1867 A. D.), accelerating the sedimentation and desalinization of the lake.
The present conditions of Lakes Shinji and Naka-umi were brought about by the dredging of a channel between the two lakes that started in 1922. The dredging reduced the danger of flood disaster on Lake Shinji's coasts, but helped the temporary invasion of brackish water from Lake Naka-umi into the lake, causing salt damage on coastal crop fields in seasons of drought. Lake Shinji is now a slightly brackish lake with a normal chlorine ion concentration of 1-2 g l-1.
Agriculture used to be the prevailing industry in the drainage basin of Lake Shinji, especially on the plain along the Hii River. Since 1966, efforts have been made to establish a new industrial zone along the coasts of the two lakes, which will be turned into freshwater lakes on completion of the project. A new dam has recently been completed at the mouth of Lake Naka-umi leading to the sea to turn it into a freshwater lake which could be the source of water for industrial and agricultural use. The partial reclamation of Lake Naka-umi is now also under way. It is, however, expected that complete desalinization of the two lakes results in accelerated eutrophication as well as in a fatal damage on fisheries which has so far mainly depended on brackish water fishes and mussels. The long controversy between the responsible government bodies and the local opponents against the development project has very recently come to an end by the former's decision in 1988 to stop ongoing works temporarily for reconsideration of the whole project.

C. PHYSICAL DIMENSIONS (Q)

Surface area [km2]	80
Volume [km3]	0.366
Maximum depth [m]	6.4
Mean depth [m]	4.5
Length of shoreline [km]	45
Residence time [yr]	0.3
Catchment area [km2]	1,966

D. PHYSIOGRAPHIC FEATURES

D1 GEOGRAPHICAL (Q)

• Bathymetric map: Fig. ASI-42-01.


• Names of main islands: Yomega-shima.


• Number of outflowing rivers and channels (name)
  3 (Ohashi R., Tenjingawa and Sadagawa Canal).

D2 CLIMATIC

• Climatic data at Matsue, 1951-1980 (2)

	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec	Ann.
Mean temp. [deg C]	3.8	4.2	7.0	12.5	17.0	20.8	25.2	26.4	22.0	16.2	11.1	6.5	14.4
Precipitation [mm]	166	150	128	129	128	187	282	159	209	138	136	144	1,956

• Number of hours of bright sunshine: 1,939 hr yr-1.


• Solar radiation (1941-1970): 11.86 MJ m-2 day-1.


• Snowfall: 0.30 m.

Fig. ASI-42-01
Bathymetric map (1).

• Water temperature [deg C](Q)

Station 1, 1985
Depth [m]	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
S*	3.6	3.8	8.1	16.5	21.0	22.0	26.2	30.3	23.0	20.7	10.5	3.8
5.5	3.9	4.5	7.2	16.4	20.0	22.1	24.5	29.7	22.5	20.6	10.5	4.0

* Surface.

• Freezing period: None.


• Mixing type: Polymictic.

E. LAKE WATER QUALITY

E1 TRANSPARENCY [m](Q)

Station 1, 1985
Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
1.5	1.0	0.7	1.5	1.4	0.7	1.4	2.0	0.9	1.1	1.4	1.0

E2 pH (Q)

Station 1, 1985
Depth [m]	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
0.5	7.4	7.6	8.7	8.0	8.0	7.6	8.8	8.5	8.5	8.3	7.6	7.4
5.5	7.6	7.6	8.7	8.1	7.5	7.2	8.5	7.4	8.3	7.9	7.5	7.5

E3 SS [mg l-1](Q)

Station 1, 1985
Depth [m]	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
0.5	7	6	10	4	4	10	6	4	7	5	4	6
5.5	6	8	8	5	6	5	7	3	6	6	9	6

E4 DO [mg l-1](Q)

Station 1, 1985
Depth [m]	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
0.5	13	14	14	8.6	8.7	8.8	9.7	7.4	10.9	9.2	10	-
5.5	13	14	13	8.7	7.6	<0.5	7.2	-	9.2	8.9	10	-

E5 COD [mg l-1](Q)

Determined by KMnO4 method.

Station 1, 1985
Depth [m]	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
0.5	5.0	3.6	4.3	3.6	3.7	4.3	4.1	4.9	5.1	4.4	2.9	3.2
5.5	3.9	4.0	4.0	3.6	3.5	3.7	4.3	4.5	4.3	4.1	3.0	3.2

E6 CHLOROPHYLL CONCENTRATION [micro l-1](Q)

Station 1, 1985
Depth [m]	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
0.5	29	9.6	41	11	9.8	18	20	20	12	40	13	21
5.5	21	9.8	49	13	8.3	10	10	30	4.8	30	9.3	21

E7 NITROGEN CONCENTRATION (Q)

• Total-N [mg l-1]

Station 1, 1985
Depth [m]	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
0.5	0.56	0.70	0.51	0.26	0.40	0.57	0.48	0.58	0.53	0.46	0.40	0.33
5.5	0.52	0.68	0.70	0.29	0.44	0.62	0.40	0.72	0.34	0.50	0.42	0.30

E8 PHOSPHORUS CONCENTRATION (Q)

• Total-P [mg l-1]

Station 1, 1985
Depth [m]	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
0.5	.056	.042	.053	.021	.027	.054	.029	.051	.046	.037	.038	.024
5.5	.048	.051	.046	.025	.037	.099	.055	.012	.044	.038	.042	.026

E9 CHLORIDE CONCENTRATION [ ](Q)

• Chlorinity

Station 1, 1985
Depth [m]	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
0.5	4.0	3.5	1.8	1.2	1.3	1.0	0.66	1.1	1.5	1.4	2.0	2.1
5.5	4.4	9.4	2.2	1.2	2.3	4.1	0.76	5.2	1.7	1.4	2.0	2.1

E10 PAST TRENDS: Fig. ASI-42-02.

Fig. ASI-42-02
Trend of transparency (4).

F. BIOLOGICAL FEATURES

F1 FLORA (Q)

• Emerged macrophytes: Zizania latifolia, phragmites communis, P. japonica.


• Floating macrophytes
  Brasenia schreberi, Lemna trisulca, Trapa japonica, T. j. var. rubeola, Spirodela polyrhiza.
• Submerged macrophytes
  Myriophyllum verticillatum, Egeria densa, Potamogeton pusillus.
• Phytoplankton
  Cyclotella nana, Cryptomonas sp., Coelosphaerium kuetzingianum, Chlamydomonas sp., Chroococcus sp.

F2 FAUNA

• Zooplankton
  Diaphanosoma brachyurum, Sinocalanus tenellus, Pseudodiaptomus inopinus, Evadne tergestina.
• Benthos
  Chironomus plumosus, Corbicula japonica, Pentaneura sp., Tubifex sp.
• Fish
  Hypomesus transpacificus, Salangichthys microdon, Anguilla japonica, Carassius gibelio.

F5 FISHERY PRODUCTS (Q)

• Annual fish catch [metric tons]
  1984: 740.
• Fishery products other than fish [metric tons]
  1984: 13,240*.
  * Mostly Corbicula.

G. SOCIO-ECONOMIC CONDITIONS

G1 LAND USE IN THE CATCHMENT AREA (Q) (1981)

	Area [km2]	[%]
Natural landscape Woody vegetation	949.0	72.2
Agricultural land	180.9	13.8
Residential area	78.6	6.0
Others	105.5	8.0
Total	1,314.0	100

• Main types of woody vegetation (3)
  Deciduous broadleaf forest (Quercus serrata, Q. acutissima, Castanea crenata); pine forest (Pinus densiflora); evergreen broadleaf forest (Castanopsis cuspidata, Quercus spp.); evergreen conifer plantation (Cryptomeria japonica, Chamaecyparis obtusa).
• Main types of herbaceous vegetation: Grassland and weed (3).


• Main kinds of crops: Rice and vegetables (Q).

G3 POPULATION IN THE CATCHMENT AREA (Q) (1980)

	Population	Population density [km-2]	Major cities (population)
Total	263,300	132	Matsue, Hirata

H. LAKE UTILIZATION

H1 LAKE UTILIZATION (Q)

Sightseeing and tourism, recreation (sport-fishing and yachting) and fisheries.

H2 THE LAKE AS WATER RESOURCE (Q) (1985)

Not used.

I. DETERIORATION OF LAKE ENVIRONMENTS AND HAZARDS (Q)

I1 ENHANCED SILTATION

• Extent of damage: None.

I2 TOXIC CONTAMINATION

• Present status: None.

I3 EUTROPHICATION

• Nuisance caused by eutrophication
  Unusual bloom of Microcystis aeruginosa, Anabaena sp. and Oscillatoria sp.
• Nitrogen and phosphorus loadings to the lake [metric tons year-1]
  1980 Sources Industrial Domestic Agricultural Natural Total T-N 29.2 251.5 701.5 432.9 1,415.1 T-P 2.9 43.1 46.4 20.4 112.8

• Supplementary notes
  Shinji-ko/Naka-umi Water Quality Management Plan has been established in December 1983 and various schemes for the reduction of pollution loads have been put in practice.

I4 ACIDIFICATION

• Extent of damage: No information.

J. WASTEWATER TREATMENTS (Q)

J3 SANITARY FACILITIES AND SEWERAGE

• Municipal wastewater treatment systems:
  Number of secondary treatment system: 1 (activated sludge).
  Number of nightsoil treatment system: 4.

L. DEVELOPMENT PLANS

Naka-umi New Industrial City Development Plan (1963-).

M. LEGISLATIVE AND INSTITUTIONAL MEASURES FOR UPGRADING LAKE ENVIRONMENTS

M1 NATIONAL AND LOCAL LAWS CONCERNED

• Names of the laws (the year of legislation)


1. For national laws see "Biwa-ko".
• Responsible authorities


1. Shimane Prefectural Government

M2 INSTITUTIONAL MEASURES

1. Izumo Construction office, Ministry of Construction, Japan
2. Naka-umi Reclamation Office, Ministry of Agriculture and Fisheries
3. Shimane Prefectural Government

M3 RESEARCH INSTITUTES ENGAGED IN THE LAKE ENVIRONMENT STUDIES

1. Shimane Prefectural Institute of Sanitation and Control of Public Nuisances
2. Shimane University

N. SOURCES OF DATA

17. Questionnaire filled by Shimane Prefectural Government.
1. Japan Map Centre (ed.)(1982) Maps of Japanese Lakes (Nihon no Kosho Zushu). Technical Data D1-No. 221, Geogr. Survey Inst., Ministry of Construction, Tsukuba.*
2. Uchida, E., Asakura, T. & Kawamura, T. (ed.)(1983) Handbook of Japanese Weather, Vol. 2 (Nihon Kisho Soran, Gekan). 1060 pp. Toyo-Keizaishinpo sha, Tokyo.*
3. Environment Agency (ed.)(1982) The 2nd National Survey on the Natural Environment (vegetation), Actual Vegetation Map. Shimane Prefecture (Dai 2-kai Shizen Kankyo Hozen Kiso Chosa (Shokusei Chosa), Genzon Shokusei-zu, Shimane-ken). Japan Wildlife Research Centre, Tokyo.*
4. Kawakami, S, (1982) Journal of Water & Waste (Yosui to Haisui), 24, 1005 1016.*

* Printed in Japanese. The titles are tentatively translated into English with original titles in romanized Japanese in parentheses.