Tidal Flat Restoration in Fushino River basin

by the cooperative works of various sectors

Masao Ukita (Yamaguchi University) and Hajime Yamano (Yamaguchi prefecture)

The 2nd Seminar of PEMSEA18th Jul.2008, Tokyo

Contents

• Introduction of Fushino River Basin and Yamaguchi Estuary

• Problems in Yamaguchi EstuaryThe causes of the decrease of short-necked clam

• Background of the Tidal Flat Restoration• Activities of the Conference of Tidal Flat Restoration in

Fushino River Basin

• Conclusion and Future Tasks for Sato-umi Restoration

Yamaguchi estuary

Fushino river

Fushino RiverArea : 322 km2

Length : 30.3 kmMountain height: ～ 700 mPopulation: 108,000Estuary: 1700 haTidal flats: 350 ha

Planned area of fertile river basin

Prefecturaloffice

写真： 第５次山口市総合計画

River mouth area of Fushino River

Upstream view of Fushino river just beneath Aratani dam reservoir

2006.5.16

There are only 2, 3 dams. Those tributary areas are not large in the river basin, totally less than 5%.

Ichinosaka river near prefecture office, nationwide famous for fire-fly river construction

Midstream view of Fushino river

2006.8.15

Fushino river is relatively nature rich even in midstream.

Over view from Yamaguchi estuary to Fushino river basinThere are wide tidal flats Naka-gata, Shinchi-gata and Minami-gata etc, totally 350 ha. We can find many kinds of bird, and endangered species horseshoe crabs are still alive.

Recent state of Fushino river basin• Fushino river is relatively familiar among people,

and there are many activities for protecting and loving river environment.

• Water quality has become very clean accom-panied by the sewage and similar system over 80%.

• Amenity evaluation is rather good too. However,• Fishery productivity of Yamaguchi estuary has

become decreased remarkably for these 40 years.• Sea grass field has decreased since 1950s.• Consequently, fishery industry decayed

remarkably.

Change of the area of eel grass field in Yamaguchi estuary

0

200

400

600

800

1000

1200

1950 1960 1970 1980 1990 2000 2010

Are

a o

f eel gra

ss f

ield

（ha）

Yamaguchi esturay

Yamaguchi PrefectureSeto Inland Sea

Damage byTyphoon 18

The area of sea grass field decreased from 700ha 1950s to almostzero 1990. Recently we can see the tendency of recovering.

図 ８　埋立域の拡大とアマモ場の衰退

After Kawabe

Decay of eel grass field in Yamaguchi Estuary

Aerial distribution of eel glass field in 2005 and 2008

Change of fishery production in Yamaguchi estuary

0

500

1000

1500

2000

1970

1980

1990

2000

2002

（to

ns／

year）

Clam shell

Total fishery product

Clam shell production decreased remarkably from 1500 t in 1970 tozero in 1991. Total fishery production decreased similarly near to 1/10.

(Shot-necked clam)

Possible causes of clam shell decrease

・ Decrease of nutrient, N,P and other Fe etc.・ Sediment changed finer （Increase of fine particles

supply, and decrease of sand supply)・ Influence of predators ( Small eagle ray Aetobatus

flagellum , Bladder moon shell Glossaulax didyma ）

relating to global warming ・ Abused fishery

of mother shellsin Suo-nada

Change of clam shell production in Yamaguchi prefectureSeto Inland Sea area

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

1958

1960

196

2

1964

1966

196

8

197

0

1972

197

4

1976

1978

198

0

198

2

1984

1986

198

8

1990

199

2

199

4

1996

1998

200

0

2002

2004

(tons

/yea

r)by mechanical diving

by manual digging

Latter purple peaks correspond to over-fishing of mother shellsof short-necked clam from the off-shore area in Suo-nada。It might be due to TV broadcasting of the good quality of “Onoda Asari”

Change of the production of short-necked clamin 3 sea areas in Japan

0

10

20

30

40

50

60

70

1965 1970 1975 1980 1985 1990 1995 2000 2005

1000 t

/ye

arSeto Inland Sea

Ariake Sea

Tokyo Bay Chiba Pref.

1966

1977

1985

The years of maximum production are 1966 Chiba, 1977 Kumamoto(Ariake Sea), and 1985 Seto Inland Sea

周防灘西部の水質と山口県瀬戸内海側の

アサリ生産量の推移

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

1978

1979

1980

1981

1982

1983

1984

1985

1986

1987

1988

1989

1990

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

2002

2003

Tra

nsp

arency

(m), C

OD

(m

g/l), C

lam

shell

(10

3t/

y)

-0.05

0.05

0.15

0.25

0.35

TN

(m

g/l),

TP

(m

g/l)

Transparency

COD

Clam shell near shore

Clam shell total

TN

TP

Transparency

TN

TP

CODJIS

Clam shell total

Clam shell near shore

Change of the water quality and the production of short-necked cram in Western Part of Suo NadaThe concentration of total nitrogen has been decreasing clearly since early 1980’s mainly due to the decrease of industrial load.

Changes of the river basin• Land use: Farmland decreased

paddy field 70 km2 (1965) → 30 km2 (2000) Agriculture: modernized (irrigation, machinery)

• Sewage treatment: 18% (1985) → 67% (2001)• Construction work: Shinkansen(-’75),Highway(-83)• Gravel mining in mountain areas and previous

sand mining in the river mouth area• Land reclamation: 340 ha since 1947

Besides, we should also think the following changes of human activitiesin the river basin for relatively long time scale of 40, 50 years.

～1927170ha

～196960ha

1947～64280ha

～‘59

～‘64

Topographic map in 1902 Land reclamation area and period

Ajisu

Totally 340 ha was reclaimed since 1947.

http://www.pref.kyoto.jp/kankyo/rdb/eco/rs/rs06.html

Change of the style of paddy field increasing turbidityhttp://www.am.zennoh.or.jp/kome/back/sisiyama2004-back/02/kome_info.htm

Cascade use

Moderatemixing

Organicfertilizer

Strongmixing

Inorganicfertilizer

50 years ago At present

Each by each use

Turbidity from paddy fields midstream

2003.5.31

2004.5.13

水田代掻き時の濁り

Rice farming starts at the beginningof rainy season in the western part of Japan.

Turbidity frompaddy field reconstructionsite 2006.6.1

農地改良工事の影響

Turbidity fromroad construction site

2005.7.3

Change of the particle size of tidal flats in Yamaguchi Estuary

The median values of surface mud have decreased even during 15 years

山口湾

秋穂湾

大海湾

椹野川

佐波川×

×

×

×

中潟

新地潟

南潟

直上水の水質時間変化の比較地点

Why fine particle size not good for short-necked clam ?

Sampling points of water quality near bottom (B+0.1m) for comparing Yamaguchi estuary and Ohmi estuary

Naka-gata

Shinti-gata

Minami-gata

Ohmi

0.0

1.0

2.0

3.0

4.0

5.0

6.0

上潮 下潮 上潮 下潮 上潮 下潮 上潮 下潮 上潮 下潮

南潟(10/16） 新地潟(10/18） 中潟相原(11/3) 大海湾(10/25） 大海湾(11/2)

Chl.a

　（μ

g/l）

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

上潮 下潮 上潮 下潮 上潮 下潮 上潮 下潮 上潮 下潮

南潟(10/16） 新地潟(10/18） 中潟相原(11/3) 大海湾(10/25） 大海湾(11/2)

Chl.a

/S

S　

（μ

g/m

g）

Comparison of overlying water quality（2004）

The amount and quality of feed inOhmi estuary was better than Yamaguchi estuary

Chl.a

Chl.a/SS

餌の量Amountof feed

餌の質Qualityof feed

山口湾 大海湾

左：上げ潮時Left Up-tide右：下げ潮時Right Web-tide

0

100

200

13:00 14:00 15:00 16:00

Chl-

a(m

g/L)

0

10

20

30

40

50

Chl.a

/S

S（μ

g/m

g）

2004年8月11日（surface layer）

Full tide

相原河口部における微細粒子性状の過去との比較

海由来の粒子の Chl.a/SS は 20年前と比べて全層水4～5‰ から、表層水でも 1‰ と小さくなっており、アサリ

の餌の量および質が、悪くなっている。

：Chl-a/SS×10

0

100

200

7:00 9:00 11:00 13:00 15:00 17:00 19:00

Chl-

a（μ

g/L）

0

10

20

30

40

50

Chl-

a/S

S*10

1982年8月11日（whole layer）

Full tide

：Chl-a

Chl-a has decreased, and Chl-a/SS has become smaller from 4-5‰ to 1‰ even in surface layer. The quality of feed particles becomes poorer than 20 years before.

Comparison of the quality of SS at the river mouthin the summer 1982 and 2004

Measures to Create a Lively River Basin～ Fushino River Model ～

• Yamaguchi Prefecture started the committee to discuss unified environmental management of river basins. Plan was proposed for Fushino river basin as the model Mar 2003 after 1 year’s discussion.

In the plan,• Target : Cyclic-Symbiotic Society connected with river

from forest to sea• Key words :

‘Local production and local consumption’‘Think of source when drink water’‘Co-operation between upper and lower basins and among various sectors’

Main Activities of River Basin Project• Sound cycle of water

Safer river protecting against floodAmple water and effective useWater quality conservation

• Preserving ecosystemsNature-rich river constructionFire-flies living and Fish ascending & descending riverRestoring productive tidal flats and sea grass field

• Activation of local industry Forestry, Agriculture, Fishery & Traditional industries

• Cooperation of upper and lower basinsContact with river, culture and legendsLocal money, Fushino River Forum, Environ.education

Citizens

Voluntary Work implementing Group

Local Money managing Organization

Local money 1 f (ushino) =1 yen

fservice

voluntary work f

contract

SupportersShops, Restaurant, Tea rooms

etc.

Structure of local money in Fushino River Basin

n=39

n=331st year 620,000 f

13,000 f

2003 ～2007, Total participants 19000Total issue, 5.3 million f

N=2700

The first conference onthe restoration of tidal flats in Fushino rivermouth area, organized

by Prefecture, Aug.2004

Conference member : 60

Academics : 9Citizens : 18Organizations : 18Local governments: 11National government: 4

Focusing on the river mouth environment, we followed the Nature Restoration Program of the Ministry of Environment.

Sarobetsuwetland

Kushirowetland

Ogasawaraisland

Inishicoral leaf

Sanbansetidal marsh

Fushino Rivermouth tidal marsh

Gamohtidal marsh

Lake Biwa

Ohdaigahara

Kunugiyama

Kashibaruwetland

11 Projects of NatureRestoration Program in Japan 2004

In 2007, the numberHas increased to 24.( National Park Areas 7Quasi National Park &Wild Animal Protectionareas12, and Other thannatural park areas 5.Our project is one of the last category.)

Basic Concepts of Nature Restoration of Fushino River Mouth / Tidal Flats

• Following the guideline for nature restorationof Ministry of Environment Apr.2003,

① Cooperation of local stakeholdersConsidering complexity of ecosystems ② Based on scientific knowledge ③ Adaptive implementation

Target: Restoration of ‘Sato-Umi’

Sato-umi （里海）

The coastal sea with high productivity andhigh biodiversity under the mankind's interaction

By Prof.Yanagi

Better life through wise and sustainable use of coastal environments

By Prof.Matsuda

Goal allocation for tidal flat environment in Yamaguchi Estuary

耕耘混合砂工法（ 東工区）

カ キ殻粉砕工法（ 西工区）

耕耘混合砂工法（東工区）

カキ殻粉砕耕耘工法（西工区）

Mechanical works for sediment improvement in Naka-gataMixing up set down and with sand Crushing oyster shell

ControlClushingoyster shell

MixingUp set down

Effect of improvement works( after 2 years )

Cla

m s

hell

dens

ity

(number/m2)

Manpower improvement of sediment and plantation in Minami-gata

Making ridges Making mound

Planting eel grassBamboo fence

Effect of cultivation of Minami-gata tidal flat ( 2007)

Den

sity

of c

lam

she

ll

larg

er th

an 2

cm(number/m2)

Bamboo fencesControlControl with net cover

Ridge with net cover

Unfortunately the effect of plowing can not be clearly seen.The effect of preventing eagle ray’s damage was only clear. The cover with fishing net on plowed mound was the best.

Voluntary work to set fish beds consist of cast iron cages and thinning wood to testthe effect of iron and humic substance

Concluding remarks (1)• Restoring project is going almost successfully

during 5 years. The effect of the project can be gradually seen, though it is not clearly monitored except that eel grass field tends to increase.

• The cause of poor fishery production is complicated and not clearly elucidated. Therefore scientific study on ecosystem is needed to clarify the cause.・ effect of global warming and predators ・ cause and effect of fine particle sediments・ others e.g. over-fishing, nutrient condition etc.

Concluding remarks (2) • Voluntary participants well keep enthusiasms to restore

‘Sato-Umi’. However, wider layers of citizens are expected to join.

• Up to now, the leading effort by prefectural government plays very important role. But, it has been becoming difficult to get budget to support the project.

• Reconstruction of social system is necessary to restore ‘Sato-umi’・ Support of budget from public sector including investigation and improvement works of large scale.・ Environmental friendly fishery, forestry and agriculture ・ Slow life with more free time in people’s mind