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