The Second International Workshop and the Sixth Annual Meetingfor Water Environmental Partnership in Asia (WEPA)Tokyo, Japan
23 February 2011

How can we save lakes affected by Climate Change?
Michio Kumagai
Lake Biwa Environmental Research Institute, Otsu, Japan

Background
Something is happening.
Many scientists studying lake and river ecosystems of the world
may have such a perspective.
Actually, water temperature in many lakes is rising, flora andfauna are changing and the dead zones with low dissolved
oxygen concentrations are expanding.
IPCC predicts air temperature will rise by 2-4˚C by the end of thiscentury, but the actual air temperature increase in the East Asia
is close to almost double the prediction.
Beside the discussion on the causes of global warming, we haveto face the real problems occurring in freshwater ecosystems.

Climate Change

1900

Global Warming

Broecker 1975, Science

Global Heating

Lovelock 1979, 2008, Nature

Case of Lake Biwa

60km

Map of Lake Biwa produced by Tadataka INOU in 1805-1806

In the case of Lake Biwa, the largest ancientlake in Japan, many fish including the gobby(benthic and endemic to Lake Biwa) werekilled in 2007. Since then, similar events have
happened every year.
We also found high concentrations of arsenicin the dead fish as well as the bottom
sediments.
These were caused by anoxic conditions in
the benthic boundary, which may be originatedfrom eutrophication and global warming.

Change of Surface Water Temperature in Lake Biwa
17.5

Water Temperature ( ℃)

17.0

Estimation
Observed Data by Fishery Station

16.5

16.0

15.5

15.0

Rise of water temperature after 1985...
14.5
1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010

Microbial ecosystem in Lake
Biwa has definitely changed
after the middle of 1980s.

This was probably caused byglobal warming.

Reduction of vertical mixing.

Depletion of dissolved oxygenin BBL

Mass mortality of benthic fishModern Monitoring basedon High Technology

AUV Tantan

Pictures taken by AUV Tantan

40cm

Seasonal Change in Dissolved Oxygen Concentration
at the deepest place in Lake Biwa from 2001 to 2007
14.0
13.0

2001年

12.0

2002年

11.0

2003年
2004年

DO （ ｍｇ／L）

10.0

2005年

9.0

2006年

8.0

2007年

7.0
6.0
5.0
4.0
3.0
2.0
1.0
0.0
JanFebMar

AprMayJunJulMonthAug

SepOctNovDecDO (mg/l)

Dead Zone in Lake Biwa

Isaza Gobi Fish（2002～2010）

Water Temperature (℃)

13.00

2002年12月
2003年10月
2003年12月
2004年12月
2005年12月
2006年12月
2007年12月dead2007年12月
2008年12月
2009年12月
2010年4月

12.00

11.00

10.00

9.00

8.00

7.00
0.00

2.00

4.00

6.00

DO（mg/L）

8.00

10.00

12.00

101976

1976

10000

20000

00

2

2442009

68
10121976

1404000

8000 12000

Mn (mg/kg)

200

400

8106001976

8101976140100As (mg/kg)

101976C

14

10000 20000 30000 40000

0022442009

68101976

14300

0200300400

2009

68101976

12F

10000

100As (mg/kg)

012D200812C02009

6Mn (mg/kg)

2009

612D

06As (mg/kg)

Depth (cm)Depth (cm)M n (m g/kg)

4

2009

14

Depth (cm)0B15212B
152

Depth (cm)

1004

2009

5Depth (cm)

2009

50

Depth (cm)0Depth (cm)Depth (cm)

01420000Mn (mg/kg)

図1 琵琶湖底泥中のマンガンとヒ素の鉛直分布の1976年と2009年の比較（愛媛大学沿岸海洋研究センター測定）

0100

F
200

300

As (mg/kg)

Comparison of Mn and As in sediments between 1976 and 2009

Picture at deepest point in lake Biwa（by AUV Tantan on August 25, 2006）

Hydrothermal plume at Lake Biwa (by AUV Tantan on December 27, 2009)

Global warming may suppress currents in BBL and ventilation system between waterand sediment can be changed

Water temperature（℃）
7.93

7.94

7.95

7.96

7.97

7.98

7.99

8

8.01

80
81
82

Depth（ｍ）

83
84
85
86
87
88
89

Inversion of watertemperature

90
91

Water temperature profile in the BBL of Lake Biwa (September 2010)

2m

Hydrothermal vent in Lake Biwa
(by AUV Tantan on December 17, 2010)

M7.6

M7.4

Air Temperature change at Lake Biwa (from bore core analysis) andYakushima Island (from tree ring analysis) （Goto et al. 2005）

Lake Biwa seems to have stepped over thetipping point as the ecological regime shifts
brought by climate change.
The dominant species of phytoplankton shiftedfrom diatoms to cyanobacteria, and domestic
fish were replaced by exotic fish such as
bigmouth bass and blue gills which preferwarm water.
What can we do to solve these nuisanceproblems?
Unfortunately, we do not have a perfectsolution to overcome the crisis.

Conclusion
We need good monitoring systems based on
science to share information and data withpeople who live in the region.
Science may be one of the most important
languages to communicate between humanbeings and nature.
If the obtained data are wrong or they do nothave enough accuracy, we will make baddecisions.

Then we need good analyses and models toevaluate the present situation and predict
future changes.
Also we are sometimes required to present
effective action plans to remediate aquaticenvironments.
We have to think that nature is changing very
dynamically over the last few decades andassess both optimistic and pessimisticscenarios.

ASLO (Advancing the Science of Limnology and Oceanography) will be heldat Lake Biwa on July 8-13, 2012.

ACKNOWLEDGEMENT

This study was financially supported by(1) Grants-in-Aid for Scientific Research(20244079) from the Japan Society for thePromotion of Science(2) the Global Environmental Research Fund
(Fa-084) of the Ministry of the Environment,
Japan.