measures in Lake Tegel and

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Lake restoration


by external and internal
measures in Lake Tegel and
Schlachtensee


Dr. Inke Schauser and Dr. Ingrid Chorus,

German Environmental Agency


OWA
OWA
Berlin:

Lake Tegel and
Schlachtensee

Lake Tegel (Main basin)


Area


3.060.379 m
2

Volume


23.148.783 m
3

Max. depth


16 m

Water retention time


~ 75 d

PEP since 1985

Schlachtensee


Area



420100 m
2

Volume



1971000 m
3

Max. depth


~ 9 m

Water retention time


~ 210 d

PEP since



1981

PEP

PEP

Lake Tegel

Schlachtensee

PEP = Phosphorus Elimination Plant

Lake Tegel: Aeration since 1979

Schlachtensee: Hypolimnetic withdrawal 1981
-
1996

Objective of external measure: Critical external load

LP
crit



= CP
target

* (1+

)*z
m
/






LP
crit



= critical P load [g m
-
2

yr
-
1
]

CP
target

= target P inlake concentration [g m
-
3
]





= water retention time [yr]

z
m



= mean lake depth [m]

Vollenweider (1976)

One
-
Box Model (Sas 1989)


LP
crit



= CP
target

* (


+

*

) * z
m
/





CP
lake


= P concentration in the lake [g m
-
3
]

CP
in


= P concentration in the inflow [g m
-
3
]




= outflow factor




= net sedimentation factor [yr
-
1
]

Before & After the Restauration

compared to Target Conditions

Lake Tegel



1984



2002



Target



Vollenweider / One


Box



External load [g m

-

2


yr

-

1

]



54



1.85



1.59 / 2.22



Net sedimentation coefficient [yr

-

1

]



5.2



-

0.09



233.7



Outflow factor [

-

]



0.95



0.81



48.31



Schlachtensee



1980



2002



Target



Vollenweider / One


Box



External load [g m

-

2


yr

-

1

]



4.7



0.1



0.46 / 0.35



Net sedimentation coefficient [yr

-

1

]



0.7



0.34



53.5



Outflow factor


[

-

]



0.95



1.03



28.5





Lake Tegel: Effect of Aeration on Net Sedimentation

-
6

-
4

-
2

0

2

4

6

1984

1986

1988

1990

1992

1994

1996

1998

2000

2002

0

50

100

150

200

250

300

Net sedimentation coefficent

Days of aeration

Net sedimentation coefficent [yr
-
1
]

Days of aeration [d yr
-
1
]

Activation of PEP Tegel

Target: 234 yr
-
1


Schlachtensee: Effect of HW on Outflow Factor

0

2

4

6

8

10

12

14

1980

1982

1984

1986

1988

1990

1992

1994

1996

1998

2000


Outflow factor



Years with Hypolimnetic Withdrawal

2002

Target: 28.5

Reduction of External Load

0.1

1.0

10.0

100.0

1980

1982

1984

1986

1988

1990

1992

1994

1996

1998

2000

2002

Schlachtensee

Lake Tegel

External P load [g m
-
2

yr
-
1
]

TP and
Chlorophyll
-
a

0

200

400

600

800

1000

1980

1982

1984

1986

1988

1990

1992

1994

1996

1998

2000

2002

2004

0

50

100

150

200

250

1984

1986

1988

1990

1992

1994

1996

1998

2000

2002

2004

0

50

100

150

200

250

0

200

400

600

800

1000

TP [µg L
-
1
]

Chl
-
a [µg L
-
1
]

TP [µg L
-
1
]

Chl
-
a [µg L
-
1
]

Activation of PEP Tegel

Lake Tegel, 1 m


Schlachtensee, 1 m


Activation of PEP Beelitzhof

Biodiversity and P
hytoplankton Species Composition

1982 at

TP
~

300 µg/L

Chl.
-
a 60
-
100 µg/L


Z
s
= 0.3


1 m





0

5

10

15

20

25

30

35

40

cm³/m³

J

F

M

A

M

J

J

A

S

O

N

D

Cryptophytes

Chlorophytes

Diatoms

Cyanobacteria

1982 at

TP
~

300 µg/L

Chl.
-
a 60
-
100 µg/L


Z
s
= 0.3


1 m





0

5

10

15

20

25

30

35

40

cm³/m³

J

F

M

A

M

J

J

A

S

O

N

D

e.g.

1989, 1998


at

TP

~ 20

µ

g/L

µ

Chl

.a 10

-

20

µ

g/L and

-

Z

s

= 1.5



4.0 m

Z

s

= 1.5



4.0 m

1998

0

5

10

15

20

cm³/m³

J

F

M

A

M

J

J

A

S

O

N

D

0

5

10

15

20

cm³/m³

J

F

M

A

M

J

J

A

S

O

N

D

1989

Cryptophytes

Haptophytes (
Chrysochromulina
)

Chlorophytes

Diatoms

Dinoflagellates

Desmids

Sulfur bacteria

Chrysophytes

Cyanobacteria

Biodiversity and P
hytoplankton Species Composition

Conclusion

External measure most effective for oligotrophication:



In Schlachtensee external load below critical external load


In Lake Tegel external load mainly still above


Internal measures have been at most supportive:



In Schlachtensee hypolimnion withdrawal only in first 2 years


In Lake Tegel aeration probably without effect on P retention

WHY ?

Requirements for Impact on P
-
Retention

For Aeration:



Aerobic sorption capacity sufficient (Fe/P>12, Jensen et al. 1992)


Sediment oxygen demand < Additionall oxygen supply


H
2
S
-
Konzentration low

For Hypolimnetic Withdrawal:



Hypolimnion size and P accumulation in hypolimnion


P transformation by mineralisation and desorption high


Water retention time 2
-

5 yr good


H
2
S
-
Konzentration low