Lake restoration

1
Lake restoration by external and internal
measures in Lake Tegel and Schlachtensee

• Dr. Inke Schauser and Dr. Ingrid Chorus,
• German Environmental Agency

2
Berlin Lake Tegel and Schlachtensee
PEP
Lake Tegel
Lake Tegel (Main basin) Area
3.060.379 m2 Volume 23.148.783
m3 Max. depth 16 m Water retention
time 75 d PEP since
1985
Schlachtensee Area 420100 m2 Volume
1971000 m3 Max. depth 9 m Water
retention time 210 d PEP since
1981
Schlachtensee
PEP
PEP Phosphorus Elimination Plant
3
Lake Tegel Aeration since 1979
4
Schlachtensee Hypolimnetic withdrawal 1981-1996
5
Objective of external measure Critical external
load
Vollenweider (1976)
LPcrit CPtarget (1 ??)zm/? LPcrit
critical P load g m-2 yr-1 CPtarget
target P inlake concentration g m-3 ?
water retention time yr zm mean lake
depth m
One-Box Model (Sas 1989)
LPcrit CPtarget (? ??)
zm/?   CPlake P concentration in the lake
g m-3 CPin P concentration in the inflow
g m-3 ? outflow factor ? net
sedimentation factor yr-1
6
Before After the Restauration compared to
Target Conditions
Lake Tegel

1984

2002

Target

Vollenweider / One
Box

-
2
-
1
External load g m
yr


54

1.85

1.59 / 2.22

-
1
Net sedimentation coefficient yr


5.2

-
0.09

233.7

Outflow factor
-


0.95

0.81

48.31

Schlachtensee

1980

2002

Target

Vollenweider / One
Box

-
2
-
1
External load g m
yr


4.7

0.1

0.46 / 0.35

-
1
Net sedimentation coefficient yr


0.7

0.34

53.5

Outflow factor

-


0.95

1.03

28.5


7
Lake Tegel Effect of Aeration on Net
Sedimentation
Target 234 yr-1
8
Schlachtensee Effect of HW on Outflow Factor
Target 28.5
9
Reduction of External Load
10
TP and Chlorophyll-a
11
Biodiversity and Phytoplankton Species
Composition
Cryptophytes
Chlorophytes
Diatoms
Cyanobacteria
12
Biodiversity and Phytoplankton Species
Composition
1982 at TP 300 µg/L Chl.-a 60-100 µg/L Zs
0.3 1 m


Cryptophytes
Haptophytes (Chrysochromulina)
Chlorophytes
Diatoms
Dinoflagellates
Desmids
Sulfur bacteria
Chrysophytes
Cyanobacteria
13
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 ?
14
Requirements for Impact on P-Retention

• For Aeration
• Aerobic sorption capacity sufficient (Fe/Pgt12,
  Jensen et al. 1992)
• Sediment oxygen demand lt Additionall oxygen
  supply
• H2S-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
• H2S-Konzentration low