Nuisance Cladophora Blooms in Lake Michigan:

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Nuisance Cladophora Blooms in Lake
Michigan Possible Causes and Management
Options Harvey Bootsma Erica Young John Berges
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The Role of Temperature
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Optimum for Cladophora growth
J J A S O N D J F M A M
J J A S O 2003
2004
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Temperature at the Linnwood Intake (15 m)
Optimum for Cladophora growth
No growth
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The Role of Light
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Irradiance at 10 m, Atwater
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Growth optimum at gt 26 mol m-2 d-1
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5
ive growth
PAR (mol photons m-2 d-1)
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3
-ive growth
2
1
0
July Aug Sep
Oct
1-Jul-04
31-Jul-04
31-Aug-04
30-Sep-04
31-Oct-04
Date
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Mussel invasion
Data provided by MMSD
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Irradiance at 10 m, Atwater
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2004
6
5
ive growth
PAR (mol photons m-2 d-1)
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3
-ive growth
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1991
1
0
July Aug Sep
Oct
1-Jul-04
31-Jul-04
31-Aug-04
30-Sep-04
31-Oct-04
Date
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10 m
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The Role of Phosphorus
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Influence of P on Cladophora Growth Rate
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Cladophora phosphorus content, September 2004
1.2
1.0
1.2
1 mg mg-1
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20-Year Phosphorus Trend at River Junction
TP
mg/L
SRP
82 83 84 85 86 87 88 89 90 91 92 93 94
95 96 97 98 99 00 01
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Is there enough phosphorus coming in from rivers
to support the Cladophora growth that we observe?
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P Sources in the nearshore zone (0 10 m)
Cladophora demand 2,000 kg/day
Milwaukee River 250 kg/day
Mussel recycling 1,700 kg/day
gg
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3-Year Comparison of Cladophora phosphorus
content Lake Michigan
Cladophora P content
mg P mg-1
2004
P limited growth
2006
2005
June July Aug Sep Oct
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1990
8oC
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2005
12oC
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Influence of P on Cladophora Growth Rate
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Conclusions The recent increase in Cladophora
growth is likely due to - Increased water
clarity (more light at lake bottom) - Warmer
water temperatures in summer - increased
phosphorus inputs Although P input from rivers
has increased, there must also be an internal
source of P in the lake that is promoting
Cladophora growth. We suspect dreissenid
mussels. Future work must focus on the fate of
river-borne phosphorus, and the importance of
mussels as a phosphorus source. An important
question to answer If we lower P input from
rivers, will there be less Cladophora?
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