Nuisance Nuisance CladophoraCladophora Blooms in Lake Michigan: Blooms in Lake Michigan:

Possible Causes and Management OptionsPossible Causes and Management Options

Harvey BootsmaHarvey BootsmaErica YoungErica YoungJohn BergesJohn Berges

HARD SUBSTRATE

NUTRIENTSPhosphorus

LIGHT

13 – 17oCTEMPERATURE

The Role of TemperatureThe Role of Temperature

Temperature at 10 m, Atwater

0

5

10

15

20

25

31-May-03 30-Jun-03 31-Jul-03 30-Aug-03 30-Sep-03 30-Oct-03 30-Nov-03 30-Dec-03 30-Jan-04 29-Feb-04 31-Mar-04 30-Apr-04 31-May-04 30-Jun-04 31-Jul-04 30-Aug-04 30-Sep-04

Date

Tem

per

atu

re (

oC

)

J J A S O N D J F M A M J J A S O 2003 2004

Optimum for Cladophora growth

456789

1011121314

1975 1980 1985 1990 1995 2000YEAR

Temperature at the Linnwood Intake (15 m)

Optimum for Cladophora growth

No growth

The Role of LightThe Role of Light

0

1

2

3

4

5

6

7

1-Jul-04 31-Jul-04 31-Aug-04 30-Sep-04 31-Oct-040

1

2

3

4

5

6

7

1-Jul-04 31-Jul-04 31-Aug-04 30-Sep-04 31-Oct-04

+ive growth

Growth optimum at > 26 mol m-2 d-1

-ive growth-ive growth

July Aug Sep Oct

PA

R (

mo

l p

ho

ton

s m

-2 d

-1)

Date

Irradiance at 10 m, Atwater

Annual Secchi Disk Data For Outer Harbor Site 13

Secch

i (Meters) Median

25%-75% Non-Outlier Range

OH-13

19901991

19921993

19941995

19961997

19981999

20002001

20020

1

2

3

4

5

6

7

8

9

10

Data provided by MMSD

Musselinvasion

0

1

2

3

4

5

6

7

1-Jul-04 31-Jul-04 31-Aug-04 30-Sep-04 31-Oct-04

+ive growth

-ive growth-ive growth

July Aug Sep Oct

PA

R (

mo

l p

ho

ton

s m

-2 d

-1)

Date

Irradiance at 10 m, Atwater

2004

1991

10 m

The Role of PhosphorusThe Role of Phosphorus

Influence of P on Cladophora Growth RateN

et

Speci

fic

Gro

wth

Rate

(d

-1)

0.6

0.00.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

0.4

0.2

Stored Phosphorus (%P)

0.8

1 g mg-1

1.2

1.0

1.2

1.0

1.7

1.6

Cladophora phosphorus content, September 2004

0

0.05

0.1

0.15

0.2

0.25

0.3

1 /1 /8 2 1 /1 /8 3 1 /1 /8 4 1 2 /3 1 /8 4 1 /1 /8 6 1 /1 /8 7 1 /1 /8 8 1 2 /3 1 /8 8 1 /1 /9 0 1 /1 /9 1 1 /1 /9 2 1 2 /3 1 /9 2 1 /1 /9 4 1 /1 /9 5 1 /1 /9 6 1 2 /3 1 /9 6 1 /1 /9 8 1 /1 /9 9 1 /1 /0 0 1 2 /3 1 /0 0 1 /1 /0 2

mg

/L

SRP

TP

82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 00 01

20-Year Phosphorus Trend at River Junction

Is there enough phosphorus coming in from rivers to support the Cladophora growth that we observe?

10 km

Milw

aukee R

.

Kinnickinnic R.

Menomonee R.

Milwaukee River = 250 kg/day

P Sources in the nearshore zone (0 – 10 m)

Mussel recycling = 1,700 kg/daygg

Cladophora demand ~ 2,000 kg/day

June July Aug Sep Oct0

0.5

1

1.5

2

0

50

100

150

200

m3 s

-1

May June July Aug Sep Oct

2004

2005

2006

Milwaukee River discharge

3-Year Comparison of Cladophora phosphorus contentLake Michigan

Cladophora P content

g P

mg

-1

2004

2005

2006

P limitedgrowth

8oC

River P

•• • ••••

••

•

•

•

•

•

•

•

••

• ••

• ••••

• •

•• •

• • •• •

• •• • ••

•

•

•• • •••• ••

•

• •••

• • • •••

••

•

•

•

•

•

••

•

• •

•

•

•

•

•

•

•

•

•

•

•

•

•

•

•

P

1990

5 m

12oC

River P

••••

•

•

•

••

•• ••• •• ••

•••••••••

•

• ••••

•

• ••

•

•

•

•

• •••

•• •

••

• •

•

•

•

• •

•

• •

•

•

•

••

•

•

P

2005

10 m

Net

Speci

fic

Gro

wth

Rate

(d

-1)

0.6

0.00.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

0.4

0.2

Stored Phosphorus (%P)

0.8

Influence of P on Cladophora Growth Rate

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?