Great Lakes Offshore Biological Desert and the Nearshore Slime Around the Tub
David Rockwell
Monitoring Indicators and Reporting Branch
US EPA, Great Lakes National Program Office
Methods• Great Lakes National Program Office
• Annual monitoring cruises, 1983-2005– Spring unstratified (April)– Summer stratified (August)
GLNPO Biology Program Measures
• Phytoplankton– Community Composition, Biomass– Deep Chlorophyll Maximum– Historical Communities
• Crustacean Zooplankton and Benthos– Community Composition– Size Structure of Community
GLNPO Sampling Stations
Different colors indicate regions assumed to be homogeneous
Methods
• 1984-1990:– Tows B-2 m– 63 m mesh net with flowmeter– Biomass calculated from avg.
length/spp generated from 20 m tows
• 1998-2005– 100 (or B-2 m) tows– 153 m mesh net with flowmeter– 20 individuals/spp measured/sample
Mary Balcer Richard P. BarbieroUniversity of Wisconsin-Superior CSC, & Loyola University Chicago
Zooplankton Communities in Lake Huron1984-2005
Total crustacean biomass with standard error bars
Northern Basin
1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004B
iom
ass
g
/m3
0
20000
40000
60000
Southern Basin
1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004
Bio
ma
ss
g/m
3
0
20000
40000
60000
80000
100000
120000
140000
160000
Daphnia
Bosmina
Cyclopoid copepod
Diaptomid copepod
Limnocalanus
#1#1#3#3
#2#2
Cladocerans Copepods
Bosmina
Biomass of major taxonomic groups
Huron North basin
1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 2006
Bio
mas
s (
g/m
3 )
0
20000
40000
Huron South basin
1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 2006
Bio
mas
s (
g/m
3 )
0
20000
40000
60000
80000
100000
120000
non daphnid clads
daphnid cladspredatory clads
adult cyclopoidsimmature cyclopoidsadult calanoidsimmature calanoids
Diporeia DeclineNorthern Basin
1998 1999 2000 2001 2002 2003 2004 2005
Dip
ore
ia abu
nda
nce
(#/m
2)
0
1000
2000
3000
Southern Basin
1998 1999 2000 2001 2002 2003 2004 2005
Dip
ore
ia abu
nda
nce
(#/m
2)
0
500
1000
1500
2000
2500
Diporeia DeclineNorthern Basin
1998 1999 2000 2001 2002 2003 2004 2005
Bio
mas
s g
/m3
0
5000
10000
15000
20000
25000
30000
Dip
ore
ia abu
nda
nce
(#/m
2)
0
1000
2000
3000
Southern Basin
1998 1999 2000 2001 2002 2003 2004 2005
Bio
mas
s g
/m3
0
20000
40000
60000
80000
100000
120000
Dip
ore
ia abu
nda
nce
(#/m
2)
0
500
1000
1500
2000
2500
non daphnid clads
daphnid cladspredatory clads
adult cyclopoidsimmature cyclopoidsadult calanoidsimmature calanoids
1998
0
1000
2000
3000
4000
5000
6000
1999
0
1000
2000
3000
4000
5000
6000
2001
0
1000
2000
3000
4000
2002
0
1000
2000
3000
4000
5000
6000
2003
0
1000
2000
3000
2004
0
1000
2000
2005
Length (mm)0 1 2 3 4
0
1000
2000
1998
0
1000
2000
3000
4000
5000
6000
1999
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
10000
11000
12000
2001
0
1000
2000
3000
4000
5000
6000
2002
0
1000
2000
3000
4000
5000
6000
2003
0
1000
2000
3000
2004
0
1000
2000
2005
Length (mm)0 1 2 3 4
0
1000
2000
Size distribution of crustacean biomass
North Basin
South Basin
2005
Length (mm)0 1 2 3 4
Bio
mas
s (
g/m
3)
0
1000
2000
2004
Length (mm)0 1 2 3 4
Bio
mas
s (
g/m
3)
0
1000
2000
Superior central basin
Huron northern basin
Diaptomus sicilis
Limnocalanus macrurus
Lake Huron and Lake Superior Zooplankton Communities
0
10000
20000
30000
0
5000
10000
15000
1965
1970
1975
1980
1985
1990
1995
2000
2005
0
2000
4000
6000
8000
0
2000
4000
6000
8000
1965
1970
1975
1980
1985
1990
1995
2000
2005
0
2000
4000
6000
8000
Phosphorus Loading Trends
Recent Loads Dolan and McGunagle 2005
Michigan
P L
oad
(to
nn
es y
r-1)
Superior
Erie
OntarioHuron
GLWQATarget
0
10
20
30
40
0
5
10
15
1965 1970 1975 1980 1985 1990 1995 2000 200505
1015202530
1965 1970 1975 1980 1985 1990 1995 2000 2005
0
2
4
6
8
Total Phosphorus Trends (Spring)
Harvey Bootsma SOLEC 2006
Michigan
TP
(g
L-1)
♦■ ■
♦ Environment CanadaUSEPA-GLNPO
Huron Ontario
Erie Central
0
2
4
6
8 SuperiorGLWQA Target
Superior
Michigan
Huron
Plots of simulation results and data for TP (gP/L) in the Upper Great Lakes: (a) Superior, (b) Michigan, and (c) Huron. The
water-quality objectives are shown as dashed lines. (RWG D Annex 3 Technical Subgroup Report DePinto et al 2006)
• Schematic of a long-term, total phosphorus model for the Great Lakes (Chapra 1977).
Nearshore Shunt Hypothetical Construct Hecky et al 2004 Can.J. Fish Aquat. Sci 61
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
Secchi disk depths near Milwaukee, Lake Michigan
Dr. Harvey Bootsman, SOLEC 2006
Data source: MMSD
Cladophora
Lake Erie Total Phosphorus, ug-P/L Pre(1983-1989)/Post (1990-2004)
Central Basin
0
10
20
30
40
50
1980 1985 1990 1995 2000 2005 2010
NoSignificantDifference
Eastern Basin
0
5
10
15
20
2530
35
40
45
50
1980 1985 1990 1995 2000 2005 2010
NoSignificantDifference
Western Basin
05
101520253035404550
1980 1985 1990 1995 2000 2005 2010Year
NoSignificantDifference
Lake Erie Total Dissolved Phosphorus, ug-P/LPre(1983-1989)/Post (1990-2004)
Eastern Basin
0
5
10
15
20
1980 1985 1990 1995 2000 2005 2010
SignificantIncrease(p=0.021)
Central Basin
0
5
10
15
20
1980 1985 1990 1995 2000 2005 2010
SignificantIncrease(p<0.001)
Western Basin
0
5
10
15
20
25
1980 1985 1990 1995 2000 2005 2010Year
NoSignificantDifference
DRP/TPMaumee
Sandusky
Cuyahoga
Grand
Figure courtesy of Dr. Peter Richards, Heidelberg College
Sandusky and Maumee River Watersheds Lake Erie
Figure courtesy of Dr. Peter Richards, Heidelberg College
Ave
rage
[P
] (p
pm)
P in Wisconsin Cropland
Bundy and Sturgul 2001
0
10
20
30
40
50
60
1968-73
1974-77
1978-81
1982-85
1986-90
1991-94
1995-99
1
10
100
1000
10000
0 500 1000 1500 2000
1
10
100
1000
10000
P Input to soil
Water [P]
Soil [P]
Sediment [P]
YearsSource: S.R. Carpenter, 2005
Long-term Influence of Soil P on Lake PSoil P inputs reduced after year 250
Ph
osp
ho
rus
De
nsi
ty (
g m
-2)
P In
pu
ts t
o S
oil
(g m
-2 y
-1)
0
1
2
3
4
5
1970 1975 1980 1985 1991 1994 1995
Ave
rage
[P
] (p
pm)
Soi
l P S
tora
ge C
hang
e (k
g ha
-1)
P in Wisconsin Cropland
Bundy and Sturgul 2001
0
10
20
30
40
50
60
1968-73
1974-77
1978-81
1982-85
1986-90
1991-94
1995-99
1
10
100
1000
10000
0 200 400 600 800 1000
1
10
100
1000
10000
Ph
osp
ho
rus
De
nsi
ty (
g m
-2)
P In
pu
ts t
o S
oil
(g m
-2 y
-1)
Long-term Influence of Soil P on Lake PSoil P budget balanced at year 250
P Input to soil Water [P]
Soil [P]
Sediment [P]
YearsSource: S.R. Carpenter, 2005
Summary• Offshore Declines in Zooplankton Biomass are observed Lake Huron.
• Phosphorus loads and open lake phosphorus concentrations have declined in the Great Lakes in response to controls
• Top down effects are observed to contribute to decline in the lower food web.
• Nearshore Cladophora increases appear to be link to Dreissena invasion via increased water clarity and cycling of nutrients
• Total phosphorus loading has increased soluble fraction and open lake concentrations in Lake Erie have a significant increase in soluble fraction in the spring.
• Total phosphorus concentrations in the Upper Great Lakes appear to below levels modeled to exist in 1800.
In the nearshore zone, increased water clarity has altered the relationship between P supply and algal abundance.
More P abatement would benefit the nearshore zone, but would it benefit pelagic zone?
Dissolved Reactive Silica increases in Lakes Michigan and Huron are linked to TP declines.
Dissolved Reactive Silica increases in Lake Erie are linked to predation by Dreissena
Nearshore shunt of nutrients redirected to the nearshore zones of the Lakes contributing to the reemergence of Cladophora while offshore P concentrations remain low.
Continued addition of P to soils may pose a challenge to the lakes well into the future.