Evaluating Phosphorus Limitation from the Maumee and Sandusky Rivers into Lake Erie
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Evaluating Phosphorus Limitation from the
Maumee and Sandusky Rivers into Lake Erie
Heather R. Kirkpatrick, Curtis C. Clevinger, Moumita M. Moitra, Darren L. Bade, Joseph D.
Conroy, David A. Culver, William J. Edwards, Douglas D. Kane
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Lake Erie & Eutrophication• 1960’s: Harmful Algal Blooms
(HABs); extreme eutrophication; hypolimnetic hypoxia
• 1972: Great Lakes Water Quality Agreement (GLWQA) signed; reduced phosphorus (P) entering Lake Erie; P detergents banned
• Late 1970’s-1980’s: Reductions in P recorded; decreased HABs and hypoxia
• Mid-1990’s: re-eutrophication of Lake Erie; increases in dissolved P; return of HABs and hypoxia
Sandusky Bay in April (OhioLink Landsat 7)
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P-limitation Paradigm
• P is considered most often limiting in freshwater
•Nitrogen fixation should reduce the occurrence of N limitation
•Managing for N may favor N limitation and N fixing cyanobacteria
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P-limitation
•Demand of P by algae exceeds supply
- Other factors are not limiting
•When P supply > demand
- Another factor is limiting
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Overall Project Goals
•To directly assess the role of P in facilitating HABs by determining:
1.How Microcystis uses the bioavailable portion of the total P?
2.Where in these systems blooms are triggered (upstream, nearshore or offshore)?
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Specific Project Goals
•To assess conditions of P-limitation by determining:
1.Where and when does P-limitation occur?
2.What are the causes and consequences of P-limitation (or lack thereof)?
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Methods• Algal Phosphorus Debt (P-debt):
- Amount of phosphate incorporated in 24 hours in dark
- The more “phosphate starved” algae are the more phosphate is taken up
- Scaled to algal biomass
- Values above 0.075 µmol P/ µg chl are considered P limited
• Phosphate Turnover Time (P-turnover):
- Fast turnover times (less than 60 minutes) indicate P-limitation
- Fast turnover times could be caused by a small phosphate pool or high demand by algae
Healey & Hendzel 1979Heath, R.T. 1986
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Methods
•Chlorophyll a
•Secchi depth
•Total phosphorus
•Nitrate
•Ammonia
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Sandusky Secchi Depth
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
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Site
Dep
th (
m) May/June
JulyAugustSeptemberOctober
Sandusky Chlorophyll a
0.0
20.0
40.0
60.0
80.0
100.0
120.0
140.0
1 2 3 4
Site
µg
Ch
l a/L
iter
May/JuneJulyAugustSeptemberOctober
Sandusky System Results
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Sandusky P-debt
0.00001
0.0001
0.001
0.01
0.1
1
10
1 2 3 4Site
µm
ol P
/ µg
Ch
l. a
May/JuneJulyAugustSeptemberOctoberLimitation
Indicates agreement with P-turnover data
LIMITED
NOT LIMITED
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Sandusky Total P
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Site
µg
P/L
May/JuneJulyAugustSeptemberOctober
Sandusky NO3
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Site
µg
N/L
May/JuneJulyAugustSeptemberOctober
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Maumee Chlorophyll a
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Maumee Secchi Depth
0.00
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Maumee System Results
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Maumee P-debt
0.00001
0.0001
0.001
0.01
0.1
1
10
1 2 3 4Site
µmo
l P/ µ
g C
hl a
May/JuneJulyAugustSeptemberOctoberLimitation
Indicates agreement with P-turnover data
LIMITED
NOT LIMITED
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Maumee Total P
0
50
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µg
P/L
May/JuneJulyAugustSeptemberOctober
Maumee NO3
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µg
N/L
May/JuneJulyAugustSeptemberOctober
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Summary
•Sandusky system limited in 40% of the samples
•Maumee system limited in 70% of the samples
•Lake and tributary sites variable
•Sandusky Bay generally not P-limited
•Maumee River generally not P-limited
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Summary
•Periods of high chlorophyll and low nitrate concentrations at Sandusky Bay and Maumee River sites
•Since P is generally not limiting at these sites, other factors (e.g. nitrogen) may be limiting
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Conclusions
•P-limitation not ubiquitous
•Nitrogen may also be important in limiting algal growth
•Although we have potential nitrogen limitation, most cyanobacteria were not N fixing
•Management considering multiple factors may be more successful
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Acknowledgements
•Funding: Lake Erie Protection Fund
•The Ohio Academy of Science
•Field collection crew
•Joshua Smith
•Dominique Guyton
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Sandusky P-Turnover
1
10
100
1000
10000
1 2 3 4Site
Min
ute
s
May/JuneJulyAugustSeptemberOctoberLimitation
LIMITED
NOT LIMITED
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Maumee P-Turnover
1
10
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1 2 3 4Site
Tu
rno
ver
Tim
e (m
inu
tes)
May/JuneJulyAugustSeptemberOctoberLimitation
NOT LIMITEDLIMITED