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

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)

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

P-limitation

•Demand of P by algae exceeds supply

- Other factors are not limiting

•When P supply > demand

- Another factor is limiting

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)?

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)?

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

Methods

•Chlorophyll a

•Secchi depth

•Total phosphorus

•Nitrate

•Ammonia

Sandusky Secchi Depth

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

1 2 3 4

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

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

Sandusky Total P

0.0

50.0

100.0

150.0

200.0

250.0

1 2 3 4

Site

µg

P/L

May/JuneJulyAugustSeptemberOctober

Sandusky NO3

0

500

1000

1500

2000

2500

3000

1 2 3 4

Site

µg

N/L

May/JuneJulyAugustSeptemberOctober

Maumee 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

Maumee Secchi Depth

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1 2 3 4Site

Dep

th (

m)

May/JuneJulyAugustSeptemberOctober

Maumee System Results

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

Maumee Total P

0

50

100

150

200

250

1 2 3 4Site

µg

P/L

May/JuneJulyAugustSeptemberOctober

Maumee NO3

0

500

1000

1500

2000

2500

3000

3500

4000

1 2 3 4Site

µg

N/L

May/JuneJulyAugustSeptemberOctober

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

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

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

Acknowledgements

•Funding: Lake Erie Protection Fund

•The Ohio Academy of Science

•Field collection crew

•Joshua Smith

•Dominique Guyton

Sandusky P-Turnover

1

10

100

1000

10000

1 2 3 4Site

Min

ute

s

May/JuneJulyAugustSeptemberOctoberLimitation

LIMITED

NOT LIMITED

Maumee P-Turnover

1

10

100

1000

10000

1 2 3 4Site

Tu

rno

ver

Tim

e (m

inu

tes)

May/JuneJulyAugustSeptemberOctoberLimitation

NOT LIMITEDLIMITED