Lake Erie Hypoxia: Lake Erie Hypoxia: Comparison of Oxygen Comparison of Oxygen

Dynamics in the Western Dynamics in the Western Basin with the Sandusky Basin with the Sandusky

SubbasinSubbasin

Brie ElkingBrie ElkingSupervisor: Dr. Doug KaneSupervisor: Dr. Doug Kane

Why do we care about Why do we care about Dissolved Oxygen?Dissolved Oxygen?

• Dissolved Oxygen (DO) is essential for most aquatic life

• Hypoxia occurs when the DO concentration drops below 2 mg/L

• Hypoxia can kill fish if it is prolonged

• Also it can become anoxic, or have no DO left

How does DO become How does DO become depleted?depleted?

• Through respiration of organisms

• Through abiotic processes

• Through decomposition of organic matter

http://www.epa.gov/lakeerie/eriedeadzone.html

Why is there no Why is there no replenishment?replenishment?• Thermal Stratification

– Separates the lake into three layers: epilimnion, metalimnion, hypolimnion

– Epilimnion- oxygen due to photosynthesis and diffusion

– Metalimnion separates the epilimnion and hypolimnion

– Hypolimnion gets oxygen from a subsurface chlorophyll maximum

– once the algae die they add to the depletion

http://www.pearl.maine.edu/windows/community/Water_Ed/Dissolved%20Oxygen/DO_whatisit.htm

Hypoxia and AnoxiaHypoxia and AnoxiaCentral Basin may Central Basin may have large areas have large areas of hypoxia/anoxiaof hypoxia/anoxiaThe Sandusky The Sandusky Subbasin Subbasin typically goes typically goes hypoxic and hypoxic and anoxicanoxicThe Western Basin The Western Basin will go anoxic will go anoxic though it is not though it is not as commonas common

Burns et al. 2005

Conroy et al. unpublished

GoalGoal• To compare the oxygen dynamics To compare the oxygen dynamics of the Western Basin and the of the Western Basin and the Sandusky Subbasin and to see Sandusky Subbasin and to see how closely their DO how closely their DO concentrations relate to each concentrations relate to each otherother

Where were samples Where were samples taken?taken?

How was this done?How was this done?• Four sampling dates between

June 26th and July 15th

• DO and temperature profiles were taken every half meter until the bottom

• The mean DO (mg/L) for the water column, epilimnion, and hypolimnion were compared

If no stratification had occurred only water column means were looked at

• Compared using a Mann-Whitney test between WB and SSB, p < 0.05

E-July 3rd, 2009

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4

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0 5 10 15 20 25

Temperature (C) and Dissolved Oxygen (mg/L)

Depth (m)

Dissolved OxygenTemperature

E- June 26th, 2009

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4

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0 5 10 15 20 25

Temperature (C) and Dissolved Oxygen (mg/L)

Depth (m)Dissolved Oxygen

Temperature

What did we find?What did we find?• That all four dates had data that were not That all four dates had data that were not statistically significantstatistically significant

• However, on July 15However, on July 15thth there was stratification there was stratification for two sites in the Sandusky Subbasin (SSB) for two sites in the Sandusky Subbasin (SSB) and no sites for the Western Basin (WB)and no sites for the Western Basin (WB)

• Even though the difference between mean DO is Even though the difference between mean DO is not significant this observation is not significant this observation is noteworthynoteworthy

• It appears that on the last sampling date WB It appears that on the last sampling date WB and SSB were starting to deviate from each and SSB were starting to deviate from each otherother

What was happening on the What was happening on the sampling dates?sampling dates?

• June 26th - all sites stratified, WB and SSB

• July 3rd - all sites isothermal, WB and SSB

• July 10th - all sites stratified, WB and SSB

• July 15th - SSB- 1 site isothermal

• 2 sites stratified

• WB all sites isothermal

Did any sites have Did any sites have hypoxia?hypoxia?• Only one site, E, experienced hypoxia over Only one site, E, experienced hypoxia over the sampling periodthe sampling period– Hypoxia was found on July 15Hypoxia was found on July 15thth

• Hypoxia is typically found by July 4Hypoxia is typically found by July 4thth, with , with stable stratification happening in early stable stratification happening in early JuneJune

• The stratification that occurred during the The stratification that occurred during the sampling period was not stable as it sampling period was not stable as it fluctuatedfluctuated

• We looked at possible reasons for this and We looked at possible reasons for this and compared them to data from the past 5 yearscompared them to data from the past 5 years– Wind speed, wind direction, and water level Wind speed, wind direction, and water level

What makes this year What makes this year different?different?

Year Wind Speed (m/s)

Wind Direction (degrees)

Wind Direction

Water Level (m)

2004 N/A N/A N/A 174.35

2005 4.34 156.08 ESE 174.30

2007 4.13 151.77 ESE 174.23

2008 4.59 195.25 SSW 174.32

2009 3.90 143.53 ESE 174.45

Wind data- 45005 - W ERIE 28NM Northwest of Cleveland, OH

Buoy Station- Marblehead OH, #9063079

All data from June 1st to July 15th

What does this mean?What does this mean?

• Stratification started later than in Stratification started later than in other years due to a higher water levelother years due to a higher water level• thus stable stratification was not observed thus stable stratification was not observed until the end of the sampling period.until the end of the sampling period.

• Hypoxia was only seen at one location Hypoxia was only seen at one location in the Sandusky Subbasin, when in in the Sandusky Subbasin, when in recent years it would be observed recent years it would be observed earlier and at more stations in the earlier and at more stations in the subbasin.subbasin.

Thanks to everyone who Thanks to everyone who helpedhelped

Dr. Joe Conroy

http://stonelab.osu.edu/_media/stonelab/fosl/membership.pdf

Dr. Doug Kane Capt. Matt Thomas

http://www.ael.osu.edu/ael-JoeConroy.html

Amy Miller