Lake Erie Hypoxia: Comparison of Oxygen Dynamics in the Western Basin with the Sandusky Subbasin Brie Elking Supervisor: Dr. Doug Kane

Why do we care about 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 depleted? Through respiration of organisms Through abiotic processes Through decomposition of organic matter

Why is there no 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 r_Ed/Dissolved%20Oxygen/DO_whatisit.htm

Hypoxia and Anoxia Central Basin may have large areas of hypoxia/anoxia The Sandusky Subbasin typically goes hypoxic and anoxic The Western Basin will go anoxic though it is not as common Burns et al Conroy et al. unpublished

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

Where were samples taken?

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

What did we find? That all four dates had data that were not statistically significant That all four dates had data that were not statistically significant However, on July 15 th there was stratification for two sites in the Sandusky Subbasin (SSB) and no sites for the Western Basin (WB) However, on July 15 th there was stratification for two sites in the Sandusky Subbasin (SSB) and no sites for the Western Basin (WB) Even though the difference between mean DO is not significant this observation is noteworthy Even though the difference between mean DO is not significant this observation is noteworthy It appears that on the last sampling date WB and SSB were starting to deviate from each other It appears that on the last sampling date WB and SSB were starting to deviate from each other

What was happening on the sampling dates? June 26 th - all sites stratified, WB and SSB July 3 rd - all sites isothermal, WB and SSB July 10 th - all sites stratified, WB and SSB July 15 th - SSB- 1 site isothermal 2 sites stratified WB all sites isothermal

Did any sites have hypoxia? Only one site, E, experienced hypoxia over the sampling period Only one site, E, experienced hypoxia over the sampling period – Hypoxia was found on July 15 th Hypoxia is typically found by July 4 th, with stable stratification happening in early June Hypoxia is typically found by July 4 th, with stable stratification happening in early June The stratification that occurred during the sampling period was not stable as it fluctuated The stratification that occurred during the sampling period was not stable as it fluctuated We looked at possible reasons for this and compared them to data from the past 5 years We looked at possible reasons for this and compared them to data from the past 5 years – Wind speed, wind direction, and water level

What makes this year different? Year Wind Speed (m/s) (m/s) Wind Direction (degrees) (degrees)WindDirection Water Level (m) 2004N/AN/AN/A ESE ESE SSW ESE Wind data W ERIE 28NM Northwest of Cleveland, OH Buoy Station- Marblehead OH, # All data from June 1 st to July 15 th

What does this mean? Stratification started later than in other years due to a higher water level Stratification started later than in other years due to a higher water level thus stable stratification was not observed until the end of the sampling period. thus stable stratification was not observed until the end of the sampling period. Hypoxia was only seen at one location in the Sandusky Subbasin, when in recent years it would be observed earlier and at more stations in the subbasin. Hypoxia was only seen at one location in the Sandusky Subbasin, when in recent years it would be observed earlier and at more stations in the subbasin.

Thanks to everyone who helped Dr. Joe Conroy stonelab/fosl/membership.pdf Dr. Doug KaneCapt. Matt Thomas JoeConroy.html Amy Miller