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The Lake Erie ecosystem faces wide and varied threats to its health and integrity, including recurring low oxygen episodes ('dead zones') in the central basin. A prominent feature of Lake Erie's central basin is the lake bottom area of severe hypoxia ( < 2-3 ppm dissolved oxygen concentration) that recurs annually during late summer. Although the size of the dead zone declined with reduced phosphorus inputs during the mid-1980s, current levels of oxygen depletion are on par with those observed during the preceding period of severe cultural eutrophication, which is of concern to both Lake Erie resource management agencies and user groups.
The Hypoxia Warning System is intended to combine observed data and forecasted surface currents to provide Lake Erie central basin drinking water managers information about the transport of hypoxic water into water intakes. The objectives of the project are to understand the chemistry and biology surrounding the microbial-driven formation of hypoxia and subsequently provide warnings of water chemistry changes, upwelling events and internal waves impacting drinking water quality at Cleveland, OH.
The Cleveland Water Department (CWD) provides drinking water to approximately 1.5 million people in 72 communities in Northeast Ohio. The water system gets its source water from the Lake Erie central basin through four water intakes covering approximately 27 miles of shoreline in the greater Cleveland area. Water treatment plants can be exposed to hypoxic waters (oxygen depleted) from Lake Erie, compromising water quality in the system (Ruberg, et al.). Hypoxic waters are low in pH and temperature, negatively impacting water treatment and subsequently drinking water quality. Low oxygen conditions also result in an increase in anaerobic bacteria that contribute high levels of manganese and iron to the hypolimnion (bottom water layer), leading to drinking water taste and odor problems. When hypoxic water reaches CWD intakes, pre-treatment operations are disrupted, and corrosion control strategies are affected by changes in temperature and pH. In addition, reduced and dissolved forms of iron and manganese from the hypolimnion enter the distribution system resulting in numerous customer water quality complaints about discolored water.
Ruberg S, E Guasp, N Hawley, R Muzzi, S Brandt, H Vanderploeg, J Lane, T Miller, S Constant. (2008). Societal Benefits of the Real-time Coastal Observation Network (ReCON): Implications for Municipal Drinking Water Safety. Marine Technology Society Journal 42:3:103-109
The following animation shows Lake Erie bottom temperature from a hydrodynamic model that is forced by nowcast (observed) and forecast meteorology. When hypoxia occurs, it is usually associated with cold bottom water (hypolimnion) that is separated from warmer surface water by a sharp temperature gradient (thermocline), which inhibits exchange of oxygen with the atmosphere. The location where the thermocline intersects the bottom moves due to seiche and internal waves, processes that are simulated by the hydrodynamic model. Movement of the thermocline may transport hypoxic water toward or away from nearshore locations.
Beneath the animation are 3 plots that show time series of temperature profiles from the hydrodynamic model used for the animation. The station locations are indicated in the animation.