Lake Erie currently experiences seasonal ‘dead zones’ larger than they have been since the mid 80’s- about 25% of the entire lake. Dead zones are areas of the lake where most organisms cannot survive due to oxygen unavailability. Dead zones not only disturb Lake Erie’s ecosystem, but also drastically cut fishing yields. Though the problem seems to be growing again this decade, the federal and state governments were able to mitigate this same problem in the early 70’s.
Dead zones are caused by both watershed contamination and drought. The Nitrogen and Phosphorous content of fertilizers used in the rust belt cause algae populations to rise, consuming more of the water’s oxygen. Drought makes the problem worse by reducing the amount of new, oxygenated water that flows into the lake. A 2012 drought pushed Lake Erie’s dead zone to 9,000 km², or 35% of the lake’s area.* Throughout the 2010’s so far, the dead zone has ranged between 20%-35% of the lake’s area.
The EPA’s Clean Water Act of 1972 regulated runoff and shrank Lake Erie’s dead zones within a few years. Introducing zebra mussels into the lake also helped, as they acted as natural Nitrogen and Phosphorous filters. Now, however, zebra mussel population size has grown too large- their presence as invasive species offsets their function as natural water filters.
The occurrence of dead zones is a natural function of seasonal temperature variation and nutrient cycling, but runoff contamination and anthropogenic drought have caused them to be far too large. Contaminated runoff flowing into the lake is the number one cause of the algal blooms that cause dead zones to occur at artificially large scales. This runoff can be eliminated through reducing the use of fertilizers and by installing green infrastructure to divert and filter nutrients in runoff.
*Figure calculated based on lake surface area. Dead zones are three dimensional, but described as two dimensional due to their length and width being vastly greater than depth