Water Pollution Case Study: Lake Erie

I grew up in Buffalo, New York in the 1960’s and 1970’s, when pollution was reaching its peak in the rust belt and the environmental movement was beginning. One of the watershed moments in the environmental movement was the discovery in 1978 of toxic waste underneath a school in Love Canal, near Niagara Falls and very close to Buffalo. Until I was six we lived down the street from Lake Erie, and I still recall walking along the shoreline with a clean-up crew. The Lake was very polluted at that time; signs posted near fishing areas stated severe limits on consumption of caught fish due to the threat of mercury poisoning. Not that there were many fish to catch; the only type of fish anyone caught was catfish. Why only catfish? Because catfish don’t need oxygen in the water to breathe; unlike other fish who use gills to extract dissolved oxygen from water, catfish obtain their oxygen by gulping air when they come to the surface. The problem in Lake Erie and many other bodies of water at that time was that it was eutrophic, i.e., oxygen-depleted. In the process of eutrophication, limiting nutrients like phosphorous and nitrogen added to the water cause algae blooms. When the algae die, they decompose:

C6H12O6 + 6O2 = 6 CO2 + 6H2O

This consumes the oxygen dissolved in the lake water. In temperate regions such as upstate New York, lakes have two layers: a shallow, warm, buoyant layer and a deep, cold, dense layer. In a eutrophic lake, the shallow layer in contact with the atmosphere is oxygen-rich, but the deep layer becomes oxygen depleted because the dead algae sink to the bottom of the lake and decompose. In the fall and spring the density difference between the two layers disappears and they mix together. The problem is that, especially in the fall, the deep water has no oxygen, so when it mixes with the shallow water the resulting mixture does not have enough oxygen for fish to breathe, and they die in large numbers. This is still a widespread problem in many areas of the U.S.. In fact, there is now a huge “dead zone” near the Mississippi delta in the Gulf of Mexico that formed because fertilizer-derived nutrients caused algae blooms and eutrophication. The good news is that there is a solution. Simply removing phosphorous from detergents in areas surrounding Lake Erie led to a decline in algae blooms, and now the lake has mostly recovered. No one is worse off for using phosphate-free detergents, but for some reason in areas where regulations allow it (including my current home state of Tennessee) most detergents still contain phosphates, and eutrophication is still a problem.

Lake Erie is still not without problems. In summers, beaches are often temporarily closed after rainfall events. Why? Because wastewater disposal systems have limited capacity, and during heavy rains they fill up and then overflow into local streams, which flow to the lake. You may have noticed that water treatment plants and pumping stations usually have overflow ponds with pipes near the top that drain into a stream. When it rains, you can observe the overflow ponds fill up. Once they are full, any additional wastewater flows out through the pipe and dumps into the stream. Ironically, water in streams is usually dirtiest after rainfall events. Currently many cities are in the process of upgrading their wastewater systems under federal mandate. The problem is the same problem we face with highways; you can add more lanes, but traffic will build until a few years later it as just as congested as it was before you added the lanes. Population growth means that the ideal size of a service system is a moving target, and these systems frequently require expensive expansion projects. The city of Nashville had to increase its water bill in 2009 in order to pay for the expansion of its wastewater system, which will cost hundreds of millions of dollars.