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Environment

The Biggest Dead Zones in America's Waterways

We often bemoan the ecological tragedies plaguing the Gulf Coast—oil spills, industrial waste, overfishing—but many of the United States' coastal waterways experience eutrophic (high nutrient) and hypoxic conditions. Here are four of the worst.

by Ruth Reader
Jul 2 2013, 7:46pm
Historic eutrophic and hypoxic zones, from the World Resources Institute's interactive map

The National Oceanic and Atmospheric Association forecasted that this year’s Gulf of Mexico hypoxic “dead” zone will be between 7,286 and 8,561 square miles—one of the ten largest on record. What’s worse is the Gulf isn't alone: dead zones, in which low oxygen causes high fish mortality, are proliferating all over the world. According to the World Resources Institute, there are 479 hypoxic waterways worldwide

Many of the United States' coastal waterways experience eutrophic (high nutrient) and hypoxic conditions. Hypoxia is usually caused by abnormal influxes of nutrients into a waterway, which cause algae blooms that initially reduce aquatic oxygen levels through respiration. Additionally, algae on surface waters blocks light from getting to marine plant life. Without light there is no photosynthesis, and without photosynthesis, underwater plants can’t produce oxygen.

Once the algae consumes all the surface level nutrients, it dies, sinks to the bottom of the body of water and rots. Bacteria decomposes the algae and in the process sucks up all the underwater oxygen. At this point fish start dying en mass and the underwater ecosystem is thrown into chaos. In the US, excess nutrients in waterways usually arrive via sewage plants, and nitrogen and phosphorous-based fertilizers washed away with agricultural run-off.

“Up until a decade ago nitrates have been under the radar,” said Mindy Selman, a senior associate at the World Resources Institute. “They're bad as they accumulate in the water, but they're not toxic, so they weren't regulated. Now people are seeing the impacts, so now they're starting to put limits on how much phosphorous or nitrogen can be output.”

Key areas where federal and state authorities have started to take notice are the Chesapeake Bay, Long Island Sound, Great Lakes, and coastal Oregon. While each of these regions share similar conditions, their causes and treatment plans are quite different. Below is a tour of the America's most hypoxic regions outside of the beleaguered Gulf Coast.

Chesapeake Bay

We often bemoan the ecological tragedies plaguing the Gulf Coast—oil spills, industrial waste, overfishing—but the East Coast is not so far behind. From the tip of Florida all the way up to Canada, the Atlantic Ocean suffers from hypoxia, largely due to farm run-off both from animal waste and overuse of chemical fertilizer.

Dead menhaden float in the Bay in this 1973 EPA photo

One of the biggest areas that has garnered attention at the federal level is the Chesapeake Bay, which is surrounded by four major farming states: Pennsylvania, Delaware, Maryland, and Virginia. The 88,000 farms in the region contribute a lot of nitrogen into the watershed, often through storm run-off, heightening nutrient levels in the bay. The District of Columbia and New York also contribute to the Chesapeake’s nutrient load. Between the five states and one district, 500 large public and industrial waste-water treatment plants filter into the bay.

The battle to clean up the Chesapeake has been going on for over 30 years. In 1987, the federal government signed the Chesapeake Bay agreement, promising to reduce nutrients in the bay by 40 percent by 2000. When it missed that deadline, it set another one for 2010. The feds missed that one too.  

In 2009, President Obama declared the Chesapeake Bay a national treasure, and in 2010 he signed an executive order to clean up the Chesapeake. That spurred the EPA to get serious, instituting a tough total maximum daily load (TMDL) schedule for all farms, waste treatment plants, and industrial plants in the five-state area to be completed by 2025.

In Maryland, which has aggressive restoration policies, the state legislature instituted a storm-water fee. The tax specifically funds storm drains, collection ponds, stream restorations and other improvements that control and slow the flow of runoff.

In 2012, hypoxia in Chesapeake Bay was down along with nitrogen and phosphorus levels. In its summer 2012 report, the NOAA attributed the decline to nutrient reduction strategies implemented by Maryland Department of Natural Resources and the Maryland Department of the Environment.

But Mary-Ann Evans, a research ecologist at US Geological Survey, said nutrient loads depends heavily on weather. “Its hard to say nutrients are lower than last year because of something someone did versus a weather pattern,” she said. "If there’s less rainfall in a given year, it means fewer nutrients will make it into waterways.”

Read the rest over at Motherboard

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