Aquatic Dead Zones

November 30, 2017

 Unlike “The Twilight Zone,” ‘dead zones’ or hypoxic and anoxic zones of coastal ocean are no fiction. These zones of little to no oxygen, once rare, are now found all around the world: the Gulf of Mexico, the Black Sea, the Baltic Sea, and even the Chesapeake Bay. They naturally occur in deep basins and fjords in the depths of the ocean, but are more frequently being found in these shallow, coastal regions.

 Hypoxic zones are caused by the nitrogen, phosphorus, and silica present in fertilizer runoff, burned fossil fuels, sewage, and other products of human activity. These nutrients, along with others, feed oceanic algae and cause a bloom and boom in the algal population and its growth. This phenomenon is known as eutrophication. O2 consumption rises as the algal population exponentially swells. In addition, dead algae sinks to the bottom of the ocean, the benthic layer, and are consumed by aerobic bacteria, contributing to the high CO2 levels in the region of water.

 The Chesapeake Bay this year had its largest hypoxic area recorded since 2014 increasing from 833 km3 to 919 km3 -- a 10% increase that has decreased the local blue crab population. In 2002, the Gulf of Mexico, to which the Mississippi River carries fertilization runoff from the Midwest’s agriculture, was 21,000 sq km and the Black Sea, the largest hypoxic area in the world, was 84,000 km. What’s concerning about statistics like these are the responses that follow from the local ecosystem. Fish, amphibian (from streams, ponds, and rivers affected), and benthic organism mortality has increased; decreased spawning; poor egg count; and increased anaerobic metabolism plus its effects. The Gulf of Mexico supplies much of the US’s seafood: 72% of shrimp, 66% of oysters, and 16% of its fish. Hypoxic zones result in severe stress on organisms. A decline in the health and reproduction of such populations can have an immense effect on America’s food sources.

A map of hypoxic (dead) zones around the world in 2008 (NASA Earth Observatory).

 Luckily, hypoxic zones can return to their normal states. We can limit fertilizer runoff, eliminate animal and human sewage waste from our waterways, regulate industrial chemical dumps, and encourage clean transportation. We can also work to restore our wetlands in areas like the Gulf of Mexico to naturally filter our waterways before they enter the ocean. This filter along with land filters, or riparian buffers can promote biodiversity in the area and reverse the effects and growth of hypoxic zones.

Sanika Kulkarni

Sanika Kulkarni is the Lead Staff Writer for the Colonial Scope.

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