In June of 2011, the National Oceanic and Atmospheric Administration (NOAA) mapped the “dead zone” in the Gulf of Mexico, below the mouth of the Mississippi River at 8,776 square miles (the largest area ever observed since dead zone mapping began there in 1985).
A “dead zone” is an area of a lake or ocean with abnormally low levels of dissolved oxygen. Dead zones are caused by nutrient pollution (from agricultural runoff and other human inputs, including release of treated wastewater and untreated sewage and soil erosion) washing into the lake or ocean. The excess nutrients support huge population explosions, or “blooms,” of certain microorganisms and algae - most problematically, a type of photosynthetic bacteria known as cyanobacteria. Zooplankton, (the tiny animals at the base of the ocean food chain) do not eat cycanobacteria, so they accumulate in the water, blocking the light other ocean plants depend on to grow, producing cyanotoxins, and soaking up oxygen as they die and decompose. The end result is the suppression or death of other algae, fish, and ocean creatures in the area.
From a human perspective, blooms of cyanobacteria can create nasty odors, turn the water odd colors (which renders it unswimmable), make any shellfish harvest in the area poisonous. At best, this reduces the reproduction and growth of fish and shellfish in the area, pushing up prices for shrimp and other tasty things. At worst, this kills fish outright, leaving them to wash up on the beaches and rot. Dead zones have a ripple effect through the bird populations that depend on fish, as well.
This washes down from the upper Midwest, starting as man-made nitrogen and phosphorus fertilizers spread on crop fields and manure from concentrated animal feeding operations (CAFOs, aka feedlots and massive barns full of pigs, chickens, or other animals). Efforts to reduce agricultural run-off in that area have so far been limited to voluntary suggestions, and no one (even the feds) really thinks voluntary measures are going to be able to cut nutrient runoff enough to allow the dead zone in the Gulf to recover even partially (the Environmental Protection Agency’s goal is to reduce it to under 1,900 square miles).
There is reason to hope, however. A few dead zones (there were 146 dead zones recognized worldwide as of 2003) have recovered or are currently recovering. The Chesapeake Bay on the East Coast of the US is showing signs of recovery, following contentious but mandatory limits on nutrient pollution entering the Bay set by the federal government in 2010 (and supported with billions of dollars in spending by the states upstream of the Bay to meet those limits). More dramatically, the Black Sea dead zone and the dead zones around Cuba experienced dramatic recoveries following the collapse of the Soviet Union and the subsequent unavailability of cheap man-made fertilizer.
What can you do?
Vote with your food and fiber dollars to support organic farming, which values and cares for the land and the environment downstream. Shop local from farmers who practice good land stewardship, and certainly avoid any products produced in CAFOs (even if they are technically organic). Maintain your own property (if you have any) with organic methods, and use rain gardens and swales to slow down and reduce stormwater runoff and soil erosion from your land. Encourage your local community groups and governments to do the same on public lands, and your local zoning boards to mandate good management practices (low fertilizer use, native plantings, permeable paving, stormwater retention) for all new development. Support responsible regulations at the State/Provence and National level.