09/20/2013 12:26 EDT | Updated 09/20/2013 12:26 EDT

We Are Quickly Turning the Ocean into a "Dead Zone"

Feeding seven billion people puts incredible pressure on the life support systems of this planet. The simple adage "everything is interconnected" rings more true than ever. Rainforests continue to be felled for cattle ranches, biofuels, and palm oil plantations; unsustainable irrigation practices are causing rapid aquatic habitat loss; and bee populations are crashing from pesticide and fungicide use.

Sometimes, we eventually deem certain farming practices to be unacceptable, such as the spraying of DDT. But it's usually not until after serious damage occurs, like bird populations crashing across North America, that we decide to take action. Humans have a tendency of only responding to a crisis long after we are aware of the looming problem and its deleterious impacts.

Another disturbing example of a looming crisis that is influenced by farming practices is with a phenomenon known as dead zones. Across the world, vast areas of oceans and lakes are running out of oxygen, making it nearly impossible for marine life to survive. In the 1960s, there were 49 dead zones throughout the ocean; today there are more than 400 and the number is still growing.

Dead zones are caused when nutrients such as nitrogen or phosphorus enter a body of water and fuel large algal blooms. When the excess algae eventually die and sink to the ocean bottom, they are consumed by bacteria that drain the water of oxygen in the process of digesting. When water becomes too low in oxygen, or "hypoxic," marine life flees and everything that is too slow or cannot move will die, creating a dead zone.

Although dead zones can occur naturally, the recent surge in their size and number is deemed by scientists to be entirely caused by human activity. Poor wastewater treatment and fossil fuel emissions are two big contributors, but the biggest inputs by far are from excess fertilizer runoff from farmland. When too much fertilizer is applied to a farmer's field, almost everything that is not absorbed by the crops will flow into streams and rivers and then out into lakes or to the sea. Just like plants on land, plants in water (known as phytoplankton and algae) happily soak up these unexpected sources of energy and grow out of control.

Of course, feeding seven billion people is currently only possible because of the use of fertilizers, but in our quest to leverage every possible acre of farmland, we are over-applying fertilizer and playing a dangerous game with the natural cycle of nutrients between land and water.

The bigger the dead zones get, the more damage they do to the economy. In the Gulf of Mexico where the world's second largest dead zone forms every summer at the mouth of the Mississippi, it means a huge amount of lost business. Some years it gets as big as 20,000 square kilometres and takes a significant chunk out of the $630-million dollar commercial fishery. By trying to grow more food on land, we are only disrupting an equally important source of human food from the ocean.

If we want to solve the dead zone problem, we must first acknowledge where the problem originates. One look at a map tells us that the world's biggest dead zones are all concentrated along the coasts of the U.S., Europe and China -- all places with very high levels of industrial and agricultural runoff. These regions also produce large amounts of crops that require the largest amounts of fertilizer to grow, most notably corn in the U.S. Populations in these regions also consume a lot of meat, which further contributes to the problem when livestock are raised in concentrated areas and their nitrogen-rich manure is not properly treated or disposed of.

Individually, some of the most powerful things we can all do to slow the spread of dead zones are to eat less processed foods that are made using corn, and eat less meat that is grown and produced with corn feed in factory farms. We can also use our cars less: car emissions are high in nitrogen, and many types of fuel are supplemented with ethanol, which is often made using corn. And if preventing dead zones is not enough to sway you, there is growing evidence that switching away from corn, and specifically products made with high-fructose corn syrup, is also good for your health.

But the bigger changes will have to come from farmers who should be given more incentives from governments to control nutrient pollution. While there are several progressive farmers doing so and staying profitable by following more sustainable practices, many more, such as in the U.S., are instead being encouraged to grow as much corn as possible through an annual $5-billion dollar corn subsidy program. Eventually this will have to change. But it makes me wonder -- how much of the ocean will need to become a dead zone before we all finally decide it is time to take action?

Alex Mifflin and brother Tyler Mifflin host the award-winning eco-adventure series, The Water Brothers, exploring the world's most important water stories. The second season airs Tuesdays at 7:30 pm from September 10 - October 22 on TVO and at Learn more about dead zones, their causes and impacts in the next episode of The Water Brothers airing September 24.