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Soil & Sea: What’s the Connection?

Soil, water, air, and plants are vital natural resources that help to produce food and fiber for humans. They also maintain the ecosystems on which all life on Earth ultimately depends. Soil serves as a medium for plant growth; a sink for heat, water, and chemicals; a filter for water; and a biological medium for the breakdown of wastes and the promotion of plant growth.

But how do soil and sea interact?

Soil productivity and loss of soil productivity resulting from soil degradation has been the bases for concern about the world’s soils. Equally important, however, are the functions soils perform in the regulation of water quality, water flow in watersheds, regulation of air and global emissions of greenhouse gases, and attenuation of natural and artificial wastes. These functions are impaired by soil degradation.

Ocean ‘Dead Zones’

“Hypoxia” also called ocean dead zones – refers to low-oxygen areas in the world’s lakes and oceans, where very few organisms can survive.

Oxygen-deprived dead zones were first identified in estuaries in the mid-19th century and their oxygen depletion was linked to the presence of urban sewage in the water, said the study’s lead author, Denise Breitburg, a marine ecologist with the Smithsonian Environmental Research Centre.

Since then, growth of industrial and agricultural activity has disrupted the ocean’s chemical balance, with regions in many areas worldwide becoming infused with pollutants and nutrients that starve the water of oxygen.

A dead zone occurs as a result of eutrophication, which happens when a body of water is inundated with too many nutrients, such as phosphorus and nitrogen. At normal levels, an organism called cyanobacteria- or blue-green algae- feeds on these nutrients. With too many nutrients, however, cyanobacteria grows out of control, which can be harmful. When the algae die and sink to the bottom of the water bed, they provide a rich food source for bacteria, which when decomposing consume dissolved oxygen from surrounding waters, depleting the supply from marine life.

What causes ocean dead zones?

In short. Human activities. Mainly because the excess nutrients washed into the ocean, are often located near inhabited coastlines.

This process has increased because of the rise in intensive agricultural practices, industrial activities and population growth, which all emit large amounts of nitrogen and phosphorus that settle into our air, soil and water. Fossil fuels also release nitrogen into the atmosphere.

In developed countries, heavy use of animal manure and commercial fertilisers are the main contributors to eutrophication, which runs off from fields into creeks and bays. In developing countries, untreated wastewater from sewage and industry are the main contributors, which is sometimes dumped into rivers, lakes or the ocean.

Agricultural run-off, due to rainfall, irrigation and other water moving over farm fields provide a super highway for excess fertilisers, pesticides and other man-made chemicals to enter bodies of water, having a negative impact on the environment.

The Environmental Impact

Phosphorus, nitrogen and other nutrients increase the productivity or fertility of marine ecosystems. Organisms such as phytoplankton, algae and seaweeds grow quickly and excessively on the water’s surface. This rapid development of algae and phytoplankton is called an algal bloom.

Algal blooms can create dead zones beneath them, because they prevent light from penetrating the water’s surface.They also prevent oxygen from being absorbed by organisms beneath them. Sunlight is necessary for plants and organisms like phytoplankton and algae, which manufacture their own nutrients from sunlight, water and carbon dioxide..

Algal blooms also cause human illness. Shellfish, such as oysters, are filter feeders. That means when they filter water, they absorb microbes associated with algal blooms. Many of these microbes are toxic to people. Algal blooms can also lead to the death of marine mammals and shore birds that rely on the marine ecosystem for food.

Lake Okeechobee, also known as Florida’s Inland Sea, is the largest freshwater lake in the state of Florida. Photo Credit:

What can be done?

Dead zones are reversible if their causes are reduced or eliminated.Countries around the world must reduce industrial emissions and improve agricultural practices in areas where dead zones are a problem especially. A dead zone in the Black Sea largely disappeared in the 1990s, following the fall of the Soviet Union, when the cost of chemical fertilisers skyrocketed.

Healthy soil and water management practices must be highlighted as a key driver toward dead zone recovery, such as placing buffers or dams to protect streams adjacent to agricultural land, and scaling up the use of perennial plants that can survive for several years and minimise soil erosion. As well as, increasing pulse production to increase soil quality, optimising the use of natural soil fertilisation.

We say: “eat more beans!” It’s good for you, and the planet!