Oceans, caught between devil and the deep blue sea… (Pun intended!) – VIII

Hello everyone and welcome back to the eighth installment of “Oceans caught between the devil and deep blue sea…”

Today, I am feeling especially sad to write, since today is Holi and under the name of tradition, in India, people waste millions of liters of water.  The water situation in this country is dire. Over 63 million people do not have access to clean drinking water. Also, water that flows with Holi colors carries with it toxic chemicals into ground waters and oceans, crippling aquatic ecosystems.  You feel further more heartbroken because of the feeling of helplessness that everyone around you, is contributing to this water menace and you are incapable of doing anything against it.  We often forget that our actions on land always affect the environment and the oceans. The destruction, however, mostly happens out of sight and out of mind. For example, polluted runoffs like Holi colors can be leading source of water pollution today in rivers, lakes, coastal waters and oceans and yet very few people know about it. 

In today’s article, I am going to write mainly about pollutants entering oceans by way of agricultural runoffs.  In oceans, agricultural or farm runoffs can trigger algae blooms in coastal waters and produce “dead zones” where there is no oxygen, and hardly any fish or wildlife can survive. As we saw in earlier articles and as depicted in below pie-chart, one of the significant contributors among pollutants entering oceans are agricultural (farm) runoffs.

Pollutants entering oceans

What is an agricultural or farm runoff?

Second only to the availability of drinking water, access to the food supply is the highest priority. Therefore, agriculture is a dominant component of the global economy.  With population boom, the pressure to produce sufficient food has had a worldwide impact on agricultural practices. In most countries, food requirements have forced expansion of irrigation and steadily increasing use of fertilizers and pesticides to achieve and sustain higher yields.

Agricultural runoff or farm runoff is water from rain or melted snow that is not absorbed and held by the soil but runs over the ground and through loose soil. As runoff moves, it picks up and carries silt and pollution, which it deposits into ponds, lakes, coastal waters, and finally into oceans.  This runoff can include contamination from soil erosion, feeding operations, grazing, plowing, animal waste, application of pesticides, irrigation water, and fertilizers. Pollutants from farming include soil particles, pesticides, herbicides, heavy metals, salts, and nutrients such as nitrogen and phosphorus. Globally, soils and waters of almost all countries have been polluted by such agricultural activities.

Farm runoff2Farm runoff 1Farm runoff9

Besides conventional farming, Industrial animal agriculture is also severely affecting our waterways and oceans. The beneficial view of animal waste as manure to a farmer breaks down because animals are fed with an endless stream of antibiotics and hormones, which are excreted and end up in our waterways and oceans. Moreover, even if the manure were from a strict grass-fed diet, the scale on which factory farms produce animal waste, creates nitrogen shocks to the environment, encouraging disease outbreak and destructive algae blooms.

Once the agriculture runoffs reach the ocean, the many nutrients, including high levels of nitrogen and phosphorus that the fertilizers are carrying are released into ocean waters. Nitrogen and Phosphorus, these two nutrients are necessary for life, and in proper quantities, they help plants grow faster. In normal circumstances, these nutrients, which are already present in the marine ecosystem, help marine plants including algae grow. However, when farm runoffs release such excessive levels of the nutrients in the ocean, some algae species explode in growth. These growth explosions are known as algal blooms or red or brown tides, depending on the type of algae affected.   

Agricultural runoff promotes and leads to eutrophication.  Eutrophication or hypertrophication, is the enrichment of a water body with excess amounts of nutrients.  This process induces growth of plants and algae in oceans and, due to the biomass load, may result in oxygen depletion of the water body. This oxygen deficiency leads to the death of many plant and animal species in a marine environment. Through agricultural runoffs, increased nutrient availability from fertilizers in the aquatic ecosystems promotes excessive photosynthesis.  This process further leads to the afore-said algal and plant growth, resulting in oxygen deficiency in that oceanic region.  Eutrophication process and oxygen depriving processes are having dramatic consequences on fisheries, aquatic life and even threat to human beings.  With severely nutrient-over-enrichments, the algal growth can be so overwhelming that they completely shut down the entire ecosystem. Whole areas may become dead spots, places where normal marine life can no longer thrive or live at all. 

These oxygen-deprived areas of oceans are called as oceanic dead-zones. 

“Dead zone” is a more common term for hypoxia, which refers to a reduced level of oxygen in the water. As stated by National Oceanic and Atmospheric Administration (NOAA), Hypoxic zones or “Dead zone” are areas in the ocean of such low oxygen concentration that life in that area suffocates and dies.  In other words, Dead zones are areas in the world’s oceans, caused by “excessive nutrient pollution from human activities coupled with other factors that deplete the oxygen required to support most marine life in bottom and near-bottom water.” 

In the 1970s, oceanographers began noting increased instances of dead zones. These occur near inhabited coastlines, where aquatic life is most concentrated. The analysis of the oxygen-starved zones was conducted by a team of scientists from the Global Oxygen Network (GO2NE), created in 2016 by the Intergovernmental Oceanographic Commission of the United Nations.

Researchers determined that open-ocean “oxygen-minimum” zones have expanded since 1950 by an area roughly equivalent to the size of the European Union. The volume of ocean water completely devoid of oxygen has more than quadrupled in that time, the study found. The number of hypoxic, or oxygen-depleted, zones along coasts has increased up to 10 times, from less than 50 zones to 500 zones by now.

These dead zones are well known off the western coasts of North and South America, off the coast of Namibia and the west coast of India in the Arabian Sea. However new research published in the journal Nature Geoscience in December 2016 shows that the Bay of Bengal also hosts a “dead zone” of an estimated 60,000-km2 and occupying water depths of between 100 and 400 meters. This dead zone will cost Indian commercial fishery over $ 300 million every year.  Can India afford this? 

Dead zones formation


  1. Tox Town; S. National Library of Medicine
  2. Sylvia Earle Alliance/Mission Blue
  3. Control of water pollution from agriculture – FAO irrigation and drainage paper 55
  4. Wikipedia
  5. Huffington Post; 6th Jan 2018, Climate Change Has Quadrupled Ocean ‘Dead Zones,’
  6. Dead Zones by Welles Liu & Justis Nguyen
  7. TruLeaf 

Milind Joshi


2 thoughts on “Oceans, caught between devil and the deep blue sea… (Pun intended!) – VIII

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