What is Eutrophication and Why is it Linked to Ulsoor Lake?

A phenomenon known as “eutrophication” is killing fish across the globe.

Eutrophication. If you’ve been following the news for the last month, chances are that you might have come across this word in the context of the horrific incident of fish deaths at Ulsoor Lake in Bangalore. But what is this term and what does it mean?

The word eutrophication comes from Greek and literally means “well-nourished”. However, the phenomenon of eutrophication has a darker side and is considered to be a type of water pollution.

Eutrophication occurs when a water body receives abnormal levels of nitrogen and phosphorus compounds – for example, when industrial effluents, excess fertiliser run-off, pesticides and untreated sewage are dumped into water. These chemicals are essential nutrients for plants which has the consequence of causing an explosion in the population of algae within the waterbody. This has several negative consequences:

• The rapid expansion of algae (also known as an algal bloom) tends to be followed by the death and decomposition of these plants. As these plants decompose, the dissolved oxygen in the water tends to be used up, thus starving fish and other aquatic life of this critical element (a phenomenon called hypoxia);
  
• The algae often cover the surface of the waterbody which blocks sunlight and fresh air from reaching the aquatic depths;
  
• Algal blooms can be toxic and poison aquatic life;
  
• The eutrophication can affect the quality of water.
  

Eutrophication is a global problem and one that isn’t always easy to control. It can have lethal long term effects too – an estimated 6000 to 7000 miles in the Gulf of Mexico is considered to be a “dead zone” because eutrophication has led to hypoxia in these areas.

The situation in Ulsoor is a good case in point. Reports have noted that sewage was regularly dumped into the lake and some residents have said that they have been warning that the situation was urgent for over two years. Other reports have also suggested that eutrophication and low levels of dissolved oxygen were responsible for the mass deaths of fish in the lake.

India needs to address the problem urgently since it has the potential to get much worse. Our waterbodies support the livelihood needs of millions in addition to a host of ecosystem services. Just take a look at some of the figures – only a tiny proportion of sewage is treated before being dumped into waterbodies and excess pesticide and fertiliser use is common in many parts of the country. They all add up to one thing – a human induced imbalance in the natural ecosystem.

We need to remember one essential fact – we might think we can pollute an ecosystem with impunity, but ultimately, there will always be a time when we have to suffer the consequence of our actions. With an estimated 80% of the surface waters of our country polluted already, how much longer do we need to wait before making an effort to change things for the better?

(Shalini Iyengar is a lawyer and Research Associate at the International University College of Turin)