The science behind Eutrophication (Allow me to digress)

Hi guys, as promised, I’m back!

Today’s post will (un)fortunately not be centred on the Killer Banana Case study, but rather on eutrophication, one of the environmental pollution caused by commercial farming. I have briefly touched on eutrophication in my previous posts, but they seem to be very disconnected, thus this post aims to tie them better. Also, I managed to chance upon this topic in my other pollution module, so it thought I’ll share! Do correct me if I’m wrong! I’ll appreciate that 😀

What is Eutrophication?

It is the natural aging process by lakes and reservoirs (water bodies) where nutrients are accumulated. As mentioned in lecture, at the initial stages, the lake of interest would be in a Oligotrophic state, where it is not “well-fed” with nutrients, thus low nutrient content and plant productivity. As nutrients are accumulated, the lake experiences an increased biological activity, resulting in phytoplankton growth (algae bloom) and decay of organic matter, and this is known as eutrophication.

Eutrophication is accelerated with human activities and the usual culprit is the agricultural activities, a diffused source of pollutants such as phosphorus and nitrates  .

Geographies of eutrophication

There is spatial and geographical distribution of the problems of eutrophication. Conditions in the tropics and the equatorial regions tend to facilitate and favour eutrophication. This is because these regions have high temperatures and high insolation which promotes biological activities such as photosynthesis and growth. Despite such theorisation, we can see from the map below that eutrophic and hypoxic coastal regions are not concentrated in the tropical regions.

Map showing the Eutrophic and Hypoxic Coastal regions

This is because there are other causes and sources of eutrophication, and nitrate and phosphorus pollution is just one of them!.Also, the next map shall explain.

Upper panel. Population in 1990 (persons km-2). Lerner et al. 1988; updated to 1990 by Bouwman, based on U.N. statistics. Lower panel. Nitrogen fertilizer use in 1990 (kg N km-2 y-1). Bouwman et al. (1995) and FAO statistics.

The high fertiliser application in north-eastern North America and central Europe that is not accompanied by high population density. In the case of India and China the population density is high, but the fertiliser application is moderate. In Africa and South America the application of fertilisers is low relative to the population density.

Problems of Eutrophication

I have mentioned in my previous post that eutrophication can cause ocean acidification, so now I’ll just explain why. The decay of algae blooms leads to dead organisms, and also the reduction in dissolved oxygen (DO) levels. Dissolved oxygen analysis measures the amount of gaseous oxygen (O2) dissolved in an aqueous solution. Oxygen gets into water by diffusion from the surrounding air, by aeration (rapid movement), and as a waste product of photosynthesis.

This drop in DO levels can lead to anaerobic conditions that solubilises toxic substances, thus increasing the toxicity of the water. This affects the aquatic lives because many organisms have very low tolerance for pH changes. Also, the anaerobic conditions suggest lesser DO, which is required for respirational purposes.

That’s all for today, I’ll be back with the continuation for monoculture farming! Stay tuned 😀

And here are some links to understand my post better:



(the 2nd link is an extremely good one because it mentions how the reduction in DO levels can be problematic)



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