Which one of the following processes takes place in lakes during eutrophication?

Eutrophication is the process of nutrient enrichment in water bodies, primarily through the excessive entry of nitrogen and phosphorus [c2][t1]. This process can occur naturally over long periods as a lake ages, but it is frequently accelerated by human activities such as agricultural runoff and sewage discharge, known as cultural eutrophication [c1][c2]. The high nutrient load stimulates the rapid and excessive growth of algae and aquatic plants, leading to algal blooms [c3][t6]. While this initially increases primary productivity, it ultimately degrades the ecosystem. As the massive volume of algae dies, aerobic bacteria decompose the organic matter, consuming the available dissolved oxygen [c4][t7]. This leads to hypoxia or anoxia (oxygen depletion), resulting in 'dead zones' where fish and other aquatic life cannot survive [t2][t8]. Therefore, the fundamental process initiating eutrophication is the excessive entry of nutrients into the water [t3][t5].

Sources

1. [1] Environment and Ecology, Majid Hussain (Access publishing 3rd ed.) > Chapter 3: MAJOR BIOMES > Eutrophication > p. 26
2. [2] Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 4: Aquatic Ecosystem > Classification of l,akes > p. 35
3. [3] Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 4: Aquatic Ecosystem > 4.4.r. What are the causes of these blooms? > p. 39
4. [4] Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 4: Aquatic Ecosystem > 4.3. EUTROPHICATION > p. 36
5. [5] https://pmc.ncbi.nlm.nih.gov/articles/PMC2266883/
6. [6] https://www.epa.gov/nutrientpollution/effects-dead-zones-and-harmful-algal-blooms
7. [7] https://oceanservice.noaa.gov/facts/eutrophication.html
8. [8] https://www.sciencedirect.com/topics/immunology-and-microbiology/eutrophication