Which one of the following is not a feature of eutrophic lakes?

Eutrophic lakes are characterized by high nutrient enrichment, particularly nitrates and phosphates, which leads to high primary productivity [c1][c3][t2]. This high productivity is a defining feature, as the abundance of nutrients stimulates the growth of algae and aquatic plants [c1][c3]. Consequently, the statement that primary productivity is 'low' is incorrect for eutrophic lakes; low productivity is instead a hallmark of oligotrophic lakes [t1][t2]. Eutrophic systems frequently experience algal blooms, often dominated by blue-green algae (cyanobacteria), which can lead to poor water quality and oxygen depletion in deeper layers [c4][t1][t2]. The plant nutrient flux in these lakes is high due to external loading from agricultural runoff or wastewater, as well as internal loading from sediments [c2][t1]. Therefore, while options 1, 2, and 4 are standard features of eutrophication, option 3 is the exception.

Sources

1. [1] Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 4: Aquatic Ecosystem > Classification of l,akes > p. 35
2. [2] Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 4: Aquatic Ecosystem > 4.2.3. General characteristics of Oligotrophic and eutrophic Lakes > p. 36
3. [3] Environment and Ecology, Majid Hussain (Access publishing 3rd ed.) > Chapter 3: MAJOR BIOMES > Eutrophication > p. 26
4. [4] Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 29: Environment Issues and Health Effects > 29.3.4. Greeenwashing > p. 420