Question

In some rice-growing parts of the world, farmers use a combination of paddy fields and a fish farm. Rice paddy fields are flooded for much of the growing cycle and water running off the fields through pens where fish are raised. Nitrogen-based fertilizers are generally very soluble in water.
Which problems could result from farmers applying excess nitrogen-based fertilizers to their paddy fields?
1.Decreased fish production in the fish pen
2.Decreased levels of oxygen in the water
3.Increased growth of algae in the fish pens.
A.1,2 and 3 are correct
B.1 and 2 only are correct
C.2 and 3 only are correct
D.1 only is correct

Answer 1

Hint: Fish pens are part aquaculture which involves raising fishes commercially in tanks or enclosures such as ponds. In these fish pens. Along with fish, crustaceans, molluscs are also raised. The most important fishes that are raised in fish pens are carp, tilapia, salmon and catfish. This process of fish pens are used prominently in China and various other parts of Asia.

Complete answer:
Nitrogen present in the fertilizers react with water to form ammonia and nitric oxide which leads to decreased level of oxygen in water and will also decrease the level of the production of fish in fish pens due to the formation of ammonia. This eventually leads to the formation of algae in fish pens.
Therefore, option (A) 1, 2 and 3 are correct.

Note:
Whenever water is stagnant in the rice fields, fishes from nearby water tanks and pools naturally enter the paddy fields and grow there until harvest. This production of fish in rice fields dates from very early days. It is mostly used to capture rather than culture. This is called integrated agriculture-aquaculture farming system.