A limiting nutrient is one that is present in less quantity or circulates very slowly in the ecosystem. Farmers generally supply the limiting nutrients to increase their production. One of the examples of limiting nutrient is Nitrogen. The best way of supplying this limiting nutrient is by using fertilizers that are rich in nitrogenous compounds.
Increase in the limiting nutrient of a place can disrupt the equilibrium of the ecosystem. Increase in nitrogen supports the life of plants and their number may increase hugely. Same situation might have occurred in the stream. Such significant increase in the aquatic plants might have created hindrance for the other forms. The aquatic forms like algae might have out grown. Algae are short lived and their decomposition takes up the oxygen from the water. Decomposing algae might have reduced the dissolved oxygen levels of the stream resulting in hypoxic condition. Since trout require dissolved oxygen for respiration, they might have died due to oxygen deficiencies.