Nutrients in wastewater and eutrophication: Discharge of nitrogen and phosphorus into lakes and ponds primarily leads to which adverse outcome?

Introduction / Context:
Excess nutrients in receiving waters trigger eutrophication, a process that disrupts aquatic ecosystems and water use. Understanding the dominant symptom guides nutrient removal strategies in wastewater treatment and watershed management.

Given Data / Assumptions:

• Wastewater contains elevated nitrogen (ammonia, nitrate) and phosphorus (orthophosphate, polyphosphates).
• Recipient is a lentic water body (lake/pond) with longer residence times.

Concept / Approach:
N and P are key limiting nutrients for algal and aquatic plant growth. When their concentrations rise, biomass blooms rapidly, forming algal mats and excessive macrophyte growth. This leads to diurnal oxygen swings, hypoxia on decay, fish kills, and taste/odour episodes. Hence the most direct and defining consequence is undesirable plant (algal) growth.

Step-by-Step Solution:

Verification / Alternative check:
Lake trophic state indices track chlorophyll-a and nutrient concentrations; control measures target nutrient reduction to curb blooms.

Why Other Options Are Wrong:

Common Pitfalls:
Confusing the immediate cause (nutrient enrichment) with downstream effects like hypoxia; the hallmark sign is explosive plant/algal growth.

Final Answer:
undesirable plant growth