Environmental engineering (assertion–reason): Effluent from oxidation ponds should not be discharged just upstream of lakes or reservoirs. Why?

Introduction / Context:

Oxidation ponds (waste stabilization ponds) are economical for polishing wastewater using sunlight, algae, and bacteria. However, their effluent often contains suspended algae and residual nutrients. Discharging such effluent directly upstream of lakes/reservoirs can trigger water-quality problems.

Given Data / Assumptions:

• Assertion (A): Discharging pond effluent just upstream of impoundments is undesirable.
• Reason (R): The discharged algae accumulate, settle or die, and undergo anaerobic decomposition, degrading water quality.
• Receiving water has low velocities and longer detention (reservoir setting).

Concept / Approach:

In quiescent reservoirs, algal cells from pond effluent may settle into bottom layers where dissolved oxygen is low. Anaerobic decay produces odours and releases nutrients (internal loading), worsening eutrophication. Additionally, sunlight and nutrients can fuel new blooms near the intake zones.

Step-by-Step Solution:

Verification / Alternative check:

Best practices route pond effluents to well-mixed river reaches or provide tertiary filtration/desludging before discharge to sensitive lakes.

Why Other Options Are Wrong:

• Since R correctly explains A, options B–D do not match the causal relationship.

Common Pitfalls:

• Ignoring algae-rich suspended solids in oxidation pond effluents when assessing receiving water impacts.

Final Answer:

Both A and R are true and R is the correct explanation of A