Groundwater contamination from excess fertilizer

Steps:

• Identify NH₄NO₃ as a soluble nitrogen fertilizer used in agriculture.
• Recognize that excess application exceeds plant uptake, leading to leaching.
• Consider environmental pathways: runoff to surface water or percolation to groundwater.
• Evaluate health risks: groundwater contamination affects drinking water supplies.

Why C is correct:

• NH₄NO₃ is highly soluble and leaches into aquifers, contaminating groundwater per percolation laws in soil hydrology, posing nitrate risks to human health like methemoglobinemia.

Why the others are wrong:

• A: NH₄NO₃ hydrolysis produces acidic conditions, not alkaline soil.
• B: While runoff causes eutrophication and algae blooms, the choice specifies rivers, not the primary leaching issue.
• D: NH₄⁺ oxidation acidifies soil, but ammonia (NH₃) is basic and raises pH, not lowers it.

Final answer: C