Which statement best describes how agricultural practices can contaminate groundwater, and what are two common mitigation strategies?

• A. Leaching of nitrates and pesticides through soil into groundwater; mitigation includes nutrient management plans and vegetative buffer zones.
• B. Soil erosion leading to sediment in surface waters; mitigation includes terracing and cover crops.
• C. Over-irrigation causing groundwater salinization; mitigation includes drip irrigation and salt-tolerant crops.
• D. Application of lime increasing soil pH; mitigation includes pH buffering.

Answer: (A)

The main idea here is that agricultural practices can move soluble nutrients and some pesticides down through the soil with percolating water, reaching groundwater. Nitrates, in particular, and many pesticides are highly mobile and can leach beyond the root zone, especially after rainfall or irrigation, contaminating drinking water supplies. Two common ways to reduce this are: implementing nutrient management plans that tailor fertilizer amounts and timing to crop needs, which minimizes excess nitrogen that can leach; and establishing vegetative buffer zones along field margins, which help filter and uptake nutrients and pesticides before they reach groundwater and reduce downward water movement. The other options describe problems or mitigations more related to surface water, salinity, or soil chemistry rather than the groundwater leaching mechanism described here, so they don’t fit as well.