Why are buffers effective in removing nitrate from runoff?

Buffers are effective in removing nitrate from runoff primarily because they create optimal conditions for denitrification processes and promote plant uptake. Denitrification is a microbial process where nitrates are converted into nitrogen gas, thus reducing the concentration of nitrates in the water. The presence of vegetation in buffer zones contributes to this process by absorbing nitrates directly from the soil and water, further lowering their levels in the runoff.

In natural buffer systems, the diverse plant species and soil microorganisms work synergistically. Plants take up nitrates for growth, which reduces their availability in the water. Meanwhile, certain microbial communities carry out denitrification under anaerobic conditions that can be found in saturated soils typical of buffer areas. This dual mechanism effectively mitigates nitrate pollution before it can reach larger bodies of water.

The other options, while having some merit in different contexts, do not directly explain the primary reasons for the effectiveness of buffers in reducing nitrate levels in runoff. For instance, increasing water temperature may enhance some microbial activities but does not specifically target nitrate removal. Filtering through fine sediments can help reduce particulate matter but is less effective compared to the biological processes occurring in established buffers. The removal of heavy metals is also a different environmental concern that buffers don't directly address in the context of nitrate