A buffer zone is a belt of shelter or permanent grassland separating agricultural land from watercourses and water reservoirs. According to the Code of Good Agricultural Practices, they are a landscape element that can limit the migration of biogenic substances. Increasing attention is paid to the fact that these barriers are effective during the growing season. However, in the autumn-winter and early-spring half-year they can be a source of nitrogen compounds leached from the catchment to surface water. In connection with this, research was undertaken to assess the content of nitrogen compounds in the soil of the zone at the channel and water of the watercourse in a small agricultural catchment. The processes occurring in the buffer zones leading to the release of biogenic compounds do not only concern leaching them to surface and groundwater, therefore the amount of nitrous oxide emissions, which is the result of the denitrification process occurring in the soil, was examined. Based on the obtained results, it was found that an increased content of nitrogen compounds in the soil of buffer zones may have an impact on the increased emission of N2O and an increased content of these substances in surface water.