Nutrient flows and management of a small watershed

Nutrient leaching from agricultural areas is one of the main concerns of watershed management. The paper examines nitrogen and phosphorus leaching from different parts of small agricultural watershed (378 ha) that was divided into 6 subcatchments. The calculations of nutrient outflow are based on the detailed measurement at the time of intensive agricultural activities during 5 years (1987–1991). The results show that nutrient leaching can vary very much even in such a small catchment area. The retention of nitrogen and phosphorus took place in the storage lake: 3,900 and 2.2 kg ha⁻¹ year⁻¹, respectively. At the same time, in the small subcatchment with high shallow groundwater outflow value, the nitrogen and phosphorus outflow was 233 and 0.90 kg ha⁻¹ year⁻¹, respectively. The most effective mitigation method is establishing buffer zones on the banks of the stream. A buffer zone of 460 m length would remove 2,200 to 2,640 kg N and 12 to 15 kg P a year, a constructed wetland on the stream would remove 1,660 to 2,760 kg N and 3 to 4.5 kg P a year. The detailed study gives good opportunity to estimate most critical areas where application of mitigation methods is most needed and ecologically and economically effective.