Nitrogen losses from small agricultural catchments in Lithuania

• We analysed the impact of various factors that affect N loss from small catchments.
• N in precipitation is significant factor controlling N export from the catchments.
• The proportion of arable land and pasture in the catchment is highly important.
• The larger pasture area may significantly reduce N losses from the soil.
• There were no trends detected in the dynamics of streamflow nitrogen loads.

A study of precipitation, runoff and total annual nitrogen concentrations in streamflow was performed in three small stream catchments (A = 1.66 ÷ 14.2 km2) located in western, middle and southeastern parts of Lithuania during 1996–2010. The studied catchments belong to different geographic districts of Lithuania in which climate, soil, land use and farming conditions differ. The main objective was to present and analyse long-term data collected from three water-quality monitoring sites and to investigate the impact of various factors that may affect nitrogen losses.The results revealed the complex and dynamic nature of the various factors affecting nitrogen losses. The nitrogen contribution from wet deposition varied from 6.3 to 56.7 kg ha−1 per year and it was found to be significant factor controlling nitrogen export from the catchments. However, the proportions of arable land and pasture within the catchment, as well as the soil conditions were also found to be important.The annual runoff varied from 54 to 403 mm and exhibited strong spatial patterns among the catchments. The highest runoff was observed in the stream in southeast Lithuania, where sandy soils and a larger groundwater supply prevail. High runoff was also found typical in the stream in western Lithuania, the catchment of which received greater precipitation, exhibited hilly topography and a large drained area. The smallest runoff and highest instream nitrogen concentration (flow-weighted annual average was 7.0 mg l−1 compared with 3.3 and 2.8 mg l−1 in the other streams) was observed in the stream in the middle Lithuanian lowland, where more intensive agricultural activity occurs. The average annual load of total nitrogen in the stream in mid-Lithuania was 15.3 kg ha−1, compared with 11.8 and 7.0 kg ha−1 for the streams in the southeast and west, respectively.The 15-year data did not show any statistically significant trend either in the dynamics of the annual nitrogen concentration or in the annual nitrogen load of the streams.