Temporal and Spatial Variation of Nutrient Leaching from Agricultural Land in Latvia: Long Term Trends in Retention and Nutrient Loss in a Drainage and Small Catchment Scale

摘要

Agricultural run-off monitoring and losses of nitrogen (N), phosphorus (P) from small (60 - 960 ha) catchments and drainage fields (12 - 77 ha) in Latvia were analyzed. The catchments represent areas with different agricultural production intensity, landscape, soils and climate. Results from the long-term monitoring show (i) large differences in levels of losses between the catchments and fields with different farming intensity, (ii) large annual and interannual variability due to climate impact and soil conditions, (iii) few time trends in nutrient losses. These results are discussed in relation to pollution from non-point and point sources. Besides, these data demonstrate changes in agriculture driven by large-scale changes in land-use intensity. However, despite the increased implementation of mitigation methods by farmers, improvements in water quality at the catchment scale can take a long time. Long-term monitoring programmes to detect trends are required.