Nutrient discharge from small agricultural catchments in Sweden characterisation and trends

Within the Swedish Monitoring Programme for Agriculture, 27 small agricultural catchments were investigated for between 9 and 14 years (6 years for one catchment), starting in the late 1980s, to determine the impact of agricultural activities on discharge water. The catchments represent major variations in climate, soil types and farming in Sweden and hence long-term average load of total nitrogen (N) and total phosphorus (P) at stream outlets varied widely among the catchments, from 2 to 41 and from 0.1 to 0.9 kg ha(-1) yr(-1), respectively. Catchments with large N loads were characterised by several factors favourable for leaching, such as mild winter climate, large precipitation, sandy or organic soils and high animal density in combination with intensive cropping systems with a low percentage of ley. Large P loads were mainly related to factors such as clay and clay loam soils, medium to high precipitation and large proportions of annual crops in the catchments. Flow-normalised time series of monthly loads of nitrate N, phosphate P and particulate P (for 24 catchments) were tested for trends. Significant downward trends were revealed for nitrate N, phosphate P and particulate P for seven, eight and three catchments, respectively, whereas, upward trends were revealed for nitrate N and particulate P for one and two catchments, respectively. Downward nitrate N trends for two catchments were correlated to smaller amounts of applied manure, especially during autumn, and to a decrease in the area of spring cereals and spring rape. (c) 2005 Elsevier B.V. All rights reserved.