Sediment production and water quality of watersheds with contrasting land use in Navarre (Spain)

An experimental watershed (Oskotz principal– Op –ca.1700 ha) covered with forest and pasture (cattle-breeding) with an equally experimental sub-watershed (Oskotz woodland – Ow – ca. 500 ha) almost entirely under forest was continuously monitored during 8 years (2001–2008). These watersheds were established by the Government of Navarre (Spain) in order to assess the impact of agricultural activities on different region of Navarre. The first results regarding exported sediment, runoff, nitrate and phosphate are presented herein. These results are compared with those from two grain-sown watersheds previously reported by the authors, elsewhere. The same as in the grain-sown watersheds, most runoff, sediment, nitrate and phosphate yields in Oskotz were generated during winter, though most erosive rainfalls occurred during summer. In Ow, average sediment, nitrate and phosphate yields were approximately: 700, 22, 0.35 kg ha year−1, respectively; for Op these figures were 550, 54 and 0.76 kg ha year−1, respectively.