Résumé :
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Results on the influence of land use and climatic changes on nutrient losses in the Porijogi River catchment, South Estonia, are presented. The main tendency in land-use changes is a significant increase in fallow lands and abandoned lands (from 1.7% in 1987 to 12.5% in 1994), and a decrease in arable lands (from 41.8 to 22.5%). In the long-term period (1951-94) significant climatic fluctuations can be observed. Warmer winters (increase from -7.9 to -5.8 °C during 1950-94) and changes in precipitation pattern have an influence on water discharge. This results in more intensive material now during cold period and decreased water runoff in summer. Changes in water discharge and land use are reflected also in mean annual runoff of TIN and total-P, which decreased in the period 1987-94 from 15.6 to 2.7 kg N ha(-1) yr(-1) (83%) and 0.32 to 0.21 kg P ha(-1) yr(-1) (34%), respectively. However, nutrient losses from the forest subcatchment (upper course) had no significant change. Contrary, the mean annual runoff of water, BOD5, TM, total-P and SO4 from cultivated subcatchments showed a significant decrease.
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