Gamtinių ir antropogeninių veiksnių įtaka azoto ir fosforo išplovai upelių baseinuose

Abstract

Trijuose Lietuvos baseinuose (Vakarų, Vidurio ir Pietryčių) vykdoma iš esmės tik žemės ūkio veikla ir jau penkiolika metų tiriama, kaip keičiasi vandens nuotėkis ir azoto bei fosforo išplovimas kintant gamtinėms sąlygoms ir žemės ūkio veiklos pobūdžiui. Skiriasi tiriamų upelių baseinų klimato sąlygos, dirvožemis, žemės naudojimas ir ūkininkavimo intensyvumas. Priklausomai nuo Lietuvos gamtinių-geografmių ir žemės naudojimo sąlygų baseinuose per tyrimų laikotarpį (1996-2010 m.) labai skyrėsi nuotėkis, bendrojo azoto (NB) ir bendrojo fosforo (PB) koncentracijos ir kiekiai. Upelių vidutinis metinis nuotėkis kito nuo 173 iki 237 mm. Didžiausias nuotėkis yra Vardo upelio kalvotoje Pietryčių Lietuvoje, jame, be paviršinio, didelę dalį sudaro ir požeminis nuotėkis

Studies of water runoff changes and total nitrogen (NB) as well as total phosphorus (PB) leaching were carried out in West, Middle and South-eastern part of Lithuania. Catchments are different in climate, soil, land use and fanning intensity. Water runoff, NB and PB concentration varied widely in the mouth of all three studied streams during 1996-2010. Mean yearly water runoff has fluctuated from 173 to 237 mm. The largest runoff was in the hiliy Southeastern part where stream beside precipitation was fed by groundwater. Mean 1996-2010 NB concentration in precipitation varied from 3.4 to 5.6 and PB-from 170 to 365 p-gl"1. Mean yearly NB concentration in Graisupis catchment precipitation 1.6 times higher than in in Vardas or Lyzena catchments. Mean 1996-2010 NB concentration m streams water varied from 2.7 to 6.6 and PB- from 53 to 152 jxgl"'. Mean yearly NB concentration in Graisupis stream water almost all the time was higher than in in Vardas or Lyzena catchments. It seems likely that higher NB and PB concentration in the Graisupis stream is because of more intensive farming and higher NB as well as PB concentration in precipitation. Since the stream is fed by surface water nitrogen and phosphorus sooner or later reaches the stream. NB concentration in the Vardas stream is lower because ground water weakens the concentration. NB and PB normalisation according water discharge load of NB and PB has not changed much. Little was changed load of nitrogen and phosphorus in streams after normalisation according discharge, NB and PB concentration in precipitation. Fluctuation of discharge and changes of NB and PB in precipitation were followed by appropriate change of NB and PB concentration in stream water. Mann-Kendall test showed that significant NB increasing trend is only on the Lyzena stream water and PB in the Vardas stream