Change of water Quality in the rivers and streams of Lithuania karst zone

The quality of water in rivers depends on physical – geographical conditions of the watershed; in addition it is affected by economical activities of people. The article analyzes variation of runoff, nitrogen compounds and total phosphorus in the rivers (Levuo, Tatula, Nemunelis) and streams (Bere and G-1) of the karst zone. The state monitoring data is used to describe the runoff and water quality in the rivers; the data of the investigations performed by the Water Management Institute of LUA is used to describe the analogous characteristics of the streams. This analysis aims to find out the overall patterns of water quality changes in the rivers and streams of same region. The nitrate nitrogen concentration has been determined to be higher in streams than it is in the rivers. During the period (1996-2005) in each river nitrate nitrogen and total phosphorus concentration patterns were different. The sources of ammonium nitrogen in the rivers and the streams tend to be different. The increase of total phosphorus concentration in rivers is due to the concentrated pollution, in streams – due to the natural soil phosphorus content and application of phosphorus fertilizersVytauto Didžiojo universitetasŽemės ūkio akademij