3-COMPONENT MODEL OF RUNOFF GENERATION, LYSINA CATCHMENT, CZECH-REPUBLIC

The forested Lysina catchment is situated in an area very susceptible to acid deposition. The streamwater is characterized py extremely high concentrations of total dissolved Al (volume weighted mean 66 mu mol L(-1)) and H+ (average pH = 3.87). In a simple two-component model, th e surface runoff component contributes only 6% of runoff in winter and 4% of runoff in summer. During flood episodes, the direct runoff cont ributes up to 20% of streamflow, There is a strong positive correlatio n between stream acidity and stream discharge. The observed exponentia l increase in streamwater acidity with discharge during high flow peri ods cannot be explained by the simple two-component model. A three-com ponent model used for hydrograph separation is based on chemical and O -18 analysis of precipitation, soil water and runoff. It incorporates a soil water component along with groundwater and rainfall components in streamwater generation. Dissociated organic acids leached during th e flow of water through the uppermost soil horizon help to balance an apparent anion deficit. The apparent anion deficit was found to increa se exponentially with flow rate. Low variability in streamwater delta( 18)O corresponds to a high contribution of indirect components (i.e., soil and ground water) in the runoff. The soil water contribution to i ndirect runoff calculated from the apparent anion deficit of streamwat er, varied from O at base flow up to 80% during floods. On average, 40 % of the streamwater is derived from soil water (from 31 to 39% in win ter and from 47 to 54% in summer).