Hydrological controls of nutrient mobilization in watersheds

The doctoral dissertation deals with the temporal dynamics of the nutrient mobilization from a forested watershed with the emphasis on the definition and analysis of the hydrological mechanisms responsible for the regulation of observed responses of the streamwater nitrate concentrations and the amounts of the flushed nitrate. In 2006 and 2007 we continuously monitored the changeability of hydrometeorological conditions on rain gauges, limnigraphs and meteorological station on the studied area, the Padež stream forested watershed. The measurements of the hydrometeorological conditions were periodically supplemented by the continuous measurements of the streamwater chemistry in different seasonal and hydrological settings. The measurements of the streamwater nitrate concentrations during the hydrological events disclosed a considerable but variable responsiveness of the concentration to the hydrological conditions. In spite of the variability of the hydrological conditions, a seasonal influence could be recognised which has a prevailing role in regulating the intensity of biogeochemical transformations of nitrogen compounds, their further availability to mobilize under the impact of the hydrological mechanisms and respond to rainfall events. In the scope of the conceptual explanation of nitrate flushing, the perceived temporal patterns of the hydrograph and peak streamwater concentration formation were linked to the temporal frequency of the soil profile saturation deficit oscillations and associated changeability of spatial extension of the saturated variable areas. An extensive database obtained through continuous measurements was used for the application of the data mining methods. Using the algorithm M5 which, based on the recognised relations between the data builds the model trees and classification rules, we supplemented our domain knowledge of the nitrate flushing from the forested watershed and modelled the streamwater nitrate concentration. Additionally, we calculated the mass flux of the nitrate which is annually washed from the studied forested watershed.