Influence of hydrometeorological and vegetation conditions on the dynamics of nitrate flushing

Procesi kroženja enega najpomembnejših elementov, dušika, so neposredno odvisni od količine padavin in njihove časovne ter prostorske razporeditve, saj voda predstavlja glavni transportni medij in gonilno silo številnih ekosistemskih procesov. Na manj kot 1 km2 velikem gozdnatem porečju v občini Polhov Gradec smo med aprilom 2018 in aprilom 2020 izvajali hkratne meritve padavin, pretokov, vsebnosti vode v tleh in kemizma vodotoka Kuzlovec. Meritve smo izvajali s kratkim časovnim korakom 20 minut. V doktorski disertaciji smo se osredotočili na analizo hidrometeoroloških in sezonskih vplivov na spremembe koncentracij in iznose nitratnega dušika s porečja. Za oceno vplivov smo uporabili multivariatne statistične analize, za identifikacijo procesov poti stekanja in virov nitratnega dušika na porečju pa smo uporabili metodo časov zakasnitve na podlagi težišč diagramov in hkratne analize časovnih sprememb obravnavanih procesov. Količine iznesenega nitratnega dušika v času padavinskih dogodkov so se izkazale kot pomemben člen v izračunih masnih bilanc. Z naraščanjem intenzitete in količine padavin pa lahko pričakujemo tudi večje spremembe koncentracij med dogodki, medtem ko se je pri količinah iznesenega dušika poleg količine padavin kot pomemben dejavnik izkazalo trajanje padavin. Trajanje padavin je tudi eden najpomembnejših kazalnikov časa pojava težišča iznosa nitratnega dušika in hidrograma. S krajšimi in intenzivnejšimi dogodki bi tako lahko pričakovali še hitrejši odziv porečja, kar bi pomenilo večje volumne vode in količine spranega nitratnega dušika v krajšem času. Raziskave na naravnih porečjih, ki pokrivajo širok spekter podnebnih dejavnikov in hidrogeoloških lastnosti porečij, so zato ključnega pomena za oceno vplivov podnebnih sprememb in človekovih dejavnosti na vodni in dušikov krog. Pri tem bodo ključnega pomena predvsem tehnologije, ki omogočajo meritve s kratkim časovnim korakom in ustrezno točnostjo. Kot se je izkazalo v pričujoči nalogi, lahko na podlagi pogostih meritev kemizma vode bolje sklepamo o prevladujočih procesih padavinskega odtoka in transporta snovi ter izboljšamo njihovo konceptualno razumevanje.Processes of nitrogen cycling are directly dependent on the amount of precipitation and its temporal and spatial distribution, as water is the main transport medium and the driving force of many ecosystem processes. Between April 2018 and April 2020 we performed simultaneous measurements of precipitation, discharges, soil moisture, and the physico-chemical parameters of the Kuzlovec stream in a forested catchment in Polhov Gradec municipality. The area of the catchment is less than 1 km2. The measurements were performed with a short time step of 20 minutes. In the doctoral dissertation, we focused on the analysis of the hydrometeorological and seasonal effects on changes in concentrations and amounts of exported nitrate nitrogen. Multivariate statistical analyses were used to assess the effects. Moreover, the methodology of centroid time lags was used to identify the processes of runoff formation,. The amounts of nitrate nitrogen exported during the rainfall events proved to be an important element in the calculations of mass balances. If the intensity of precipitation increases, we can expect higher absolute changes of concentrations during events, whereas rainfall duration, besides rainfall amount, proved to be important for the amounts of exported nitrogen. The rainfall duration proved to be one of the most important indicators of the time of occurrence of the centroid of nitrate nitrogen export diagram and of the hydrograph. With shorter and more intense events, we could expect an even faster response of the river catchment, which would mean larger volumes of water and amounts of flushed nitrate nitrogen in a shorter time. Research in a natural river catchment, covering a wide range hydrometeorological factors is therefore crucial for assessing the impacts of climate change and human activities on the water and nitrogen cycle in the future. Technologies that enable measurements with a short time step and appropriate accuracy will be of key importance. As shown in this dissertation, based on high-frequency measurements of water chemistry we can better infer the predominant processes of rainfall-runoff and transport of nutrients and improve their conceptual understanding