The role of forest vegetation seasonality on the dynamics of nitrate-nitrogen export during rainfall events

Afforestation is recognized as one of the commonly used nature-based solutions for flood risk mitigation as well as for reduction of anthropogenic impacts on sediment and nutrient flushing. Processes of nutrient cycles (e.g., nitrogen cycle) 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 for many ecosystem processes. To understand the natural background of biogeochemical processes and transport of their products, it is therefore necessary to improve understanding of the hydrological control mechanisms, especially the formation of rainfall-runoff. Forest ecosystems without any or with negligible anthropogenic influences represent such kind of a reference, i.e. natural state in the field of nutrient flushing research. For this reason, we established an experimental monitoring system in the small, almost completely afforested Kuzlovec river catchment, Slovenia. Most of the hydrometeorological variables were measured continuously at a 20-min time step accompanied with measurements of concentrations of nitrate-nitrogen in the stream and leaf area index, which was used as an indicator of seasonal growth periods. Based on a two-year data set of various variables, we identified rainfall events for which we investigated: i) the influences of rainfall characteristics on the nitrate-nitrogen flushing, ii) the rainfall-runoff formation processes taking into account nitrate-nitrogen concentration changes during rainfall events, and iii) the role of the forest on the dynamics of the nitrate-nitrogen flushing (i.e., are there differences between the seasons). The focus of this contribution will be on the latter. We will present the most important findings obtained by using statistical analyses, such as hierarchical clustering, k-means, and principal component analysis. We believe that information obtained from such research is extremely important for improving the understanding of the processes’ controlling factors in areas with anthropogenic activities that affect the circulation and amount of nutrients exported to water bodies.