Quantification, modeling, and regionalization of seepage losses of phosphorus from forest soils

The characterization of P fluxes is important to indicate the nutrient state of an ecosystem. However, the quantitative understanding of P fluxes in temperate forests is considerably limited by a lack of detailed research data. For P export fluxes, the dynamic character of losses induced by heavy rainfall events has been investigated only sporadically in forest ecosystems by previous research. Our previous studies revealed that storm events are a main driver for P losses, and preferential flow pathways (PFP) are the predominant transport paths for P. Therefore, we will focus on the characterization of preferential flow (PF) in forest soils. Within the frame of the proposed project, we will apply an in-situ sampling approach in contrasting SPP sites and investigate PF quantitatively (fluxes) as well as qualitatively (solution chemistry). Furthermore, we will apply our sampling approach at the test plots of the joined N x P application experiment (coordinated by the SPP 1685 service project) to examine P export fluxes under changed nutrition conditions. All data from the plot scale will be included in a new modeling approach CMF-P to simulate P fluxes by matrix flow and PF at all SPP sites, including the plots of the N x P application experiment. Here, results from our project of SPP 1685/1 will also be involved, especially regarding the distribution of PFP in soils, the P fractions in PFP and matrix at different SPP core sites, and P export fluxes in streamwater. Finally, we will upscale the acquired process understanding using the CMF-P model to simulate P fluxes for spruce and beech forest stands in Germany.