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

SPP1685的一个主要假设是，土壤中磷(P)的枯竭促使森林生态系统从磷获取系统(有效地从矿物相动员)到磷循环系统(高效循环)。在这里，磷通量的特征对于指示生态系统的营养状态变得很重要。然而，由于缺乏详细的研究数据，对温带森林磷通量的定量了解受到相当大的限制。对于磷的输出通量，以往的研究仅在森林生态系统中零星地研究了暴雨事件造成的损失的动态特征。我们以前的研究表明，风暴事件是磷损失的主要驱动因素，优先流路径(PFP)是P的主要输送路径。因此，我们将重点研究森林土壤中优先流的特征。在拟议项目的框架内，我们将应用现场采样方法对比SPP站点，并对PF进行定量(通量)和定性(溶液化学)研究。此外，我们将把我们的抽样方法应用于联合N x P施肥试验(由SPP 1685服务项目协调)的试验区，以检查在变化的营养条件下P的出口通量。小区尺度的所有数据将被纳入一种新的建模方法CMF-P中，该方法通过基质流和PF模拟所有SPP站点的P通量，包括N×P应用试验的小区。在这里，我们正在进行的SPP 1685/1项目的结果也将被包括在内，特别是关于PFP在土壤中的分布，PFP中的P组分和不同SPP核心位置的基质中的P，以及溪水中P的输出通量。最后，我们将使用CMF-P模型来模拟德国云杉和山毛榉林地的P通量，从而对所获得的过程理解进行升级。

A main hypothesis of the SPP 1685 is that phosphorus (P) depletion in soils drives forest ecosystems from P acquiring system (efficient mobilization from the mineral phase) to P recycling systems (highly efficient cycling). Here, the characterization of P fluxes becomes 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 ongoing 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.