Geometric configurations of particulate matter in terrestrial solutions of a temperate beech forest

The heterogeneous nature of the size and shape of particulate matter (PM) deposited onto forest canopies is acknowledged. However, it is uncertain how PM interacts with the forest canopy and how it is transported and cycled via the hydrological processes of throughfall and stemflow. To improve our understanding of particulate cycling in forested watersheds, this study quantifies the geometric configuration of PM in bulk precipitation, throughfall, stemflow, and upper soil (Oa horizon) solution in both leafed and leafless periods in a European beech (Fagus sylvatica L.) forest in Germany. Circular equivalence diameter, circularity, elongation ratio, perimeter-to-area ratio, and fractal dimension were calculated for all 43,278 individual particulates in bulk precipitation, throughfall, stemflow, and Oa solutions. Loss on ignition measurements were also conducted to determine the organic matter content of the particulates. From a physical point of view, the opposite trends for circular equivalence diameter and perimeter-to-area ratio of PM between stemflow or throughfall and bulk precipitation during both leafless and leafed periods were the most striking. For bulk precipitation, the PM's mean circular equivalence diameter was significantly larger in the leafless period than the leafed period, with the reverse observed for throughfall and stemflow. Mean perimeter-to-area ratios (μm⁻¹) of PM of both stemflow and throughfall were significantly larger in the leafless period than the leafed period. The opposite trend was observed for bulk precipitation and Oa solution. The percent organic matter of PM was not statistically significantly different across solutions or canopy state. Our results indicate that the differential routing of PM through the canopy indeed influences the geometry of PM among solution types as compared to the bulk precipitation. The effects of these changes on the chemistry of the PM and its impact of particulate cycling, and the impacts of shifting seasonality with climate change, warrants further investigation.