Fig. 2.

Cell phone photos (without scale) and microscope photos (with scale) illustrating different aspects of size fractionation, sieve residue transfer, and microscopy. (a) Sieve cascade (sieve diameter: 75 mm) with top-down decreasing mesh size. (b) A particle trapped in the edge of a 300 µm-sieve without additional soldered seam. (c) Filtration setup for 47 mm filters consisting of (top-down): flipped sieve, glass funnel, filtration funnel, filter plate, and vacuum flask (not shown). (d) Top view on the filtration funnel's undersurface where particles can stick to after a vacuum filtration. (e) Cellulosic filter (diameter: 47 mm) on its filter plate loaded with a fractionated post-density-separation riverbed sample (size fraction: 500–1000 µm). (f) Petri dish containing the sample from e (diameter of the petri dish: 90 mm). (g) Sample residues < 300 µm sticking to a cellulosic filter after the larger particles were rinsed off. (h) A suspicious particle from riverbed samples of local river Lahn illuminated by reflected light. (i) The same particle shown in h illuminated by reflected and transmitted light revealing cellular structures.