Sediment was sampled on 22nd of May 2019 by removing the uppermost 2 cm sediment. In the laboratories the sediment was wet-sieved to gain a grain size of < 125 µm (test sieve, Gilson, Columbus, USA). Sediment was heated for 30 minutes to 40 °C in a drying oven (UT 6, Heraeus, Hanau, Germany). Afterwards, they were dried for 36 h at 50 °C in a drying oven (UT 6, Heraeus, Hanau, Germany), weighed again to determine dry mass and then ashed for 24 h at 500 °C in a muffle furnace (LV 5/11/B 170, Nabertherm, Lilienthal, Germany) and weighed again to determine ash-free dry mass
