## 2 Materials and Methods  
### Field Campaign and Sample Collecting  
Sampling of reservoir sediments took place in both drained reservoirs in late summer 2018. To ensure the representativeness of the sampling, samples were collected from areas near the dams with sediment thicknesses >1 m, as well as from the back areas of the reservoir basins (<1 m sediment thickness) near the inflow of the main tributaries (Figure 2). All samples originated from lacustrine areas of the reservoirs. Samples from sediment profiles were basically divided into intervals of 5-10 cm. This allowed a detailed record of vertical variations in sediment quality. Conversely, only relatively small sample volumes could be obtained with this method; thus, the grain size analyses could only be performed on a reduced number of samples due to the high sample consumption. In the Einsiedel Reservoir, a total of five sediment cores were taken near the dam (i.e., ES-S, ES-B and ES-III), near the centre (i.e., ES-II) and near the inflow (i.e., ES-I) of the reservoir with the help of PVC pipes, with sediments collected from depths of 20-40 cm. The sediment cores were subdivided into a total of 18 sediment sections with 5-10 cm thickness. In spring 2019, an additional field campaign took place around the Einsiedel Reservoir to collect soil samples from the surrounding watershed and sediment samples from the main tributaries. Soils were sampled from 6 plots (1 \(\times\) 1 m), where an input of soil components into the reservoir basin due to the fact of erosion was assumed to be possible. Within each plot, the soil types were classified [34] before samples were taken from the topsoil (0\(-\)10 cm) and subsoil (11\(-\)25 cm) horizons at three locations and combined into one composite sample per depth level (12 composite samples in total). The organic cover layer, which was dominated by needle litter, was removed before the topsoil samples were collected. Brook sediments (3 samples) were collected from 0 to 15 cm depth as disturbed samples with a shovel in flow-calmed areas of the main tributaries.  
The Berthelsdorf Smelter Pond (BSP) was investigated using five sediment profiles sampled with a Purchkauer drilling rod and a PVC pipe. The samples were collected at the backwater location of the basin (i.e., HT-3 and HT-5), the middle of the reservoir (i.e., HT-4)  
\begin{table}
\begin{tabular}{c c c} \hline  & **Einsiedel Reservoir** & **Berthelsdorf Smelter Pond (BSP)** \\ \hline
**Catchment** & & \\ Size (km2): & 1.8 & 4.78 \\ Geologic formations: & Phyllite, clay shale, amphibolite & Biotit gneiss, biotit-twofeldspar genesis, quartzite \\ Predominant soils: & Gleyic Fluvisols, & Gleyic Fluvisols, Stagnic Fluvisols, \\  & Dystric Cambisols & Umbric Planosols, Skeletic Regosols \\ Predominant land use: & Forestry (_Picea abies_) & Grassland, agriculture, settlement \\ \hline \end{tabular}
\end{table}
Table 1: Cont.  
and near the reservoir outlet (i.e., HT-1 and HT-2). Depending on the location, the sediment profiles reached thicknesses of 20\(-\)100 cm and were divided into sections of 10 cm, resulting in a total of 36 samples. Soil sampling in the catchment of the BSP was not carried out because the balanced relief did not allow for the tracing of potential sediment sources without further effort.