## 4 Discussion  
The studied sample groups show some characteristic differences between their physico-chemical properties, from which the existing element enrichment differences can be partially explained. Differences in grain sizes already became apparent in the results of laser diffractometry. The volumetric proportions of the grain fractions prove the presence of the finest particles within the RS. The low clay concentrations of this sample group are attributed to the presence of organic fine particles, which are assumed to correspond predominantly to the silt fraction and are detected as mineral grains by laser diffraction. The fact that at least the RS must contain not insignificant amounts of clay is expressed in their high quantities of Al, whose concentration usually correlate strongly with the gravimetric proportion of clay minerals [43]. The concentrations of Al, which turn out to be much higher in the RS than in the CS or the SS, prove increasing concentrations of all studied elements associated with increased fine grain contents. This is evident in the numerous strong correlations, which are particularly pronounced for Al and the concentrations of Cr (r\({}_{\text{sp}}\): 0.91) and V (r\({}_{\text{sp}}\): 0.89). Together with As and Fe, similarities of Al, Cr, and V are also supported by the results of the PCA, which expressively summarizes these elements by the same component. The accumulation of trace elements in the fine fraction is a frequently described process [44; 45; 46], which explains the, generally, highest concentrations of all studied elements within the RS and proves the classical sink function of reservoirs. The fact that Cr and V are only slightly enriched within the study areas investigated agrees with the comparatively lowest mobility in the CS, which relies on a relatively strong binding in soils or sediments without relevant anthropogenic enrichments [47; 48]. By largely matching geogenic background values for sedimentary and granitic rocks [49], the concentrations of both elements are interpreted to preferentially result from a geogenic origin and an almost exclusive deposition within the studied water bodies after erosion processes as described by [PERSON] and [PERSON] (2007) [50]. Since Cr and V are rather immobile during anoxic conditions and neutral pH [51; 52], the deposition of fine sediment is supposed to be the only relevant process controlling their enrichment in the studied reservoirs. A similar situation can be assumed for As, although it seems to be slightly lower depending on the accumulation of mineral fine particles, and it can be redistributed within the sediment under anoxic conditions [53]. The comparatively higher average EF is explained by higher concentrations  
\begin{table}
\begin{tabular}{c c c c c c c c c c c c c c c c} \hline \hline  & \multicolumn{4}{c}{**CS (_Air-Dried_)**} & \multicolumn{10}{c}{**RS (_Field Fresh_)**} \\ \hline  & **As** & **Cd** & **Cr** & **Mn** & **Ni** & **Pb** & **V** & **Zn** & **As** & **Cd** & **Cr** & **Mn** & **Ni** & **Pb** & **V** & **Zn** \\ \hline
**Mean (\%)** & 0.76 & 48.1 & 0.33 & 42.5 & 11.2 & 5.97 & 0.17 & 20.1 & 0.64 & 0.04 & 0.01 & 13.1 & 0.48 & 0.04 & 0.01 & 0.11 \\
**Median (\%)** & 0.36 & 47.1 & 0.25 & 32.7 & 5.75 & 3.95 & 0.06 & 11.0 & 0.32 & 0.02 & 0.01 & 14.1 & 0.33 & 0.02 & 0.01 & 0.08 \\
**SD** & 1.13 & 25.5 & 0.30 & 33.4 & 12.3 & 7.66 & 0.28 & 21.8 & 0.97 & 0.04 & 0.00 & 7.49 & 0.30 & 0.06 & 0.01 & 0.13 \\ \hline \(n\) & 89 & 89 & 89 & 89 & 89 & 89 & 89 & 89 & 33 & 33 & 33 & 33 & 33 & 33 & 33 & 33 \\ \hline \hline \end{within reservoirs of the Ore Mountains, where an elevated geogenic background and historic anthropogenic activities [54,55] may have contributed to the enrichment of As at some locations in the study areas. The lowest correlation coefficients of Al are found with the, comparatively, most mobile elements Cd (r\({}_{\text{sp}}\): 0.46) and Mn (r\({}_{\text{sp}}\): 0.36), as well as with Pb (r\({}_{\text{sp}}\): 0.37).