Normalized mean values covering all lakes and elements (As, Cd, Cr, Cu, Ni, Pb, S, Zn) are shown in Fig. Five-year means of concentrations of ∑DDX (left) as well as TEs (right) of all ten lakes normalized to the respective maximum of each sum parameter in each lake (excluding Lake WM for ∑DDX). A detailed explanation about the calculation is given in the text (section 2.13). Light gray points depict implausible measurement results, that are probably caused by carry-over during sampling