## 3 Results and Discussion  
### Heavy Metals in Sediments  
Mean values are shown in Table 1, whereas detailed concentrations are provided in the Supplementary Information (Table S1). Cadmium was above the LOD (0.005 mg/kg dw) in 99% of the samples. The highest mean concentration was recorded in soil samples from the irrigation area (0.142 \(\pm\) 0.053 mg/kg dw), which is significantly lower than the background soil value for Cd (0.265 mg/kg dw) described by [84]. In lake samples, the highest Cd concentrations were recorded at sediment depths 5-10 cm (0.063 \(\pm\) 0.060 mg/kg dw) and 10-15 cm (0.066 \(\pm\) 0.046 mg/kg dw). Compared with other lake studies, our results were slightly but significantly lower than those reported in Lake Acigol (0.185 mg/kg dw) [85], considered as unpolluted by Cd, and about ten times lower than those reported in Yang-zonghai Lake (0.68 mg/kg dw) [86], where Cd pollution in surface sediments is mainly attributed to high inputs of Cd-bearing pesticides and industrial wastewaters. The Cd concentrations in the lake samples did not differ significantly with depth (F\({}_{(5,85)}\) = 1.36). Nevertheless, comparison of sediments from different areas at 5 cm revealed significant differences (F\({}_{(3,36)}\) = 14.45). [PERSON]'s post hoc tests separated the samples into two homogeneous subsets consisting of (i) surface lake samples and (ii) wastewater ponds, dryland cultivation, and irrigation croplands. \"Surface lake sample\" concentrations of Cd at 5 cm were significantly lower (0.035 \(\pm\) 0.032 mg/kg dw) compared to the other group. The sequence of decreasing Cd concentration within this group was irrigation \(>\) dryland \(>\) wastewaters. \begin{table}
\begin{tabular}{l c c c c c c c} \hline \hline \multirow{2}{*}{**Sediments Zone**} & \multicolumn{2}{c}{**Sediment**} & \multirow{2}{*}{**Cd**} & \multirow{2}{*}{**Hg**} & \multirow{2}{*}{**Cu**} & \multirow{2}{*}{**Pb**} & \multirow{2}{*}{**Zn**} & \multirow{2}{*}{**OC**} & \multirow{2}{*}{**Reference**} \\  & & & & & & & & \\ \hline Petrola Lake (\(n\) = 28) & 0–5 & 0.035 \(\pm\) 0.032 & 0.014 \(\pm\) 0.034 & 4.28 \(\pm\) 4.83 & 16.2 \(\pm\) 25.4 & 18.7 \(\pm\) 17.9 & 9.5 \(\pm\) 6.1 & This study \\ Petrola Lake (\(n\) = 17) & 5–10 & 0.063 \(\pm\) 0.060 & 0.031 \(\pm\) 0.058 & 6.92 \(\pm\) 6.55 & 34.0 \(\pm\) 27.7 & 29.0 \(\pm\) 25.6 & 10.8 \(\pm\) 5.6 & This study \\ Petrola Lake (\(n\) = 17) & 10–15 & 0.066 \(\pm\) 0.046 & 0.038 \(\pm\) 0.039 & 8.37 \(\pm\) 4.41 & 51.6 \(\pm\) 48.7 & 37.4 \(\pm\) 35.5 & 14.6 \(\pm\) 5.6 & This study \\ Petrola Lake (\(n\) = 28) & \textgreater{}15 & 0.047 \(\pm\) 0.020 & 0.029 \(\pm\) 0.044 & 5.77 \(\pm\) 3.12 & 32.4 \(\pm\) 22.8 & 24.8 \(\pm\) 9.73 & 10.6 \(\pm\) 4.8 & This study \\ Wastewaters (\(n\) = 4) & 0–5 & 0.053 \(\pm\) 0.042 & 0.030 \(\pm\) 0.043 & 6.39 \(\pm\) 4.79 & 32.3 \(\pm\) 31.6 & 27.5 \(\pm\) 23.3 & 11.4 \(\pm\) 5.6 & This study \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Mean (\(\pm\)SD) concentrations of heavy metals (mg/kg dry weight) and organic matter content (OC, %), and comparison with other locations and sediment quality guidelines. ERM: effects range median. ISOG: interim. Mercury was above the LOD (0.008 mg/kg dw) in 74.5% of the sediment samples (Table S2). The highest values were measured in subsurface lake sediments and in surface soils/sediments affected by wastewaters (\(\approx\)0.030 mg/kg dw; Table 1). Measured Hg concentrations in this study were significantly lower than mean background soil values reported in soils from UK (0.13 mg/kg dw) [84], in soils from other European countries (\(<\)1 mg/kg dw) [93], or the values specified in the Spanish national directive RD1310/1990 (\(<\)1 mg/kg dw) [94]. The highest Hg concentration was found in core AL (0.251 mg/kg dw) between 5 and 10 cm depth. Nevertheless, these values are far below the effects range median (ERM) quality guideline value from NOAA (0.71 mg/kg dw) [90].