## 3 Results and Discussion
### Heavy Metals in Sediments
No statistically significant differences were detected between depths in lake sediment samples (F\({}_{(5,85)}\) = 0.85) or among land use areas (F\({}_{(3,36)}\) = 1.03). A Hg contamination in sediments and soil can therefore be excluded. in the 10-15 cm lake sediment layer (51.6 \(\pm\) 48.7 mg/kg dw) (Figure 3). In the top layer (0-5 cm), the mean Pb concentration was similar to values observed in the Caspian Sea (15.9 mg/kg dw) [88], both below the threshold effect range low (ERL) values reported in the Marine Quality Guidelines NOAA (46.7 mg/kg dw) [90] and the Canadian sediment quality guidelines (ISQG) (30.2 mg/kg dw) [91]. However, the remaining mean values of the profile were close to the threshold value or, as noted above in layer 10-15 cm, above it (51.6 mg/kg dw). Concerning surface soils and sediments (5 cm depth), we determined differences between the background soil value (12.3 mg/kg dw) [84] and mean values per sediment location. Soils affected by wastewaters (32.3 mg/kg dw; Table 1) had significantly higher values of Pb (\(t_{(3)}\) = 5.37), unlike lake sediments (16.2 mg/kg dw; \(t_{(27)}\) = 0.81), dry-land cultivation sediments (12.2 mg/kg dw; \(t_{(3)}\) = 0.04), irrigation cropland sediments (14.0 mg/kg dw; \(t_{(3)}\) = 0.82). In the samples analyzed by sequential extraction, surface samples showed that Pb was mostly bound to the residual fraction, ranging from 37.4% (lake) to 67.4% (irrigation croplands) (Figure 2). In samples from the lake and from those affected by wastewaters, however, the fraction of Pb bound to organic matter (F4; 34.6% and 28.1%, respectively) and to Fe oxides (F5; 11.9% and 8.7%) was significantly higher than in agricultural soils (10% and 6.2% for dryland and irrigation croplands, respectively). Zinc was detectable in all studied samples (Table S2), but no significant differences in concentration were found either among areas (F\({}_{(3,36)}\) = 2.43) or among lake sediment depths (F\({}_{(5,85)}\) = 1.12). Table 1 and Figure 3 show the maximum mean value in lake sediments at 10-15 cm depth (37.4 mg/kg dw). The maximum value (161.5 mg/kg dw) was also measured at this depth in core AF (control point 2648, lake sediments). This still is far below the ERM quality guideline value of NOAA (410 mg/kg dw) [90]. Surface sediments from Petrola Lake also showed a concentration (18.7 mg/kg dw) lower than that reported in other unpolluted lacustrine sediments (e.g., Maharlu Saline Lake, 37.0 mg/kg dw) [87]. Moreover, all mean Zn concentrations were lower than the general background soil value (56.5 mg/kg dw) [84]. The sequential extraction indicated that Zn was predominantly present in the residual fraction (F6) in wastewater pond sediments (30.5%), dryland (42.9%), and irrigation cropland soils (47.2%). In lake sediments, however, the most Zn-rich fraction was that bound to Fe oxides (26.8%). Finally, lake sediments and wastewater sediments  
Figure 2: Distribution of Cu, Pb, and Zn in the different fractions for the studied sediment samples (\(n\) = 14). F1: exchangeable fraction. F2: bound to carbonates. F3: bound to Mn oxides. F4: bound to organic matter. F5: bound to Fe oxides. F6: residual fraction. showed a significant contribution of the fraction bound to carbonates (18.1% and 19.4%, respectively) (Figure 2). Overall, these results show a certain Pb enrichment in subsurface (below 5 cm) sediments, with a maximum in the 10-15 cm layer from Petrola Lake (Figure 3). These values were close to or above the threshold levels in marine and lacustrine guidelines (NOAA and ISQG). In addition, soils affected by wastewaters also had values slightly exceeding the background levels. Even though other elements (i.e., Zn) in lake sediments followed the same depth pattern as Pb, the measured concentrations remained below the quality guideline values and/or were similar to comparable lacustrine systems [86; 87; 88]. Sequential extraction provided important information about the mobility of Cu, Pb, and Zn.