2.2. Sampling

Sediment samples in the tributaries were collected from the riverbed with a plastic shovel. In the reservoir, a gravity tubular sampler of the kajak type was used. The sediment samples were packed in polyethylene bags and approximately 1 kg of each point was collected. Surface water in the tributaries and reservoir was collected approximately 20 cm from the surface in 1 L polyethylene vials, which were previously left in HCl 10% solution for at least 8 h and rinsed with water from the Milli-Q purification system. When collecting water samples, the vials were rinsed with water from the sampling point before sample storage. All samples were identified, transported to the laboratory, and kept refrigerated (4 °C) until sample preparation.