# Heavy Metals in Post-Exploitation Reservoirs--The Bagry Lake Case Study (Poland)
## 2 Data, Methods and Techniques
### Materials and Methods  
The study focused on the presence of Fe, Mn, Cu, Pb, Zn, Cd and Ca in the sediment and in the supernatant (layer of water just above the sediment) of the lake; Ca was not analyzed in the supernatant. In addition, a granulometric analysis of the sediment and its volatile (organic) fraction were determined. Samples of the sediment and the supernatant were collected at 18 sampling points, along the transects in 2021; the transects were located along the northern and southern shores of Bagry Lake and the central part of the lake (Figure 1a). The lake is an artificial water reservoir resulting from the extraction of sand and gravel. It is a place of rest of the inhabitants of Cracow. For this reason, water quality control is very important. It is located near residential buildings. There are swimming pools on its banks. It is a place for water sports and fishing. Extreme points of the lake have coordinates \(50^{\circ}02^{\prime}06.83^{\prime\prime}\) N, \(19^{\circ}58^{\prime\prime}59.08^{\prime\prime}\) E and \(50^{\circ}01^{\prime}49.11^{\prime\prime}\) N, \(19^{\circ}59^{\prime}51.69^{\prime\prime}\) E; it is located at an altitude of 195 m above sea level. All sediment samples were taken with the Ekman scoop (Figure 1c); the thickness of the series was about 5 cm. The supernatant samples were collected with a scoop (Figure 1b). Before analyzation for heavy metals (Fe, Mn, Cd, Cu, Ni, Pb and Zn), the sediment samples were dried at 105 \({}^{\circ}\)C, crushed and sieved through a sieve mesh size of 0.2 mm. The heavy metals in both supernatant and sediment samples was determined (in duplicate) at the accredited laboratory of Cracow Water. In the water sample, the concentration of iron was determined using the Hach PB-W-02 cuvette test, of manganese using the ICP-OES method (PN-EN ISO 11885:2009), of zinc using the AAS flame method (PN-ISO 8288:2002, contrAA 800 analyzer) and of lead, copper  
Figure 1: (**a**)—Map of Bagry Lake with the measuring points and transects (red lines), (**b**)—Scoop, (**c**)—Ekman scoop. and cadmium using the AAS method with graphite tube furnace (PN-EN ISO 1115586:2002, contrAA 800 analyzer). Metals in sediments were determined after mineralization of sediments. In the obtained liquid samples, the concentration of iron was determined using the Hach PB-W-02 cuvette test, of manganese using the AAS method with the graphite tube furnace (PN-EN ISO 1115586:2002, contrAA 800 analyzer), of zinc, lead, copper and cadmium using the AAS method in a flame (PN-ISO 8288:2002, contrAA 800 analyzer) and of calcium by ion chromatography (PN-EN ISO 14911:2002). In the case of water samples, the mean relative errors of cadmium, copper, lead and zinc concentration measurements were, respectively, 12.4%, 3.4%, 11.2% and 4.6%. To check granulometric composition and volatile fractions, the samples were dried at 105 \({}^{\circ}\)C and sieved through a sieve mesh size of 1.0 mm. Then, particles smaller than 1.0 mm were sieved through a 0.06 mm sieve. This way, two fractions were obtained: sandy (diameter 1.0-0.06 mm) and fine, comprising silty clay (0.06-0.002 mm) and clay (<0.002 mm) fractions. The volatile fraction was separated by burning the sample in a muffle furnace at 550 \({}^{\circ}\)C until a constant weight was obtained [30]. The granulometric composition of the sediments and both fractions were then determined with the gravimetric method. Sediment samples contained salts of carbonic acid, mainly calcium carbonate; it originates from limestone rocks and mollusks (mussels, snails) currently residing in Bagry Lake. The high burning temperature results in calcination (decarbonization) of calcium carbonate and other carbonates and a loss of carbon dioxide. To correct for the weight losses, the samples were treated with water saturated with carbon dioxide, dried at 105 \({}^{\circ}\)C and then weighed again [30].