Potential effect of pH on the leaching of heavy metals from sediments of the Carpathian dam reservoirs

Eutrophication processes occurring in the Carpathian dam reservoirs (southern Poland) have resulted in a drastic increase of incidences of decrease of pH and oxygen content in near-bottom water, which may affect metal remobilization from the sediment. The study is aimed to determine the buffer capacity and effects of decreasing pH on the remobilization of heavy metals (Cd, Pb, Cu, Zn, Mn and Fe) from sediments of the Dobczycki Reservoir (DR), the Czorsztyński Reservoir (CR), and the Rożnowski Reservoir (RR), the right side tributary of the Vistula River. Buffering capacity and the leaching of heavy metals from sediments accompanied with an increase in acidity were analyzed in 0.00-0.24 M HNO3 solutions. Studied sediments had a high buffer capacity. Buffer capacity of sediments at studied sites of the DR and CR was different due to differences in the composition of sediments. The reservoir sediments had a variable ability to release heavy metals with increasing acidity. At pH ~5 and pH ~3, a considerable leaching of Mn (up to 60% and 85% of the total amount, respectively), Cd (up to 35% and 56% respectively), Pb (up to 25% and 39%), the lower leaching of Cu (up to 18% and 30%) and Zn (up to 14% and 20%), and the lowest leaching of Fe (below 5%) were found. The decrease of pH of the water-sediment system caused by eutrophication processes may affect the mobilization of certain heavy metals (mainly Mn, Cd and Pb) from sediment into the water column of the studied Carpathian reservoirs.