Patterns, origin and possible effects of sediment pollution in a Mediterranean lake

Abstract

Vegoritis is a large, deep, mesotrophic, karstic lake in NW Greece, located in Ptolemais basin. Dramatic lowering of the lake’s level has occurred during the last half century due to human pressures. The Ptolemais Basin and the lake itself are subjected to serious human pressures. Pollutants are carried into the lake through both, the atmosphere and surface runoff. In order to identify the levels, and assess the origin of heavy metals in surface lake sediments, 24 samples were collected and analyzed for their grain size, as well as for their mineral, organic matter, major element and heavy metal content. The origin of heavy metals has been attributed to specific geogenic and anthropogenic sources. Despite the anthropogenic disturbance, the levels of micropollutants were low, possibly due to the low retention time of lake water and the recent increase of sedimentation rates. Only Cr, Ni, Co As, and Ba were present in relatively high concentrations. Ba is derived from the erosion of acid silicate rocks, Cr primarily from mafic rocks and secondarily from pollution, whereas for Ni and Co the opposite is true, while As is primarily attributed to fly ash deposition. The lowering of the lakes’ water level exposes sediments, which are then being oxidized. Mobilization of As and Cr could impair humans’ and ecosystems’ health.