Impact of river damming on sediment texture and trace metals distribution along the watershed and the coastal zone of Nestos River (NE Greece)

This study examines the sediment particle size distribution and the trace metal concentrations from a dammed-river watershed (Nestos River) to its deltaic zone in NE Greece. The study area is relatively unpolluted. The distribution of trace metals (Cu, Cr, Cd, Ni, Pb, Hg) in sediments throughout the catchment area showed selective trapping of certain elements behind the two artificial dams (Thissavros and Platanovrisi dams) in the watershed and a sudden reduction downstream (83% for Cd, 81% for Cr, 94% for Cu, 90% for Ni, 86% for Hg and 33% for Pb). Marked sediment particle separation is observed at the upstream dam (Thissavros), where coarse material including sand is trapped (coarse fraction 12.9-49.3%). Finegrained material (< 63 mu m) is trapped behind the Platanovrisi dam (68.1%), and the reservoir showed elevated metal concentrations, especially for Cu and Cd (16.3 and 0.5 mu g/g, respectively). Lead exhibited a homogenous distribution throughout the watershed (20.1-32.3 mu g/g). All other trace metals (Cu, Cr, Cd, Ni and Hg) decline sharply downstream of the dam complex. In the delta system, nearshore sediments consist of shallow deposits in the vicinity of river mouth and are enriched in Cr (4.4-53.0 mu g/g) and Ni (2.6-44.3 mu g/g), while the further offshore and slightly deeper (20-40 m) sediments illustrate elevated Hg (0-0.07 mu g/g), Cd (0.09-0.18 mu g/g), Cu (11.5-18.3 mu g/g) and Ni (38-54.5 mu g/g).