Reconstruction of temporal variations of metal concentrations using radiochronology (239+240Pu and137Cs) in sediments from Kizilirmak River, Turkey

Sediment cores retrieved from rivers, lakes, and coastal marine environment have been widely utilized to reconstruct historical variations of anthropogenic pollutants. A sediment core was collected in the Kizilirmak River, Turkey during 2014 and analyzed for a suite of metals (Cu, Pb, Zn, Ag, Ni, Co, Mn, As, Cd, Sb, V, Cr, Hg and Se) to reconstruct their temporal variations. Chronology was attempted using excess(210)Pb (Pb-210(xs)),Cs-137 and(239,240)Pu in the sediment cores. The vertical profile of excess(210)Pb indicates that this core is not datable using excess(210)Pb method. The(137)Cs-based linear and mass apparent accumulation rates were estimated to be 0.84 cm year(-1)and 0.93 g cm(-2) year(-1), respectively. These values are in agreement with the(239+240)Pu peak-based linear (0.88 cm year(-1)) and mass apparent accumulation (0.97 g cm(-2) year(-1)) rates. There is considerable broadening in the peaks of both(137)Cs and(239,240)Pu, likely due to post-depositional mixing processes. The measured sediment inventories of(210)Pb(xs),Cs-137 and(239+240)Pu were 38, 29, and 0.42 dpm cm(-2), respectively, which were generally higher than the expected inventories based on local atmospheric depositional inventories. We attribute these enhanced inventories to potential sediment focusing and additional watershed erosional input. The Al-normalized enrichment factors (ANEF) were used to evaluate the contribution from natural versus anthropogenic sources. The ANEF of Ag, Ni, As, Cd and Se were > 1.5, which suggests a significant contribution of anthropogenic sources for these trace metals varied between 226% and 1163%. The geoaccumulation index (I-geo) values of the sediment column suggest that Cu, Pb, Zn, Co, Mn, Sb, V and Hg were in an unpolluted level and the others were in a polluted level. Besides, both the ANEF and I(geo)values of Cu, Pb, Zn, Ag, As, Se, Cd and Hg showed a peak at 28-30 cm layer (corresponds to 1978-1981), which is attributed to maximum metal release during 1970s.

Automated summary

Sediment cores from the Kizilirmak River in Turkey were analyzed for metals to reconstruct historical pollution variations. The profiles of lead and plutonium indicate mixing processes, with a peak in metal release during the 1970s.