The geochemistry of river and stream sediments depends on several factors, including the nature of exposed lithologies in the source area; the weathering and erosion rates, also driven by climate changes; the different grain-size and sorting due to hydraulics and sediment dynamics; recycling processes and anthropogenic inputs. In particular, the response to post-depositional weathering depends on sediment mineralogical composition, since some mineral decomposes chemically and mechanically relatively swiftly, while others are more stable retaining certain elements. Trace elements, including potentially toxic elements (PTEs), from river and stream sediments can enter the aquatic ecosystem, affecting water quality, and may both concentrate in the detrital fraction or be adsorbed on the surface of the clay-size fine-grained fraction. In the Chirchik-Akhangaran basin (CAB) in the Tashkent Province of Uzbekistan (Central Asia), little is still known about the dominant geogenic and/or anthropogenic sediment sources in rivers and streams. In the present study, stream and river sediments were collected in 21 sampling stations in the CAB upstream catchments and floodplain, and the grain-size control on trace element geochemistry was investigated. Some of the observed geochemical patterns are attributable to the different contribution from geogenic sources; however, enrichments in some trace elements such as Zn, Cu, Ni, Cd, and Pb, in particular in the Akhangaran catchment, are attributable to the increasing of elements from mining activities and/or weathering of mineralized rocks entering waterways. The comparison with freshwater sediment quality guidelines TEC (Threshold Effect concentrations) and PEC (Probable Effect Concentrations) indicates potential threats for aquatic biota, in particular for As, in both the Chirchik and Akhangaran river systems. The possible anthropogenic contribution is highlighted by indices such as the Geoaccumulation Index and Contamination Factor.
Geochemical assessment of river and stream sediments in the Chirchik-Akhangaran river basin (Uzbekistan, Central Asia)
Silvia Fornasaro;Lisa Ghezzi;Riccardo Petrini
2024-01-01
Abstract
The geochemistry of river and stream sediments depends on several factors, including the nature of exposed lithologies in the source area; the weathering and erosion rates, also driven by climate changes; the different grain-size and sorting due to hydraulics and sediment dynamics; recycling processes and anthropogenic inputs. In particular, the response to post-depositional weathering depends on sediment mineralogical composition, since some mineral decomposes chemically and mechanically relatively swiftly, while others are more stable retaining certain elements. Trace elements, including potentially toxic elements (PTEs), from river and stream sediments can enter the aquatic ecosystem, affecting water quality, and may both concentrate in the detrital fraction or be adsorbed on the surface of the clay-size fine-grained fraction. In the Chirchik-Akhangaran basin (CAB) in the Tashkent Province of Uzbekistan (Central Asia), little is still known about the dominant geogenic and/or anthropogenic sediment sources in rivers and streams. In the present study, stream and river sediments were collected in 21 sampling stations in the CAB upstream catchments and floodplain, and the grain-size control on trace element geochemistry was investigated. Some of the observed geochemical patterns are attributable to the different contribution from geogenic sources; however, enrichments in some trace elements such as Zn, Cu, Ni, Cd, and Pb, in particular in the Akhangaran catchment, are attributable to the increasing of elements from mining activities and/or weathering of mineralized rocks entering waterways. The comparison with freshwater sediment quality guidelines TEC (Threshold Effect concentrations) and PEC (Probable Effect Concentrations) indicates potential threats for aquatic biota, in particular for As, in both the Chirchik and Akhangaran river systems. The possible anthropogenic contribution is highlighted by indices such as the Geoaccumulation Index and Contamination Factor.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
