Geochemistry of organic matter in river waters of the Amur basin, Russia

Organic matter (OM) plays an important role in the biochemical C cycle and in river waters, in particular. The paper considers a huge area of the Amur basin and its subbasins. The concentrations and distribution of OM in river waters were investigated during the summer of 2008 and 2010–2012. The conducted studies identified total, dissolved and particulate organic carbon (TOC, DOC and POC), humic substances (HS)–humic acids (HA) and fulvic acids (FA), and suspended matter (SM). It was established that concentrations of OM vary significantly along the river flow and hydrological cross sections due to inflows from major tributaries originated in various physio-geographical zones. The results showed that concentrations of TOC varied from two to several tens of mg C/L, but were dominantly high. In the Upper Amur basin water, concentrations of DOC were dominant; the amount of HS was 17–48 % of DOC. Upstream of the Songhua mouth, the amount of HS (up to 60 % of DOC) was mainly due to inflows from the Zeya and Bureya running over the taiga zone. High concentrations of OM and SM were detected in the water discharge from the Songhua, the amount of HS accounted for 20 % of DOC. In the Ussuri basin, formed in the coniferous broad-leaved forest zone, concentrations of OM were lower compared to the Amur water. In the summer of 2011 and 2012, fluxes of TOC over the Amur River to the Amur Liman were 9.168 × 103 and 11.029 × 103 t C/day, respectively.