Organic carbon, major and trace element release from and adsorption onto particulate suspended matter of the Ob River, western Siberia.

Particulate suspended matter (PSM) of rivers is a significant factor for carbon, nutrient, and trace metal transfer from land to ocean. Towards better understanding the role that PSM exerts on major and trace elements in riverine systems, here we report the results of an experimental study which utilizes a two-fold approach to assess interaction between PSM and riverine solutes. First, we measured element leaching (via desorption and dissolution in distilled water, simulating snow melt) from PSM of the largest Siberian river, the Ob River. Second, we quantified the capacity of PSM to adsorb dissolved organic carbon (DOC), macro- and micronutrients and trace elements from organic-rich waters of the river floodplain. We documented sizable desorption of organic carbon, some major and trace metals, oxyanions and insoluble elements from PSM; the majority (>50 %) of elements were released over the first hour of reaction. In contrast, PSM of the Ob River was capable of removing 20 to 90 % of dissolved OC, nutrients (Si, P), and trace elements from the tributary and floodplain fen. Our experiments demonstrated preferential adsorption of aromatic compounds large molecular size colloids. Taken together, the adsorption of solutes by PSM can sizably decrease the concentration and modify the molecular size distribution, and therefore the potential bioavailability of major (DOC, P, Si) and trace micronutrients. Overall, the PSM of the Ob River exhibited high reactivity with respect to natural waters and was capable of modifying the elemental composition of the tributary and floodplain fen waters. This transfer of organic carbon and nutrients in the surface-adsorbed (particulate) form is especially important during spring flood and requires specific consideration in short-term biogeochemical cycles of elements in continental waters.