Biogenic silica composition and δ¹³C abundance in the Changjiang (Yangtze) and Huanghe (Yellow) Rivers with implications for the silicon cycle

The study was carried out to address a method for separation of terrestrial and marine biogenic silica (BSi) in estuaries based on BSi compositions and δ¹³C values in BSi associated organic matter (δ¹³C_BSi). We used two world-class major rivers - the Changjiang (Yangtze) and Huanghe (Yellow) Rivers as examples to illustrate our approach. Our results for these rivers indicate that riverine BSi is comprised mainly of phytoliths and diatoms. River BSi concentrations vary with terrestrial inputs and in-stream primary production. Although the fluvial BSi sources are complex, the terrestrial δ¹³C_BSi signals are quite unique (− 24.7 ± 0.8), significantly lower than the marine δ¹³C_BSi values (− 21.3 ± 0.07, central Yellow Sea) (p < 0.01). Thus, the variation of δ¹³C within BSi organic matter can provide terrestrial source information on the biogeochemistry of silicon in estuaries and the adjacent shelf. The δ¹³C_BSi combination could potentially act as an efficient tool to study environmental change in coastal areas on decadal time-scales since this index may respond to variable terrestrial fluxes from land, as well as to changed phytoplankton assemblages in the coastal ocean. - Highlights: • A method for measurement of terrestrial and marine biogenic silica (BSi) was developed. • River BSi composition varies with terrestrial inputs and in-stream primary production. • δ¹³C can be used as a tracer of terrestrial inputs of BSi into the coastal area.