Export and dissolution of biogenic silica in the Yellow River (Huanghe) and implications for the estuarine ecosystem

Abstract

Abstract Biogenic Silica (BSi) plays an essential role in availability of dissolved silicate (DSi) in aquatic ecosystems , but its role in silica cycling is still poorly characterized in the river and estuary systems. This study addressed the riverine BSi composition and reactive silica (RSi) export in the Yellow River, and estimated the contribution of terrestrial BSi dissolution to the estuary silica pool. Our results indicated that phytoliths comprised 1.3%–87% of the riverine BSi, while diatoms accounted for 13%–99% of the riverine BSi. The Yellow River transported 24 Gg yr −1 of BSi and 26 Gg yr−1 of DSi loadings, respectively; 63% of the riverine BSi and 54% of the riverine DSi fluxes were transported during the period from April to July. In total 46% of annual BSi loading was contributed by phytolith BSi in the Yellow River. The terrestrial BSi dissolution in the estuary would represent 15%–63% of riverine DSi loading on the basis of dissolution test, and low salinity could play an important role in enhancement of terrestrial BSi solubility, especially in the first few days during the estuarine mixing process. Although the terrestrial BSi represents a significant DSi contribution to the silica biogeochemical cycle in coastal waters, it tends to be refractory with the increasing of salinity.