Dissolved aluminum and silica in the Changjiang (Yangtze River): Impact of weathering in subcontinental scale

Abstract

[1] Water samples were collected from the river mouth upstream over a distance of 3500-4000 km in the Changjiang (Yangtze River) and its 15 tributaries in April-May 1997, and at Nantong close to the river mouth in 1996-1998. Dissolved Al and Si were determined and compared with data of water flow, total suspended matter, and alkalinity. Data obtained show that dissolved Al in the Changjiang illustrates a rather uniform distribution from upstream toward river mouth, and a broad increasing of Al with higher Si to alkalinity ratio in tributaries has been found. The plots of Al:Si ratio against specific runoff and sediment yields reveal different weathering mechanisms involved in tributaries. At Nantong, concentration of Al is considerably stable relative to important seasonal variations of water discharge and sediment load. Acidification of bulk riverine samples releases an amount of Al that can be one order of magnitude higher than the natural concentrations, indicating potential remobilization by acid deposition and/or waste drainage. Compared with other world rivers, concentration of Al in the Changjiang is low and similar to those from primitive systems.

Cosmogenic 32Si as a tracer of biogenic silica burial and diagenesis: Major deltaic sinks in the silica cycle

“…Therefore, silica burial in the proximal Amazon delta and diagenetic consumption along the mobile Guianas coastline together account for ~50% (0.4 Tmol/yr) of the annual dissolved Si delivered to the global ocean by the Amazon River (total ~0.8 Tmol/yr). Other major coastal dispersal systems such as the Changjiang‐East China Sea system, which supplies ~0.1 Tmol/yr dissolved Si to the global ocean [ Zhang et al ., ; Ran et al ., ], likely behave similarly [ Yao et al ., ]. Taken together, ~0.4–0.5 Tmol/y of Si may be buried in these two deltaic dispersal systems alone, accounting for 30–50% of the global coastal Si sink presently attributed to authigenic clay burial in estuarine, shelf, and deltaic environments [ Laruelle et al ., ; Tréguer and De La Rocha , ] and implying that the latter is an underestimate.…”

The Missing Silica Sink: Revisiting the Marine Sedimentary Si Cycle Using Cosmogenic 32Si

“…We extend this bSi clay estimate to the subtropical delta and coastal regions of the Changjiang Estuary and Yellow Sea. If the Changjiang‐Zhejian Fugian mudbelt dispersal system, with its regions of mobile muds, behaves similarly to the Amazon‐Guianas system or the Mississippi Delta, then an additional 0.05 Tmol/yr Si, 50% of the ~0.1 Tmol Si/yr supplied by the river, may be buried there (Zhang et al, ; Liu et al, ; Ran et al, ; Yao et al, ). Recent studies of early diagenesis of biogenic silica, Fe, S, K, and Mg, in the East China Sea inner shelf and Changjiang Estuary indicate prevalent neoformation of Fe‐rich clays and diagenetic alteration of biogenic silica, consistent with an increased estimate of storage (Zhu et al, , ; Wang et al, ; Zhao et al, ).…”

Moderate Chemical Weathering of Subtropical Taiwan: Constraints from Solid‐Phase Geochemistry of Sediments and Sedimentary Rocks

“…Therefore, the very high H/L ratios of Taiwan rivers and their huge suspended load (∼400 t/yr; Dadson et al 2003) are also probably not conducive to chemical weathering. Further, extensive erosion results in reduction of soil particle retention in the weathering crust, coupled with incomplete chemical reaction caused by reduction of water-particle contact and segregation of elements (e.g., Al and Si;Zhang et al 2003).…”