Exploring Long-Term Changes in Silicon Biogeochemistry Along the River Continuum of the Rhine and Yangtze (Changjiang)

Abstract

This paper presents the spatially explicit (0.5° spatial resolution) Dynamic InStream Chemistry (DISC)-SILICON module, which is part of the Integrated Model to Assess the Global Environment-Dynamic Global Nutrient Model global nutrient cycling framework. This new model, for the first time, enables to integrate the combined impact of long-term changes in land use, climate, and hydrology on Si sources (weathering, sewage, and soil loss) and sinks (uptake by diatoms, sedimentation, and burial) along the river continuum. Comparison of discharge and dissolved silica results with observations shows good agreement both in the Rhine and Yangtze. The simulated total Si export for the Rhine is stable during the period 1900–2000. The total Si export for the Yangtze decreased (155–51 Gmol yr –1 ) because of damming and transformation of 40% of the natural vegetation to cropland. As a result of dam construction in the Yangtze, diatom primary production (from 24 to 48 Gmol yr –1 ) and burial (15 to 32 Gmol yr –1 ) increased and the DSi export decreased (139–46 Gmol yr –1 ) from the 1950s to 1990s. The Three Gorges Reservoir has a large contribution to diatom primary production (11%) and burial (12%) in the Yangtze basin. DISC-SILICON reproduces a flooding-induced increase in Si inputs and burial and the legacy of this temporary storage in subsequent dry years.

Exploring Spatially Explicit Changes in Carbon Budgets of Global River Basins during the 20th Century

“…For the Amazon River and its tributaries, floodplains are major components 81−83 and have large standing stocks of biomass and limited agricultural land use, which cause large C inputs to the water during flooding periods in forested areas (POC input from litterfall, with a high SRC of 0.85 for CO 2 emission). In contrast, the Mississippi and Yangtze Rivers have extensive agricultural areas, 84,85 and floodplain processes are less important (SRC of 0.39 and 0.2 for CO 2 , respectively, Tables SI5c and e) than those in the Amazon. With its extensive forested area in upstream areas, the Nile basin also has a high SRC of 0.58 for CO 2 emission because of variation in litterfall (Table SI5d).…”

Long-term response of an estuarine ecosystem to drastic nutrients changes in the Changjiang River during the last 59 years: A modeling perspective

“…Dam construction is also a cause that should be mentioned. Since the 1950s, the increased damming has led to sediment retention and reduced the suspended sediment concentration in Changjiang (Yang et al, 2011;Yang et al, 2018a;Liu et al, 2020); (Guo et al, 2020). According to relevant research, the annual sediment load at the Yichang station decreased by 97% from the 1950s to the 2010s (Guo et al, 2020), and at the DT station, it decreased by 16% from the 1960s to the 2010s (Figure 2A).…”

Modelling the origin and fate of carbon in the aquatic continuum

“…In contrast, the Mississippi and Yangtze Rivers have extensive agricultural areas (Chen and Simons, 1986;Liu et al, 2020), and floodplain processes are less important (SRC of 0.39 and 0.2 for CO2, respectively, Tables SI5c and e) than in the Amazon.…”