Abstract
This study presents detailed suspended sediment budget for the four Siberian river deltas, representing contrasting conditions between Northern and Southern environments. Two of the studied rivers empty their water and sediments into the marine located in the permafrost zone in the Arctic region (Lena and Kolyma), and the other two (Selenga and Upper Angara) flow into Lake Baikal located in the steppe and forest-steppe zone of Southern Siberia. For the first time, these poorly monitored areas are analyzed in terms of the long-term and seasonal changes of spatial patterns of suspended sediment concentrations (SSC) over distributaries systems. Remote sensing reflectance is derived from continuous time series of Landsat images and calibrated with the onsite field measurements of SSC. Seasonal variability of suspended sediment changes over deltas was captured for the period from 1989 to 2020. We identify significant variability in the sedimentation processes between different deltas, which is explained by particularities of deltas networks and geomorphology and the existence of specific drivers—continuous permafrost impact in the North and abundant aquatic vegetation and wetland-dominated areas in the South. The study emphasizes that differences exist between Northern and Southern deltas regarding suspended sediments transport conditions. Mostly retention of suspended sediment is observed for Southern deltas due to sediment storage at submerged banks and marshlands located in the backwater zone of the delta during high discharges. In the Northern (arctic) deltas due to permafrost impacts (melting of the permafrost), the absence of sub-aquatic banks and river to ocean interactions of suspended sediment transport is mostly increased downwards, predominantly under higher discharges and along main distributary channels. These results shine light on the geochemical functions of the deltas and patterns of sequestering various metals bound to river sediments.
Highlights
Most of the World’s rivers deltas are hot spots in productive land construction [1], where the main river distributes water among comprehensive channel networks and connected wetlands [2]
The calculations for the four deltas show that both erosion (∆S > 0) and deposition (∆S < 0) patterns can be observed under changing hydrological conditions at various parts of particular deltas
The observed results indicate that sedimentation processes over Northern and Southern deltas are driven by opposite factors
Summary
Most of the World’s rivers deltas are hot spots in productive land construction [1], where the main river distributes water among comprehensive channel networks and connected wetlands [2]. Deltas with complex channel networks influence terrestrial sediment flux [3,4,5]. The stored material contributes to the sub-aerial growth of a delta, affects the morphology of channel networks, and influences the overall distribution of floating particles. According to Passalacqua et al [6], river deltas should have a high sediment supply and a long-term net profit in the land area. The deltas are recognized as an important lateral geochemical barrier, where over 90% of suspended and 40% of dissolved carbon associated with global geochemical fluxes is trapped [7]. Knowledge about the spatiotemporal distribution of sediment properties within the deltas is limited due to the infrequent single character of sediment monitoring, and does
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