North to South Variations in the Suspended Sediment Transport Budget within Large Siberian River Deltas Revealed by Remote Sensing Data

Passalacqua P., Giosan L., Goodbred S., Overeem I.

Arising from the non-uniform dispersal of sediment and water that build deltaic landscapes, morphological change is a fundamental characteristic of river delta behavior. Thus, sustainable deltas require mobility of their channel networks and attendant shifts in landforms. Both behaviors can be misrepresented as degradation, particularly in context of the “stability” that is generally necessitated by human infrastructure and economies. Taking the Ganges-Brahmaputra-Meghna Delta as an example, contrary to public perception, this delta system appears to be sustainable at a system scale with high sediment delivery and long-term net gain in land area. However, many areas of the delta exhibit local dynamics and instability at the scale at which households and communities experience environmental change. Such local landscape “instability” is often cited as evidence that the delta is in decline, whereas much of this change simply reflects the morphodynamics typical of an energetic fluvial-delta system and do not provide an accurate reflection of overall system health. Here we argue that this disparity between unit-scale sustainability and local morphodynamic change may be typical of deltaic systems with well-developed distributary networks and strong spatial gradients in sediment supply and transport energy. Such non-uniformity and the important connections between network sub-units (i.e., fluvial, tidal, shelf) suggest that delta risk assessments must integrate local dynamics and sub-unit connections with unit-scale behaviors. Structure and dynamics of an integrated deltaic network control the dispersal of water, solids, and solutes to the delta sub-environment and thus the local to unit-scale sustainability of the system over time.

Ahmed R., Prowse T., Dibike Y., Bonsal B.

Spring freshet is the dominant annual discharge event in all major Arctic draining rivers with large contributions to freshwater inflow to the Arctic Ocean. Research has shown that the total freshwater influx to the Arctic Ocean has been increasing, while at the same time, the rate of change in the Arctic climate is significantly higher than in other parts of the globe. This study assesses the large-scale atmospheric and surface climatic conditions affecting the magnitude, timing and regional variability of the spring freshets by analyzing historic daily discharges from sub-basins within the four largest Arctic-draining watersheds (Mackenzie, Ob, Lena and Yenisei). Results reveal that climatic variations closely match the observed regional trends of increasing cold-season flows and earlier freshets. Flow regulation appears to suppress the effects of climatic drivers on freshet volume but does not have a significant impact on peak freshet magnitude or timing measures. Spring freshet characteristics are also influenced by El Niño-Southern Oscillation, the Pacific Decadal Oscillation, the Arctic Oscillation and the North Atlantic Oscillation, particularly in their positive phases. The majority of significant relationships are found in unregulated stations. This study provides a key insight into the climatic drivers of observed trends in freshet characteristics, whilst clarifying the effects of regulation versus climate at the sub-basin scale.

Perignon M., Adams J., Overeem I., Passalacqua P.

Abstract. The morphology of deltas is determined by the spatial extent and variability of the geomorphic processes that shape them. While in some cases resilient, deltas are increasingly threatened by natural and anthropogenic forces, such as sea level rise and land use change, which can drastically alter the rates and patterns of sediment transport. Quantifying process patterns can improve our predictive understanding of how different zones within delta systems will respond to future change. Available remotely sensed imagery can help, but appropriate tools are needed for pattern extraction and analysis. We present a method for extracting information about the nature and spatial extent of active geomorphic processes across deltas with 10 parameters quantifying the geometry of each of 1239 islands and the channels around them using machine learning. The method consists of a two-step unsupervised machine learning algorithm that clusters islands into spatially continuous zones based on the 10 morphological metrics extracted from remotely sensed imagery. By applying this method to the Ganges–Brahmaputra–Meghna Delta, we find that the system can be divided into six major zones. Classification results show that active fluvial island construction and bar migration processes are limited to relatively narrow zones along the main Ganges River and Brahmaputra and Meghna corridors, whereas zones in the mature upper delta plain with smaller fluvial distributary channels stand out as their own morphometric class. The classification also shows good correspondence with known gradients in the influence of tidal energy with distinct classes for islands in the backwater zone and in the purely tidally controlled region of the delta. Islands at the delta front under the mixed influence of tides, fluvial–estuarine construction, and local wave reworking have their own characteristic shape and channel configuration. The method is not able to distinguish between islands with embankments (polders) and natural islands in the nearby mangrove forest (Sundarbans), suggesting that human modifications have not yet altered the gross geometry of the islands beyond their previous “natural” morphology or that the input data (time, resolution) used in this study are preventing the identification of a human signature. These results demonstrate that machine learning and remotely sensed imagery are useful tools for identifying the spatial patterns of geomorphic processes across delta systems.

Shiklomanov A., Déry S., Tretiakov M., Yang D., Magritsky D., Georgiadi A., Tang W.

Various estimates of freshwater discharge to the Arctic Ocean with different methods and for different drainage areas have shown a good consistency in long-term mean runoff ranging from 200 mm/year to 226 mm/year. Most of the estimates are derived from available discharge measurements at the downstream gauging stations. According to the most recent assessment of the total discharge to the Arctic Ocean is approximately 4300 km3 year−1 and continental contributions to the river input into the Arctic Ocean for Asia, North America, and Europe are 55%, 28%, and 17%, respectively. The river flux to the Arctic Ocean has significantly changed with an increase of 210 km3 over 1936–2015 across Eurasia, and 36 km3 over 1964–2015 for northern Canada. These changes were especially pronounced during the last 30-years, associated with most intense warming of air temperature over the northern hemisphere and significant declines in sea ice extent over the Arctic Ocean. The significant increase in annual river flow is mainly due to increases in winter (60%) and spring (33%) discharge. Winter flows have a very consistent and significant increase throughout the Eurasian pan-Arctic. All six largest Eurasian Arctic rivers show a significant increase in winter river flows over the long-term period 1936–2015. Similar but less significant trends in winter and spring discharge were found for Canadian northern rivers. Seasonal discharge has been altered as the result of human activity, particularly reservoir regulation. Eliminating reservoir effect in the largest Arctic rivers of Yenisei, Lena, and Ob, using the hydrograph transformation model, show significant increase in annual discharge, i.e., increase in spring by 49%, winter by 31%, and summer-fall by 20%. These results are different from those obtained from the observational discharge data. Thus, for hydroclimatic analysis to understand possible changes in river flux to the Arctic Ocean, it is necessary to take into account human impact on the discharge regime and change. Sea surface salinity (SSS) links various components of the Arctic freshwater system, including river discharge. Analysis of remote sensed SSS data has shown that SSS distribution pattern in the Arctic Ocean during warm period is partly defined by river flux. There is a great potential of using remote sensing data for a better understanding of variability in the Arctic freshwater system.

Osadchiev A., Silvestrova K., Myslenkov S.

The Lena, Kolyma, and Indigirka rivers are among the largest rivers that inflow to the Arctic Ocean. Their discharges form a freshened surface water mass over a wide area in the Laptev and East-Siberian seas and govern many local physical, geochemical, and biological processes. In this study we report coastal upwelling events that are regularly manifested on satellite imagery by increased sea surface turbidity and decreased sea surface temperature at certain areas adjacent to the Lena Delta in the Laptev Sea and the Kolyma and Indigirka deltas in the East-Siberian Sea. These events are formed under strong easterly and southeasterly wind forcing and are estimated to occur during up to 10%–30% of ice-free periods at the study region. Coastal upwelling events induce intense mixing of the Lena, Kolyma, and Indigirka plumes with subjacent saline sea. These plumes are significantly transformed and diluted while spreading over the upwelling areas; therefore, their salinity and depths abruptly increase, while stratification abruptly decreases in the vicinity of their sources. This feature strongly affects the structure of the freshened surface layer during ice-free periods and, therefore, influences circulation, ice formation, and many other processes at the Laptev and East-Siberian seas.

Wrzesiński D., Sobkowiak L.

Identification of river flow regime and its possible changes caused by natural factors or human activity is one of major issues in modern hydrology. In such studies different approaches and different indicators can be used. The aim of this study is to determine changes in flow regime of the largest river in Poland—the Vistula, using new, more objectified coefficients and indices, based on data recorded in 22 gauges on the Vistula mainstream and 38 gauges on its tributaries in the multi-year period 1971–2010. The paper consists of three main parts: in the first part, in order to recognize changes in the flow regime characteristics along the Vistula, data from gauges located on the river mainstream were analyzed with the help of the theory of entropy. In the second part gauging stations on the Vistula mainstream and its tributaries were grouped; values of the newly introduced pentadic Pardé’s coefficient of flow (discharge) (PPC) were taken as the grouping criterion. In the third part of the study a novel method of determining river regime characteristics was applied: through the recognition of the temporal structure of hydrological phenomena and their changes in the annual cycle sequences of hydrological periods (characteristic phases of the hydrological cycle) on the Vistula River mainstream and its tributaries were identified and their occurrence in the yearly cycle was discussed. Based on the detected changes of the 73-pentad Pardé’s coefficients of flow four main types of rivers were distinguished. Transformation of the flow regime was reflected in the identified different sequences of hydrological periods in the average annual cycle. It was found that while transformation of the Vistula River regime occurred along its whole course, the most frequent changes were detected in its upper, mountainous reaches, under the influence of the flow characteristics of its tributaries. This allowed the Vistula to be considered the allochthonous river. These findings are interesting not only from a theoretical point of view, but they also can be valuable to stakeholders in the field of the Vistula River basin water management and hydrological forecasting, including flood protection, which has recently become a matter of growing concern due to the observed effects of climate change and human impact.

Nienhuis J.H., Ashton A.D., Edmonds D.A., Hoitink A.J., Kettner A.J., Rowland J.C., Törnqvist T.E.

River deltas rank among the most economically and ecologically valuable environments on Earth. Even in the absence of sea-level rise, deltas are increasingly vulnerable to coastal hazards as declining sediment supply and climate change alter their sediment budget, affecting delta morphology and possibly leading to erosion1–3. However, the relationship between deltaic sediment budgets, oceanographic forces of waves and tides, and delta morphology has remained poorly quantified. Here we show how the morphology of about 11,000 coastal deltas worldwide, ranging from small bayhead deltas to mega-deltas, has been affected by river damming and deforestation. We introduce a model that shows that present-day delta morphology varies across a continuum between wave (about 80 per cent), tide (around 10 per cent) and river (about 10 per cent) dominance, but that most large deltas are tide- and river-dominated. Over the past 30 years, despite sea-level rise, deltas globally have experienced a net land gain of 54 ± 12 square kilometres per year (2 standard deviations), with the largest 1 per cent of deltas being responsible for 30 per cent of all net land area gains. Humans are a considerable driver of these net land gains—25 per cent of delta growth can be attributed to deforestation-induced increases in fluvial sediment supply. Yet for nearly 1,000 deltas, river damming4 has resulted in a severe (more than 50 per cent) reduction in anthropogenic sediment flux, forcing a collective loss of 12 ± 3.5 square kilometres per year (2 standard deviations) of deltaic land. Not all deltas lose land in response to river damming: deltas transitioning towards tide dominance are currently gaining land, probably through channel infilling. With expected accelerated sea-level rise5, however, recent land gains are unlikely to be sustained throughout the twenty-first century. Understanding the redistribution of sediments by waves and tides will be critical for successfully predicting human-driven change to deltas, both locally and globally. A global study of river deltas shows a net increase in delta area by about 54 km2 yr−1 over the past 30 years, in part due to deforestation-induced sediment delivery increase.

Wójcik, Bialik, Osińska, Figielski

A Parrot Sequoia+ multispectral camera on a Parrot Bluegrass drone registered in four spectral bands (green, red, red edge (RE), and near-infrared (NIR)) to identify glacial outflow zones and determined the meltwater turbidity values in waters in front of the following Antarctic glaciers: Ecology, Dera Icefall, Zalewski, and Krak on King George Island, Southern Shetlands was used. This process was supported by a Red-Green-Blue (RGB) colour model from a Zenmuse X5 camera on an Inspire 2 quadcopter drone. Additional surface water turbidity measurements were carried out using a Yellow Springs Instruments (YSI) sonde EXO2. From this research, it was apparent that for mapping low-turbidity and medium-turbidity waters (<70 formazinenephelometricunits (FNU)), a red spectral band should be used, since it is insensitive to possible surface ice phenomena and registers the presence of both red and white sediments. High-turbidity plumes with elevated FNU values should be identified through the NIR band. Strong correlation coefficients between the reflectance at particular bands and FNU readings (RGreen = 0.85, RRed = 0.85, REdge = 0.84, and RNIR = 0.83) are shown that multispectral mapping using Unmanned Aerial Vehicles (UAVs) can be successfully usedeven in the unfavourable weather conditions and harsh climate of Antarctica. Lastly, the movement of water masses in Admiralty Bay is briefly discussed and supported by the results from EXO2 measurements.

Antokhina O.Y., Latysheva I.V., Mordvinov V.I.

Mongolia and Transbaikalia (M-TB) have experienced severe drought over the past 20 years due to the increased frequency of anticyclogenesis. However, in the summer of 2018, as a result of the formation of a series of cyclones over Mongolia and their move to the Transbaikalia, abnormally high precipitation was observed in the M-TB region. The dynamics of long Rossby waves and atmospheric blocking in the middle and upper troposphere were investigated to identify the causes of cyclogenesis over Mongolia. It was revealed that a sequence of events predefined the extreme precipitation in M-TB in the 2018 summer – the intensification of heat flux over the North Atlantic while maintaining cyclonic vorticity over Central Europe, the development of blocking ridges in the Urals and the Russian Far East, and an upper-level trough oriented to the eastern regions Mongolia. For a long time, the persistent advection of cold air in the rear part of the upper-level trough, as well as increased heat advection during the activation of the East Asian summer monsoon, caused meridional oriented upper-level front strengthening over the eastern regions of Mongolia and extreme precipitation.

Shinkareva G.L., Lychagin M.Y., Tarasov M.K., Pietroń J., Chichaeva M.A., Chalov S.R.

This study aims to evaluate the biofiltration ability of higher aquatic vegetation of the Selenga delta as a barrier for heavy metals and metalloids (HMM) flows into the Lake Baikal. Main aquatic vegetation species have been collected from deltaic channels and inner lakes: Nuphar pumila, Potamogeton perfoliatus, P. pectinatus, P. natans, P. friesii, Butomus umbellatus, Myriophyllum spicatum, Ceratophyllum demersum, Phragmites australis. Analysis of the obtained data showed that regardless of the place of growth hydatophytes spiked water-milfoil (M. spicatum) and the fennel-leaved pondweed (P. pectinatus) most actively accumulate metals. Opposite tendencies were found for helophytes reed (Ph. australis) and flowering rush (B. umbellatus), which concentrate the least amount of elements. This supports previous findings that the ability to concentrate HMM increases in the series of surface – floating – submerged plants. Regarding river water, the studied macrophyte species are enriched with Mn and Co, regarding suspended matter – Mo, Mn and B, regarding bottom sediments – Mn, Mo and As. We identified two associations of chemical elements: S-association with the predominant suspended form of migration (Be, V, Co, Ni, W, Pb, Bi, Mn, Fe and Al) and D-association with the predominant dissolved form of migration (B, U, Mo, Cr, Cu, Zn, As, Cd, Sn and Sb). Due to these associations three groups of macrophytes were distinguished – flowering rush and reed with a low HMM content; small yellow pond-lily and common floating pondweed with a moderate accumulation of S-association and weak accumulation of D-association elements; and clasping-leaved pondweed, fennel-leaved pondweed, and pondweed Friesii accumulating elements of both S and D groups. The results suggest that macrophytes retain more than 60% of the total Mn flux that came into the delta, more than 10% – W, As, and from 3 to 10% B, Fe, Co, Mo, Cd, V, Ni, Bi, Be, Cu, Zn, Cr, U, Al. The largest contribution is made by the group of hydatophytes (spiked water-milfoil and pondweed), which account for 74 to 96% of the total mass of substances accumulated by aquatic plants.

Bomer E.J., Wilson C.A., Datta D.K.

The tidal to fluvial transition (TFT) of estuaries and coastal rivers is one of the most complex environments on Earth with respect to the transportation and deposition of sediment, owing in large part to competing fluvial and marine processes. While there have been recent advances in the stratigraphic understanding of the TFT, it is still unclear whether these findings are site-specific or representative of mixed tidal-fluvial systems worldwide. Yet, research from this depositional domain holds profound societal and economic importance. For instance, understanding the underlying stratigraphic architecture of channel margins is critical for assessing geomorphic change for fluvio-deltaic settings, which are generally vulnerable to lateral channel migration and resultant erosion. Findings would also benefit paleo-geographic reconstructions of ancient tide-influenced successions and provide an analog for hydrocarbon reservoir models. In the Ganges-Brahmaputra Delta of Bangladesh, the Gorai River is one of two Ganges distributaries actively connected to the Bay of Bengal. With fluvial input from the Ganges and meso-scale (2–4 m range) tides at the coast, the Gorai exhibits a variety of hydrodynamic regimes across its 350-km reach, providing a unique opportunity to investigate along-channel depositional patterns across the TFT. This study integrates multiple datasets—core sedimentology, river channel bathymetry, and remote sensing—to provide a process-based framework for determining the relative position of sedimentary deposits within the tidal-fluvial continuum of the Gorai River. The results of this investigation reveal coincident, abrupt shifts in river channel morphology and sediment character, suggesting the occurrence of backwater-induced mass extraction of relatively coarse sediments (i.e., fine sand). Despite being situated in an energetic tidal environment, evidence of tidal cyclicity in cored sediments is relatively rare, and the bulk stratigraphy appears strongly overprinted by irregularly spaced cm- to dm-scale sediment packages, likely derived from monsoonal flood pulses. Such findings differ from previously-studied mixed tidal-fluvial systems and underscore the site-specific complexities associated with this depositional domain.

Dolgopolova E.N.

Trinh L.H., Zablotskii V.R., Le T.G., Hien Dinh T.T., Le T.T., Trinh T.T., Nga Nguyen T.T.

The traditional methods for measuring water quality variables are timeconsuming and do not give a synoptic view of a water body or, more significantly, a synoptic view of different water bodies across the landscape. However, remote sensing technology with advantages such as wide area coverage and short revisit interval have been effectively used for environmental pollution applications, such as for monitoring water quality parameters. Many studies around the world show that optical satellite imagery can be used effectively in evaluating suspended sediment concentration. This article presents results of monitoring suspended sediment concentration in Red River, Hanoi, Vietnam through ground truth measurements and VNREDSat-1A multispectral data. The results obtained in the study can be used to serve the management, monitoring and evaluation of surface water quality.

Pietroń J., Nittrouer J.A., Chalov S.R., Dong T.Y., Kasimov N., Shinkareva G., Jarsjö J.

AbstractThe Selenga River delta (Russia) is a large (>600 km2) fluvially dominated fresh water system that transfers water and sediment from an undammed drainage basin into Lake Baikal, a United Nations Educational, Scientific, and Cultural Organization World Heritage Site. Through sedimentation processes, the delta and its wetlands provide important environmental services, such as storage of sediment‐bound pollutants (e.g., metals), thereby reducing their input to Lake Baikal. However, in the Selenga River delta and many other deltas of the world, there is a lack of knowledge regarding impacts of potential shifts in the flow regime (e.g., due to climate change and other anthropogenic impacts) on sedimentation processes, including sediment exchanges between deltaic channels and adjacent wetlands. This study uses field measurements of water velocities and sediment characteristics in the Selenga River delta, investigating conditions of moderate discharge, which have become more frequent over the past decades (at the expense of peak flows, Q > 1,350 m3 s−1). The aims are to determine if the river system under moderate flow conditions is capable of supporting sediment export from the main distributary channels of the delta to the adjacent wetlands. The results show that most of the deposited sediment outside of the deltaic channels is characterized by a large proportion of silt and clay material (i.e., <63 μm). For example, floodplain lakes function as sinks of very fine sediment (e.g., 97% of sediment by weight < 63 μm). Additionally, bed material sediment is found to be transported outside of the channel margins during conditions of moderate and high water discharge conditions (Q ≥ 1,000 m3 s−1). Submerged banks and marshlands located in the backwater zone of the delta accumulate sediment during such discharges, supporting wetland development. Thus, these regions likely sequester various metals bound to Selenga River sediment.

Schild K.M., Hawley R.L., Chipman J.W., Benn D.I.

ABSTRACTMarine-terminating outlet glaciers discharge mass through iceberg calving, submarine melting, and meltwater run-off. While calving can be quantified by in situ and remote-sensing observations, meltwater run-off, the subglacial transport of meltwater, and submarine melting are not well constrained due to inherent difficulties observing the subglacial and proglacial environments at tidewater glaciers. Remote-sensing and in situ measurements of surface sediment plumes, and their suspended sediment concentration (SSC), have been used as a proxy for glacier meltwater run-off. However, this relationship between satellite reflectance and SSC has predominantly been established using land-terminating glaciers. Here, we use two Svalbard tidewater glaciers to establish a well-constrained relationship between Landsat-8 surface reflecance and SSC and argue that it can be used to measure relative meltwater run-off at tidewater glaciers throughout a summer melt season. We find the highest correlation between SSC...

Hines C., Piliouras A.

AbstractRiver fluxes to the Arctic Ocean impact sea ice extent, nutrient availability, and coastal ecosystems. Arctic river deltas modulate fluxes of water, sediment, and nutrients reaching the Arctic Ocean. Many large rivers have estimates or measurements of discharge and sediment concentration upstream of the delta apex, but the magnitude, timing, and spatial distribution of sediment fluxes to the Arctic coast are unknown. We developed a novel reduced‐complexity model of suspended sediment transport in Arctic deltas to address this knowledge gap. The model estimates suspended sediment delivery to the coast based on a computed channel network and sediment transport rules. We applied this model to six high‐latitude deltas during their open water seasons with different boundary conditions to account for their differences in morphology, seasonality, and hydrology. Flux distributions at the coast are found to be more uneven in larger deltas due to uneven channel spacing and larger variability in channel widths compared with smaller deltas. Given typical active season conditions, the deltas exhibit periods of deposition and erosion but are net depositional overall. Net sediment trapping during the active season ranges from 10% to 70%. Our results suggest that larger, more complex deltas with higher sediment supply and less flashy hydrographs store the most sediment and may therefore be more resilient to land loss. The sediment flux distribution can be used in future studies of coastal biogeochemistry and geomorphology and in regional models to capture the impacts of fluxes on turbidity, marine primary productivity, and Arctic warming.

Shkolnyi D., Magritsky D., Chalov S.

Chalov S., Prokopeva K., Magritsky D.

The Lena River delta is the largest Arctic delta with an area of about 32,000 km2. It consists of more than 800 branches with a total length of 6,500 km. The Lena delta is underlined by continuous permafrost 500–600 m thick and located in remote and unpopulated area in the Arctic continental climate with the mean annual air temperature by −12.5 °C. Increase in warming rate from an average air temperature of 4.1 °C for the period 1950–99 to 6.1 °C during 2000–21 over the Lena Delta both with streamflow and sediment yield entering the Lena Delta increase since 1988 by 56.3 km3 and 6.1 × 106 t, respectively, are the key drivers of channel banks active degradation. Due to this fact, Lena Delta can be recognized as the global hot spot in terms of the hydrological consequences of climate change which together with streamflow alters sediment regimes, stream hydromorphology and carbon transport.

Tulla P.S., Kumar P., Vishwakarma D.K., Kumar R., Kuriqi A., Kushwaha N.L., Rajput J., Srivastava A., Pham Q.B., Panda K.C., Kisi O.

Water erosion creates adverse impacts on agricultural production, infrastructure, and water quality across the world, especially in hilly areas. Regional-scale water erosion assessment is essential, but existing models could have been more efficient in predicting the suspended sediment load. Further, data scarcity is a common problem in predicting sediment load. Thus, the current study aimed at modeling the suspended sediment yield of a hilly watershed (i.e., Bino watershed, Uttarakhand-India) using machine learning (ML) algorithms for a data-scarce situation. For this purpose, the ML models, viz., adaptive neuro-fuzzy inference system (ANFIS) and fuzzy logic (FL) were developed using data from ten years (2000–2009) only. Further, runoff and suspended sediment concentration (SSC) were obtained as the primary influencing factors. Varying combinations of lagged SSC and runoff data were considered as model inputs. The ANFIS and FL models were compared with the conventional multiple linear regression (MLR) model. Results indicated that the ANFIS model performed better than the FL and MLR models. Thus, it was concluded that the ANFIS model could be used as a benchmark for sediment yield prediction in hilly terrain in data-scarce situations. The research work would help field investigators in selecting the proper tool for estimating suspended sediment yield/load and policymakers to make appropriate decisions to reduce the devastating impact of soil erosion in hilly terrains.

Chalov S., Prokopeva K., Magritsky D., Grigoriev V., Fingert E., Habel M., Juhls B., Morgenstern A., Overduin P.P., Kasimov N.

Water and sediment supply are essential to the health of deltaic ecosystems. Diverse datasets were integrated to better understand how climate change is shifting the supply of water and sediment to the largest polar distributary channel pattern – the Lena River Delta. Here the increase in warming rate from an average air temperature is from 4.1 °C for the period 1950–99 to 6.1 °C during 2000–21, which is higher than in the adjacent polar regions. Streamflow and sediment yield entering the Lena Delta have increased since 1988 by 56.3 km3 and 6.1×106 t, respectively; meanwhile, the Lena River’s increases in water temperature in June, July–August and September were found to be as much as 1.1, 0.6 and 0.05 °C. These changes have a pronounced effect on sediment regimes in particular parts of the delta. Based on analyses of correlations between various hydroclimatic drivers and sediment concentration changes across particular distributaries of the Lena Delta extracted from Landsat datasets, bank degradation driven by thermal erosional processes (which are in turn related to air and soil temperature increases) is proved to be the primary factor of the sediment regime in the delta. The study also highlights that sediment load changes are sensitive to wind speed due to remobilization of bottom sediment. Sums of daily air temperature and wind speed over 3 days are correlated with sediment concentration changes in the delta. The results also indicate that carbon transport across the delta (both POC and DOC) depends on sediment transport conditions and water discharge and might increase by up to 10 %. We conclude that the Lena Delta can be recognized as the global hot spot in terms of the hydrological consequences of climate change, which is altering sediment regimes, stream hydromorphology and carbon transport.

Sankaran R., Al-Khayat J.A., Aravind J., Chatting M.E., Sadooni F.N., Al-Kuwari H.A.

Suspended sediment concentration (SSC) in water increases temperature and turbidity, limits the photosynthesis of aquatic plants, and reduces biologically available oxygen. It is important to study SSC in the coastal waters of the Arabian Gulf. Thus, this study mapped the SSC of coastal water between Al Arish and Al Ghariyah in northern Qatar using the spectral bands of the MultiSpectral Imager (MSI) of Sentinel-2 by calculating the Normalized Difference Suspended Sediment Index and Normalized Suspended Material Index. The results are studied using the Normalized Difference Turbidity Index and Modified Normalized Difference Water Index. The mapping of SSC in the water using NDSSI showed the presence of a high concentration of suspended sediments between Al Arish and Al Mafjar and a low concentration between Al Mafjar and Al Ghariyah. The mapping of NSMI showed values between 0.012 (clear water) and 0.430 (more suspended material) for the occurrence of suspended materials and supported the results of NDSSI. The study of turbidity using an NDTI image showed turbidity index values ranging from −0.44 (clear water) to 0.12 (high turbidity) and confirmed the occurrence and distribution of suspended sediments and materials in the water. The MNDWI image was able to discriminate clear water with bright pixels from silty sand and mud flats. The relationships between NDSSI, NSMI, and NDTI were correlated with in-situ measurements and studied to find suitable indices to map SSC. Regression analyses showed the strongest relationship between NSMI and NDTI (R2 = 0.95) next to NDSSI and NDTI, where NDTI had the strongest effect on NDSSI (R2 = 0.86). The satellite data results were evaluated by studying the physical parameters and spatial distribution of suspended sediments in the surface and bottom waters. In addition, the grain size distributions, mineral identification, and chemical element concentrations in the bottom sediment samples were studied.

Chalov S.R., Zavadsky A.S., Golovlev P.P., Ivanov V.A.

Bank and riverbed erosion produce a significant part of the sediment flux, i.e. its channel component. The article deals with the quantitative assessment of the channel sediment input for more than 14 000 km of the lower reaches of the Ob, Yenisei, Lena, Kamchatka and the Selenga River net. The absolute volumes of sediments supplied by bank erosion are maximum for the lower and middle Lena River (up to 38,7 million tons per year per 100 km of the channel). They are significantly lower for the lower and middle Ob River (down to 19,9 million tons per year per 100 km of the channel), and an order of magnitude smaller (about 2 million tons per year) for the Yenisei River because of the limited conditions for the development of channel processes, and for the Selenga and Kamchatka rivers because of the smaller size of rivers. The volume of sediments of channel origin is two times smaller, than the sediment runoff, for the Yenisei River and exceeds the sediment runoff up to 9 times for other rivers. The maximum rates of bank erosion are common for meandering and branched channels with wide floodplains. Most of the bank erosion within the braided sections of channels is the deformation of islands.

Szumińska D., Kozioł K., Chalov S.R., Efimov V.A., Frankowski M., Lehmann‐Konera S., Polkowska Ż.

AbstractPermafrost regions are under particular pressure from climate change resulting in widespread landscape changes, which impact also freshwater chemistry. We investigated a snapshot of hydrochemistry in various freshwater environments in the lower Kolyma river basin (North‐East Siberia, continuous permafrost zone) to explore the mobility of metals, metalloids and non‐metals resulting from permafrost thaw. Particular attention was focused on heavy metals as contaminants potentially released from the secondary source in the permafrozen Yedoma complex. Permafrost creeks represented the Mg‐Ca‐Na‐HCO3‐Cl‐SO4 ionic water type (with mineralisation in the range 600–800 mg L−1), while permafrost ice and thermokarst lake waters were the HCO3‐Ca‐Mg type. Multiple heavy metals (As, Cu, Co, Mn and Ni) showed much higher dissolved phase concentrations in permafrost creeks and ice than in Kolyma and its tributaries, and only in the permafrost samples and one Kolyma tributary we have detected dissolved Ti. In thermokarst lakes, several metal and metalloid dissolved concentrations increased with water depth (Fe, Mn, Ni and Zn – in both lakes; Al, Cu, K, Sb, Sr and Pb in either lake), reaching 1370 μg L−1 Cu, 4610 μg L−1 Mn, and 687 μg L−1 Zn in the bottom water layers. Permafrost‐related waters were also enriched in dissolved phosphorus (up to 512 μg L−1 in Yedoma‐fed creeks). The impact of permafrost thaw on river and lake water chemistry is a complex problem which needs to be considered both in the context of legacy permafrost shrinkage and the interference of the deepening active layer with newly deposited anthropogenic contaminants.

Chalov S., Ivanov V.

This paper presents a comparative study of fluvial sediment budgets for the largest Siberian rivers of Northern Eurasia - Ob', Yenisey and Lena which cover over 14 % of the Eurasia continent. Each component of the sediment budget was assessed using an independent approach. The Revised Universal Soil Loss Equation model (RUSLE) was used to calculate catchment erosion based on the GMTED 2010 DEM with a resolution of 250 m. Channel erosion was quantified through automatic image decoding integrated with riverbank elevation estimated from ArcticDEM and hydromorphological 1D modeling of streamflow depths, whereas sediment yield was assessed based on a combination of long-term suspended sediment load monitoring at the outlet gauging stations and bed load estimates. Large differences between total (catchment and riverbank) erosion (1622 Mt year−1 for the Ob', 898 Mt year−1 for the Yenisey, 1218 Mt year−1 for the Lena) and yearly sediment export (58.2 Mt year−1 for the Ob', 32.5 Mt year−1 for the Yenisey and 38.6 Mt year−1 for the Lena) suggest that catchment, in-channel and overbank sediment sinks and storage dominate the sediment budget. The throughflow from the sources to the sea is less than 4 % of the suspended sediment inflow (total erosion). This data enhances the knowledge of the sediment delivery rates in large river systems. Over ∼96 % decline of sediment transport compared to catchment total erosion is explained by storage in various buffer zones of the catchment and river network including mainly hillslopes, as well as reservoirs and floodplains.

Dzhamalov R.G., Vlasov K.G., Galagur K.G., Safronova T.I., Grigor’ev V.Y., Efimov V.A., Reshetnyak O.S., Oboturov A.S.

Ji Z., Guo B., Mantravadi V.S., Wang J., Che Y.

Sediment transport in coastal waters has an important impact on the siltation of port channels and changes in the estuary ecological environment. The southeast coast of China is often hit by typhoons, which can affect the suspended sediment concentration (SSC) in coastal waters. In this study, we used Geostationary Ocean Color Imager (GOCI) data to analyze SSC variations in Hangzhou Bay during Typhoon Maria (2018), and the influencing factors were also analyzed. The results showed that: (1) During the typhoon’s transit, the SSC in Hangzhou Bay (HZB) increased by 200–800 mg/L, which was one-fold higher than the day before the typhoon. The variation of SSC on the south bank was noticeable, and the typhoon effect on SSC lasted for 2–3 days; (2) The wind speed and significant wave height (SWH) increased during the typhoon. In general, in the early stage of the typhoon, the SSC in HZB was affected by the wind, and in the interim and late period, SSC was influenced by the effect of wind and wave height; (3) Typhoon “Maria” accelerated the transport of sediment and land-based pollutants from land to sea; the effect of residual current and wind stress are the driving mechanisms for seaward sediment transport. However, mechanisms and driving factors of sediment transport in coast water are complex and diverse. The results of this study can help to understand the processes of riverbed erosion and deposition in Hangzhou Bay and adjacent waters. They are also significant for the study of nearshore hydrodynamic characteristics of typhoons and channel engineering.

Mukhopadhyay A., Acharyya R., Habel M., Pal I., Pramanick N., Hati J.P., Sanyal M.K., Ghosh T.

Satellite data shows that the Bhagirathi-Hugli River’s riverbank has faced severe erosion during the last decades (1990 to 2020), with the middle stretch of the river being more prone to erosion. This huge sediment load derived from upstream erosion is coming to the estuary. The suspended sediment concentration dynamics of the Hugli estuary were calculated using in-situ data and remote sensing reflectance by establishing a linear regression. A continuous huge sediment load is found in the estuarine water. The sediment concentration was higher pre-monsoon than post-monsoon as the region is highly influenced by monsoonal rainfall and runoff. The sediment concentration was also higher in the estuary’s southwestern section than in the northern part. The impact of this high sediment load contributes to the deposition. This depositional area assessment was performed using an object-based classification approach called Support Vector Machine utilizing Grey Level Co-occurrence Matrix to create cluster textural indices. Despite the impact of continuous sea level rise in the estuary, the result shows that effective island and Chars areas have increased in the past decade due to the upstream erosion-driven sediments.

Dzhamalov R.G., Vlasov K.G., Galagur K.G., Safronova T.I., Grigor’ev V.Y., Efimov V.A., Reshetnyak O.S., Oboturov A.S.

The space and time variations of the concentrations of the most informative hydrochemical characteristics in the Lena R. basin are analyzed for two periods (2010–2014 and 2015–2019) in accordance with the most stringent standards for water bodies used for fishery. The constructed maps of the normal annual unit-area discharge for these components give a space and time characteristic of water quality and reveal the dynamics of hydrochemical runoff variations in the recent years. The effect of climate on surface-water regime in the Lena basin is also considered. The unit-area discharge for the majority of dissolved substances, primarily, the major ions and nutrients, was found to increase at an increase in the total precipitation and to decrease at an increase in the temperature, in which case the effect of precipitation is higher. The effect of temperature on chemical runoff is more noticeable in rivers with predominantly snow feeding, and the effect of precipitation, in rain-fed rivers

Acharyya R., Mukhopadhyay A., Habel M.

River deltaic estuaries are dynamic ecosystems characterised by linkages between tidal currents, river water discharge, and sediment from the basin. The present study is based on the application of remote data: multispectral satellite images, DEM, LULC (Land use and land cover), lithology, and hydroclimatic factors. The standardised methodology was based on the adoption of a coupled modelling approach for this work, involving the semi-distributed catchment scale hydrological Soil and Water Assessment Tool (SWAT) model and the statistical Digital Shoreline Analysis System (DSAS) for (1) identifying environmental drivers of sediment transport changes of the estuarine reach; (2) analysis of retrospective changes in shoreline configuration; (3) assessing discharge and sediment dynamics of the estuarine section, and (4) generating future projection scenarios for the estuary’s state to take action for its long-term ecological stability. Our study employs a coupled modelling framework to fill the research gap for Subarnarekha deltaic estuary. Integrating outputs derived from DSAS and SWAT, a comprehensive understanding of the changes in watershed hydrology, water diversions, and damming of rivers have altered the magnitude and temporal patterns of freshwater flow and sediment, which potentially contributed to the receding of the Digha Coast shoreline.

Chalov S., Prokopeva K.

Lena River is one of the largest “pristine” undammed river systems in the World. In the middle and low (including delta) 1500 km course of the Lena main stem river forms complex anabranching patterns which are affected by continuous permafrost, degradation of the frozen ground and changes in vegetation (taiga and tundra). This study provides a high-resolution assessment of sediment behavior along this reach. Comprehensive hydrological field studies along the anabranching channel located in the middle, low and delta courses of the Lena River were performed from 2016 to 2022 including acoustic Doppler current profiler (ADCP) discharge measurements and sediment transport estimates by gravimetric analyses of sediment concentration data and surrogate measurements (optical by turbidity meters and acoustic by ADCP techniques). These data were used to construct regional relationships between suspended sediment concentrations (SSC, mg/L), turbidity (T, NTU) and backscatter intensity (BI, dB) values applicable for the conditions of the Lena River. Further, field data sets were used to calibrate the seasonal relationships between Landsat reflectance intensities and field surface sediment concentration data. Robust empirical models were derived between the field surface sediment concentration and surface reflectance data for various hydrological seasons. Based on the integration of in situ monitoring and remote sensing data we revealed significant discrepancies in the spatial and seasonal patterns of the suspended sediment transport between various anabranching reaches of the river system. In the middle course of the Lena River, due to inundation of vegetated banks and islands, a downward decrease in sediment concentrations is observed along the anabranching channel during peak flows. Bed and lateral scour during low water seasons effects average increase in sediment load along the anabranching channels, even though a significant (up to 30%) decline in SSC occurs within the particular reaches of the main channel. Deposition patterns are typical for the secondary channels. The anabranching channel that was influenced by the largest tributaries (Aldan and Viluy) is characterized by the sediment plumes which dominate the spatial and temporal sediment distribution. Finally, in the distributary system of the Lena delta, sediment transport is mostly increased downwards, predominantly under higher discharges and along main distributary channels due to permafrost-dominated bank degradation.