Delta Islands Research Articles

Revisiting the stratigraphic development of the postglacial, transgressive paleo-Changjiang (Yangtze River) mouth: A journey from tide-dominated estuary to delta

Abstract The transition between a tide-dominated estuary and a tide-dominated delta, which is observed in modern settings and repeatedly throughout the geologic record, is a critical process for understanding sea-level and environmental changes. This transition remains poorly documented, however, leaving a knowledge gap about the sedimentary and stratigraphic processes involved. To help bridge the gap, we reexamined the postglacial transgressive system beneath the modern Changjiang (Yangtze River) Delta, built by one of the world’s largest rivers, using new chirp data supplemented by correlation with previously documented boreholes. Our results revealed a previously undocumented tide-dominated estuary-to-delta transition around the Younger Dryas, with the pretransition evolution dominated by the retrogradation of the tide-dominated estuary, which fills most of the accommodation space in the lowstand incised valley. This transition occurred when the middle and seaward parts of the estuary reached the subaqueous modern Changjiang Delta area and underwent extensive tidal erosion. Overlying the tidal ravinement, a series of ridge-and-swale structures formed due to tidal/fluviotidal channelization on the mud-dominated heterolithic substrate, primarily consisting of delta-front sediments characterized by flat, stratified reflections (bedding) with shallowing-upward trends. Ridge orientation rotates clockwise from north to south, with intervening swales bifurcating from a common apex point, and these features are flanked by inclined and sigmoidal levee-like channel fills dominated by homogeneous mud (acoustically transparent material). We reinterpret these features as tide-dominated delta islands and distributary channels, rather than the previously interpreted erosional mud ridges in the seaward part of the estuary, as they align with patterns observed in classic tide-dominated deltas. These patterns also suggest a shift from delta-front to delta-plain environments coinciding with shoreline advance ca. 10 k.y. B.P., but this was preceded by the evolution of a backstepping delta. Our study highlights the interplay between sediment supply and sea-level fluctuations in controlling the large-scale stratigraphic and environmental evolution of tidal-dominated river mouth systems. In the transgressive, paleo-Changjiang mouth, this interplay drove the system to evolve through stages of retrogradational estuary, backstepping delta, and progradational delta, and each environment differs significantly from the pattern observed in the modern Changjiang Delta. This study provides important insights for evaluating the evolution and sequence-stratigraphic reconstruction of other tidal depositional systems.

Genomic potential and physiological characteristics of C1 metabolism in novel acetogenic bacteria.

Acetogenic bacteria can utilize C1 compounds, such as carbon monoxide (CO), formate, and methanol, via the Wood-Ljungdahl pathway (WLP) to produce biofuels and biochemicals. Two novel acetogenic bacteria of the family Eubacteriaceae ES2 and ES3 were isolated from Eulsukdo, a delta island in South Korea. We conducted whole genome sequencing of the ES strains and comparative genome analysis on the core clusters of WLP with Acetobacterium woodii DSM1030T and Eubacterium limosum ATCC8486T. The methyl-branch cluster included a formate transporter and duplicates or triplicates copies of the fhs gene, which encodes formyl-tetrahydrofolate synthetase. The formate dehydrogenase cluster did not include the hydrogenase gene, which might be replaced by a functional complex with a separate electron bifurcating hydrogenase (HytABCDE). Additionally, duplicated copies of the acsB gene, encoding acetyl-CoA synthase, are located within or close to the carbonyl-branch cluster. The serum bottle culture showed that ES strains can utilize a diverse range of C1 compounds, including CO, formate, and methanol, as well as CO2. Notably, ES2 exhibited remarkable resistance to high concentrations of C1 substrates, such as 100% CO (200 kPa), 700 mM formate, and 500 mM methanol. Moreover, ES2 demonstrated remarkable growth rates under 50% CO (0.45 h-1) and 200 mM formate (0.34 h-1). These growth rates are comparable to or surpassing those previously reported in other acetogenic bacteria. Our study introduces novel acetogenic ES strains and describes their genetic and physiological characteristics, which can be utilized in C1-based biomanufacturing.

Sustainability assessment of Indian Sundarban delta islands using DPSIR framework in the context of natural hazards

Since the inception of the concept, sustainability has been interpreted as encompassing social, economic, and environmental dimensions of it. It is now rapidly shifting from a concept to a measurable state of the human-ecological dynamic system. Recent research is focusing on an integrated approach, due to the absence of a perfectly defined sustainable condition with the presence of some driving forces in the environmental system as a reference. In the recent world, severe natural hazards are increasingly having a fatal impact on societal and economic strata. The islands of Indian Sundarban Delta are the focus of this study as their sustenance is highly at stake due to climate change induced sea level rise, cyclone, tidal surge, and severe land erosion. The main objective of this study is to design a model for obtaining a composite sustainability index of three adjacent islands of western part of Indian Sundarban Delta (ISD) Sagar, Mousani and Ghoramara which are facing severe hazard impact based on the ‘Driving Force-Pressure-State-Impact-Response’ (DPSIR) framework integrating all three dimensions. Indicators have been categorised into state indicators and driving forces under ten profiles chosen from three dimensions of sustainability. The impact score of driving forces over any profile has been considered as a product of values of drivers and states from that profile. The total sustainability score was attained by summarizing the impact scores assigning the same weights and different weights respectively, to the sustainability indicators. The sustainability score shows that Sagar is in a better position than the other two islands.

Modern Dynamics of the Northern Dvina Delta: A Study by Multitemporal Space Images

The long-term dynamics of the Northern Dvina delta was studied with the comparison of space images of 1977 and 2020. A map of delta dynamics, compiled by them, shows that the islands at the delta coastline keep increasing and join to the delta, channel islands in the main branches are increasing, and small watercourses in delta islands become narrower and disappear. However, this long-term tendency of the continuing increase in delta area is now accompanied by the processes of shore erosion in islands at delta coastline from the side of the Dvina Bay.

The Municipal Water Quality Investigations Program: A Retrospective Overview of the Program’s First Three Decades

This paper presents the history and evolution of the California Department of Water Resources’ Municipal Water Quality Investigations (MWQI) program. This program tracks source water quality in the Sacramento–San Joaquin Delta (Delta) for drinking water supply for nearly two-thirds of California. The program provides early warning of changing conditions in source water quality, provides data and knowledge-based support for operational decision making, and provides scientific support to a variety of urban water users. This retrospective (i) documents program formation, (ii) describes its evolution in response to regulations and technological advances in water treatment and field monitoring, and (iii) notes how the development of federal drinking water quality regulations such as the Disinfection By-Products Rule impacted the program. The MWQI program is believed to be the first drinking water supply program in the United States to conduct continuous, real-time monitoring of organic carbon, bromide, and other anions and to report these data on the internet. In addition to its regular use for operational decision making, the data may be used for evaluating long-term trends and responses to specific changes in the Delta and its watershed. Future program directions will likely be guided by factors that may trigger changes in treatment plant processes and operations, such as emerging contaminants, changes in land and water management practices, permanent Delta island flooding, sea level rise, and climate change. While this retrospective focuses on one region, its multi-decade interplay of science, treatment and monitoring technology, and regulations (as well as practical aspects of managing such a large-scale program) are broadly relevant to professionals engaged in drinking water quality management in other urbanized and developed regions of the world.

Nutrient and Trace Element Contributions from Drained Islands in the Sacramento–San Joaquin Delta, California

Inventorying nutrient and trace element sources in the Sacramento-San Joaquin Delta (the Delta) is critical to understanding how changes—including alterations to point source inputs such as upgrades to the Sacramento Regional Wastewater Treatment Plant (SRWTP) and landscape-scale changes related to wetland restoration—may alter the Delta’s water quality. While island drains are a ubiquitous feature of the Delta, limited data exist to evaluate island drainage mass fluxes in this system. To better constrain inputs from island drains, we measured monthly discharge along with nutrient and trace element concentrations in island drainage on three Delta islands and surrounding rivers from June 2017 to September 2018. These data were used to calculate island-level fluxes and then upscaled to estimate Delta-wide contributions from island drains. Based on these results, we present (1) new estimates of gross and net nutrient and trace element fluxes from Delta island drains, and (2) concomitant N stable isotope data to improve our understanding of island N cycling. Over 60% of nearly all island drainage gross nutrient and trace element loads occurred in winter and spring. Upscaled island drainage net annual total nitrogen (TN), total dissolved nitrogen (TDN), and NH4+ loads comprised an estimated 9%, 7%, and 4%, respectively, of annual inputs to this system in 2018, before the SRWTP upgrade. Under a post-upgrade scenario, we estimated net annual island drainage TDN contributions to increase to 11% and NH4+ contributions to 45% of total Delta inputs as the SRWTP NH4+ load diminished to near zero. Our results suggest that island drainage is a measurable N source that has likely become increasingly important now that the SRWTP upgrade is complete. With over 200 potential active outfalls, these inputs may affect aquatic biogeochemical cycling in many regions of the Delta, especially in areas with long residence times.

Regionmaking and conceptual development in South China: Perceiving islands, the Pearl River Delta, and the Greater Bay Area

The Pearl River Delta in South China is today associated with one of the world's largest megaregions. Even though scholarship often treats the Pearl River Delta as a natural region and unit for analysis, this area has only recently been regionalised. This paper undertakes a critical rewriting and remapping of the Pearl River Delta's history, starting in precolonial times in which the Chinese population saw the area as composed of islands and waterways, moving through the period when colonial powers saw the area as a pathway up from the colonial island enclaves of Hong Kong and Macao and into China's interior, and ending in the Reform and Opening Up era when the modern Chinese state has implemented a succession of planning-oriented conceptions of the region. As the area has moved conceptually from a world of islands to a delta and now to the Greater Bay Area, perceptions about what the area means have changed as well. From a position in urban island studies and critical reflexivity, this paper troubles taken-for-granted colonial, technocratic, and governmental visions and regionalisations, focusing on how physical and cultural geographies develop in tandem. The notion of the interstitial island is used to help understand how the Pearl River Delta's island geography has influenced the area's conceptual development.

Features of the methodology for studying the dynamics of tidal rivers deltas in the northern regions using satellite images 
 (the Northern Dvina as example)

Using satellite images from the KeyHole 1977 and Sentinel-2B 2020 satellites, the dynamics of the tidal delta of the Northern Dvina River was investigated. When choosing images, it is necessary to take into account seasonal and tidal fluctuations in the water level; images for the dry season with a close tide phase at the moments of shooting in different years were selected. The first compiled map of delta dynamics for the period 1977–2020 shows that the growth of delta, noted by researchers earlier, continues – the attachment of islands along the sea edge to it, the accumulation of sediments and an increase in the area of channel islands in the main river-branches, narrowing and disappearance of small streams on the delta islands. But to the long-term tendency of delta growth, the processes of erosion of the coast on the islands of the sea edge are added from the side of the Dvina Bay.

The Dangerous Disappearance of Delta Dirt

Across the Sacramento-San Joaquin Delta, spongy soil is sinking at a rapid rate! This issue, known as subsidence, happens in places with peat soils that have been drained. Peat soils are created over thousands of years by decaying wetland plants. Following European colonization of California, the Delta’s wetlands and their peat soils were drained, and levees were built to keep the land dry. Farms now thrive on this fertile landscape. However, as drained soils are exposed to oxygen, tiny microbes rapidly consume the peat soil, which makes the land sink. Now, many Delta islands look like giant salad bowls up to 9 m deep, with fragile levees holding the rivers back. This puts communities, farms, ecosystems, and water supplies at risk from floods. The microbes in the soil release carbon dioxide into the atmosphere, which contributes to climate change. Scientists and land managers are creating new wetlands to combat subsidence in the Delta.

Apparent Seasonal Bias in Delta Outflow Estimates as Revealed in the Historical Salinity Record of the San Francisco Estuary: Implications for Delta Net Channel Depletion Estimates

Accurate estimates of freshwater flow to the San Francisco Estuary are important in successfully regulating this water body, in protecting its beneficial uses, and in accurately modeling its hydrodynamic and water-quality transport regime. For regulatory purposes, freshwater flow to the estuary is not directly measured; rather, it is estimated from a daily balance of upstream Delta inflows, exports, and in-Delta water use termed the net Delta outflow index (NDOI). Field research in the 1960s indicated that NDOI estimates are biased low in summer–fall and biased high in winter–spring as a result of conflating Delta island evapotranspiration estimates with the sum of ungauged hydrologic interactions between channels and islands referred to as net channel depletions. In this work, we employed a 50-year observed salinity record along with gauged tidal flows and an ensemble of five empirical flow-salinity (X2) models to test whether a seasonal bias in Delta outflow estimates could be inferred. We accomplished this objective by conducting statistical analyses and evaluating whether model skill could be improved through seasonal NDOI flow adjustments. Assuming that model residuals are associated with channel depletion uncertainty, our findings corroborate the 1960s research and suggest that channel depletions are biased low in winter months (i.e., NDOI is biased high) and biased high in late summer and early fall months (i.e., NDOI is biased low). The magnitude of seasonal bias, which can reach 1,000 cfs, is a small percentage of typical winter outflow but represents a significant percentage of typical summer outflow. Our findings were derived from five independently developed models, and are consistent with the physical understanding of water exchanges on the islands. This work provides motivation for improved characterization of these exchanges to improve Delta outflow estimates, particularly during drought periods when water supplies are scarce and must be carefully managed.

Decomposition and Seasonal Variation of Nutrient Composition of Mangrove Apoplankton in the Emerging Delta Island (Nayachar) of Hooghly River, West Bengal, India: Soil Microarthropods R.E,F

Decomposition and Seasonal Variation of Nutrient Composition of Mangrove Apoplankton in the Emerging Delta Island (Nayachar) of Hooghly River, West Bengal, India: Soil Microarthropods R.E,F

Active and passive seismic surface wave methods for levee assessment in the Sacramento–San Joaquin Delta, California, USA

ABSTRACTSeismic surveys were performed using a novel application of combined active and passive surface wave methods to evaluate the integrity of levees protecting islands in the Sacramento–San Joaquin Delta, California, USA, from flooding. Delta islands have been undergoing rapid subsidence during the past century due to farming practices that have led to the loss of a surficial peat layer. A large earthquake on any one of several active faults in the region could cause multiple levee failures and extensive flooding in the Delta. Surface wave surveys were carried out along the crest of levees using the active method (2D multichannel analysis of surface waves) and along the base of levees using the passive method (microtremor array method). This allowed 2D seismic S‐wave velocity (VS) profiles to be prepared for each site by combining shallow data from the active survey along the crown of the levee with deeper data from a passive survey along the toe of the levee. TheseVS profiles reveal a low‐velocity peat layer beneath the levee body that was confirmed by geotechnical borehole logs. Lateral variability of the levee was evaluated using average velocity to the base of the levee versus along‐levee distance.

Spatial vegetation distribution and zonal vegetation type on islands in southern part of the Lena Delta (Eastern Siberia)

In this research spatial distribution of the different vegetation types on Lena Delta islands described in connection with their relief, time of formation and geological substrates. It was shown that zonal vegetation can be find only on third river terrace on gentle slopes. Because of continuous permafrost predominant vegetation is presented by hydro serial communities united into successional cycles. Zonal vegetation types occupy not more than 1-2% of the whole area.

Aboveground biomass distributions and vegetation composition changes in Louisiana's Wax Lake Delta

The Wax Lake Delta (WLD) is an actively prograding delta in the Mississippi River Delta Plain that is otherwise experiencing widespread degradation and submergence of its coastal wetlands. The WLD is actively accumulating mineral and organic sediment that increases soil surface elevation, changing emergent wetland communities as the young delta develops. There is uncertainty in how the dynamics of community composition respond to net changes in soil elevation and determine aboveground biomass and carbon storage. This study utilizes high resolution imaging spectrometer data captured on October 17, 2016, to map the delta's dominant vegetation species and wetland types. We validated this vegetation map (overall accuracy = 77.62%, Kappa = 0.72) and compared it with a published species map that used WorldView-2 data collected five years earlier on October 16, 2011. This allowed us to map changes resulting from five years of delta development to determine changes in wetland forest species (Salix nigra), two dominant herbaceous wetland species (Colocasia esculenta and Polygonum punctatum), and various grass species. Results show an increase in C. esculenta and a marginal increase in forested wetlands (S. nigra). C. esculenta's expansion occurred largely from the delta island heads toward the fringes into wetland area previously occupied by P. punctatum, which saw a corresponding decline. Additionally, this study leveraged these species distributions with a published aboveground biomass (AGB) dataset to examine the dominant plant types' growth patterns across elevational gradients. We characterized variability in AGB by marsh platform elevation and across different elevational zones categorized by hydroperiod, or hydrogeomorphic zones. We found that the herbaceous plant species peak in AGB in the low intertidal zone and decrease with elevation before increasing slightly in the higher elevations, consistent with previous field-based mesocosm experiments for C. esculenta. With vegetation distributions, succession, and growth patterns in the WLD characterized, this study may inform future restoration efforts throughout the Mississippi River Delta Plain regarding the changing vegetation composition that may emerge following changes in surface elevation with sediment deposition.

Short-Term Ecogeomorphic Evolution of a Fluvial Delta from Hindcasting Intertidal Marsh-Top Elevations (HIME)

Understanding how delta islands grow and change at contemporary, interannual timescales remains a key scientific goal and societal need, but the high-resolution, high frequency morphodynamic data that would be most useful for this are as yet logistically prohibitive. The recorded water levels needed for relative elevation analysis are also often lacking. This paper presents a new approach for hindcasting intertidal marsh-top elevations (HIME) to resolve ecogeomorphic change, even in a young, rapidly changing fluvial delta setting, at sub-decadal temporal resolution and at the spatial resolution of widely available optical remote sensing imagery (e.g., 30 m Landsat). The HIME method first calculates: (i) the probability of land exposure in a set of historical imagery from a user-defined discrete timespan (e.g., months or years); (ii) the probability of water level non-exceedance from water level records, which need not be complete nor coincident with the imagery; and (iii) the systematic variation in local mean water level with distance along the primary hydraulic gradient. The HIME method then combines these inputs to estimate a marsh-top elevation map for each historical timespan of interest. The method was developed, validated, applied, and results analyzed to investigate time-lapse evolution of the Wax Lake Delta in Louisiana, USA, every three years, over two decades (1993–2013). The hindcast maps of delta island extents and elevations evidenced ecogeomorphic system self-organization around four stable attractors, or elevation platforms, at about −0.3 m (subtidal), 0.2 m, 0.4 m, and 0.9 m (supratidal) NAVD88. The HIME results also yielded a time series of net subaerial sediment accumulation, and specific locations and magnitudes of gains and losses, at scales from 30 m to delta-wide (~100 km3) and 6 to 21 years. Average subaerial net sediment accumulation at the Wax Lake Delta (WLD) was estimated as 0.6 cm/yr during the study period. Finally, multiple linear regression models were successfully trained on the HIME elevation maps to model evolving delta island morphologies based on simple geometric factors, such as distance down-delta and position on a delta island; the models also successfully reproduced an average delta topset slope of 1.4 cm. Overall, this study’s development and application of the HIME method added detailed insights to recent, transient ecogeomorphological change at the WLD, and demonstrated the potential of the new approach for accurately reconstructing past intertidal topographies and dynamic change.

Anywhere but here: Experiences of islandness in Pearl River Delta island tourism

Anywhere but here: Experiences of islandness in Pearl River Delta island tourism

The effect of flood intermittency on bifurcations in fluviodeltaic systems: Experiment and theory

AbstractThe dimensions and organization of deltaic islands and channels dictate delta morphology. This study presents experimental results modelling deposition at a river mouth and flow bifurcation around delta islands. Mouth bar formation and channel bifurcation is achieved in a laboratory setting by alternating input of suspended load transport and bedload transport. These two modes of transport produce two characteristic deposits with different advection lengths. Suspended load transport creates a steep deposit far from the inlet, while bedload creates a low angle, levéed deposit near the inlet. This study found that flow bifurcations occur where the proximal and distal deposits encroach on one another; and determined that there is a relationship between the frequency of suspended load transport and the length to channel bifurcation. Frequent flooding causes shorter length to bifurcations, whereas infrequent flooding causes greater length to bifurcations. This work overturns the hitherto understood mechanism of bifurcation location as a function of only high‐transport conditions. Instead, the interactions between the sediment transport and deposition from normal flow and large‐scale flooding events dictate delta island morphology.

Naagan ge bezhig emkwaan

Bkejwanong—the place where the waters divide (the delta islands of Lake St. Clair)—has been called the “soul” of Anishinaabe territory. Long before Europeans arrived, the Anishinaabe occupied territory which includes parts of present-day Ontario, Michigan and Ohio. The resources found there are integral to their way of life and identity. The Anishinaabe defended this territory against Haudenosaunee warriors in the seenteenth century and its integrity was at the core of the peace they concluded in Montreal in 1701, a key element of which was the Naagan ge bezhig emkwaan, or Dish with One Spoon. The dish represented the territory and the single spoon symbolized that people from other territories would be able to eat together while peace was maintained. Recently, however, the Dish with One Spoon has been popularized as an agreement to protect the environment. The original treaty has been incorporated into “land recognition statements” that blur the territorial rights of individual First Nations. This transformation is damaging to First Nations who seek to protect their territories and resources. Walpole Island First Nation (the Council of Three Fires) is working to reclaim their Dish.

Integrating Geospatial Data and Measures of Disability and Wealth to Assess Inequalities in an Eye Health Survey: An Example from the Indian Sunderbans.

The Sunderbans are a group of delta islands that straddle the border between India and Bangladesh. For people living on the Indian side, health services are scarce and the terrain makes access to what is available difficult. In 2018, the international non-governmental organisation Sightsavers and their partners conducted a population-based survey of visual impairment and coverage of cataract and spectacle services, supplemented with tools to measure equity in eye health by wealth, disability, and geographical location. Two-stage cluster sampling was undertaken to randomly select 3868 individuals aged 40+ years, of whom 3410 were examined. Results were calculated using standard statistical processes and geospatial approaches were used to visualise the data. The age–sex adjusted prevalence of blindness was 0.8%, with higher prevalence among women (1.1%). Cataract Surgical Coverage for eyes at visual acuity (VA) 3/60 was 86.3%. The study did not find any association between visual impairment and wealth, however there were significant differences by additional (non-visual) disabilities at all levels of visual impairment. Geospatial mapping highlighted blocks where higher prevalence of visual impairment was identified. Integrating additional tools in population-based surveys is critical for measuring eye health inequalities and identifying population groups and locations that are at risk of being left behind.

Islas sarmientinas: paisaje y política

En tres textos que abarcan desde 1849 hasta 1885, Sarmiento se centra en las islas: la de Más-a-fuera en Viajes (1849), Martin García en Argirópolis (1850) y las del Delta en El Carapachay (1855-1885). Este artículo analiza el modo en que Sarmiento utiliza los tópicos de la isla para desarrollar sus ideas sobre la civilización y para proyectar el futuro de la nación. En cada realización, la isla es a la vez un territorio concreto y un espacio ideal, una dualidad que le permite a Sarmiento interpretar el paisaje como factor de determinación o usarlo para construir sociedades imaginarias con vistas a la transformación del espacio, los habitantes, las costumbres y la sociedad del territorio más amplio de la nación.