Deltaic Landscape Research Articles

Twenty-Eight Years of Plant Community Development and Dynamics in the Balize Mississippi River Delta, Louisiana, USA

Deltaic landscapes go through cycles of birth, growth, decline, and death governed by intertwined geological, biological, and ecological processes. In this study, we tracked deltaic lobes in the Balize Mississippi River Delta, Louisiana, USA, over 28 years (1984–2012). Hydrologic and geomorphic patterns as well as sustained patterns of wetland plant richness, diversity, and biomass are described. Plant diversity and biomass were modeled by nMDS ordination. Taxa (53) were harvested and dried (116,706 g) from 965 (0.25 m2) plots and divided into three groups: I. four foundation species, corresponding to 78.9% of the total harvest; II. nine pioneer species, corresponding to 13.6% of the total harvest; and III. all other taxa, corresponding to 7.5% of the total harvest (eight miscellaneous grasses, eight miscellaneous sedges, and twenty-four miscellaneous herbs). Autogenic/allogenic processes (sedimentation, subsidence, plant colonization, and succession events) affected composition and biomass. Eleven important species were identified. Taxon richness increased on mudflats during primary succession (fifteen to twenty-five taxa per site), then declined to fewer than five taxa per site. The niche space theory explained patterns of community change, with a similar total biomass/yr (~500 g/m2/yr) at all study sites. Quantile regression analyses showed that the water quality and quantity of the Mississippi River influenced biomass, especially in springtime waters. Stochastic events (storms, herbivory, salt burn, and flood pulses) impacted biomass. Long-term studies like this are required in a future of climate unknowns.

Mid-to late Holocene vegetation and environmental change at local and regional scales based on a multi-proxy analysis of the upper Danube Delta, Romania

The Danube Delta is Europe's largest wetland system and of unique biogeographical character. Whilst its geomorphological evolution is relatively well-known its ecological history is poorly understood, including the history of human impact, as a result of the dynamic nature of deltaic systems, and the scarcity of reliably dated successions. In this paper, we report a multi-proxy record of palynology, sediment texture, geochemistry, and ostracods from the upper reaches of the Danube Delta. We use these data to reconstruct a mid-to-late Holocene history of vegetation and environmental changes at local and regional scales, which serve as a model for understanding baseline conditions in delta apex regions. From 7500 to 6200 ​cal ​yr BP, the study site was part of an inter-distributary channel-levee system connected to coastal lagoons and sensitive to sea-level fluctuations but transitioned to a partially-disconnected lacustrine environment after 5700 ​cal ​yr BP. These geomorphologically-driven landscape changes strongly influenced the pollen source area making it complex to interpret palynoassemblages. Prior to 5700 ​cal ​yr BP, palynoassemblages were predominantly river-transported, reflecting widespread hinterlands, and providing information for the regional reconstruction of the vegetation history in the northern Dobrogea region. These data reveal the early presence of Carpinus and Fagus in southeastern Romania, prior to their spread through the Carpathian Basin. After 5700 ​cal ​yr BP, initiated by a slowdown in the relative rate of rise of the Black Sea, peat accumulation commenced within the shallow lake depocentre and airborne pollen became the dominant source. These pollen data record an expansion of herbaceous taxa and highly diverse marsh and aquatic taxa. Tree cover became dominated by Quercus, with low percentages of Carpinus, Betula, Ulmus, and Tilia. The earliest pollen evidence indicative of human impact commences c. 6500 ​cal ​yr BP) and, after 3200 ​cal ​yr BP, the decline in Quercus and a synchronous rise in archaeological artifacts, points to an opening of the landscape by forest clearance and an enlargement of arable areas. In particular, clearance and agriculture during the development of the Hallstattian Babadag culture (c. 3200-2800 ​yr BP) reflects an increase in population and settlement density during that late interval. Our paper comprises the first mid-to-late Holocene palynological record for the Danube Delta and highlights how human activity has profoundly altered the dryland region, creating landscapes comparable to today from around 3200 years BP, while the local deltaic landscape retained its character over the last six millennia.

Lessons learned from 30-years of operation of the Caernarvon Freshwater Diversion, Louisiana USA

Wetland loss is a worldwide issue with estimates of loss ranging from 50% to 71% in the 20th century. Louisiana's coastal zone lost approximately 4,830 km2, or 25% of the land area between 1932 and 2016 due to a variety of natural and anthropogenic forces that both erode and prevent the growth or maintenance of existing land. Freshwater diversions were constructed along the Mississippi River to convey freshwater, nutrients, and sediment from the Mississippi River to Louisiana's coastal basins to combat saltwater intrusion, nourish the marshes, and stimulate fisheries. The Caernarvon Freshwater Diversion (CFD) was authorized by the Flood Control Acts of 1928 and 1965, the 1974 Water Resources Development Act, and a 1984 Environmental Impact Statement, with construction completed and operations started in 1991. The CFD has been largely successful from the standpoint of the project's authorized goals. Early on in the project, the CFD helped combat saltwater intrusion in a 2,730 km2 basin and re-established the gradient from fresh to salt marsh, by creating conditions favorable to fresh marsh species. Although not a specific project goal, the CFD also built more than 700 acres of new emergent wetland between 1991 and 2016. By critically assessing 30 years of CFD governance, operations, monitoring, and adaptive management, lessons learned are developed that provide valuable information for making the operations and governance of current and future diversions more effective, transparent, adaptive, and trusted by the basin communities. Louisiana's Coastal Master Plan pivots to the use of river diversions to focus on land building and large-scale ecosystem restoration by mimicking natural processes that originally built the Louisiana deltaic landscape, rather than the more common small-scale restoration that has occurred over the past decades. However, large-scale restoration projects, by their nature, impact a wide variety of stakeholders and tend to cross political boundaries. Lessons learned from the CDF highlight the need for flexibility in the long-term and specificity in the short term in governing the operations of a large-scale coastal project. Recommendations developed for modernizing project implementation into the future given changing estuaries and climate will help increase effective implementation of larger-capacity river sediment diversions and other ecosystem-scale projects. It is time for big and bold action to restore south Louisiana and other coastal environments worldwide, and critical to success is using results from numerous past studies, applying lessons learned from existing projects like the CFD, and projections of future conditions.

Impacts of human modifications on material transport in deltas

Abstract. As humans continue to inhabit and modify river deltas, the natural processes governing material transport through these landscapes are altered. Two common engineering projects undertaken on deltas are the dredging of channels to enable shipping and the construction of embankments to reduce flooding. While the impact of these topographic modifications has been studied at a local level for specific sites, there is a gap in our generalized understanding of how these landscape modifications impact material transport. To narrow this gap, we conduct exploratory numerical modeling to develop deltaic landscapes with different input sediment compositions, modify their topography to mimic dredging and embankments, simulate different flow conditions, and then model the transport of passive particles. We find that human modification of topography lowers hydrological connectivity by reducing the area visited by fluvial inputs. The amount of time particles spend within the delta is reduced by the construction of polders and is lengthened by dredging. Material buoyancy has a greater impact on nourishment areas and exposure times than flow regime or topographic modification, with positively buoyant particles spending longer and visiting a greater area of the delta than neutral and negatively buoyant material. The results of this study can help guide the design of future engineering projects by providing estimates of their likely impact on transport processes.

Geomorphometric characterization and sediment connectivity of the middle Brahmaputra River basin

Knowledge of geomorphic characteristics and sediment connectivity is critical in understanding basin-scale surface processes that include steep mountainous and flat lowlands, particularly if the mid-basin and downstream areas are densely populated and disaster-prone. However, the lack of fluvial and sediment connectivity studies in downstream portions of large rivers of South Asia (particularly Bangladesh), where upper basin morphodynamics, hydrology, and sediment flux highly influence the repeated sediment disasters, limits our understanding of the large-scale fluvial geomorphic processes and basin-scale sustainable river management. Therefore, this article attempts to characterize the morphometric and topographic features along with the spatial sediment connectivity pattern of the middle Brahmaputra River basin (Teesta, Torsa, and Manas basins) covering ~75,000 km2 that influences the hydro-geomorphic response of the deltaic landscape of lowland Bangladesh. This work considers a set of morphometric and topographic parameters including the stream network, longitudinal profiles, stream power index (SPI), and topographic wetness index (TWI) for geomorphometric characterization. The linkage between the sediment sources to downstream areas also has been evaluated with the sediment connectivity (IC) index to understand better the sediment dynamics of the middle Brahmaputra River basin, draining towards lowland Bangladesh from the basin's upstream countries of India and Bhutan. The result of this study demonstrates a highly potential hydro-geomorphic response of the downstream areas attributed to steep topography, steep channel longitudinal profiles, high rainfall, and high sediment connectivity in upstream regions. However, the low topography, presence of anthropogenic stressors, almost flat longitudinal channel profiles with limited change in elevation, and lowered sediment connectivity potential in the mid-to-downstream areas depicts sensitivity to the depositional processes therein, impacting the basin-scale geomorphic connectivity from the upstream to the downstream region. These results will be the basic information for exploring the large-scale hydro-geomorphic response and structural sediment dynamics to understand the complex geomorphological processes in the South Asia region, where the fluvial sedimentation process is not fully understood with limited accessibility for field-based investigations.

The ‘Fluid Landscape’ of the Sundarbans: Critically Reviewing the ‘Managed Retreat’ Discourse

The Sundarbans, spread across 10,200 sq. km in the lower deltaic region of Bengal, is the world's largest pro-grading delta. Most climatologists acknowledge that this fragile ecosystem, cutting across Bangladesh and India, will bear the brunt of climate change. It is estimated that the region, facing sea level rise and intensification of cyclonic activities, will experience the disastrous effects of global warming; and scientists have been expressing their concerns about the viability of human settlements there in the foreseeable future. In India, some researchers have floated the idea of 'Managed Retreat' of people from certain areas of the deltaic floodplains in a bid to 'conserve the mangroves and the ecosystem' of the Sundarbans. This postulation, first published as the Delta Vision: 2050 for the World-Wide-Fund for Nature India (WWF-India) in 2011, and discussed in the following years, in various platforms and research journals, has been advocating a 'phased and systematic outmigration' (Ghosh 2012) from the region, citing the 'Dutch Room for River' project as an exemplary ideal to be mirrored. This article will try to unpack the impact of this proposal on the local communities, living in tandem with the deltaic landscape for generations, if such a strategy is adopted.

Hydro-morphodynamics triggered by extreme riverine floods in a mega fluvial-tidal delta

Maintaining accretion and progradation in a mega delta is crucial to its geomorphic stability and ecology. Extreme riverine floods can disturb hydro-sediment dynamics with great damage to the deltaic landscape, as for instance deltaic erosion. Nowadays, most mega deltas suffer from sediment starvation. Understanding the impact of extreme floods is a priority to determine the long-term fate of deltaic systems. Herein, we used the Delft 3D model and field data to study the hydraulics and morphodynamics of the 2016 extreme riverine floods in the South Passage (SP) of the Yangtze Delta. Results reveal that extreme floods can increase water levels, velocities, and bed shear stresses in an inner estuarine channel and mouth bar, while the flood has a weak effect in offshore areas. High-energy floods trigger strong tidal asymmetry and Euler residual currents, which intensifies downstream suspended sediment transport and bottom riverbed erosion. In comparison with those during extreme floods in 2016, net erosion after floods passed away was generated with seaward weakened magnitudes, the corresponding mean bathymetric erosion thickness was 19.97 cm, 12.71 cm and 4.62 cm in inner estuarine channel, mouth bar and offshore area, respectively. Even though the seaward deposition patches were due to lower scouring effect and converged sediment. Hydrodynamic increments in deeper channels were more significant, while shoals and deeper areas were strongly eroded with the lowest erosion between −5 m to −6 m isobath. These results further clarified the bathymetric patterns with highlights of extreme riverine floods that can amplify the sediment-insufficient risks in such mega fluvial-tidal delta.

Human–environment interactions during the mid-late Holocene and the Anthropocene – lessons from NW Indian plains and Bengal Delta

Abstract The Indian subcontinent today houses about one-third of the global population and is one of the most vulnerable regions to future climate variability. This region has seen changes in civilizations, kingdoms and more recently political regimes, that were intricately linked to the changing environment over the mid–late Holocene. A comparative analysis of human–environment interaction within different regions at different time scales of the Quaternary is, however, lacking. In this paper we discuss the human–environment interactions taking case studies from two diverse time periods and geographically different regions from the Indian subcontinent. First, we review and analyse the role of environmental change in the evolution of Indus civilization on the northwestern Indian subcontinent during the mid–late Holocene and secondly, we discuss the role of both the anthropogenic activities and environmental change during the Anthropocene in shaping up the Bengal Delta. Overall, during the mid–late Holocene, Indus cultural transformations were driven by natural environmental changes, whereas the anthropogenic activities in the last few centuries have modified the Bengal deltaic landscape, which has intensified the impacts of natural disasters – in both cases a change in socio-political scenarios occurred. Such studies can be used as benchmarks to understand the future response of societies to environmental changes.

Stable ≠ Sustainable: Delta Dynamics Versus the Human Need for Stability

AbstractArising 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.

The Ecosystems of the Danube Delta Biosphere Reserve state-of the-art

Taking into account the morphologic-hydrographic configuration of natural ecosystems or ecosystems partly modified by man the area, its flora and fauna communities and the long-term human impact, the two main categories of Danube Delta ecosystems associated with Razim-Sinoie lake complex, coastal marine waters and the Danube flood plain between Isaccea and Tulcea, as part of Danube Delta Biosphere Reserve, have been delimited: natural ecosystems or ecosystems partly modified by man; anthropic ecosystems. To identify and characterize ecosystems, there have been analysed the data on hydrography, morphology, biodiversity, human settlements, types of land use, spatial changes through the construction of agricultural, fisheries, forestry polders, modification of the network of channels and canals with consequences on the water circulation system inside the delta. The first category, of natural and partly modified by man ecosystems comprises 23 types (water bodies: running waters-Danube and its main branches, channels and canals; standing freshwater-lakes; standing brackish and salt waters-coastal lagoons, coastal, marine zones; wetlands: water fringe vegetation-flooded reed beds, floating reed beds , riparian willow formations, frequently flooded river levees; forests, shrubs and herbaceous vegetation: temperate riverine forests-mixed oak woods, shrubs and herbaceous vegetation, steppe meadows, meadows on low marine levees; dunes, beaches).The second category, of anthropic ecosystems includes 7 types (agricultural lands, forest areas-plantation on the river banks, fish farms, settlements-villages, towns). With the establishment of the Danube Delta Biosphere Reserve in 1990, with the statutory provisions on the protection and conservation of biodiversity, the deltaic landscape, some of the previous pressures were reduced, but the pollution of the Danube waters less consolidated beaches (Sulina, Sfântu Gheorghe, Chituc) and related with touristic activities, on ecosystems as a whole. The tourism activities also must represent not only a positive and dynamic development factor but also a practical solution to keeping the environment unaltered. These aspects were mentioned in the characterization of the ecosystems presented in this article.

‘Bonbibi’ Could Wait Till Our Boss Decides: Looking at the Changing Face of the Indian Sundarbans

Internal migration constitutes a major source of steady flow of population in India, and reports published by the World Economic Forum (WEF),1 2017 state that interstate migration in the country has doubled during 2001–2011, compared to the previous decade.2 In developing countries, such migration is often considered to be an effective way for income diversification for the economically marginalised sections of the society, even though its effect on ‘human development’ is oft debated. This article would engage with this debate and bring out how migration from the Indian part of the Sundarbans to other parts of the country is not only changing the demography of the region but is also having a strong impact on the local perception and attachment towards the deltaic landscape. By bringing in ethnographic details from a village in the Indian Sundarbans, which was predominately inhabited by the fishing community earlier, this article would bring out how traditional occupations like fishing are slowly losing their popularity in the face of the lure of out-migration, as the very identity of the ‘indigenous’ Sundarban fisher folks—who were once rightfully considered to be the true conservator of the forests—is changing. From there, this article would engage with the broader debate of rethinking whether migration can be considered as a positive indicator of development in such ecologically fragile areas like the Sundarban deltas, which used to indeed have a distinct economic, social and cultural life of its own.

What and where are periglacial landscapes?

AbstractUncertainties about landscape evolution under cold, nonglacial conditions raise a question fundamental to periglacial geomorphology:what and where are periglacial landscapes?To answer this, with an emphasis on lowland periglacial areas, the present study distinguishes between characteristic and polygenetic periglacial landscapes, and considershow complete is the footprint of periglaciation?Using a conceptual framework of landscape sensitivity and change, the study applies four geological criteria (periglacial persistence, extraglacial regions, ice‐rich substrates, and aggradation of sediment and permafrost) through the last 3.5 million years of the late Cenozoic to identify permafrost regions in the Northern Hemisphere. In limited areas of unglaciated permafrost regions are characteristic periglacial landscapes whose morphology has been adjusted essentially to present (i.e., Holocene interglacial) process conditions, namely thermokarst landscapes, and mixed periglacial–alluvial and periglacial–deltaic landscapes. More widespread in past and present permafrost regions are polygenetic periglacial landscapes, which inherit ancient landsurfaces on which periglacial landforms are superimposed to varying degrees, presently or previously. Such landscapes comprise relict accumulation plains and aprons, frost‐susceptible and nonfrost‐susceptible terrains, cryopediments, and glacial–periglacial landscapes. Periglaciation can produce topographic fingerprints at mesospatial scales (103–105m): (1) relict accumulation plains and aprons form where long‐term sedimentation buried landsurfaces; and (2) plateaux with convexo–concave hillslopes and inset with valleys, formed by bedrock brecciation, mass wasting, and stream incision in frost‐susceptible terrain.

Tropicality of Colonial Heritage Buildings in a Deltaic Landscape: British Colonial Architecture in Khulna

During the 17th-18th century colonial period on the Indian subcontinent, British colonial architecture flourished – including in the Bengal Delta. Although colonial architecture was inherently different from the traditional architecture of this tropical region, the monsoon climate and deltaic landscape forced colonial style buildings to incorporate a number of tropical architectural features to ensure climatic comfort. In the contemporary period, due to pressure from population density, many colonial buildings have been demolished and replaced with multi-story buildings. However, the tropical forces of this deltaic region need to be evaluated in order to re-create climate responsive architecture. This study aims to identify tropical architectural features inherent within colonial buildings of Khulna, Bangladesh, a city which formed a junction in the deltaic region during the colonial period. Four colonial buildings have been selected as case studies: two residential buildings, one mixed-use building, and a school. Tropical features were analysed from photographic data, and reproductions of plans and sections of the selected buildings, in order to reveal the significant tropical architectural features of these colonial period buildings. The case studies reveal structural and design elements that aided ventilation and air flow, and controlled solar radiation, humidity and driving rain. The findings aim to encourage practicing architects to rethink climate responsiveness in contemporary buildings in Bangladesh, by revealing how, a century ago, colonial buildings were influenced by the tropical deltaic climate, which impacted foreign architectural ideology and practice.

What controls the coarse sediment yield to a Mediterranean delta? The case of the Llobregat River (NE Iberian Peninsula)

Abstract. The human pressure upon an alluvial river in the Mediterranean region has changed its riverine and deltaic landscapes. The river has been channelized in the last 70 years while the delta has been retreating for more than a century (a set of data unknown, so far). The paper concentrates on the fluvial component, trying to connect it to the delta evolution. Is the channelization responsible for the delta retreat? We develop a method to compute the actual bed load transport with real information of the past river morphology. The paper compares the computation with very limited measurements, among which are bulk volumes of trapped material at a modern, deep river mouth. The decrease in sediment availability in the last 30 km of the channelized river is deemed responsible for the decrease in the sediment yield to the delta. Moreover, power development and flood frequency should be responsible for a baseline delta retreat during the 20th century. The sediment trapping efficiency of dams is less important than the flow regulation by dams, in the annual sediment yield. Therefore, it is more effective to dismantle channelization than to pass sediment at dams, to provide sand to the beaches.

Monitoring and Projecting Land Use/Land Cover Changes of Eleven Large Deltaic Areas in Greece from 1945 Onwards

Wetlands are areas of high biodiversity and provide many ecosystem services of high value. However, they are under constant threat from intense anthropogenic pressures, mainly agriculture intensification, urbanization, pollution, and climate change. The temporal and spatial patterns of land use/land cover (LULC) changes within eleven large wetlands in Greece were analyzed based on thematic maps generated from aerial orthophotos taken in 1945, 1975, and 2007. Socio-economic developments and the consequent need for more arable land and utilization of water resources are among the factors that mainly determine their evolution. In 2007, LULC classes related to wetland vegetation were reduced to one third as compared to 1945 and they were mainly replaced with croplands and urban infrastructures. Each of the different sub-periods that was considered (1945–1975 and 1975–2007) was distinguished by characteristic patterns of change. Agricultural land increased up to 42% from 1945 to 1975 and became the dominant LULC class in all deltaic areas but Evros. A considerable stability was observed for the period 1975–2007 for all LULC classed but it is remarkable the extent of urban areas that doubled. There is a tendency of landscape simplification and homogenization among the deltaic areas and the output of Markov chain analysis indicates that future composition of deltaic landscapes will be similar to the current one if the main driving forces remain constant. Changes in LULC composition and structure are also combined with coastal erosion in all deltaic areas. This is attributed to the modification of sedimentary deposits due to dam construction. The results summarize the change trajectories of the major deltaic areas in Greece from 1945 to 2007 thus offering a great outlook of changes that allows managers to understand how policies and socio-economic requirements affect the deltaic ecosystems and what decisions should be made to protect and enhance them.

Wetland delineation simulation and prediction in deltaic landscape

Abstract Present study attempts to delineate wetland in Indic part of mature Ganges delta with the help of satellite images applying convenient water body extraction indices. It is found that the existing methods are bringing noise in fulfilling the purpose and therefore a new index, Re-modified Normalized Difference Water Index (RmNDWI) is introduced. After proving the viability of the new index, it was used to simulate multiple land use changes and wetland area using Cellular Automata (CA) with Artificial Neural Network (ANN) along with other convenient indices. Results show a significant shrinkage of overall wetland area in both pre-monsoon and post-monsoon seasons, with complete disappearance of scattered wetland in pre-monsoon season in next ten to twenty years. Adaptive exponential smoothing method is used for simulating depth of wetland and results revealed that wetland depth may reduce by 70% in about >60% wetland areas in next 10 years. Some patches in the outskirts however exhibit increasing trend which is attributed by the local fishing activities.

Consequences of Mississippi River diversions on nutrient dynamics of coastal wetland soils and estuarine sediments: A review

Coastal Louisiana is dominated by the Mississippi River Deltaic Plain, which is composed of a series of overlapping and truncated sub-delta lobes that formed an extensive coastal wetland – open water shallow bay and low relief upland mosaic across the entire coastal zone (∼25,000 km2). These coastal wetlands have been eroding at an alarming rate during the past century, coincident with major modifications to the deltaic landscape. One of these former modifications included extensive leveeing of the Mississippi River, essentially isolating the river from the coastal basins. One restoration technique involves re-connecting the previously isolated coastal basins to the river via diversions, which would once again allow the influx of freshwater, sediments and nutrients into the coastal basins. We review issues on potential impacts of nutrient loading from the river as a consequence of river diversions, focused on nitrogen (N) and phosphorus (P) dynamics including denitrification related to carbon dynamics. We also examined how water residence times in these shallow systems, compared to deeper, often seasonally stratified, coastal systems, are more likely to lead to greater N removal potential in the context of a large scale river diversion helping to reduce N transport to the coastal ocean.

CHALLENGES AND STRATEGIES FOR ECOSYSTEM RESTORATION OF A SINKING DELTA PLAIN

Coastal erosion is a major global problem and is most acutely felt along developed coastal areas where coastal communities and infrastructures are threatened by storm surge flooding. This situation gets compounded to a bigger challenge around most of delta plains which are rapidly subsiding. The degree and magnitude of challenges associated with erosion and submergence along muddy deltaic coasts is intricately related to population density. It is estimated that about 500 million people in the world live on river deltas (Syvitski et al., 2009). Coastal populations and their associated industries/economies (oil & gas, fisheries, port and commerce etc.) are thus threatened by rapid degradation of the deltaic landscapes. This situation is further complicated by sea level rise and high-energy events such as hurricanes (cyclones, typhoons).

Pristine vs. human-altered Ebro Delta habitats display contrasting resilience to RSLR

River deltas are ecologically and economically valuable coastal ecosystems but low elevations make them extremely sensitive to relative sea level rise (RSLR), i.e. the combined effects of sea level rise and subsidence. Most deltas are subjected to extensive human exploitation, which has altered the habitat composition, connectivity and geomorphology of deltaic landscapes. In the Ebro Delta, extensive wetland reclamation for rice cultivation over the last 150 years has resulted in the loss of 65% of the natural habitats. Here, we compare the dynamics of habitat shifts under two departure conditions (a simulated pristine delta vs. the human-altered delta) using the Sea Level Affecting Marshes Model (SLAMM) under the 4.5 and 8.5 RCP (Representative Concentration Pathways) scenarios for evaluating their resilience to RSLR (i.e. resistance to inundation). Results showed lower inundation rates in the human delta (~10 to 22% by the end of the century, depending on RCP conditions), mostly due to ~4.5 times lower initial extension of coastal lagoons compared to the pristine delta. Yet, inundation rates from ~15 to 30% of the total surface represent the worst possible human scenario, assuming no flooding protection measures. Besides, accretion rates within rice fields are disregarded since this option is not available in SLAMM for developed dry land. In the human delta, rice fields were largely shifted to other wetland habitats and experienced the highest reductions, mostly because of their larger surface. In contrast, in the pristine delta most of the habitats showed significant decreases by 2100 (~2 to 32% of the surface). Coastal infrastructures (dykes or flood protection dunes) and reintroduction of riverine sediments through irrigation channels are proposed to minimize impacts of RSLR. In the worst RCP scenarios, promoting preservation of natural habitats by transforming unproductive rice fields into wetlands could be the most sustainable option.

Assessment of LiDAR and Spectral Techniques for High-Resolution Mapping of Sporadic Permafrost on the Yukon-Kuskokwim Delta, Alaska

Western Alaska’s Yukon-Kuskokwim Delta (YKD) spans nearly 67,200 km2 and is among the largest and most productive coastal wetland ecosystems in the pan-Arctic. Permafrost currently forms extensive elevated plateaus on abandoned floodplain deposits of the outer delta, but is vulnerable to disturbance from rising air temperatures, inland storm surges, and salt-kill of vegetation. As pan-Arctic air and ground temperatures rise, accurate baseline maps of permafrost extent are critical for a variety of applications including long-term monitoring, understanding the scale and pace of permafrost degradation processes, and estimating resultant greenhouse gas dynamics. This study assesses novel, high-resolution techniques to map permafrost distribution using LiDAR and IKONOS imagery, in tandem with field-based parameterization and validation. With LiDAR, use of a simple elevation threshold provided a permafrost map with 94.9% overall accuracy; this approach was possible due to the extremely flat coastal plain of the YKD. The addition of high spatial-resolution IKONOS satellite data yielded similar results, but did not increase model performance. The methods and the results of this study enhance high-resolution permafrost mapping efforts in tundra regions in general and deltaic landscapes in particular, and provide a baseline for remote monitoring of permafrost distribution on the YKD.