Land subsidence over oilfields in the Yellow River Delta

Subsidence in river deltas is a complex process that has both natural and human causes. Increasing human activities like aquaculture and petroleum extraction are affecting the Yellow River delta, and one consequence is subsidence. The purpose of this study is to measure the surface displacements in the Yellow River delta region and to investigate the corresponding subsidence source. In this paper, the Stanford Method for Persistent Scatterers (StaMPS) package was employed to process Envisat ASAR images collected between 2007 and 2010. Consistent results between two descending tracks show subsidence with a mean rate up to 30 mm/yr in the radar line of sight direction in Gudao Town (oilfield), Gudong oilfield and Xianhe Town of the delta, each of which is within the delta, and also show that subsidence is not uniform across the delta. Field investigation shows a connection between areas of non-uniform subsidence and of petroleum extraction. In a 9 km2 area of the Gudao Oilfield, a poroelastic disk reservoir model is used to model the InSAR derived displacements. In general, good fits between InSAR observations and modeled displacements are seen. The subsidence observed in the vicinity of the oilfield is thus suggested to be caused by fluid extraction

The Geology and environmental processes that govern the origin of the continental shelf of Iberia

The continental shelves are dynamic systems that started to be explored only after early 20th century. The arrival of more sophisticated technologies allowed the acquisition of detailed maps of the seafloor that displayed the variety of the submarine features but also brought the first debates on the definition and concepts of the continental shelves. This work makes use for the first time of high-resolution bathymetry data provided from EMODnet Portal (115 m × 115 m) for a large-scale study about the Iberian continental shelf, providing a general and detailed compilation of morphologic features. The coupling of these data with tectonic, geologic, hydrographic and oceanographic information allowed generating maps that described the environmental processes acting on the Iberian Peninsula continental shelf. The study has been accompanied by seismic stratigraphic analysis on some areas of the Portuguese shelf, with seismic data taken during the research surveys off the Tagus River estu-ary, on Alentejo and Algarve shelves. As a result, a first characterization of the Iberian shelf in ten selected sectors depicting a series a significant number of features such as lineaments, rocky outcrops, submarine highs and dep-ositional bodies is presented. These are mostly related to past eustatic changes or structural features determined by the existent geologic substrate. Occasionally, these local features have been linked to river submerged deposits. The work also includes a stratigraphic analysis on seismic profiles in four study areas (Estremadura, Tagus Delta, Alentejo and Algarve shelves). These allowed to identify sectors of the continental shelf controlled by different processes that help to classify the entire Iberian shelf sectors in three types depending on their formation/evo-lution: i) Orogenic shelf; ii) Depositional shelf; iii) Inherited/Structural shelf

Oceanus.

v. 26, no. 4 (1983

Modeling deltaic lobe‐building cycles and channel avulsions for the Yellow River delta, China

River deltas grow by repeating cycles of lobe development punctuated by channel avulsions, so that over time, lobes amalgamate to produce a composite landform. Existing models have shown that backwater hydrodynamics are important in avulsion dynamics, but the effect of lobe progradation on avulsion frequency and location has yet to be explored. Herein, a quasi‐2‐D numerical model incorporating channel avulsion and lobe development cycles is developed. The model is validated by the well‐constrained case of a prograding lobe on the Yellow River delta, China. It is determined that with lobe progradation, avulsion frequency decreases, and avulsion length increases, relative to conditions where a delta lobe does not prograde. Lobe progradation lowers the channel bed gradient, which results in channel aggradation over the delta topset that is focused farther upstream, shifting the avulsion location upstream. Furthermore, the frequency and location of channel avulsions are sensitive to the threshold in channel bed superelevation that triggers an avulsion. For example, avulsions occur less frequently with a larger superelevation threshold, resulting in greater lobe progradation and avulsions that occur farther upstream. When the delta lobe length prior to avulsion is a moderate fraction of the backwater length (0.3–0.5L_b), the interplay between variable water discharge and lobe progradation together set the avulsion location, and a model capturing both processes is necessary to predict avulsion timing and location. While this study is validated by data from the Yellow River delta, the numerical framework is rooted in physical relationships and can therefore be extended to other deltaic systems

DUNE AND COASTAL EVOLUTION IN ISLA SALAMANCA NATIONAL PARK, COLOMBIA

This project analyzes natural variables influencing the coastal and dune evolution in Isla Salamanca National Park (ISNP), a biosphere reserve and Ramsar site located in Colombia, on the Caribbean coast. Since at least the early 1950s, the park has been affected by eroding trends along most of the shoreline. Particularly, most modern dunes are located close to the coastline, forming scarped dunes regularly affected by storm wave-action. The trends through time of rain, bathymetry and coastline changes during the last six decades were studied through statistical analysis, mapping of landscape features, and satellite images and historical aerial photograph interpretation. Once these trends were identified, six vegetation transects were developed over dunes located in areas under contrasting morphodynamic regimes: moderate erosion rates (east area), high erosion rates (central area), and accretion (west area). The findings of this work indicate that those dunes located at the east extreme and central areas of ISNP are scarped and impeded dunes fixed in position by an abundant vegetation cover. In contrast, mobile embryo dunes, either without vegetation or covered only by vegetation species that can thrive under sand burial, are common at the west end of the study site, a sector where accretive processes have been occurring over the last six decades. This findings contribute to understanding the morphodynamics producing the accelerated coastal retreat taking place in ISNP, thereby providing useful data to support sound decisions for the management of the coastal zone in this National Park

Role of delta-front erosion in sustaining salt marshes under sea-level rise and fluvial sediment decline

Accelerating sea-level rise and decreasing riverine sediment supply are widely considered to lead to global losses of deltaic marshes and their valuable ecosystem services. However, little is known about the degree to which the related erosion of the seaward delta front can provide sediments to sustain salt marshes. Here, we present dataf rom the mesomacrotidal Yangtze Delta demonstrating that marshes have continued to accrete vertically and laterally, despite rapid relative sea-level rise (approx.10 mm yr−1) and a \u3e 70% decrease in the Yangtze River sediment supply. Marsh progradation has decelerated at a lower rate than fluvial sediment reduction, suggesting an additional source of sediment. We find that under favorable conditions (e.g., a mesomacrotidal range, strong tidal flow,flood dominance, sedimentary settling lag/scour lag effects, and increasing high-tide level), delta-front erosion can actually supply sediment to marshes, thereby maintaining marsh accretion rates in balance with relative sea-level rise.Comparison of global deltas illustrates that the ability of sediment remobilization to sustain marshes depends on coastal processes and varies by more than an order of magnitude among the world’s major delta

Sources and transformations of dissolved lignin phenols and chromophoric dissolved organic matter in Otsuchi Bay, Japan

Dissolved lignin phenols and optical properties of dissolved organic matter (DOM) were measured to investigate the sources and transformations of terrigenous DOM (tDOM) in Otsuchi Bay, Japan. Three rivers discharge into the bay, and relatively high values of syringyl:vanillyl phenols (0.73 ± 0.07) and cinnamyl:vanillyl phenols (0.33 ± 0.10) indicated large contributions of non-woody angiosperm tissues to lignin and tDOM. The physical mixing of river and seawater played an important role in controlling the concentrations and distributions of lignin phenols and chromophoric DOM (CDOM) optical properties in the bay. Lignin phenol concentrations and the CDOM absorption coefficient at 350 nm, a(350), were strongly correlated in river and bay waters. Measurements of lignin phenols and CDOM in bay waters indicated a variety of photochemical and biological transformations of tDOM, including oxidation reactions, photobleaching and a decrease in molecular weight. Photodegradation and biodegradation of lignin and CDOM were investigated in decomposition experiments with river water and native microbial assemblages exposed to natural sunlight or kept in the dark. There was a rapid and substantial removal of lignin phenols and CDOM during the first few days in the light treatment, indicating transformations of tDOM and CDOM can occur soon after discharge of buoyant river water into the bay. The removal of lignin phenols was slightly greater in the dark (34%) than in the light (30%) during the remaining 59 days of the incubation. Comparison of the light and dark treatments indicated biodegradation was responsible for 67% of total lignin phenols removal during the 62-day incubation exposed to natural sunlight, indicating biodegradation is a dominant removal process in Otsuchi Bay.Ministry of Education, Culture, Sports, Science, and Technology; 1504137 - National Science Foundatio

Drivers and impacts of water level fluctuations in the Mississippi River delta: Implications for delta restoration

This review synthesizes the knowledge regarding the environmental forces affecting water level variability in the coastal waters of the Mississippi River delta and relates these fluctuations to planned river diversions. Water level fluctuations vary significantly across temporal and spatial scales, and are subject to influences from river flow, tides, vegetation, atmospheric forcing, climate change, and anthropogenic activities. Human impacts have strongly affected water level variability in the Mississippi River delta and other deltas worldwide. Collectively, the research reviewed in this article is important for enhancing environmental, economic, and social resilience and sustainability by assessing, mitigating, and adapting to geophysical changes that will cascade to societal systems in the coming decades in the economically and environmentally important Mississippi River delta. Specifically, this information provides a context within which to evaluate the impacts of diversions on the hydrology of the Mississippi delta and creates a benchmark for the evaluation of the impact of water level fluctuations on coastal restoration projects worldwide