Deltaic Plain Research Articles

КОМПЬЮТЕРНОЕ МОДЕЛИРОВАНИЕ ИСТОРИИ ОСАДКОНАКОПЛЕНИЯ ПЕСЧАНЫХ ТЕЛ СРЕДНЕЮРСКОГО НЕФТЕГАЗОНОСНОГО КОМПЛЕКСА (НА ПРИМЕРЕ ГЕРАСИМОВСКОГО МЕСТОРОЖДЕНИЯ, ЗАПАДНАЯ СИБИРЬ)

The present paper describes the DIONISOS software package (Beicip-Technologies), where the reconstruction of the accumulation conditions and facies modeling of sand reservoirs Yu10, Yu9, Yu8, Yu7 and Yu6 of the Tyumenskaya Formation and carbonaceous-clay members acting as fluid seals within the Gerasimovskoye oil and gas condensate field located in the south of the Parabel district of the Tomsk region. Reconstructions of facies environments make it possible to consistently restore conditions and create a general principled model of the accumulation of sandy-argillaceous deposits of the Middle Jurassic PP in a given territory. Polyfacies deposits of the Bajocian are represented by sands of distributaries and stream-mouth bars, underwater slope of delta, above-water and underwater delta plains, argillaceous-carbonaceous sediments of floodplain lakes, bogs, marshes and lagoons, clays formed at the border of the above-water and underwater deltaic plains, silt deposits of above-water and underwater delta plains, prodelta clays. As a result of the 3D facies model construction, it is shown that the subcontinental sedimentary environments of sand reservoirs Yu10–Yu8 are replaced by deltaic and floodplain-lacustrine-boggy ones, and the formation of Yu7–Yu6 reservoirs occurs in conditions of coastal plain, periodically flooded by the sea. In total, 5 lithotypes of sand deposits have been identified, 1 – argillaceous-carbonaceous, 2 – argillaceous and 1 – silty. Computer facies 3D modeling of the sand bodies assemblage (hydrocarbon reservoirs) of the Bajocian age for the Gerasimovskoye oil and gas condensate field has been performed.

Soil Minerals Serving as Source of Arsenic in Alluvial Aquifers of Holocene: A Case Study from Indus Delta, Sindh, Pakistan

Groundwater arsenic contamination is recently reported in the alluvial aquifers of Indus deltaic plain. Since the source of arsenic is believed to be natural as widely reported in other deltaic aquifers of same age (Holocene), it is imperative to evaluate the soil characteristics for identifying the sources of arsenic and its mobilization mechanism. For this purpose, 49 soil samples were collected from near aquifer sites in all three talukas of Tando Muhammad Khan district. Visual analysis revealed that soil is light grey in color with fine texture ranging from silt to silty-clay. The X-ray diffraction study reveals the occurrence of quartz, mica and clay minerals in all collected soil samples. Plagioclase feldspar is second dominant mineral group in the order of albite (calcian) >albite>albite (disordered) = anorthite > anorthite (sodian) = anorthite (disordered). Calcite is major carbonate mineral which is detected in 40 out of total 49 soil samples. The occurrence of other occasional minerals includes amesite, nitro-calcite, rutile and zinnwaldite. The frequency of micaceous minerals in collected samples is in the order of clinochlore> polylithionite> Biotite > phlogopite> muscovite. Polylithionite is found in about half of the total soil samples, where most of the aquifers contain arsenic >20 μg/L (Khan, 2014). Phlogopite is observed in seven soil samples which are also associated with clinochlore. On the other hand, biotite is found in 14 sediment samples collected from Tando Muhammad Khan and Bhulri Shah Karim talukas and muscovite occurs in three soil samples of Tando Muhammad Khan taluka. It can be concluded from present study that fine-grained Phyllosilicates have strong affinity for arsenic retention. These sediments are important source of arsenic Indus delta and other deltaic plains of the world.

Subsurface structure revealed by seismic reflection images to the southwest of the Cerro Prieto pull-apart basin, Baja California

This work aims to characterize the crustal architecture and structure in an area of the Mexicali Valley between the southwestern part of the Cerro Prieto pull-apart basin, which contains the geothermal field of same name, and the southeastern edge of the Sierra Cucapah, Baja California, Mexico. Although the region surrounding the geothermal field has been extensively studied, the structural features in the vicinity are poorly known. Interpretations based on processed crooked-line 2D seismic reflection images made here reveal evidence of structural deformation and seismostratigraphic features in the study area. Two structural domains were identified adjacent to the Cerro Prieto fault: the northeastern domain, which belongs to the pull-apart basin, and the southwestern domain, which exhibits deformation associated with the Sierra Cucapah uplift. Subsurface images indicate the presence of the Cerro Prieto fault through lateral discontinuities in the reflectors; the fault is sub-vertically oriented and dips ∼80° to the east. Two seismic reflectors were identified to west of the Cerro Prieto fault, one of which corresponds to the acoustic basement. The other is associated with the top of an alluvial and deltaic facies and is described here for the first time. Three other seismic reflectors to the east of the Cerro Prieto fault correspond to gray shale sequences with interspersed sandstones in the Cerro Prieto geothermal field that were reported previously by other authors. The presence of two previously unknown structures are reported for the first time. The Sonora and Nayarit faults, with azimuths of ∼305° and ∼307° and lengths of ∼12 km and ∼9 km, respectively, are both located within the block bounded by the Cerro Prieto fault to the northeast and the Indiviso fault to the southwest. The La Puerta fault is also described for the first time, which exhibits reverse fault characteristics and lies transverse to the fault system of the Sierra Cucapah. The acoustic basement between the Sierra Cucapah and the Cerro Prieto fault is sub-horizontal and dipping slightly westward, and differs from the eastward-dipping acoustic basement observed to the south between the Sierra Las Pintas and the deltaic plain. Subsidence in the sequences within the Cerro Prieto basin can be more clearly observed after 500 m, with evidence in profile L-25 suggesting greater vertical displacement towards the southeast. Two areas of opportunity are reported for geothermal interest purposes. Despite the additional knowledge about regional tectonics and strucural background provided by this work, further studies are needed. The fault geometry remains poorly defined and due to its location, much of the fault is buried by sediments that prevent a full understanding of the potential danger in the region. Here, previously unknown structures are reported that represent geological and seismic risks. In addition to their scientific value, the findings have a potentially large societal impact due to the presence of several cities in the study area. The results should therefore be incorporated into future regional risk assessments.

Late Pleistocene - Holocene Sedimentary Evolution of Nam Bo Plain and Correlation from the Ca Mau Peninsula to the Mekong River Delta in Midle-Late Holocene

Located in southern Vietnam, the Southern plain is one of the largest in Asia. Within the coastal area, this study has indicated that there are two plains forming by different hydrodynamic mechanisms: the river dominated Mekong Delta plain and the tidal dominated plain of the Ca Mau peninsula. Studying lithofacies based on: (i) sedimentary parameters indicating environment of 29 boreholes in tidal flat and coastal plains, hundreds of surveyed surface sediment stations; (ii) stratigraphy seismic characteristics of the 21 seismic sections; and (iii) absolute age data, evolutionary history of late Pleistocene - Holocene sediments in the Southern plain and the relationship between the Mekong Delta and the tidal plain of the Ca Mau peninsula in the middle Holocene - late be clarified. Both plains are characterized by 3 lithofacies complexes corresponding to 3 phases of sea-level change: (i) lowstand alluvial facies complex (arLST Q13b); (ii) coastal facies complex (amtTST Q21-2) and shallow marine-lagoon greenish-gray clay facies (mtTST Q21-2); (iii) the phase of the middle-late Holocene (Q22-3 HST) has a differentiation between the two plains. The Me Kong delta is characterized by three deltaic facies complexes: (1) the late middle-late Holocene buried submarine deltaic facies complex (amh1Q22-3); (2) late Holocene deltaic plain facies complex (amh2Q23) and modern submarine deltaic facies complex (amh3Q23). The tidal plain of Ca Mau peninsula is characterized by a complex of sandy bars, tidal plains and tidal channels. In the regressive process, four periods of relative sea-level stopped, creating three ancient shoreline (5ka BP, 2.5ka BP; and 1 ka BP). The delta plain is marked by deltaic lobes turning to the southeast sea, while the Ca Mau plain characterized by the sand bars that tend to change direction from the east (2.5 ka BP) to the southeast (0.5ka BP and 0.2ka BP).
 

Water Quality Studies of the Kapadak River Basin, South-Western Bangladesh with Special Emphasis on Environmental Degradation

The Kapadak River basin in SW Bangladesh lies on late Holocene-Recent alluvium of the Ganges deltaic plain in the north and Ganges estuarine plain in the south. The anion and cation trends in the analyzed shallow-tube well and river water are $${\bf{C}}{{\bf{l}}^ - }{\bf{ > HCO}}_{\bf{3}}^ - {\bf{ > NO}}_{\bf{3}}^ - {\bf{ > S}}{{\bf{O}}_{\bf{4}}}^{{\bf{2}} - }$$ and Na+>K+>Ca2+>Mg2+ respectively. The groundwater of the area is of sodium-calcium cation facies and chloride-bicarbonate to carbonate- sulfate anion facies. The river water is of sodium-potassium cation facies and chloride-bicarbonate—sulphate to chloride —sulphate-bicarbonate anion facies. The shallow tube well is contaminated with arsenic which exceeds the WHO recommended value for drinking water (10 µg/l). The shallow water contains salinity above the standard which is unsuitable for drinking as well as for agricultural activities. The concentration of arsenic, sodium, calcium, potassium, chlorine, bicarbonate, percentage of salinity and specific electrical conductance decreases with increasing depth. The shallow tube well water of the study area is very saline exceeding the permissible limit and requires treatment. The deep tube-well water contains lower amount of arsenic and sodium, lower percentage of salinity and specific electrical conductance in comparison to shallow tube-well water. As a result, the deep tube-well water is free from arsenic toxicity and has low to high salinity hazard, but is also hard that exceeds the tolerable limit of hardness of groundwater for drinking, public health and agricultural purposes and requires softening. The Kapadak river water is highly concentrated with sodium, potassium, magnesium, calcium, chloride, bicarbonate, and specific electrical conductance which cause the deterioration of river water quality for agricultural purposes. According to the values of TDS, EC, boron concentration, Na%, and SAR, the shallow tube-well water as well as river water is of poor quality and unsafe for irrigation purposes, while the deep tube-well water is poorly safe for drinking and irrigation purposes. As a whole in the study area groundwater quality degrades from north to south as southern part is inundated regularly by saline estuarine water. The chemical weathering of rock-forming minerals influences the groundwater quality. Entrapped saline water in the aquifers during the Holocene time is the main source of salinity in this area with minor contribution from dissolution of halides and saline estuarine water in the Kapadak river due to tidal inundation.

GEOMORPHOLOGICAL MAPPING OF PART OF THE NIGER DELTA, NIGERIA USING DEM AND MULTISPECTRAL IMAGERY

This study utilised geo-information technology to carry out a geomorphological mapping of a part of the Niger Delta. Satellite image analysis was based on bi-annual seasonal approach using a combination of visual analysis of the geometry, site, situation, colour, and season for analysis of the non-topographic features. The study also utilised virtual and onsite fieldworks and existing geomorphologic information to interpret and analyse topographic and bathymetric features. First-order topographic features (elevation) and second level features including slope, aspect, curvature and mathematically exaggerated shaded relief were extracted from DEM. Relief classification was based on average elevation differences, hill shade, slope, and aspect. Three main non-topographic landforms were identified; the permanent rivers with stable meanders, perennially-active systems of creeks and fluvial landforms including scroll bars and oxbows. With the exception of higher elevation values towards the north-western fringe, the elevation ranges between mean sea level and 1 metre above sea level thus establishing a somewhat flat terrain. These areas were filled with meandering streams, sinuous creeks and watercourses flanked by mangrove vegetation. In the north-western area, elevation rose close to approximately 4 metres in most of the area with a peak of 10 metres. Generally, the cumulative area-slope analysis yielded a deltaic plain with generalised slope ≤ 20. Overall two elevation-based geographically differentiated morphological units were identified; tidal mudflats and saltmarshes. The study recommends that to provide needed information for resource planning and management, further investigation should be carried out with a view to modelling probable ecological and geomorphological changes in the entire Niger Delta.
 

The evolution of the transboundary Evros river delta (Northeast Aegean Sea) under human intervention: a seven-decade analysis

ABSTRACT The Evros deltaic plain (North Aegean Sea, Greece) covers an area of 188 km2 and is shared by Greece and Turkey by its current main channel. This paper investigates deltaic plain evolution during the last seven decades (1945–2017), taking into consideration human interventions and their impacts on deltaic processes. Outcomes indicate that the construction of more than 25 major dams in the Evros River catchment resulted in >80% reduction in fluvial suspended load. Moreover, the alignment and relocation of the main distributary channel to the southeast was accompanied by the transformation of >40% of the deltaic plain to agricultural land. The combination of human interventions supports the coastline advance of the active main mouth (current rate of 3.9 *10−3 km2/yr), retreat of the old (abandoned) Evros mouth (current rate 7.7 *10−3 km2/yr), and signs of remarkable vulnerability in the middle mouth area.

The rainfall and discharge trends of Surma River area in North-eastern part of Bangladesh: an approach for understanding the impacts of climatic change

BackgroundBangladesh is known as a deltaic plain at the confluence of the Ganges, Brahmaputra and Meghna River Basins (GBM) and their tributaries. The rainfall pattern of northeastern part of Bangladesh is changing along with the discharge pattern of Surma River. In this study, the changes in precipitation of Sylhet and river discharge of Surma River and the relationship between them were investigated. The study emphasizes on the influence of climatic component (rainfall) on the hydro-characteristics of river. The time series data from 1973 to 2016 (44 years) of rainfall and river discharge of Surma River were collected and analyzed. The basic hydro-characteristics, including arithmetic mean, variability, skewness, distribution type, persistence, dependence, trend, and correlation have been studied through various statistical methods, including coefficient of variation, Mann–Kendall test, Sen’s slope estimator, and Pearson’s coefficient of correlation.ResultsThe rainfall trend shows moderate year-to year variability although there is an indication of declining rainfall trend. As with rainfall, the river discharges show moderate year to year variations that are related to the variability in rainfall. The decreasing rate is 1.53 mm for rainfall and − 1.51 m3/s for discharge (Mann–Kendall test). The rainfall was increasing from 1973 to 1989 but after 1990 it is reduced. The mean discharge of Surma River was 845.99 M3/s. The rainfall started to fall down extremely from 1990 to 2016 but before that the rainfall showed an increasing trend with modest slope. It is possible that the declining trend in rainfall observed in Sylhet is a result of climate change which causes the declining of Surma River discharge. Over these 44 years analysis, the rainfall and discharge shows a very decreasing trend and both rainfall and discharge were highly related for most of the time.ConclusionIn conclusion, it can be noticed that the rainfall in Sylhet has been reduced from the time 1973 to 2016 which directly affects the discharge of Surma River. Consequently, this result might be the indication about the effect of climatic change in the local as well as global level.

Nitrogen Mineralization in Mississippi River Deltaic Plain Freshwater Floating Marshes

ABSTRACTThe mineralization of soil organic nitrogen in two floating marshes types in Louisiana, USA with different vegetation and mat thickness (and biomass) was measured by incubating peat soil in situ in polyethylene bottles at depths of 10 and 25 cm. The size of the extractable inorganic N (NH4+ – N) pool was related to mat thickness and soil bulk density. The N mineralization rates were twice as great at the thick mat site (1.5 mg N/kg soil/day) compared to the thin mat floating marsh (0.71 mg N/kg soil/day). The amount mineralized on a volume basis to 30 cm depth were 22 mg N/m2/day for the thick mat marsh and 6 mg N/m2/day for the thin mat marsh. The nitrogen mineralization rates observed in this study reflect plant biomass differences between the thick mat and thin mat marshes, with the former exhibiting approximately 7-fold greater biomass. These low overall mineralization rates suggest that nitrogen entering these freshwater floating marshes from Mississippi River water percolating through the root zone, would result in increased plant productivity-increasing marsh stability and also providing a natural mechanism contributing to the processing and removal of dissolved inorganic nitrogen in river water entering these wetlands.

Deltaic sedimentary environments in the Niger Delta, Nigeria

This study is focused on the geomorphology of surface sedimentary environments contained in the fluvial, tidal and wave-dominated areas of the Niger Delta. GIS techniques applied to high-quality Landsat and SPOT images were used to identify and map landforms and processes, as well as quantitatively characterise their metrics and spatial distribution. A detailed analysis shows that the extent of the Niger Delta is 70,000 km2, contrary to previous publications that reported 75,000 km2. The delta has also been remapped and classified into mega sedimentary environments: the upper deltaic plain is 69% of the total extent, while the lower deltaic plain and delta front are 25% and 6% respectively. Other subunits were distinguished and mapped within the upper deltaic plain such as fluvial channels, point bars, braid bars, oxbow lakes, and other lakes. Tidal channels, beaches and spits were identified in the lower deltaic plain and delta front. The geometries of these sedimentary bodies (landforms) appear to be relatively scale-invariant, thus meaning that from the measurement of some dimensional parameters (e.g. the length) it is possible to estimate all others (e.g. the width and overall extent). This is an aspect of great relevance in subsurface analyses where it is often difficult to predict the extent of sedimentary bodies. The correlation between channel width and length (r2 = 0.9), is the strongest relationship found between sedimentary body metrics.

Bajocian transgressive-regressive sequences of the Tecocoyunca Group, southern Mexico, with maximum flooding surfaces marked by Thalassinoides

Bajocian (Middle Jurassic) transgressive-regressive sequences (TRS), outcropping in the Rosario Nuevo Creek (Tezoatlan Basin, Tecocoyunca Group) in Oaxaca State, Mexico, represent one of the Jurassic phases of opening and widening of a trans-Pangaean marine corridor (called also the Hispanic Corridor) and show a retrogradational-progradational set of sedimentary successions with decipherable and diverse facies. Two TRSs have been distinguished. The lower one starts with fluvio-deltaic sandstones including pedogenic horizons. Drowning of the deltaic plain and gradual rising of the water table is marked by change in vegetation: from large trees to low-rise vegetation with characteristic clumps of dense roots cemented by siderite. The delta plain succession is topped by a thin coal seam, followed by a transgressive surface. Ensuing laminated mudstones of restricted marine origin pass into open marine deposits, represented by bioturbated heterolithic strata with ammonites followed by nearshore sandstones, deposited in a storm-dominated basin. A similar succession, although without the deltaic part, is repeated in the next TRS. Of note are two thin (15–20 cm) continuous beds with Thalassinoides isp. networks, present within open marine deposits. Although large Thalassinoides networks are mostly known from shallow-marine and coastal environments, the case from Mexico represents less common occurrences from a deeper marine (offshore) setting, associated with maximum flooding surfaces, sediment starvation and firmgrounds ( Glossifungites ichnofacies). Occurrences of Thalassinoides meshes, precisely marking maximum flooding surfaces, are helpful in defining the hierarchy of sequence stratigraphic cycles.

Sedimentary records of paleoseismic events in the Late Pleistocene sediments of the Southern Yangtze River deltaic plain, East China, and their implications for differential subsidence of the Taihu block

Drilling cores from the Hangjiahu Coastal plain in the southwestern corner of the Southern Yangtze River deltaic plain, East China, contain a variety of soft-sediment deformation structures in the Late Pleistocene lacustrine and tidal sediments. They include load-flame structures, ball-and-pillow structures, diapir structures, liquefied sand veins, liquefied breccias, syn-sedimentary fault, seismo-cracks and brittle breccias. Sedimentary facies assessment of host deposits and development features rule out an exogenic origin of the soft-sediment deformation structures, such as gravity-flow, storm activity, wave action or flood. These soft-sediment deformation structures in the study area are interpreted as seismites, their spatial distribution suggest that the earthquakes were sourced from the intersection of the Majin-Wuzhen Fault and the Huzhou-Jiashan Fault. Seismites recognized in cores indicate three episodes of short and sudden seismicity (magnitude > 5), which are interpreted as a response to syn-depositional tectonic activity and differential subsidence of the Taihu block during the Late Pleistocene period. Systematic study of spatial and temporal distribution of these seismites improves the understanding of the tectonic context and evolutionary history of sedimentary basement.

The recent fossil turtle record of the central plain of Thailand reveals local extinctions

With more than 50 extant turtle species, Southeast Asia is currently a hotspot of turtle biodiversity. However, the distribution areas of most species are decreasing as a consequence of human activities. The causes of this decline are multiple: habitat and natural resources destruction, introduction of invasive species, hunting, etc. Historical data are however still lacking for a detailed understanding of that regional trend as well as for forecasting its evolution in the future. Indeed, while oral testimonies and text data can provide a rather good appreciation of the decline of biodiversity over the last few decades; nothing is known about the dynamic of turtle biodiversity over the Holocene. This lack of data is especially damaging in area where human activities are interacting for a long time with the wild fauna, as the central plain of Thailand, which is now dominated by agricultural landscape. In order to solve these issues, we investigated five Holocene localities in Thai central plain which provided assemblages of turtle remains ranging from Neolithic to Dvaravati periods (4000 to 1000 BP). The studied archaeological assemblages showed a very high species richness. Species such as Malayemys macrocephala, Cuora amboinensis, Heosemys annandalii, Heosemys grandis, Siebenrockiella crassicolis, Amyda ornata were among the most abundant. We also found several plates and a cranial material belonging to a species of the genus Batagur and tortoise remains including Indotestudo elongata and a few plates belonging to the genus Geochelone. The Batagur and Geochelone genera are absent from living turtle assemblages in the central plain but are present in Myanmar, Cambodia, Indonesia or Southern Thailand for Batagur and far in the West for Geochelone (Myanmar) respectively. Batagur is usually found in coastal areas and its disappearance from central plain is interpreted as resulting from the destruction of a fragile habitat and possibly from the rapid geomorphological evolution of the Chao-Phraya deltaic plain, the disappearance of tortoises could result from deforestation. Cutting traces showed that most turtles were used as food resources at these times, suggesting that turtle hunting was a common practise. Furthermore, occurrence of holes in the margin of the carapace of specimens from Kheed Khin (Saraburi Province) and Promthin Tai (Lopburi Province) suggests that turtles were sometimes kept captive alive or transported. This study shows that investigation of recent fossil localities allows for a better understanding of the role of past human populations in the alteration of the biodiversity through time, and for a more accurate estimation of the rates of species extinction.

A review of sediment diversion in the Mississippi River Deltaic Plain

One of the proposed methods for restoring the disappearing Mississippi Delta is sediment diversion which uses channels and structures to divert water and sediment from the Mississippi and Atchafalaya Rivers into adjacent basins. This study presents a comprehensive review of geological and physical aspects of sediment dynamics in the Mississippi River Deltaic Plain (MRDP), with special reference to diversion studies over the past two decades. We synthesize these studies, present the current understanding of sediment diversions in the context of sediment dynamics, identify multiple key knowledge gaps, and make recommendations for future studies.To maximize net land building in the MRDP, management strategies should be focused on (a) enhancing river sediment delivery (both mud and sand), (b) increasing sediment retention in receiving basins and (c) minimizing erosion in bays and estuaries. Compared with extensive studies of land building, there have been relatively fewer studies of erosional processes. A heterogeneous coastal geological framework, cohesive sediment erodibility and subsidence together play complicated yet critical roles in future sediment dynamics in bays and estuaries of the MRDP. Sediment retention rates are highly sensitive to spatial and temporal scales, types of sediments and delivery season. Sediment diversions to seaward receiving basins provide more surge protection but tend to have lower sediment retention due to active coastal processes. Structures and devices that improve sediment retention, trap sediments, dissipate waves, and build living shorelines should be explored and cost-to-benefit analysis is needed. Long-term planning should consider more landward diversions, strategic community relocation, and nonlinear response of the complex sedimentary system of the MRDP.

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.

Soil quality index for paddy fields based on standard scoring functions and weight allocation method

ABSTRACTRice ecosystems are currently impacted by numerous issues resulting in reduced returns from rice production. In order to sustainably increase rice yields, it is important to understand the soil quality of paddy fields. The aim of this study was to determine the quality of soil of the Çarşamba Deltaic Plain in Turkey for rice cultivation. For that purpose, the integrated Soil Quality Index (SQI) model, which is based on standard scoring functions and the weight assignment approach, was used. A total of 14 soil quality parameters, based on the key predictor variables for determining rice yield, were included in the SQI model by grouping them within three indicator classes, namely physical, chemical and nutrient element content. Soil samples were collected from 160 grid points in total in the study area which had been divided into 600 m × 600 m grid squares. Very high-quality soil was not detected in the study area. However, 36.1% of the soil was classified as high quality whereas 23.2% of the total area had low and very low soil quality for rice cultivation. The SQI model provides comprehensive guidance for land allocation for the cultivation of rice and potentially for other crops.

High-resolution molecular stratigraphy of Oligocene\u2013Miocene sequence of Tumaco-1-ST-P well, Tumaco forearc Basin, Colombia

In the present work, high-resolution molecular stratigraphy technique has been applied to the rock samples from Tumaco-1-ST-P well to investigate vertical variations of the deposited organic matter (O.M.) based on screening parameter and high-resolution biomarkers in both saturate and aromatic fractions in order to establish its origin, organic facies, depositional paleoenvironment, thermal maturity, biodegradation processes and to evaluate the exploratory potential in this frontier forearc basin. The O.M. is immature with a high concentration of biolipids (early diagenesis) and with poor to fair generation potential originated from a type II/III or III kerogen. Original total organic carbon (TOCo) and original hydrocarbon index (HIo) values for each formation and lithology are determined to evaluate the hydrocarbons potential in the basin. n-alkanes, isoprenoids, and tricyclic terpanes suggest an algal/bacterial and terrestrial input deposited on a marine-deltaic shale under oxic to suboxic conditions. The O.M. was deposited on siliciclastic rocks in a marine-continental (transitional) environment, although carbonate rocks were also deposited in the bottom of the column (late Oligocene). The molecular stratigraphic interpretation allows to conclude that organic facies and lithology in Tumaco-1-ST-P are characterized in Cascajal and Tangareal del Mira Fms. (1000–5000 ft) by a marine-deltaic paleoenvironment with an important terrestrial contribution and varying between deltaic plain and prodelta during the late Miocene. At the top of Tumaco Fm (5000–9000 ft) in the late to medium Miocene, the depositional environment was like the marine delta of the Tangareal del Mira Fm, changing to a marine platform environment at 8000 to 10,000 ft depth in the middle to early Miocene. Toward the bottom of the column (10,000–12,000 ft), Tumaco Fm was deposited in the late Oligocene under a marine shelf environment. In the present paper, we propose a modeling approach, based on the evolution of the thermal maturity through the stratigraphic column, that at 17,000 feet depth could exist rocks with O.M. in the hydrocarbon generation window for Tumaco Basin, Colombia.

Use of NDVI and Landscape Metrics to Assess Effects of Riverine Inputs on Wetland Productivity and Stability

Alterations to Louisiana’s river systems and local hydrology have resulted in reduced freshwater, sediment, and nutrient inputs to wetland landscapes, causing significant negative impacts on marsh productivity and stability. This study set out to assess regional- and basin-scale impacts of river connectivity and sediment availability on wetland productivity. Satellite data were used in conjunction with river discharge, river sediment concentration, and wetland accretion data to evaluate correlations between river connectivity and wetland productivity and stability. Significant correlations were observed between river connectivity and Normalized Difference Vegetation Index (NDVI) and Aggregation Index (AI) values across a 10 year period of analysis. Moderate correlations (r2 = 0.51) between mean NDVI and AI values were observed for all wetland vegetation in coastal Louisiana. Middle Coast wetlands had the highest river connectivity and significantly higher aboveground productivity, spatial integrity, and wetland area. The Chenier Plain, with moderate sediment and nutrient inputs, consisted primarily of moderate productivity and integrity. The majority of the inactive Deltaic Plain, which is largely sediment deprived, consists of landscapes with the lowest wetland productivity and spatial integrity. This study linked wetland area, configuration, and productivity with river connectivity to provide an enhanced understanding of river and sediment importance for wetland stability and restoration.

Comparisons of Population Structure and Morphology of a Saltmarsh Keystone Species (Malaclemys terrapin) Across Coastal Louisiana

Diamondback terrapins (Malaclemys terrapin) are an ecologically important species in salt marsh habitats, and they occur along the Gulf of Mexico and the Atlantic coastlines of the USA. Terrapins are subjected to a myriad of threats including loss of coastal marsh/nesting habitat and differential adult mortality in fisheries bycatch. In Louisiana, knowledge of terrapin populations is lacking even though they likely face these same threats. To address this knowledge gap, we sampled terrapins across coastal Louisiana from 2011 to 2015 using unbaited fyke nets at six study sites. We sexed all individuals and measured morphometric characters (including plastron length, PL and carapace height, CH). We captured 1111 individuals at all sites, and each site was represented by ≥ 96 individuals. Skewed sex ratios were found at five of the six sites, while three of the six populations were lacking individuals in the 13–15 cm PL size classes. Male and female PL varied, with Chenier Plain males being larger than Deltaic Plain males, while Deltaic Plain females were larger than Chenier Plain females. Similarly, CH also varied, with Deltaic Plain males and females being relatively deeper than individuals from the Chenier Plain. A number of biotic, abiotic, and anthropogenic factors likely interplay to influence population structure, shell morphology, and demographics. However, the latter, including bycatch in crab traps, is possibly influencing terrapin population structure at some study sites via selective mortality of males and juvenile females. We suggest that future studies research the effects of anthropogenic factors on terrapin populations.

Exploring wetland transformations in moribund deltaic parts of India

Moribund deltaic part of Ganga–Padma region possesses hydro-ecologically precious dynamic wetlands of different kinds. The present paper endeavours to map, monitor wetlands and assess the changing hydro-ecological states of these in the moribund deltaic plain. Multi-temporal Landsat images since 1987–2016 are used for mapping and monitoring the wetlands. Normalized Difference Water Index (NDWI), Water Presence Frequency (WPF) approaches are applied for time series water body extraction and integration of water body maps for making frequency continuum of wetlands. The fragmentation analysis is done to show the transformation pattern of wetland landscape. Total wetland areas are 46.66 and 88.55 km2 in pre- and postmonsoon seasons respectively. Out of the total wetlands area of pre and postmonsoon seasons 18.21 km2 (54.09%), 35.83 km2 (62.14%) areas respectively have witnessed transformation from phase I (1987–1996) to phase III (2006–2016). The Fragmentation statistics shows that 35% of medium and large core wetlands have been changed into smaller one and numerous small wetlands have been lost. Different landscape ecological indices like Shannon's diversity index (SHDI) and Simpson's diversity index (SIDI) depict disaggregated pattern of wetlands. Maintenance of ecologically relevant channel flow and inundation is highly essential for minimizing transformation.