Evolution and preservation potential of fluvial and transgressive deposits on the Louisiana inner shelf: understanding depositional processes to support coastal management

The barrier-island systems of the Mississippi River Delta plain are currently undergoing some of the highest rates of shoreline retreat in North America (~20 m/year). Effective management of this coastal area requires an understanding of the processes involved in shoreline erosion and measures that can be enacted to reduce loss. The dominant stratigraphy of the delta plain is fluvial mud (silts and clays), delivered in suspension via a series of shallow-water delta lobes that prograded across the shelf throughout the Holocene. Abandonment of a delta lobe through avulsion leads to rapid land subsidence through compaction within the muddy framework. As the deltaic headland subsides below sea level, the marine environment transgresses the bays and wetlands, reworking the available sands into transgressive barrier shorelines. This natural process is further complicated by numerous factors: (1) global sea-level rise; (2) reduced sediment load within the Mississippi River; (3) diversion of the sediment load away from the barrier shorelines to the deep shelf; (4) storm-induced erosion; and (5) human alteration of the littoral process through the construction of hardened shorelines, canals, and other activities. This suite of factors has led to the deterioration of the barrier-island systems that protect interior wetlands and human infrastructure from normal wave activity and periodic storm impact. Interior wetland loss results in an increased tidal prism and inlet cross-sectional areas, and expanding ebb-tidal deltas, which removes sand from the littoral processes through diversion and sequestration. Shoreface erosion of the deltaic headlands does not provide sufficient sand to balance the loss, resulting in thinning and dislocation of the islands. Abatement measures include replenishing lost sediment with similar material, excavated from discrete sandy deposits within the muddy delta plain. These sand bodies were deposited by the same cyclical processes that formed the barrier islands, and understanding these processes is necessary to characterize their location, extent, and resource potential. In this paper we demonstrate the dominant fluvial and marine-transgressive depositional processes that occur on the inner shelf, and identify the preservation and resource potential of fluvio-deltaic deposits for coastal management in Louisiana.     

Polybrominated diphenyl ethers and their methoxylated analogs in mullet (Mugil cephalus) and sea bass (Dicentrarchus labrax) from Bizerte Lagoon, Tunisia

Concentrations of ten polybrominated diphenyl ethers (PBDEs) and eight methoxylated polybrominated diphenyl ethers (MeO-PBDEs) in mullet (Mugil cephalus) and sea bass (Dicentrarchus labrax) collected from the Bizerte Lagoon and the Mediterranean Sea were investigated. To the best of our knowledge, this is the first report of these compounds in marine fishes from Tunisia. The PBDE mean concentrations in fish from Bizerte Lagoon were 45.3 and 96.2 ng g(-1) lw respectively in mullet and sea bass, while the concentrations of these compounds in mullet and sea bass from Mediterranean Sea were 7.80 and 27.9 ng g(-1) lw respectively. MeO-PBDE concentrations in mullet and sea bass from Bizerte Lagoon ranged from 6.46 to 286 ng g(-1) lw and from 49.4 to 798 ng g(-1) lw respectively, while the concentrations of these compounds in mullet and sea bass from Mediterranean Sea ranged from 190 to 401 ng g(-1) lw and from 353 to 578 ng g(-1) lw respectively. The total PBDEs and total MeO-PBDEs concentration in fish from Bizerte Lagoon were similar or slightly lower than those reported for other species from other locations around the world.     

Determination of crustal movements in Turkey by terrestrial geodetic methods

In Turkey, neotectonic activity originated from the collision of the Arabian and Anatolian land masses during the Middle Miocene. As a result of the collision, westward escape of the Anatolian block introduced E-W compression in Western Turkey which began to be relieved by N-S extension. The North Anatolian Fault (NAF) is the major active strike-slip fault that was formed under the neotectonic regime. The rates of the motion along this fault estimated by several authors are in the range of 0.4–2.9 cm/a according to kinematic data. In Turkey, the first studies of crustal movements by geodetic methods were started in the west section of the NAF in 1972. So far, individual activities and studies coordinated by multidisciplinary projects have been realized in this region. The results obtained from available geodetic data indicate the motion of the Anatolian block relative to Eurasia.     

Mean wind-direction shear through a forest canopy

The equations of motion applying to the wind field in a forest canopy are simplified to a balance between the shearing stress gradient and either the form-drag of the leaves in the upper dense canopy, or the overall horizontal pressure gradient in the more open space beneath. The equations imply that, in descending through the forest, the stress and wind vectors turn through an angle which depends on the forest characteristics and on the stability and the speed of the airflow above the forest. The turning is roughly confirmed by an overall average measured on a very flat site near Thetford, Norfolk, covered by an extensive uniform pine forest.     

The Air Force Global Weather Central operational boundary-layer model

A limited-area seven-layer physical-numerical model for the lower tropospheric region (surface - 1600m) is described. The grid interval, approximately 190km, is half that of the standard numerical weather-prediction grid used in the hemispheric free atmospheric operational model at the Air Force Global Weather Central (AFGWC). This model is an integral part of the complete AFGWC meso-scale (sub-synoptic) numerical analysis and prediction system and is used to provide greater horizontal and vertical resolution in both numerical analyses and forecasts.Important features of this boundary-layer model include: a completely automated objective analysis of input data; the transport of heat and moisture by three-dimensional wind flow; latent heat exchange in water substance phase changes; and eddy fluxes of heat and water vapor.Input data are conventional synoptic surface and upper air reports. Other operational AFGWC prediction models provide input in the form of horizontal wind components at the upper boundary and an estimate of cloudiness above the boundary layer. Forecasts for the lower boundary and surface layer are empirically derived. Despite some approximations which broadly simplify the real planetary boundary-layer processes, operational use for highly weather-sensitive Air Weather Service support indicates that the model is capable of producing accurate detailed forecasts for periods of up to 24h.A modified version of this paper was presented at the IUGG-IAMAP-AMS conference on Planetary Boundary Layers at Boulder, Colo., 18–21 March, 1970, and at the 5th annual Congress of the Canadian Meteorological Society, at Macdonald College, 12–14 May, 1971.     

Some evaluations of drag and bulk transfer coefficients over water bodies of different sizes

Three recent experiments allow evaluation of the bulk transfer coefficients for momentum, water vapour and sensible heat over water bodies of different sizes. As part of a study of evaporation rates from a swamp, measurements of latent and sensible heat fluxes were made over Lake Wyangan in southern N.S.W., Australia. This lake is of several kilometers diameter. In a later experiment, Reynolds stress and sensible heat transfer were measured from a natural-gas platform standing in Bass Strait, south of mainland Australia. The most recent experiment involved the direct measurement of each of these turbulent fluxes from a fixed tower erected in Lake Michigan, U.S.A.Perhaps the most important of the results is the finding that drag coefficients measured over Bass Strait are not significantly different from those over Lake Michigan, despite the obvious differences in depth, fetch, and hence surface wave structure. At both locations, drag coefficients are found to increase slightly with increasing wind speed, while at low wind speeds they are not significantly different from those corresponding to aerodynamic smoothness.Near-neutral bulk transfer coefficients for sensible heat and for water vapour are found to be similar. An average value of about 1.4 × 10^–3 is obtained.It is emphasized that stability effects should be considered in any discussion of drag coefficients or bulk transfer coefficients. Large errors can result if near-neutrality is incorrectly assumed.     

The Darfur Dome,western Sudan: the product of a subcontinental mantle plume

Field investigations, K-Ar age determinations and chemical data were used to describe the development of an intraplate volcanic province, the Darfur Dome, Sudan. Magmatism started 36 Ma ago at a small subvolcanic complex (Jebel Kussa) in the center of the dome and was active in the same area between 26 and 23 Ma. Two major volcanic fields (Marra Mountains and Tagabo Hills) developed between 16 and 10 Ma. Volcanism started again at 6.8 Ma with a third volcanic field (Meidob Hills) and at 4.3 Ma in the Marra Mountains and with the reactivation of the center. Activity then continued until the late Quaternary. Having started in the center of the Darfur Dome, volcanism moved in 36 Ma 200 km towards the NNE and 100 km SSW No essential difference in the alkaline magma types (basanitic to phonolitic-trachytic, with different amounts of assimilation of crustal material) in the different fields, was observed. Magmatism is thought to have been produced by a rising mantle plume and volcanism was triggered by stress resolution along the Central African Fault Zone.     

Determination of organophosphorus insecticide residues in the rice paddies

In most rice paddies in Mazandaran Province, diazinon is applied to control Chilo suppressalis. Due to the extensive application of insecticides in the rice paddies of the Caspian coasts of Iran, this investigation was carried out on the rice fields in order to obtain the necessary data and information on the concentration of insecticide residues. A total of 125 samples were taken from five areas of Amol township in 2007. Then, according to the analysis of variance procedures, the water samples were statistically analyzed after the spraying of diazinon. Results indicate that the insecticide was used frequently to control stem boring caterpillar of rice. The residuals of this toxic chemical were observed in the majority of stations from the day after the spraying until one to two months later. The greatest level of diazinon was observed in station 1 in amount of 1.14 ppm. This study revealed that the physical and chemical properties of the studied diazinon such as fumigation characteristic as well as the ecological conditions and soil type influence the reduction and eventual removal of the insecticides during the cultivation and harvest periods.     

Strain softening of K0-consolidated Changi sand under plane-strain conditions

Experimental results are presented in this paper to study the strain softening behaviour of a marine dredged sand under plane-strain conditions. K₀ consolidated drained and undrained tests were conducted using a new plane-strain apparatus to characterize the strain softening behaviour of the sand under plane-strain conditions. For medium dense specimens, strain softening and shear bands were observed to occur under both drained and undrained conditions. For very loose specimens, no shear bands were observed and critical states were reached within the homogeneous deformation region in both drained and undrained tests. Strain softening was observed to occur at small strain for very loose specimens under undrained conditions. Two types of strain softening, the homogenous softening and banding softening, were identified and the conditions for strain softening were established. The results obtained from this study were compared with the studies by Han and Vardoulakis (Géotechnique 41(1):49–78, 1991), Finno et al. (J Geotech Eng ASCE 122(6):462–473, 1996, Géotechnique 47(1):149–165, 1997) and Mokni and Desrues (Mech Cohes-Frict Mat 4:419–441, 1998).