Growth and Anchorage of Myriophyllum spicatum L. in Relation to Water Depth and the Content of Organic Matter in Sediment

A large body of evidence suggests that the physical and chemical characteristics of the sediment in lakes that have undergone eutrophication have been significantly altered. However, the effects of alterations in sediments on submersed macrophytes remain unknown. In this study, we present the results of an outdoor experiment that examined how the growth and anchorage of the widespread submersed macrophyte Myriophyllum spicatum L. responded to the enrichment of organic matter in the sediments and whether water depth affects these responses. We found that low levels of enrichment with organic matter (≤7%) enhanced the growth of M. spicatum. In contrast, high levels of enrichment with organic matter (from 12 to 18%) slightly inhibited its growth. Although the anchorage force of M. spicatum slightly decreased with an increase in the content of organic matter in the sediment, it was much higher than the hydraulic drag force on plants at a relatively high current velocity, indicating that the plants were unlikely to be uprooted in these sediments. The water depth did not alter the responses of growth and anchorage of M. spicatum to enrichment with organic matter. Our results suggest that M. spicatum could be a potential species to restore eutrophic lakes, since it can grow well and anchor stably in sediments with relatively high organic matter and manage low light stress.

Modelling of Tsunami Forces on Coastal Structures: a Review

This paper reviews methods applicable to assess the impact of tsunami forces on coastal structures. Countries affected by tsunamis have proven that this environmental disaster has costed billions of losses, such as the event occurred during year 2004 Andaman tsunami. Therefore, there is a need to assess the structural behaviour upon the impact of tsunami forces in order to minimize the damages and to ensure that coastal structures are able to sustain loading from high current-velocity waves. Currently in practice, there are two approaches of accessing the impacts of tsunami on structures namely physical modelling and experiment or numerical modelling and simulation. Numerical modelling methods are expected to produce acceptable analysis on the stability and condition of structures subjected to tsunami loadings since it incorporates several important parameters which are not implemented in physical modelling. The result from this study is expected to prompt engineers and relevant authorities to revise the current design guidelines on coastal structures which could sustain possible tsunami event in the future.

Water quality and potamoplankton evaluation of the Nile River in Upper Egypt

Aim: The composition, abundance, community structure of potamoplankton and major physical and chemical variables of the Nile water in Upper Egypt were investigated to assess its status in different seasons during 2007.MethodsWater samples were collected seasonally during 2007 from six investigated sites from variable depths at levels of 0, 2.5 and 5 m. The area of this investigation is defined as the southern 120 Km of the main stream of the Nile in Upper Egypt (24° 04’ – 25° 00’ latitudes and 32° 51’ – 32° 54’ longitudes), downstream of Aswan Old Dam.ResultsAltogether, 121 potamoplankton species, of which 85 related to phytoplankton and 36 appertaining to zooplankton were recorded. Most numerous phytoplankton were Chlorophyceae (42 species) followed by Bacillariophyceae (30 species). Cyanobacteria and Dinophyceae were less numerous with only 11 and 2 species, respectively. Zooplankton species were mainly belonging to three systematic groups namely; Rotifera (24 species), Copepoda (3 species) and Cladocera (9 species). Besides, other rare zooplankton including Platyhelminthes, Nemata and Ciliophora were sparsely encountered. The main hydrological conditions characterizing the investigated area include water level fluctuations (˂82 - ˃85 m above sea level), relatively high current velocity (0.8 - 1.3 m sec–1) and disposal of wastewater. Plankton populations were variably but rather weakly dependent on the major nutrients due to their excessive availability in accessible form for uptake by the producers. For phytoplankton, the community structure was categorized in relation to temperature, pH, SO42– and Mg2+. For zooplankton, the community structure was categorized in relation to conductivity as well as Mg2+. Sampling intervals were inadequate to demonstrate the existing successional pattern of the Nile potamoplankton community. Alterations in the phytoplankton community structure accompanied changes in water temperature represented by the alternate dominance between diatoms and cyanobacteria, while zooplankton community was always dominated by rotifers. Phytoplankton populations were numerically more abundant in autumn and zooplankton peaked in spring.ConclusionsWastewater disposal restricted the abundance of the Nile zooplankton assemblages mainly due to the numerical decline of Rotifera and Cladocera. Otherwise, wastewater did not exert major limits for phytoplankton. The data obtained in this investigation will be crucial to understand potamoplankton regulation and contribute to the knowledge regarding the Limnology of the Nile basin.

A Revised Methodology for the Calculation of Wellhead Fatigue due to VIV

In regions of high current velocity such as East Africa, South America and the GoM, VIV (Vortex Induced Vibrations) of drilling riser systems is a very real risk. Much work has been carried out by the offshore industry in order to predict the VIV and resultant fatigue in top tensioned production and drilling risers and to develop standardized methodologies for performing these calculations. In addition a number of commercially available VIV analysis tools have been developed over the years. These VIV analysis tools and industry methodologies however, are focused on the global response of the riser string alone and have not been developed to account for the intricacies of wellhead loading & stress distributions. VIV response of the top tensioned riser (TTR) system (whether production TTR or drilling riser) results in load transfer into the wellhead via VIV induced motions. As commercially available VIV analysis tools generally only consider a riser model consisting of a slender beam, the more complex geometry and load path associated with the wellhead and conductor are not accurately modeled. Thus VIV induced damage of the wellhead cannot be predicted with confidence using these VIV analysis tools alone. Based on a review and critique of both existing and proposed methods it has become apparent that existing methods for the calculation of VIV induced fatigue of the wellhead and conductor system are overly conservative and do not capture the level of detail required to predict the level of fatigue damage with confidence. Thus a revised methodology for calculation of wellhead and conductor fatigue due to VIV is required to build up a more representative picture of the associated fatigue damage accumulation. Proposed VIV fatigue calculation methodologies, including the use of VIV analysis tools alone and application of the results of the VIV analysis tools in combination with non-linear global finite element models, are described and the challenges associated with each are discussed herein.

Distributed Wake-Body Resonance of a Long Flexible Cylinder in Shear Flow

The fluid-structure interaction mechanisms involved in the development of narrowband and broadband vortex-induced vibrations of long flexible structures placed in non-uniform currents are investigated by means of direct numerical simulation. We consider a tensioned beam of aspect ratio 200, free to move in both the in-line and cross-flow directions, and immersed in a sheared flow at Reynolds number 330. Both narrowband and broadband multi-frequency vibrations may develop, depending on the velocity profile of the sheared oncoming current. Narrowband vibrations occur when lock-in, i.e. the synchronization between vortex shedding and structure oscillations, is limited to a single location along the span, within the high current velocity region; thus, well-defined lock-in versus non-lock-in regions are noted along the span. In contrast, we show that broadband responses, where both high and low structural wavelengths are excited, are characterized by several isolated regions of lock-in, distributed along the length. The phenomenon of distributed lock-in impacts the synchronization of the in-line and cross-flow vibrations, and the properties of the fluid-structure energy transfer, as function of time and space.

The use of otolith chemistry to determine the juvenile source of spawning cod in Icelandic waters

Thorisson, K., Jónsdóttir, I. G., Marteinsdottir, G., and Campana, S. E. 2011. The use of otolith chemistry to determine the juvenile source of spawning cod in Icelandic waters. – ICES Journal of Marine Science, 68: 98–106. Chemical fingerprinting was used to discriminate spatial groups of juvenile cod (Gadus morhua) and to backtrack spawning cod in Icelandic waters to their area of origin as 0-group juveniles. Juvenile 0-group cod were collected around Iceland in August 1996 and 1997 to establish the spatial distribution of otolith chemistry at the juvenile stage. Spawning cod from the same year classes were sampled in the same areas in April 2002 and April/May 2003. The core, corresponding to the juvenile otolith, was extracted from the adult otolith and its content of Ba, Mn, and Sr compared with the chemistry of whole otoliths of juveniles of the same year class. High Atlantic inflow into the shelf area north of Iceland in 1997 mixed the juveniles from different areas, and the spawners of that year class were not backtraceable to their origin. For the 1996 year class, however, mixed-stock analysis indicated that most of the spawning cod northwest, north, and northeast of Iceland originated from juveniles off the central part of the north coast. Using otolith chemistry to backtrace the origin of spawners appears well suited for areas with limited mixing, but less well suited for areas or years of high current velocity.

Numerical Simulation of a Pipeline Installation Procedure at the Negro River

The installation of pipelines is among the most challenging offshore operations. Conventional offshore pipeline installation operations in Brazil have been performed in an S-Lay procedure employing the BGL-1 barge, owned by Petrobras. The BGL-1 is a second generation lay barge and performs installation operations by moving forward using its own mooring lines. The objective of this work is to present the numerical simulation of a pipeline installation operation performed at a particular scenario, Negro river in the Amazon forest. The high current velocity, very irregular bathymetry and heterogeneous soil make this procedure a real challenge. The numerical simulations employ the SITUA-Prosim computational tool, which is able to incorporate the correct definition of the bottom from bathymetric curves. The two crucial points in the performed analyses are: (a) first, to verify if it is possible to move the barge using its own mooring lines in such environmental condition and (b) second, to analyze the pipeline behavior in such scenario.

Revision of the pentacrinid stalked crinoids of the genus Endoxocrinus (Echinodermata, Crinoidea), with a study of environmental control of characters and its consequences for taxonomy

A revision of the stalked crinoid species attributed to the genus Endoxocrinus A.H. Clark, 1908 (Diplocrininae, Pentacrinitidae, Crinoidea, Echinodermata) is conducted using studies on phenotype variation and its relation with environment. Specimens collected via submersible at five sites in the Bahamas exhibit distinct phenotypes that correlate with different apparent ecological niches and serve as references for interpreting specimens dredged in Atlantic and Pacific Oceans where detailed information on their benthic environment is unknown. Documentation of ecophenotypic convergences or divergences allows us to distinguish between adaptive characters and those revealing genetic affinities, and to discuss allopatric evolution and bathymetric zonation. The results suggest the following taxonomy: the genus Endoxocrinus is subdivided into two subgenera, i.e., Endoxocrinus A.H. Clark, 1908 and Diplocrinus Döderlein, 1912 (Annacrinus A. H. Clark, 1923 becomes a junior synonym of Diplocrinus); the subgenus Endoxocrinus is monospecific with E. (E.) parrae [Gervais (in Guérin, 1835)] from the western tropical Atlantic; the subgenus Diplocrinus includes E. (D.) alternicirrus (Carpenter, 1882) from the western and central Pacific, E. (D.) maclearanus (Thomson, 1872) from the western tropical Atlantic, and E. (D.) wyvillethomsoni (Jeffreys, 1870) from the northeastern Atlantic. Endoxocrinus (E.) parrae includes three subspecies adapted to different habitats and depths: E. (E.) parrae parrae usually in 154–518 m with moderate to high current velocity and moderate turbulence to laminar flow, E. (E.) parrae carolinae (A.H. Clark, 1934) in 504–724 m with moderate current velocity and high turbulence, and E. (E.) parrae prionodes H.L. Clark, 1941 in 402–832 m with high current velocity in laminar flow. E. (D.) alternicirrus includes two subspecies, E. (D.) alternicirrus alternicirrus in 625–1476 m and E. (D.) alternicirrus sibogae (Döderlein, 1907) usually in 364–800 m. E. (D.) maclearanus has a depth range of 432–878 m and occurs as a dwarf variety minimus n. var. in high current velocities and high turbulence. E. (D.) wyvillethomsoni from depths of 1214–2070 m lives on various substrates under a variety of hydrodynamic conditions.

Experimental Validation of a Quasi-Explicit Hydrodynamic Model: Fishtailing Instability of a Single-Point Moored Tanker in Rigid-Hawser Configuration

The extended hydrodynamic model derived in Simos et al (2001), where the yaw velocity terms have been incorporated to the model proposed by Leite et al (1998) while preserving its quasi-explicit feature, is used here to study some typical dynamic problems of moored ships, specifically the fishtailing shtailing instability that may occur in a single-point mooring (SPM) system. Since the intention was to check the hydrodynamic model, the hawser was assumed rigid to avoid the complex dynamics that may occur when the actual hawser slackens and the obtained results were confronted with experimental ones, obtained at the IPT wave tank. The agreement is very good in the sense that not only the limit-cycle amplitudes are compatible but also the time series are very similar. For the VLCC model in ballasted condition (40%) the fishtailing shtailing instability occurs only for a relatively high current velocity and some Froude effect is then detectable. Using results from the static bifurcation experiment an ad hoc correction is proposed for such effect, showing a relatively close agreement between experiments and the theoretical model. This Froude effect correction is, however, not relevant for an actual SPM system subjected to a usual ocean current.