Variation in suspended sediment concentration during storm discharges in three small streams in upper osun basin,Central Western Nigeria

The suspended sediment concentration response of three small streams draining quartzites and quartz-schists in southwestern Nigeria to storms of varying magnitude are presented. A total of 1468 water samples from 62 storm responses with peak stream discharge values ranging from 80 to 120 l s^?2 were analysed and storm and suspended sediment concentration hydrographs and hysteresis loops were used to depict the response patterns. The six different types of responses identified include the single and multiple discharge peak rises with sediment lead and lag and also the mixed response patterns. Both valley slope and channel erosion constituted important sources of suspended sediment. However, sediment availability, exhaustion, and flushing effects determined the variation in the different response types.     

Biogeochemistry of sterols in plankton, settling particles and recent sediments in a cold ocean ecosystem (Trinity Bay, Newfoundland)

In the context of a multidisciplinary study to determine current and past ecosystem health and the relative contributions of sources of organic matter (marine vs. terrestrial and natural vs. anthropogenic input), sterols were determined in plankton, settling particles and sediments from Trinity Bay, Newfoundland, a sub-polar Atlantic Ocean ecosystem. The centric diatoms Chaetoceros spp., Thalassiosira spp. and Leptocylindrus danicus were all prominent in the plankton samples, and centric diatoms predominated in the settling particles. Plankton samples contained 0.4±0.4 mg/g dw (1995) or 1.4±1.3 mg/g dw (1996) total sterols, with cholesta-5,24-dien-3β-ol (mean 26% of total sterols), cholest-5-en-3β-ol (24%) and cholesta-5,22(E)-dien-3β-ol (13%) chief among these, denoting diatom and zooplankton sources. In settling particles, the prominence of cholesta-5,24-dien-3β-ol (24%), cholest-5-en-3β-ol (24%), cholesta-5,22(E)-dien-3β-ol (13%) and 24-methylcholesta-5,22(E)-dien-3β-ol (9%) again suggested mainly marine sources. The sterol composition of plankton and settling particles from different sampling periods showed a high degree of consistency. Higher plant C₂₉ sterols (notably 24-ethylcholest-5-en-3β-ol, 9–26%) were prominent in sediments from both inshore and offshore sites. No decreasing trend in total or individual sterols was observed down the 30-cm sediment cores, suggesting good overall preservation. No 5β-stanols such as 5β-cholestan-3β-ol (coprostanol) were detected in offshore sediments, plankton or settling particles, with only low levels (5β-cholestan-3β-ol max. 4.4%, 5β-cholestan-3α-ol max. 5.1%) in certain inshore sediments. This suggests that raw sewage discharges in rural Newfoundland are being efficiently degraded or dispersed, or that inputs are highly localized. Source apportionation of organic matter in the sediment samples based on sterol composition was attempted. This highlighted the large terrestrial contribution to the sterols in marine sediments (up to 58% of sterols inshore, 24% offshore) and suggests either degradation or effective recycling of marine sterols.     

Preliminary study on responses of marine nematode community to crude oil contamination in intertidal zone of Bathing Beach, Dalian

This study investigated the responses of marine nematodes to crude oil contamination in polluted and relatively uncontaminated sites in Dalian Xingang, China, 40 days after an oil spill. Samples were taken at different tide levels on the beach and at different positions along the beach. We present the results of a comparison of nematode assemblages from undisturbed sediment from the Xiajiahezi Bathing Beach with those from sediment from the Xinghai Bathing Beach contaminated with crude oil. A total of 1666 nematodes from 26 genera were found in this study. Results showed significant differences in nematode assemblages between samples from undisturbed controls and those from the polluted area. Nematode abundance, number of species, diversity and species richness decreased significantly with increasing levels of crude oil contamination. Fifteen genera were eliminated and seemed to be composed of species intolerant to crude oil contamination; only the abundance of Marylynnia sp. increased slightly.     

Temporal and geographical trends in the genotoxic effects of marine sediments after accidental oil spill on the blood cells of striped beakperch (Oplegnathus fasciatus)

To determine the impact of genetic toxicity caused by the Hebei Spirit oil spill on December 7, 2007, we measured DNA damage in the blood cells of striped beakperch in vitro after exposure to extracts from sediments in the Taean area. The objective of this study was to investigate temporal changes of toxic effects caused by residual PAHs in the sediments up to 18 months after an oil spill. In conclusion, DNA damage had reduced over this 18-month period; that is, the sediments recovered quickly from the oil pollution. In addition, statistically significant correlations between PAHs and DNA damage were observed. Because the comet assay is sensitive to DNA damage induced by genotoxic substances from the polluted sediments, the comet assay can be considered a useful tool as a biomarker in investigating genetic toxicity in environmental monitoring and elucidating the recovery of oil pollution after oil spill as well.     

Metal (Al, Fe, Mn and Cu) distributions and origins of polycyclic aromatic hydrocarbons (PAHs) in the surface sediments of the Marmara Sea and the coast of Istanbul, Turkey

In this study, total metal (Al, Fe, Mn and Cu) and PAHs analyses have been done in the surface sediments. Sediment samples have been collected from seven parts of the Marmara Sea and the coast of Istanbul during 2009. Total Al, Fe, Mn and Cu contents vary between 1.8% and 5.4%; 1.1% and 2.8%; 122 and 259 μg g⁻¹; 27 and 416 μg g⁻¹, respectively. EF and CF values of Fe and Mn are lower than 1.5 and 1, respectively, in all the stations. Total PAH contents range between 135 and 6009 ng g⁻¹ in the surface sediments. The origin of PAHs has been found pyrolitic according to the Phe/Ant ratio in the all stations. Contrastingly, at K0, MKC and MY1 Stations, PAH origins have been observed petrogenic according to the Flu/Pyr ratio.     

Parameterization of bedform morphology and defect density with fingerprint analysis techniques

A novel method for parameterizing the morphology of seafloor ripples with fingerprint analysis numerical techniques is presented. This fully automated analysis tool identifies rippled areas in two-dimensional imagery of the seafloor, and returns ripple orientation and wavelength as well as a new morphological parameter, the spatial density of ripple defects. In contrast to widely used manual and spectral parameterization methods, this new technique yields a unique probability distribution for each derived parameter, which describes its spatial variability across the sampled domain. Here we apply this new analysis technique to synthetic and field collected side-scan sonar seafloor images in order to assess the methods capacity to define bed geometry across a wide range of simulated and observed morphological conditions. The resulting orientation and wavelength values compare favorably with those of the existing manual and spectral parameterization methods, and are superior under environmental conditions characterized by low signal to noise ratios as well as high planform ripple sinuosity. Furthermore, the resulting ripple defect density values demonstrate correlation with ripple orientation, wave direction, and the Shields parameter, which is consistent with recent investigations that have theoretically linked this parameter to hydrodynamic forcing conditions. The presented fingerprint analysis method surpasses the capacity of existing methods for ripple parameterization and promises to yield greater insight into theoretical and applied problems associated with the temporal and spatial variability of ripple morphology across a wide spectrum of marine environments.     

Benthic biogeochemical cycling of mercury in two contaminated northern Adriatic coastal lagoons

Previous research recognized most of the Northern Adriatic coastal lagoon environments as contaminated by mercury (Hg) from multiple anthropogenic sources. Among them, the Pialassa Baiona (P.B.) Lagoon, located near the city of Ravenna (Italy), received between 100 and 200 tons of Hg, generated by an acetaldehyde factory in the period 1957-1977. Further east, the Grado Lagoon has been mainly affected by a long-term Hg input from the Idrija mine (western Slovenia) through the Isonzo River since the 16th century. Hg cycling at the sediment-water interface (SWI) of the two lagoons was investigated and compared by means of an in situ benthic chamber, estimating diffusive Hg and Methyl-Hg fluxes in the summer season. Major chemical features in porewaters (Fe, Mn, H₂S, dissolved inorganic (DIC) and organic carbon (DOC), nutrients) and in the solid phase (C_org, N and S) were also explored to understand the general biogeochemical conditions of the system in response to benthic respiration. The daily integrated flux for the methylated Hg form was extremely low in P.B. Lagoon, accounting for only 7% of the corresponding flux calculated for the Grado Lagoon. Despite a higher sedimentary Hg content in the P.B. Lagoon (14.4-79.0 μg g⁻¹) compared to the Grado Lagoon (10.7-12.5 μg g⁻¹), the in situ fluxes of Hg in the two experimental sites appeared similar. A selective sequential extraction procedure was applied to the solid phase, showing that the stable crystalline mineral phase cinnabar (HgS) is the predominant Hg fraction (about 50%) in the Grado Lagoon surface sediments. Conversely, Hg mobilization and sequestration in the P.B. Lagoon is related to the extremely anoxic redox conditions of the system where the intense sulfate reduction, by the release of sulfur and the formation of sulfides, limits the metal recycling at the SWI and its availability for methylation processes. Thus, the environmental conditions at the SWI in the P.B. Lagoon seem to represent a natural “barrier” for the potential risk of Hg transfer to the aquatic trophic chain.     

Curvilinear immersed boundary method for simulating coupled flow and bed morphodynamic interactions due to sediment transport phenomena

The fluid-structure interaction curvilinear immersed boundary (FSI-CURVIB) numerical method of Borazjani et al. [3] is extended to simulate coupled flow and sediment transport phenomena in turbulent open-channel flows. The mobile channel bed is discretized with an unstructured triangular mesh and is treated as a sharp-interface immersed boundary embedded in a background curvilinear mesh used to discretize the general channel outline. The unsteady Reynolds-averaged Navier-Stokes (URANS) equations closed with the k − ω turbulence model are solved numerically on a hybrid staggered/non-staggered grid using a second-order accurate fractional step method. The bed deformation is calculated by solving the sediment continuity equation in the bed-load layer using an unstructured, finite-volume formulation that is consistent with the CURVIB framework. Both the first-order upwind and the higher-order hybrid GAMMA schemes [12] are implemented to discretize the bed-load flux gradients and their relative accuracy is evaluated through a systematic grid refinement study. The GAMMA scheme is employed in conjunction with a sand-slide algorithm for limiting the bed slope at locations where the material angle of repose condition is violated. The flow and bed deformation equations are coupled using the partitioned loose-coupling FSI-CURVIB approach [3]. The hydrodynamic module of the method is validated by applying it to simulate the flow in an 180° open-channel bend with fixed bed. To demonstrate the ability of the model to simulate bed morphodynamics and evaluate its accuracy, we apply it to calculate turbulent flow through two mobile-bed open channels, with 90° and 135° bends, respectively, for which experimental measurements are available.     

Macroinvertebrates in the bed sediment of the Yellow River

Extensive agricultural,industrial and urban development in the Yellow River,China,have modified the sediment-water balance,flow and inundation regimes,longitudinal connectivity,integrity of riparian vegetation,and water quality.Macroinvertebrate assemblages in the bed sediment of main channel and major reservoirs of the Yellow River are described in detail for the first time.A total of 74 taxa comprising 17 taxa of oligochaetes,48 taxa of aquatic insects,5 taxa of molluscs,and 4 taxa of other animals were recorded.A range of feeding guilds were represented,including, collector-gatherers(32 taxa),predators(17 taxa),scrapers(16 taxa),shredders(6 taxa)and collector-filterers(2 taxa).Both the mean density and biomass of macroinvertebrates were significantly higher in sites located in the artificial reservoirs compared with the main river channel. Assemblages varied spatially;Oligochaetes dominated assemblages in upper reaches,insects dominated in middle reaches and other animals(e.g.Crustacea)dominated in lower reaches. Collector-gatherers were dominant throughout the entire river.Classification analysis identified five site-groups on the basis of macroinvertebrate presence/absence:downstream of reservoirs;vegetated sites;reservoir sites;polluted sites,and;lower-reach sites.Lower macroinvertebrate richness,density and biomass,compared with other similar large rivers,were attributed to modification of the sediment-water balance and associated disturbance of benthic habitats.Pollution,stability of sediment and sediment concentration combined to influence the distribution of macroinvertebrates.This knowledge will substantially benefit the recent focus on the health and environmental water requirements of the Yellow River.     

Effects of hydraulic structures on river morphological processes

Study of hydraulic structures such as groins and bandal-like structures can provide valuable information on their influences on morphological processes in natural rivers.These structures usually used for bank protection and formation of deep navigation channel can locally create complex flow patterns,reduce flow velocities and also increase the flood levels.Most of the previous studies are focused on structures like groins under non-submerged flow condition.However,the recent demand of nature friendly low cost and sustainable methods for river bank protection and channel formation leads to the necessity of study different type of structures like bandal-like structures.In this context, this study investigates the flow characteristics and sediment transport process influenced by bandal-like structures through laboratory experiments.The experiments were carried out under live-bed scour condition with sediment supplied from the inlet for two submergence(non-submerged and submerged)conditions.The experimental measurements contribute to better understand the mechanism of deposition/erosion process around different type of hydraulic structures.The performance of bandal-like structures considering the erosion around the structures,the deposition near the bank and the formation of deep main channel show promising results compared with conventional structures such as groins(impermeable and permeable ones).