Infiltration effects on sediment mobility under waves

Sediment mobility measurements with a horizontal sand bed under non-breaking waves are reported. Conditions include no seepage and steady downward seepage corresponding to head gradients up to 2.5. The results indicate that infiltration tends to inhibit sediment mobility for a horizontal bcd of 0.2 mm quartz sand exposed to moderated wave induced bed shear stresses. The effect is weak for the parameter range of the present study. The two opposing effects of shear stress increase due to boundary layer thinning and the stabilizing downward drag are successfully accounted for through the modified Shields parameter of Nielsen [Nielsen, P., 1997. Coastal groundwater dynamics. Proc. Coastal Dynamics '97, Plymouth, ASCE, Dp, 546-555] using coefficients derived from independent studies. That is, from the shear stress experiments of Conley [Conley, D.C., 1993. Ventilated oscillatory boundary layers. PhD Thesis, University of California, San Diego, 74 pp.] and the slope stability experiments of Martin and Aral [Martin, C.S. and M.M. Aral, 1971. Seepage force on interfacial bed particles. J. Hydraulics Div., proc. ASCE, Vol. 97, No. Hy7, pp. 1081-1100]. (C) 2001 Elsevier Science B.V. All rights reserved.

Historical PCDD Inputs and Their Source Implications from Dated Sediment Cores in Queensland (Australia)

Recent investigations have demonstrated the presence of an unidentified source of polychlorinated dibenzo-p-dioxins (PCDDs) in the coastal zone of Queensland (Australia). The present study provides new information on the possible PCDD sources and their temporal input to this environment. Two estuarine sediment cores were collected in northern Queensland for which radiochemical chronologies were established. Core sections from different depositional ages, up to three centuries, have been analyzed for 2,3,7,8-substituted PCDDs and polychlorinated dibenzofurans (PCDFs). Variations of PCDD concentrations in the sediment cores over several centuries of depositional history were relatively small, and elevated PCDD levels were still present in sediment slices from the early 17th century. PCDD/F isomer patterns and congener profiles in sediments deposited during the last 350 years were almost identical and correlated well to the characteristic profiles observed in surface sediments and soils from the entire Queensland coastline. Profiles were dominated by higher chlorinated PCDDs, in particular octachlorodibenzodioxin (OCDD), whereas PCDF concentrations were below or near the limit of detection. These results indicate the presence of a PCDD source prior to industrialization and production of commercial organochlorine products. Further, the present study demonstrates that PCDD input patterns have been similar along an extensive but localized area over at least several centuries, contributing relatively high concentrations of PCDDs to the coastal system of Queensland.

PCDDs in the water/sediment-seagrass-dugong (Dugong dugon) food chain on the Great Barrier Reef (Australia)

Polychlorinated dibenzo-p-dioxin (PCDD) and dibenzofuran (PCDF) concentrations were measured in sediment and seagrass from five locations in or adjacent to the Great Barrier Reef Marine Park. A full spectrum of Cl(5-8)DDs were present in all samples and, in particular, elevated levels of Cl8DD were found. PCDFs could not be quantified in any samples. The PCDD concentrations ranged over two orders of magnitude between sites, and there was a good correlation between sediment and seagrass levels. There were large quantities of sediment present on the seagrass (20-62% on a dry wt. basis), and it was concluded that this was a primary source of the PCDDs in the seagrass samples. The PCDD levels in the seagrass samples were compared with the levels in the tissue of three dugongs stranded in the same region. The relative accumulation of the 2,3,7,8-substituted PCDD congeners in the dugongs decreased by over two orders of magnitude with increasing degree of chlorination. This was attributed to the reduced absorption of the higher chlorinated congeners in the digestive tract, a behaviour that has been observed in other mammals such as domestic cows. (C) 2001 Elsevier Science Ltd. All rights reserved.

Sediment yield and impacts from river catchments to the Great Barrier Reef lagoon

Land use intensification is estimated to result in an overall increase in sediment delivery to the Great Barrier Reef lagoon by a factor of approximately four. Modelling suggests that, following land use intensification, croplands cause the greatest increase of sediment yield and sediment concentration, whereas erosion of grazing land is the main contemporary source of sediments, primarily owing to the large spatial extent of this land use. The spatial pattern of sediment yield to the coast after land use intensification is strongly correlated with the pattern under natural conditions, although the greatest increase is estimated to have occurred in the wet-dry catchments. Sediment transport and resuspension processes have led to the development of a strongly sediment-partitioned shelf, with modern mud-rich sediments almost exclusively restricted to the inner and inner-middle shelf, northward-facing embayments and in the lee of headlands. Elevated sediment concentrations increase the potential transport rates of nutrients and other pollutants. Whether increased sediment supply to the coastal zone has impacted on reefs remains a point of contention. More sediment load data need to be collected and analysed in order to make detailed estimates of catchment yields and establish the possible sediment impact on the Great Barrier Reef.

Shear stress and sediment transport calculations for swash zone modelling

It is shown that the observed difference in sediment transporting efficiency by the swash uprush, compared with the downrush, could be mainly due to greater bed shear stress for a given velocity in the more abruptly accelerated uprush. The bed shear stress generated by an arbitrary free stream velocity time series is modelled in terms of usual wave boundary layer models plus a phase lead (phi(tau) of the bed shear stress compared with the free stream velocity at the peak frequency. With this approach, the total transport amounts in uprush and downrush can be modelled satisfactorily with the same sediment transport formula, without the need for different uprush and downrush coefficients. While the adaptation of sediment transport formulae from steady flow can thus lead to the right total amounts of sediment moved by this method, the timing of the instantaneous sediment transport rates are probably not accurately modelled due to the highly unsteady nature of the swash and the presence of pre-suspended sediment in the uprush. Nevertheless, the proposed method is a useful intermediate step before we have a complete understanding of sediment transport under very rapid accelerations and of the relative contribution of pre-suspended sediment to the onshore sediment transport in swash zones. (C) 2002 Published by Elsevier Science B.V.

Shear stress and sediment transport calculations for sheet flow under waves

A simple method is provided for calculating transport rates of not too fine (d(50) greater than or equal to 0.20 mm) sand under sheet flow conditions. The method consists of a Meyer-Peter-type transport formula operating on a time-varying Shields parameter, which accounts for both acceleration-asymmetry and boundary layer streaming. While velocity moment formulae, e.g.., = Constant x calibrated against U-tube measurements, fail spectacularly under some real waves (Ribberink, J.S., Dohmen-Janssen, C.M., Hanes, D.M., McLean, S.R., Vincent, C., 2000. Near-bed sand transport mechanisms under waves. Proc. 27th Int. Conf. Coastal Engineering, Sydney, ASCE, New York, pp. 3263-3276, Fig. 12), the new method predicts the real wave observations equally well. The reason that the velocity moment formulae fail under these waves is partly the presence of boundary layer streaming and partly the saw-tooth asymmetry, i.e., the front of the waves being steeper than the back. Waves with saw-tooth asymmetry may generate a net landward sediment transport even if = 0, because of the more abrupt acceleration under the steep front. More abrupt accelerations are associated with thinner boundary layers and greater pressure gradients for a given velocity magnitude. The two real wave effects are incorporated in a model of the form Q(s)(t) = Q(s)[theta(t)] rather than Q(S)(t) = Q(S)[u(infinity)(t)], i.e., by expressing the transport rate in terms of an instantaneous Shields parameter rather than in terms of the free stream velocity, and accounting for both streaming and accelerations in the 0(t) calculations. The instantaneous friction velocities u(*)(t) and subsequently theta(t) are calculated as follows. Firstly, a linear filter incorporating the grain roughness friction factor f(2.5) and a phase angle phi(tau) is applied to u(infinity)(t). This delivers u(*)(t) which is used to calculate an instantaneous grain roughness Shields parameter theta(2.5)(t). Secondly, a constant bed shear stress is added which corresponds to the streaming related bed shear stress -rho ($) over bar((u) over tilde(w) over tilde)(infinity) . The method can be applied to any u(infinity)(t) time series, but further experimental validation is recommended before application to conditions that differ strongly from the ones considered below. The method is not recommended for rippled beds or for sheet flow with typical prototype wave periods and d(50) < 0.20 turn. In such scenarios, time lags related to vertical sediment movement become important, and these are not considered by the present model. (C) 2002 Elsevier Science B.V. All rights reserved.

Vertical fluxes of sediment in oscillatory sheet flow

Time series of vertical sediment fluxes are derived from concentration time series in sheet flow under waves. While the concentrations C(z,t) vary very little with time for \z\ < 10d(50), the measured vertical sediment fluxes Q(zs)(z,t) vary strongly with time in this vertical band and their time variation follows, to some extent, the variation of the grain roughness Shields parameter 02,5(t). Thus, sediment distribution models based on the pickup function boundary condition are in some qualitative agreement with the measurements. However, the pickup function models are only able to model the upward bursts of sediment during the accelerating phases of the flow. They are, so far, unable to model the following strong downward sediment fluxes, which are observed during the periods of flow deceleration. Classical pickup functions, which essentially depend on the Shields parameter, are also incapable of modelling the secondary entrainment fluxes, which sometimes occur at free stream velocity reversal. The measured vertical fluxes indicate that the effective sediment settling velocity in the high [(0.3 < C(z,t) < 0.4] concentration area is typically only a few percent of the clear water settling velocity, while the measurements of Richardson and Jeronimo [Chem. Eng. Sci. 34 (1979) 1419], from a different physical setting, lead to estimates of the order 20%. The data does not support gradient diffusion as a model for sediment entrainment from the bed. That is, detailed modelling of the observed near-bed fluxes would require diffusivities that go negative during periods of flow deceleration. An observed general trend for concentration variability to increase with elevation close to the bed is also irreconcilable with diffusion models driven by a bottom boundary condition. (C) 2002 Published by Elsevier Science B.V.

Differences in benthic fauna and sediment among mangrove (Avicennia marina var. australasica) stands of different ages in New Zealand

Management of coastal environments requires understanding of ecological relationships among different habitats and their biotas. Changes in abundance and distribution of mangroves, like those of other coastal habitats, have generally been interpreted in terms of changes in biodiversity or fisheries resources within individual stands. In several parts of their range, anthropogenically increased inputs of sediment to estuaries have led to the spread of mangroves. There is, however, little information on the relative ecological properties, or conservational values, of stands of different ages. The faunal, floral and sedimentological properties of mangrove (Avicennia marina var. australasica) stands of two different ages in New Zealand has been compared. Older (>60 years) and younger (3-12 years) stands showed clear separation on the basis of environmental characteristics and benthic macrofauna. Numbers of faunal taxa were generally larger at younger sites, and numbers of individuals of several taxa were also larger at these sites. The total number of individuals was not different between the two age-classes, largely due to the presence of large numbers of the surface-living gastropod Potamopyrgus antipodarum at the older sites. It is hypothesized that as mangrove stands mature, the focus of faunal diversity may shift from the benthos to animals living on the mangrove plants themselves, such as insects and spiders, though these were not included in the present study. Differences in the faunas were coincident with differences in the nature of the sediment. Sediments in older stands were more compacted and contained more organic matter and leaf litter. Measurement of leaf chemistry suggested that mangrove plants in the younger stands were able to take up more N and P than those in the older stands. (C) 2003 Elsevier Science B.V. All rights reserved.

Selective entrainment of sediment graded by size and density under waves

The influence of near-bed sorting processes on heavy mineral content in suspension is discussed. Sediment concentrations above a rippled bed of mixed quartz and heavy mineral sand were measured under regular nonbreaking waves in the laboratory. Using the traditional gradient diffusion process, settling velocity would be expected to strongly affect sediment distribution. This was not observed during present trials. In fact, the vertical gradients of time-averaged suspension concentrations were found to be similar for the light and heavy minerals, despite their different settling velocities. This behavior implies a convective rather than diffusive distribution mechanism. Between the nonmoving bed and the lowest suspension sampling point, fight and heavy mineral concentration differs by two orders of magnitude. This discrimination against the heavy minerals in the pickup process is due largely to selective entrainment at the ripple face. Bed-form dynamics and the nature of quartz suspension profiles are found to be little affected by the trialed proportion of overall heavy minerals in the bed (3.8-22.1%).

Functional role of macrobenthos in estuarine sediment dynamics

Thesis submitted to the Universidade Nova de Lisboa,Faculdade de Ciências e Tecnologia for the degree of Doctor of Philosophy in Environmental Engineering

Mathematical modelling of shallow flows: closure models drawn from grain-scale mechanics of sediment transport and flow hydrodynamics

Canadian Journal of Civil Engineering 36(10) 1605–16

Integration of sediment contamination with multi–biomarker responses in a novel bioindicator candidate (Sepia officinalis) for risk assessment in impacted estuaries

Dissertação para obtenção do Grau de Mestre em Engenharia do Ambiente

QUANTITATIVE VS. CONVENTIONAL PCR FOR DETECTION OF HUMAN ADENOVIRUSES IN WATER AND SEDIMENT SAMPLES

SUMMARY Human Adenoviruses (HAdV) are notably resistant in the environment. These agents may serve as effective indicators of fecal contamination, and may act as causative agents of a number of different diseases in human beings. Conventional polymerase chain reaction (PCR) and, more recently, quantitative PCR (qPCR) are widely used for detection of viral agents in environmental matrices. In the present study PCR and SYBR(r)Green qPCR assays were compared for detection of HAdV in water (55) and sediments (20) samples of spring and artesian wells, ponds and streams, collected from dairy farms. By the quantitative methodology HAdV were detected in 87.3% of the water samples and 80% of the sediments, while by the conventional PCR 47.3% and 35% were detected in water samples and sediments, respectively.

Can the complex mixture of sediment contaminants cause endocrine disruption on a benthic fish? A case study with Solea senegalensis

Pollution in coastal ecosystems is a serious threat to the biota and human populations there residing. Anthropogenic activities in these ecosystems are the main cause of contamination by endocrine disruption compounds (EDCs), which can interfere with hormonal regulation and cause adverse effects to growth, stress response and reproduction. Although the chemical nature of many EDCs is unknown, it is believed that most are organic contaminants. Under an environmental risk assessment for a contaminated estuary (the Sado, SW Portugal), the present work intended to detect endocrine disruption in a flatsfish, Solea senegalensis Kaup, 1858, and its potential relationship to organic toxicants. Animals were collected from two areas in the estuary with distinct influences (industrial and rural) and from an external reference area. To evaluate endocrine disruption, hepatic vitellogenin (VTG) concentrations in males and gonad histology were analysed. As biomarkers of exposure to organic contaminants, cytochrome P450 (CYP1A) induction and the ethoxyresorufin-O-deethylase (EROD) activity were determined. The results were contrasted to sediment contamination levels, which are overall considered low, although the area presents a complex mixture of toxicants. Either males or females were found sexually immature and showed no significant evidence of degenerative pathologies. However, hepatic VTG concentrations in males from the industrial area in estuary were superior than those from the Reference, even reaching levels comparable to those in females, which may indicate an oestrogenic effect resulting from the complex contaminant mixture. These individuals also presented higher levels of CYP1A induction and EROD activity, which is consistent with contamination by organic substances. The combination of the results suggest that the exposure of flatfish to an environment contaminated by mixed toxicants, even at low levels, may cause endocrine disruption, therefore affecting populations, which implies the need for further research in identification of potential EDCs, their sources and risks at ecosystem scale.

Mineralogical and geochemical influences on sediment color of Amazon wetlands analyzed by visible spectrophotometry

Based on sedimentological and geochemical data, this work relates spectrophotometric measurements with sediment composition and its application in palaeoecological studies of Amazon wetlands. The CIELAB values are directly related to mineralogical and chemical composition, mostly involving quartz, iron oxyhydroxides and sulfides (e.g. pyrite), and total organic carbon. Total organic carbon contents between 0.4-1%, 1-2%, 3-5% and 15-40% were related to L* (lightness) data of 27, 26-15, 7-10 and 7 or less, respectively. The CIELAB values of a deposit in Marabá, Pará, were proportional to variations in quartz and total organic carbon contents, but changes in zones of similar color, mainly in the +a* (red) and +b* (yellow) values of deposits in Calçoene, Amapá and Soure, Pará, indicate a close relationship between total organic carbon content and iron oxyhydroxides and sulfides. Furthermore, the Q7/4 diagram (ratio between the % re?ectance value at 700 nm to that at 400 nm, coupled with L*) indicated iron-rich sediments in the bioturbated mud facies of the Amapá deposit, bioturbated mud and bioturbated sand facies of Soure deposit, and cross-laminated sand and massive sand facies of the Marabá core. Also, organic-rich sediments were found in the bioturbated mud facies of the Amapá deposit, lenticular heterolithic and bioturbated mud facies of the Soure deposit, and laminated mud and peat facies of the Marabá deposit. At the Marabá site, the data suggest an autochthonous influence with peat formation. The coastal wetland sites at Marajó and Amapá represent the development of a typical tidal flat setting with sulfide and iron oxyhydroxides formation during alternated flooding and drying.