Dredged Material Disposal Research Articles

Spatial distribution and temporal trends of butyltin compounds (TBT, DBT & MBT) in short sediment cores of the SW Portuguese Shelf (western Iberian Margin, NE Atlantic)

Spatial patterns and temporal trends of the butyltin compounds tributyltin (TBT), dibutyltin (DBT), and monobutyltin (MBT) were investigated in a set of sediment samples collected along the SW Portuguese continental shelf. This region did not reach the Good Environmental Status (GES) in accordance with the Marine Strategy Framework Directive (MSFD) during a first evaluation carried out in 2012. Overall, MBT and DBT were the predominant organotin species detected, but high concentrations of TBT were found in and around disposal sites for dredge sludge derived from the dredging in navigation channels, harbours, and shipyard facilities of the Tagus and Sado estuaries. Although Portuguese regulations for monitoring sediment quality in relation to dredging activities consider only PAH, PCB and HCB, they also dictate that other organic contaminants such as butyltin compounds (BTs) should be monitored if suspicion of high values exists, but no action limits are defined for these (MAOTDR, 2007). Without action limits, the monitoring recommendation given in the regulations is not put into practice. Considering their toxicity, BT derivates should be integrated in the legislation, because they represent an environmental threat in the relocation of dredged material, especially when derived from harbour and shipyards areas. Based on this study, we recommend giving more attention to the amounts and impacts of BTs in sediments at dredged material disposal sites (DMDS) and their surroundings. Or even better, in order to be more efficient, monitoring should be done at the source of the dredged materials and not at the sink. In case it is not done, the monitoring of concentrations of TBT (and other BTs) in sediments and organisms, including imposex studies, at all Portuguese sites for disposal of dredged material receiving slightly to strongly contaminated dredged material must be developed.

Impact of Dredged Material Disposal on Heavy Metal Concentrations and Benthic Communities in Huangmao Island Marine Dumping Area near Pearl River Estuary

The Huangmao Island dumping area is adjacent to the Pearl River Estuary in the South China Sea. From its first dumping activity in 1986 to 2017, 6750 × 104 m3 dredged materials were dumped in this dumping area. Sediment pollution levels, ecological risk, and benthic communities in 2011–2017 were evaluated; the results showed that the concentrations of the heavy metals (HMs; except Hg) in surface sediments of the dumping area met the class I standard of marine sediment quality (GB 18668-2002). HMs in the surface sediments were relatively high in the northern and central areas but relatively low in the south of the dumping area. Speculation was that the spatial variation in HM concentrations might be caused by dumping activities. The Nemerow index implied that the contaminated area was mainly in the north of the dumping area (S1, S2, and S3), where the dumping amount was the largest. The potential ecological risk (Eir) indices of Zn, As, Cu, and Pb indicate that these metals posed a low risk to the ecosystem of the dumping area, whereas Cd and Hg posed a high risk at some stations. The geoaccumulation indices (Igeo) of Zn, As, Cu, and Pb specified no pollution or light pollution in the study area, whereas those of Cd and Hg in most years indicated mild contamination levels. Benthic organisms in the study area were arthropods, chordates, annelids, mollusks, echinoderms, nemertinean, coelenterate, and echiuran, among which arthropods were the most abundant. The abundance of taxa and density of benthic organisms had a little difference among the stations within the dumping area, but were significantly lower than those of the stations outside the dumping area. In addition, non-metric multidimensional scaling analysis confirmed that the observed patterns separated the stations within the dumping area from stations outside the dumping area. The evaluation results of the HMs revealed that the dumping area with a large dumping amount was more severely polluted. Dumping dredged materials seemed to have a negative impact on the benthic community in the dumping area.

Marine macrofaunal traits responses to dredged material disposal

Currently, our understanding of the mechanisms for, and potential functional implications of, changes in seabed assemblages resulting from dredged material disposal is relatively unknown. Based on empirical data from 17 disposal sites, we address this by quantifying the nature and magnitude of shifts in the relative composition of response and effects traits within disposal site assemblages relative to their reference assemblages.Differing shifts in both response and effects traits were observed across sites, regardless of the trait composition of the reference assemblages. Notable differences in the magnitude of traits changes were also observed for both trait types. Traits shifts are difficult to predict as they appear to reflect both environmental conditions and disposal regime. Temporal data revealed that some sites display relatively consistent responses while others presented large inter-annual variability. These findings are discussed in relation to dredged material monitoring and with respect to conservation objectives of marine protected areas.

Effect of aqueous environment on sedimentation of dredged mud and kaolinite

Port development results in production of large quantities of dredged marine sediments. Once dredged, sediments often have high water contents and are pumped to near-shore or in-water bunded marine impoundments for port expansion. However, dredged material disposal to freshwater onshore or empty impoundments typically changes sedimentation conditions that may change the effective grain-size distribution, mineral specific surface areas, settling particle orientations, resulting in settling rate changes. Salinity, temperature, water content, mineralogy, filling rate, and organic matter content may also influence sediment settlement and resulting consolidation. This study investigates the effect of salinity and sediment mineralogy on sediment settlement behaviour when deposited in saltwater, freshwater, or to empty ponds. For this purpose, slurries of dredged mud and kaolinite with water contents of 1.7 times their liquid limit were prepared and disposed into a series of 1000 mm long, 50 mm wide, and 500 mm high settlement columns. Result shows that the sediments settle faster in saltwater than freshwater or air, through divalent surface complexation and flocculation provided by seawater Ca and Mg. However, this is true if the salinity remains below 10 PSU, but the mixed mineral dredge spoil ultimately provides the densest sediment and lowest water sediment interface.

Development and validation of new analytical methods using sea urchin embryo bioassay to evaluate dredged marine sediments

Management of dredged materials disposal is regulated by several environmental normative requirements, and it is often supported by the integration of chemical data with ecotoxicological characterization. The reliability of a bioassay to assess the potential toxicity of dredged sediments requires the selection of quality criteria that should be based on simple analytical methods and easily understandable hazard for politicians and environmental managers. The sea urchin embryo-toxicity bioassay is considered an essential component for evaluating the quality of sediments in harbour areas but its use, when based exclusively on the observation of normal vs. abnormal embryos, may alter the interpretation of the results, overestimating the risk assessment. To improve the reliability of this assay in establishing a causative relationship between quality of sediments and sea urchin embryonic development, here we developed and validated three Integrative Toxicity Indexes (ITI 2.0, ITI 3.0, ITI 4.0), modifying the already-known ITI (here ITI 1.0). Based on this aim, we used Taranto harbour as a model pilot-study to compare results to those obtained from standard criteria. Among the tested indexes, the ITI 4.0, discriminating strictly developmental delay and morphological defects from fertilized egg to gastrula stage, resulted in the most promising.

Environmental consequences of dredged-material disposal in a recurrent marine dumping area near to Guadalquivir estuary, Spain

In this study we assessed the effects of the recurrent disposal of dredged material from the Guadalquivir estuary (south-western Spain) in a marine disposal area. We analysed shifts in sediment characteristics as well as bioaccumulation and biomagnification of heavy metals through the benthic food web. Results showed that the significant increase in concentration of some heavy metals observed in the marine disposal area after the latest disposal event could be attributed to the deposition of river-dredged sediments. This increase could also explain the decreased amphipod survival in the ecotoxicology analysis. Heavy metal concentrations in organisms indicated some bioaccumulation in deposit feeders and predators but with no clear patterns nor biomagnification through the food web. Hence, combining studies that monitor shifts in sediment characteristics and their possible consequences for the food web seems to be an interesting approach that should be assessed further in this type of studies.

Development of a Dredging Sensitivity Index, applied to an industrialized coastal environment in Brazil

Ports link world commerce via maritime routes, and dredging services are essential to establish and maintain these connections. However, one question is critical when dredging is being considered: where are the best places to do it? To try to answer this question, a Dredging Sensitivity Index (DSI) was developed as a management tool to be used in project planning steps. In order to diminish environmental damages and quality-of-life losses, DSI provides alternatives by identifying sensitivity areas. This new methodology quantifies impacts caused by the sediment removal step and points out favorable areas to dredge, with a simple map. Parameters such as fine-grain content (% < 63 μm), Acid Volatile Sulfides (AVS), Shannon-Wiener Index and fisheries, among others, were used to calculate the DSI. Formulas were used to weight and aggregate both, the parameters and the DSI itself. Sepetiba Bay was chosen to apply this methodology because of its relevant economic and environmental aspects. The methodology was applied to dredging situations, but it can be used to indicate areas for dredged material disposal, with a few modifications in the DSI formulas. A DSI map was a final result of this methodology, and showed that the northern portion of the bay, close to the littoral is a more sensitive area, where dredging should be avoided, or carried out very carefully. DSI is a very useful tool for reducing damages from dredging services, it contributes with zonation and it provides alternatives to decision-makers who manage these areas.

Field of dreams: Restoring estuarine habitat and structure in Mississippi after the Deepwater Horizon oil spill

This paper presents a Mississippi Department of Marine Resources (MDMR), Office of Coastal Restoration and Resiliency, perspective on adaptation and innovation in restoration permitting, collaboration, and design in an era shaped by the Deepwater Horizon oil spill (DWH). These adaptations and innovations lay groundwork to support Mississippi’s future address of challenges stemming from its ongoing geomorphic evolution and loss of primary landforms. The Round Island project in Jackson County, Mississippi (MS), will serve as a principal example. Completed through the efforts of four agencies via a Memorandum of Understanding (MOU) and funded by the National Fish and Wildlife Foundation (NFWF) this project helped break a long-standing practice of dumping large quantities of federal navigation channel dredged materials in an Offshore Dredged Material Disposal Site (ODMDS). Not only were 220 acres of new island and marsh habitat created in the Mississippi Sound, the Round Island project saved millions in federal navigation dollars because it could be more efficiently accessed than the ODMDS site. The Round Island project represents a collective, multi-agency step toward strategic scale, nature-based approaches more capable of managing Mississippi’s burgeoning restoration and resource needs.

Video sleds effectively survey epibenthic communities at dredged material disposal sites

This research assessed the effectiveness of benthic video sleds for monitoring the impacts of dredged material disposal on epifauna at shallow and deep water disposal sites near the mouth of the Columbia River, USA. Video sleds collected visual transects at the two disposal sites and comparable reference areas during 2014 and 2015 within a Before-After, Control-Impact (BACI) experimental design. These flat, soft-bottom habitats are populated by demersal fish and benthic invertebrates, including the economically important Dungeness crab (Cancer magister). At the shallow site, results from multivariate Similarity Profile Analysis (SIMPROF) and univariate ANOVA tests on prominent species did not detect any significant differences between disposal and reference communities. At the deep site, the multivariate and univariate analyses detected differences in communities and abundances between years, rather than between disposal and reference locations. At the scale of this research, there was no detectable impact of dredged material disposal on the epifauna communities at these two Pacific Northwest disposal sites. While the species resolution of cryptic or small organisms was found to be limited, the video sled technique had sufficient power to detect potential differences in most epifaunal species densities with a BACI statistical design. We found the video sleds were an effective tool to assess potential impacts of dredged material disposal on epifauna.

WORKING THROUGH STATE DIFFERENCES TO CREATE A REGIONAL DREDGED MATERIAL MANAGEMENT PLAN FOR FEDERAL HARBORS IN LONG ISLAND SOUND

On January 11, 2016 the U.S. Army Corps of Engineers (USACE) New England District (NAE) completed a Final Dredged Material Management Plan (DMMP) for Long Island Sound (LIS). The DMMP was requested by the Governors of Connecticut and New York, in their letter of February 8, 2005 to the Chief of Engineers, following the U.S. Environmental Protection Agency’s (EPA) publication in April 2004 of the Long Island Sound Dredged Material Disposal Site Designation Study Final Environmental Impact Statement. The LIS is a large coastal estuary located between Long Island, New York on the south, and the shores of New York, Connecticut and southwestern Rhode Island on the north. A total of nearly 240 harbors, coves, bays and rivers supporting various levels of navigational access are located along these shores. Twelve Congressional districts and 112 municipalities border the Sound and its adjacent waters in the three states. The ideals, goals, and needs along the LIS do not always align and thus the need for open communication throughout each dredging project.

Impact of dredged-material disposal on soft-bottom communities in a recurrent marine dumping area near to Guadalquivir estuary, Spain

This study assesses the effects of dredged material disposal in a recurrent marine dump near the Guadalquivir Estuary (south-western Spain). We compared the changes observed with two reference areas combining a classical ecological approach with new stable isotope techniques to analyse trophic structure. We detected permanent changes in the macrofaunal community structure as well as in the diversity and biotic indices applied, which showed higher values in the disposal area. The community in the marine dump had lost the natural temporal variations observed in the reference areas. These effects could be due to the last disposal event carried out in the summer of 2015 or to the recurrent disposals since 2010. Despite the structural changes shown by the benthic community, these impacts were not reflected in the food web structure of the marine dump. Our results confirm the high variability of disposal disturbances. Hence, we recommend performing studies in every disposal event, merging different functional and structural approaches.

Impact of disposal of dredged material on sediment quality in the Kaohsiung Ocean Dredged Material Disposal Site, Taiwan

Kaohsiung Ocean Dredged Material Disposal Site (KODMDS) that located in the southwest offshore of Taiwan, has been annually disposed about 500,000 ton dredged sediments of Kaohsiung Harbor from 2003 to 2012. Five sediment cores collected from KODMDS and three from nearby reference sites were analyzed to evaluate their sedimentation rates, vertical profiles of heavy metal, and heavy metal pollution indices to assess the impact of dumping harbor dredged sediments into the ocean on the sediment quality in KODMDS. The sedimentation rate of 0.24 cm/y was estimated by the 210Pb method, which means that the effected depth of the top layer of a core of D1 was affected in the period of dumping dredging sediments. The vertical distribution of heavy metals in the sediment cores from KODMDS showed the concentrations of most heavy metals were slightly elevated in the top layers of the sediment cores, which may be affected by the dumping of harbor dredged sediments. According to the analyzed results of the heavy metal pollution indices, the level of heavy metal pollution, the potential eco-toxicity and the potential ecological risk of the sediments in KODMDS exhibited only a slight increase, which indicated that the increase in concentration of heavy metals may potentially pose the insignificant impact on benthos inhabiting the disposal site.

Phthalate ester distributions and its potential-biodegradation microbes in the sediments of Kaohsiung Ocean Dredged Material Disposal Site, Taiwan

The aim of this study was to examine the effect of dumping harbor dredged sediments into the ocean on the phthalate esters distribution in the sediments of Kaohsiung Ocean Dredged Material Disposal Site (KODMDS). Compared with the sediments outside the disposal site (Area R), the particle size distribution of sediment in disposal site has no significant difference, because the pattern of particle size distribution in the dredged sediments is similar to that in the sediments of KODMDS. Results indicated that the mean phthalate ester content in the centres of the four disposal areas (Area I) were significantly (p < 0.05) higher than those in Area R, whereas those in the vertex angles of disposed area (Area II) were no significantly higher than those in Area R. This result implied that the dredged sediments were mainly deposited inside the disposal area, and the surface sediments in KODMDS may be impacted by the disposal of dredged sediments. The percentage of sediment samples for phthalate esters content exceeding Maximum Permissible Concentrations (MPC) and/or Ecotoxicological Serious Risk Concentrations (SRCeco) in Areas I and II was higher than that in Area R, indicated that the disposal of dredged sediments may increase the potentially ecological risks for benthic organisms that lived in the surface sediments of KODMDS. However, the present study has found the bacteria have the ability to degrade PAEs in KODMDS, indicating PAEs in KODMDS could be biodegraded eventually.

Metal distributions in the Kaohsiung Ocean dredged material disposal site, Taiwan

Metal distributions in the Kaohsiung Ocean dredged material disposal site, Taiwan

The application of Diffusive Gradients in Thin Films (DGT) for improved understanding of metal behaviour at marine disposal sites

Assessment of the effects of sediment metal contamination on biological assemblages and function remains a key question in marine management, especially in relation to disposal activities. However, the appropriate description of bioavailable metal concentrations within pore-waters has rarely been reported. Here, metal behaviour and availability at contaminated dredged material disposal sites within UK waters were investigated using Diffusive Gradient in Thin films (DGT). Three stations, representing contrasting history and presence of dredge disposal were studied. Depth profiles of five metals were derived using DGT probes as well as discrete analysis of total metal concentrations from sliced cores. The metals analysed were: iron and manganese, both relevant to sediment biogeochemistry; cadmium, nickel and lead, classified as priority pollutants. DGT time-integrated labile flux profiles of the metals display behaviour consistent with increasingly reduced conditions at depth and availability to DGT (iron and manganese), subsurface peaks and a potential sedimentary source to the water column related to the disposal activity (lead and nickel) and release to pore-water linked to decomposition of enriched phytodetritus (cadmium). DGT data has the potential to improve our current understanding of metal behaviour at impacted sites and is suitable as a monitoring tool. DGT data can provide information on metal availability and fluxes within the sediment at high depth-resolution (5mm steps). Differences observed in the resulting profiles between DGT and conventional total metal analysis illustrates the significance of considering both total metals and a potentially labile fraction. The study outcomes can help to inform and improve future disposal site impact assessment, and could be complemented with techniques such as Sediment Profile Imagery for improved biologically relevance, spatial coverage and cost-effective monitoring and sampling of dredge material disposal sites. Additionally, the application of this technology could help improve correlative work on biological impacts under national and international auspices when linking biological effects to more biologically relevant metal concentrations.

Application of biological traits to further our understanding of the impacts of dredged material disposal on benthic assemblages

While the effects of coastal disposal of dredged material on benthic assemblage structure have been well studied, our understanding of the mechanism of such responses, and their potential ecological implications, remain relatively unknown. Data from a licenced disposal site off the northeast coast of England are analysed to address this and improve our ability to make informed licencing decisions for this activity. Assemblages within the disposal site displayed reduced number of species and total invertebrate density, an altered assemblage taxonomic structure, and a shift towards a greater numerical dominance of less-productive individuals. Following separate analyses of biological response and effect traits, a novel approach for marine benthic trait analysis, we identify the traits responsible (i.e. response traits) for the observed structural alterations. Furthermore, analysis of the effect traits revealed that the assemblages characterising the disposal site possess a greater bioturbative capability compared to those not directly impacted by disposal.

Impacts of dredged-material disposal on the soft-bottom communities in a marine dumping area near to Guadalquivir estuary, Spain.

Impacts of dredged-material disposal on the soft-bottom communities in a marine dumping area near to Guadalquivir estuary, Spain.

Distribution of river-borne particulate Pb in the Basque continental shelf (Bay of Biscay)

The Sediment, Oil spill and Fish Tracking model (SOFT) was used to simulate the river-borne particulate Pb dispersion and sedimentation in the Basque continental shelf (BCS). In this case, SOFT used 3D current fields obtained with the Regional Ocean Modeling System (ROMS). From the SOFT results, connectivity matrices were obtained to analyze source-sink relationships. Considering the studied 12 rivers, the Ibaizabal River is the major contributor, accounting for 69 % of the total particulate Pb release. On a yearly basis, Pb accumulates mostly in the West sector of the BCS. The differences between the observations for the 2000–2011 period and the modeling results could be due to the fact that SOFT used climatological information on currents and discharges from the Basque rivers (the Adour River was not included) and did not estimate the resuspension process. To improve the results, the SOFT outputs together with Hs12 data (significant wave height exceeding 12 h per year) and observed sedimentary Pb concentrations were integrated into a Geographic Information System (GIS) environment to adopt a multivariate approach. At the BCS spatial scale, the combination of numerical models and GIS-assisted statistics did not provide an accurate prediction of the distribution of river-borne particulate Pb accumulation. At smaller scales, areas influenced by the inputs of Basque rivers and others affected by additional factors (i.e., dredged material disposal activities, contributions from neighboring rivers and sub-grid scale transport processes) were identified. Under the current European marine legislative framework, the improved knowledge obtained on river-borne particle dispersal dynamics can assist the assessment of the marine contamination from the local to the regional scale.

Polycyclic aromatic hydrocarbons in sediments at dredged material disposal sites around England: Concentrations in 2013 and time trend information at selected sites 2008–2013

The maintenance of navigation channels to ports and the development of their facilities present a need to conduct dredging operations, and the subsequent disposal of dredged material at sea. Contaminant concentrations in candidate dredged material are determined and their possible impacts considered during the licensing process, which can result in the exclusion of some material from sea disposal. Monitoring of disposal sites is conducted in order to ensure that no undesirable impacts are occurring. In this study we consider the levels of polycyclic aromatic hydrocarbons (PAHs) in sediments at a number of disposal sites monitored in 2013 and variations in concentrations over time at three sites during the period 2008–2013. These were assessed using established sediment quality guidelines. Elevated PAH concentrations were generally observed only within the boundaries of the disposal sites studied.

Maintenance Dredging at Port of Townsville

The Port of Townsville conducts regular annual maintenance dredging to maintain depths of its harbor basin and approach channels for the navigational safety of the vessels against the natural accumulation of marine sediments. In addition to the regular maintenance dredging, the port undertakes emergency dredging in cases where large quantities of sediments are mobilized and deposited in port waters by cyclone or major flood events. The maintenance dredging material derived from the port may be disposed at sea or on land in accordance with relevant state and commonwealth regulations. For the land disposal, the dredged mud slurry is hydraulically placed into containment ponds and left to undergo sedimentation and self-weight consolidation to form fill material for land reclamation. This paper provides an overview of the maintenance dredging at the Port of Townsville and emphasis on maintenance dredging requirements, sediment quality, bathymetry, dredging methods used, and dredged material disposal options.