Dredged Disposal Research Articles

Recovery and Restoration of Disturbed Sand Bars of the Apalachicola River, Florida

abstract: Large, low-lying rivers have a variety of societal uses and show a wide range of disturbances. One such example, the Apalachicola River in the Florida Panhandle, experienced anthropogenic activities that altered its hydrologic, geomorphic, and ecologic condition. The river's sand bars enlarged more than threefold in area because of dredge disposal and localized incision from anthropogenic activities during a navigation project. Once dredging ended, the river experienced passive recovery through the slow regrowth of riparian vegetation, with sand bars reducing in area ~18% from 2005 to 2015. The outcomes of tree-line change analyses from 1999 to 2019 indicate a higher recovery rate in the first decade (1999-2010), migrating fastest in locations where vegetation islands stabilize sediments. To help accelerate vegetation regrowth, during the growing seasons of 2018 and 2019, we planted willow stakes at various positions and microhabitats covering ~3.6 ha of three enlarged sand bars near Blountstown, FL. Our mapping shows some synergies between passive recovery and active restoration as tree-line expansion had the fastest rates between 2019 and 2021. Our study gives insights and guidance into passive recovery and restoration projects involving plantings on large, low-lying rivers.

Transfer of industrial contaminants from the inner to the outer region of Sepetiba Bay (SE Brazil) by dredge spoil dumping activities: a temporal record

A multiproxy approach involving grain size, geophysical (resistivity, magnetic susceptibility, and P-wave velocity), mineralogical (XRD), and geochemical (elemental, stable isotopes) data has been applied to core SP9 (128 cm long) to reconstruct natural and anthropogenic changes since ≈1850 AD (anno domine) (dating by 210Pb and 127Cs methods) in a distal region of Sepetiba Bay (SB), Rio de Janeiro State (SE Brazil). The analyzed core is a fine-grained sedimentary sequence (except its upper 20 cm). It comprises detrital particles derived from felsic and intermediate source rocks, as suggested by the fields defined by the biplot Zr vs TiO2 and the Al2O3/TiO2 ratios. Despite the increase in particle size at the top of the core, there was a progressive increase in the organic matter and potentially toxic elements (PTEs) contents and nutrients such as N and P. The geophysical data allowed us to identify the presence of subsurface (biogenic) gas, which suggests the occurrence of eutrophication processes in the study area despite its location in the outer region of the bay. Core SP9 records cyclical changes over the last ≈170 years in the mineralogical and elemental composition of the sediments and type of organic matter supplied to the bottom. These changes are associated with phases of more significant oceanic influence, salinity variations in the study area, and greater or lesser oxygen depletion in the sediment. These changes may have resulted from climatic oscillations or variations in the configuration and extension of the Ponta da Pombeba spit. The extent of this structure and the anthropic activities have contributed to the contamination of this area since 1975 AD. However, statistical analyses (Pearson correlations and principal components analysis) suggest that the transport and accumulation of PTEs (mainly Cd and Zn) did not strictly follow the general pattern of sedimentary dynamics prevailing in the studied area. Results indicate that this area became strongly polluted by Cd and Zn and with high ecological risk due to dredging and spoil disposal activities at sites close to the study area. It is noted that the environmental degradation reached higher levels here than in areas close to the primary source of the metals, the disabled Ingá Mercantil Company, in Madeira Island. This work demonstrates the temporal effect of dredge disposal activities in a distal region of Sepetiba Bay for the first time. It is a strong indicator that dredged spoil areas must be selected carefully, since healthy areas can become degraded due to the dumping of polluted waste.

Geochemical footprint of dredged material discharges and sediment health status in Todos Santos Bay, Mexico

Total Al, Fe, Mn, Cu, Zn, Pb and organic carbon concentrations in Todos Santos Bay (TSB) surficial sediments were analyzed over three different years. A geochemical “fingerprint” associated with material dredged in the Port of Ensenada, was clearly identified on the surficial sediments via spatial analysis of standard scores (Zscores), within TSB prior to 2006 (1992/1994) when discharges were first conducted outside the bay. Values of Zscores > +3, considered substantial, encompassed 41%–50% of the TSB area (240 km2) and were located around the dredge disposal site. Anthropogenic toxic elements, evaluated from 10 different geochemical indices, showed no clear evidence of health deterioration, potential ecological risk and/or adverse effects on TSB marine biota. However, total Pb concentration doubled from 1994 to 2018, averaging (3.02 ± 0.75) x 10−2 and (5.73 ± 0.67) x 10−2μmol g−1, respectively. If this trend continues, Pb could in future become a contaminant capable of deteriorating the health of TSB and its biota.

Distribution and sources of macrolitter on the seafloor in Belgian fisheries areas

Marine litter is recognized as a global environmental concern. Seafloor litter can provide important information to help assess the status of the marine ecosystem and is relatively easy to collect on a regular basis. The Belgian fisheries area covers different parts of the OSPAR Greater North Sea region and the Celtic Seas. In these regions, seafloor litter data were gathered by quantifying the litter items caught in the trawl net during two different fisheries surveys to investigate litter distribution on both regional and local scales. In the international beam trawl survey (BTS), covering essentially the OSPAR Greater North Sea and Celtic Seas, an average of 2.2 ± 0.05 items.ha-1 were caught with a median of 1.4 items.ha-1. In the environmental monitoring survey (EMS) only the Belgian part of the North Sea was covered and a smaller cod-end mesh size was used, resulting in 12.7 ± 1.7 litter items.ha-1 in the coastal zone (< 12 nm) and 2.8 ± 0.2 items.ha-1 in the more offshore zone (> 12 nm). In both surveys plastic items were predominant, representing up to 88% of the collected litter in the Belgian part of the North Sea. The impact of human activities at sea such as fisheries, sand extraction, wind farms and dredge disposal was investigated. A significant correlation was found between fishing activities and the amount of litter registered in the Belgian part of the North Sea, but not for the OSPAR Greater North Sea and Celtic Seas.

Functional trait responses to different anthropogenic pressures

There is an increasing awareness that knowledge of the functional diversity of a community is key to understand how the community responds to environmental and anthropogenic pressures. The Belgian Part of the North Sea (BPNS) represents a highly dynamic area that is subject to a variety of human activities. The main objective of this study is to investigate the usefulness of functional diversity indices and fuzzy correspondence analysis (FCA) to evaluate their applicability in assessing changes in benthic functional properties in the frame of environmental impact assessments (EIAs) for dredge disposal, sand extraction and offshore wind energy exploitation. Ten traits were selected, subdivided in 47 modalities, including both response- and effect traits. Functional diversity was quantified through different functional indices while shifts in trait composition due to anthropogenic pressure were determined by FCA. The analyses were based on a benthic dataset of 1262 samples.Results revealed that under chronic pressure of high disposal or sand extraction, the functional diversity indices – especially functional richness - showed a clear response. However, considerable variation (decrease/increase) was found for the index values between the impacted sites. Within the offshore wind farms, findings for the functional diversity indices were less pronounced. The FCA graphs revealed a shift in trait composition in all cases except for Macoma balthica and Nephtys cirrosa habitat in the dredge disposal case.The BPNS - with different types of pressure and levels of impact - provided the ideal platform to assess the potential of biological trait-based indicators. While responses are complex and dependent on several aspects such as local habitat, pressure type or level of impact, our results proved that functional trait analyses are a necessary and complementary tool in future environmental impact assessments.

Large-scale morphological changes and sediment budget of the Western Scheldt estuary 1955–2020: the impact of large-scale sediment management

Abstract In the Western Scheldt estuary, like in many estuaries, safe navigation, flood protection, and ecological targets require a balanced and sustainable sediment management. A thorough understanding of the morphodynamic functioning of the estuary and its response to changes in hydrodynamics (natural sediment transport) and large-scale interventions is imperative. This paper presents a detailed overview of over 65 years of morphological changes and a comprehensive sediment budget of the Western Scheldt estuary that is based on analysis of a unique series of frequent bathymetric surveys and historical data on human–sediment interactions of dredging, dredge disposal and sand mining. Solving the sediment budget reveals an annual sediment import of 2.2 million m3. The highest sediment imports occurred between 1980–1994 and 2005–2020 (2.9 and 3.7 million m3/year). A 1.3 million m3/year net export prevailed between 1994 and 2005. Natural variations in the hydrodynamics (e.g., tidal asymmetry and amplification) and sediment transports cannot explain the derived temporal variations in sediment import rates. Anthropogenic activities play a dominant role. Capital dredging of the main navigation channel has led to channel deepening and significantly increased dredge and disposal volumes. Disposal on tidal flats and in the secondary channel leads to a long-term storage of sand and, consequently, a local increase in bed level and a sand deficit in the remainder of the system that results in increased sediment imports. Large-scale disposal in the western part of the estuary can (temporarily) reverse the sediment exchange between the estuary and its mouth area, as observed between 1994 and 2005. Apparently, large-scale anthropogenic reallocation of sediment by dredging and/or disposal as part of navigation channel improvement, sand mining or nourishment essentially influences the morphological development of the Western Scheldt estuary. This reveals responsibilities as well as opportunities of sediment management for the Western Scheldt and similar estuaries worldwide.

Remote-Sensing Measurements of Wave Breaking at Two Pacific Northwest Jettied Inlets

Breaking waves constitute one of the main environmental stressors on coastal structures as well as a leading hazard to navigation in nearshore regions. In this paper, we use camera-based methods to measure wave breaking over two jetty systems in the Pacific Northwest; the North jetty of the Columbia River, Washington state, and the two jetties of Coos Bay, Oregon, as well as over three nearby nearshore dredge disposal areas. Data were collected using the “brightest” images and Argus camera technology over a span of 847 days for the Columbia River and 202 days for Coos Bay. Wave breaking over the Columbia north jetty reached 100% for wave heights greater than 3 m and for tides above mid-tide level and was concentrated on the seaward half of the jetty. For Coos Bay, the south jetty saw substantially more breaking than the north one with the worst overtopping occurring mid-jetty and seeming to be associated with sediment transport through the jetty and into the inlet, as well as possibly the navigation channel. Wave breaking at the Coos Bay inlet mouth was enhanced during ebb flow conditions. Argus imagery analysis showed no evidence of enhanced breaking over any of the three dredge material placement sites.

Quantifying decadal volumetric changes along sandy beaches using improved historical aerial photographic models and contemporary data

AbstractTechnological advances have reinvigorated the aerial photogrammetric technique using both historical and contemporary imagery, and fostered new perspectives in geomorphology studies. On sandy beaches, however, the dynamic processes, the lack of tonal contrast and reduced texture, make the application of photogrammetry extremely more difficult than in most other landscapes. This study quantifies decadal volumetric changes along the beaches of the Great Ocean Road, Australia, using improved digital surface models (DSMs) derived from structure‐from‐motion (SfM) photogrammetry applied to historical archives and a contemporary unmanned aerial vehicle survey. Alongside surficial sediment analysis, this approach demonstrates the potential to relate present‐day to historical morphological changes at sandy beaches worldwide. The discussion highlights the influence of photographic scale, lens distortions, ground control points in segmented blocks, and the use of shoreline as a proxy of volumetric change. DSMs were derived using datasets obtained in 1946, 1966, 1971, 1977, 1986 and 2019, and compared to a 2007 light detection and ranging (LiDAR)‐derived DSM. The emerging approach produced suitable DSMs for volumetric analysis, except for the 1946 dataset, which had the smallest scale and was significantly vertically offset. Volumetric losses of up to 60 m3/m of beach length were calculated for parts of Mounts Bay between 1977 and 2007, and up to 21 m3/m in recent years. At Apollo Bay, the construction of the port in the early 1950s significantly impacted the natural longshore drift to the beach. The adjacent stretch of coastline accreted at a rate of ~35 m3/m between 1966 and 2007, as a function of dredge disposal and changes in sediment transport, whereas a maximum volumetric loss of ~47 m3/m was detected further north between 1977 and 2007. A volume of ~71,330 ± 15,200 m3 was lost from the system from 2007 to 2019, despite the continued deposition along the northern section of the beach.

Decadal (2006-2018) dynamics of Southwestern Atlantic's largest turbid zone reefs.

Tropical reefs are declining rapidly due to climate changes and local stressors such as water quality deterioration and overfishing. The so-called marginal reefs sustain significant coral cover and growth but are dominated by fewer species adapted to suboptimal conditions to most coral species. However, the dynamics of marginal systems may diverge from that of the archetypical oligotrophic tropical reefs, and it is unclear whether they are more or less susceptible to anthropogenic stress. Here, we present the largest (100 fixed quadrats at five reefs) and longest time series (13 years) of benthic cover data for Southwestern Atlantic turbid zone reefs, covering sites under contrasting anthropogenic and oceanographic forcing. Specifically, we addressed how benthic cover changed among habitats and sites, and possible dominance-shift trends. We found less temporal variation in offshore pinnacles’ tops than on nearshore ones and, conversely, higher temporal fluctuation on offshore pinnacles’ walls than on nearshore ones. In general, the Abrolhos reefs sustained a stable coral cover and we did not record regional-level dominance shifts favoring other organisms. However, coral decline was evidenced in one reef near a dredging disposal site. Relative abundances of longer-lived reef builders showed a high level of synchrony, which indicates that their dynamics fluctuate under similar drivers. Therefore, changes on those drivers could threaten the stability of these reefs. With the intensification of thermal anomalies and land-based stressors, it is unclear whether the Abrolhos reefs will keep providing key ecosystem services. It is paramount to restrain local stressors that contributed to coral reef deterioration in the last decades, once reversal and restoration tend to become increasingly difficult as coral reefs degrade further and climate changes escalate.

Environmental characterization of a dredging disposal site on the continental shelf of Espírito Santo, Brazil

Dredge material placement is among the major problems in coastal management. Sedimentation caused by dredge-spoil disposal presents a series of impacts, including the burial of benthos and the suffocation of filter-feeding benthic organisms. To minimize dredging impacts, studies in dredging disposal sites shall be performed to allow better approaches to adverse ecological risks. The goal of the present study was to map the sea bottom environment of a potential dredge disposal site by performing its geomorphology and ecology characterization, in the continental shelf of Espirito Santo state. Acoustic images were obtained using side scan sonar to characterize sediment texture and the geometry of deposits, along with a bathymetric survey. Additionally, underwater footage provided images and the description of the biota communities. The bathymetric survey revealed a relatively plain and homogenous bottom, with the presence of a paleochannel. Smooth elevations, with approximately 0.50m high, were found and characterized as calcareous biogenic concretions, among benthic and nektonic organisms. The organisms revealed a heterogeneous composition and a scattered distribution throughout the sampling stations, with the presence of a threatened species.

EFFECT OF DREDGING ON HG DISTRIBUTION IN WATER AND SEDIMENTS IN THE MUCURIPE HARBOR, FORTALEZA, NE BRAZIL

Dredging and tailings disposal can mobilize mercury (Hg) accumulated in bottom sediments, increasing the exposure of the aquatic biota. In the Mucuripe Harbor, NE, Brazil, dredging is performed regularly, but the impact on Hg mobilization is unknown. This paper presents results from the monitoring of a dredging operation to characterize and quantify an eventual Hg mobilization. The results showed that remobilization is significant and is associated with suspended solids. Further deposition of the Hg-enriched, remobilized, suspended solids increased Hg concentrations by a factor of 1.2 and 2.0 in harbor and shelf sediments, respectively. Maximum concentrations in harbor and shelf sediments reached 79.9 ng.g-1 and 32.4 ng.g-1 (20 and 9 higher than the regional background, respectively). The progressive increase in Hg concentrations may result in higher exposure to the local biota.Keywords: metals, mobilization, contamination, coastal sediments.

Sediment Disposals in Estuarine Channels Alter the Eco‐Morphology of Intertidal Flats

Dredging of navigation channels in estuaries affects estuarine morphology and ecosystems. In the Western Scheldt, a two‐channel estuary in the Netherlands, the navigation channel is deepened and the sediment is relocated to other parts of the estuary. We analyzed the response of an intertidal flat to sediment disposals in its adjacent channel. Decades of high‐frequency monitoring data from the intertidal flat show a shift from erosion toward accretion and reveal a sequence of cascading eco‐morphological consequences. We document significant morphological changes not only at the disposal sites, but also at the nearby intertidal flats. Disposals influence channel bank migration, driving changes in the evolution of the intertidal flat hydrodynamics, morphology, and grain sizes. The analyzed disposals related to an expansion of the channel bank, an increase in bed level of the intertidal flat, a decrease in flow velocities on this higher elevated flat, and locally a decrease in grain sizes. These changes in turn affect intertidal flat benthic communities (increased in quantity in this case) and the evolution of the adjacent salt marsh (retreated less or even expanded in this case). The shifts in evolution may occur years after dredged disposal begins, especially in zones of the flats farther away from the disposal locations. The consequences of sediment disposals that we identify stress the urgency of managing such interventions with integrated strategies on a system scale.

The Dredge Disposal Sediment Index (D2SI): A new specific multicriteria index to assess the impact of harbour sediment dumping

At present, there are few operational indexes to assess the impact of a given human pressure taken alone. Nevertheless, the current challenge in the management of coastal marine environments in the framework of cumulative impacts and climatic change is to identify the relative contribution of each activity on ecosystem functioning. The objective of the present study is to propose an integrative approach to assess the environmental impacts of dumping operations, via the development of a new index, the Dredge Disposal Sediment Index (D2SI). From the selection of two types of station: impacted and unimpacted, D2SI integrates six sub-indices considering the biological and physical changes generated by dredge disposal on the seabed. A final score is proposed, according to the five classes of the European Water Framework Directive. The initial development of D2SI was conducted on the experimental dumping site of Machu (Bay of Seine), by applying a BACI (Before-After-Control-Impact) approach. An additional implementation (D2SI2) is used in the case of absence of data on ichthyofaunal or biological traits of life of macrobenthic fauna, which yields a comparable assessment of dumping pressure. In the future, the D2SI or D2SI2 indexes should be tested on other dumping sites with a view to comparing the assessment of this dumping activity.

Geomorphic and Sedimentary Impacts on the Continental Shelf after Accumulated Dredge Disposal from Rio de Janeiro Harbor, Brazil

ABSTRACT.Marine dredging is a subaquatic excavation activity executed around the globe for various purposes by many industries. The negative impacts ofdredged material discharge on benthic ecosystems are diverse. Researches on the results of dredging on estuarine geomorphology and its sedimentary regime areusual. Still, the results of dumping dredged material off the coast, in the Brazilian continental shelf, are not easily found in the literature. The present research evaluatedthe geomorphic disturbance resulted from discharging dredged material from Rio de Janeiro Harbor in the inner Rio de Janeiro continental shelf. Grain size analysisof the dredged and dumped sediments was compared to the inner shelf original seabed sediments. The geomorphological impact was evaluated through bathymetricand high resolution seismic and side scan sonar imagery methods. Obtained data revealed significant geomorphologic changes on the offshore bottom caused by theaccumulation of compacted mud from the dredge site underlying the recent soft mud bottom of the harbor area. Besides the morphological sea bottom disturbance,sediment accumulation, and local grain size characteristics exhibited significant change, potentially impacting the surrounding benthic environment.Keywords: Guanabara Bay, seafloor geomorphology, marine sediments, marine pollution.RESUMO.A dragagem marinha é uma atividade de escavação subaquática executada em todo o mundo por muitas indústrias para diferentes fins. Os impactosnegativos do descarte de material dragado nos ecossistemas bentônicos são diversos. Pesquisas sobre os resultados da dragagem na geomorfologia estuarina e o seuregime sedimentar são frequentes. Ainda assim, os resultados do despejo de material dragado ao longo da costa, na plataforma continental brasileira, não são facilmenteencontrados na literatura. A presente pesquisa avaliou o distúrbio geomórfico resultante do descarte de material dragado do Porto do Rio de Janeiro na plataformacontinental interna do Rio de Janeiro. A granulometria dos sedimentos dragados e descartados foi comparada com os sedimentos originais do fundo marinho naplataforma interna. O impacto geomorfológico foi avaliado através de métodos batimétricos, sísmica de alta resolução e imageamento por sonar de varredura lateral.Os dados obtidos revelaram mudanças geomorfológicas significativas no fundo causadas pelo acúmulo de lama compactada do local dragado, subjacente ao fundode lama mole recente da área do porto. Além do distúrbio morfológico do fundo marinho, o acúmulo de sedimentos e as características locais de tamanho de grãoapresentaram mudança significativa, potencialmente impactando o ambiente bentônico circundante.Palavras-chave: Baía de Guanabara, geomorfologia submarina, sedimentos marinhos, poluição marinha.

A large-strain radial consolidation theory for soft clays improved by vertical drains

A system of vertical drains with combined vacuum and surcharge preloading is an effective solution for promoting radial flow, accelerating consolidation. However, when a mixture of soil and water is deposited at a low initial density, a significant amount of deformation or surface settlement occurs. Therefore, it is necessary to introduce large-strain theory, which has been widely used to manage dredged disposal sites in one-dimensional theory, into radial consolidation theory. A governing equation based on Gibson's large-strain theory and Barron's free-strain theory incorporating the radial and vertical flows, the weight of the soil, variable hydraulic conductivity and compressibility during the consolidation process is therefore presented.

Study on the Effects of Hydraulic Dredging and Disposal Operations on Water Quality of Nworie River, South-Eastern Nigeria

A study was done to ascertain the effect of hydraulic dredging and spoils disposal on the physicochemical parameters of Nworie River. The study was carried out from July 2010 to January, 2012. Water samples were collected prior to, during and monitored several months after dredging. The samples were collected from 5 stations: station 1 was the dredging point, stations 2 and 3 were 250m and 500m upstream of the point, while and stations 4 and 5 were 250m and 500m downstream of it respectively. The physicochemical parameters of the water were analysed prior to dredging and most of the values obtained were within acceptable limit of established water standards. The pH was within the range of 6.5-7.8, Temperature 27.6-29.9°C, Conductivity 34-196µs/cm, Turbidity 0-76NTU, TDS 22.1-127.4 mg/l, TSS 9-51 mg/l, Nitrate 1.2- 33.6mg/l, Phosphate 0.2-3.7mg/l, Sulphate 0- 33 mg/l, Dissolved Oxygen 4.3-9.4 mg/L and BOD5 2.5 - 7.9 mg/l. During the dredging, the water physicochemistry changed: pH values decreased drastically to 4.6, DO to 1.3mg/l, Nitrate to 1.2 mg/l. Temperature increased to 30. 2°C, Turbidity 620NTU, TSS 349mg/L, Conductivity 498µs/cm, TDS 249 mg/l, BOD5 19.1mg/l, Sulphate 33mg/l and Phosphate was 0.92mg/l. Three months after the dredging, the values for the parameters returned to their pre-dredging concentrations, however during rainy season, as the leachates and silts from the spoils were washed into the river, this prolonged the recovery of the river system to 9 months. This implies that the effect of dredging on the river is of short term but the disposal of the excavated materials at the river bank compounded and prolonged these impacts.

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.

Mesophotic coral ecosystems under anthropogenic stress: a case study at Ponce, Puerto Rico

Mesophotic coral ecosystems (MCEs) were compared between La Parguera and Ponce, off the south coast of Puerto Rico. In contrast to La Parguera, Ponce has a narrow insular shelf and hosts several river outlets, a commercial port, a regional sewage treatment plant with associated deep water outfall, and three deep dredge disposal sites. Off Ponce, MCEs receive higher (16×) rates of sedimentation than off La Parguera, a less impacted site. The most impacted sites were located offshore of Cayo Ratones and are in or down-current and in close proximity to one of the dredge disposal sites. There, MCEs are characterized by a steep, irregular, rocky slope with a cover of fine-grained, dark brown sediment, which increases with depth. At shallower depths, scattered rocky outcroppings are colonized by sponges, black corals and algae. The sediment cover contains two to three times the terrigenous content and a significantly higher percentage of the fine-grained fraction than off La Parguera. Thirteen remotely operated vehicle (ROV) dives east and west of Ponce showed that the deepest depth at which corals were observed increased with distance from Cayo Ratones and did not approach depths observed off La Parguera except at the eastern-most (up-current) site, Caja de Muertos, which was also significantly further offshore. Benthic communities off Caja de Muertos were comparable to those at La Parguera, while off Cayo Ratones, there were no mesophotic corals and sparse development of other benthic macrobiota except sponges. Management authorities should include MCEs when assessing potential impacts from anthropogenic activities and take the necessary steps to reduce local threats.

Laubieriopsis petersenae n. sp. and L. cf. cabiochi (Amoureux, 1982) (Polychaeta: Fauveliopsidae) from dredge disposal sites off Honolulu, Hawaii.

Fauveliopsid polychaetes have been collected at dredge disposal sites off Honolulu from 397-507 m depth. We report and describe the first Pacific record of Laubieriopsis cf. cabiochi (Amoureux, 1982), originally described from the North Atlantic. A new species, Laubieriopsis petersenae, n. sp. is described as being the species in the genus with the lowest number of body segments (15). Other distinctive features are the presence of bidentate aciculars on thoracic chaetigers, and unpaired genital papilla present on the right side of chaetiger 6/7. The new species is most similar to the L. brevis complex from the Atlantic and L. hartmanae and L. brevis japonica from the Pacific Ocean, but differs on the combination of the characters cited above. We provide an emended diagnosis for this genus to include the ultrastructure of the acicular with rows of spines, and a key to all described species.

Occurrence and possible sources of arsenic in seafloor sediments surrounding sea-disposed munitions and chemical agents near Oʻahu, Hawaiʻi

The Department of Defense disposed of conventional and chemical munitions as well as bulk containers of chemical agents in US coastal waters including those surrounding the State of Hawaiʻi. The Hawaiʻi Undersea Military Munitions Assessment has been collecting biota, water, and sediment samples from two disposal areas south of the island of Oʻahu in waters 500 to 600m deep known to have received both conventional munitions and chemical agents (specifically sulfur mustard). Unlike a number of other sea-disposed munitions investigations which used grabs or corers lowered from surface vessels, we used manned submersibles to collect the samples. Using this approach, we were able to visually identify the munitions and precisely locate our samples in relation to the munitions on the seafloor. This paper focuses on the occurrence and possible sources of arsenic found in the sediments surrounding the disposed military munitions and chemical agents. Using nonparametric multivariate statistical techniques, we looked for patterns in the chemical data obtained from these sediment samples in order to determine the possible sources of the arsenic found in these sediments. The results of the ordination technique nonmetric multidimensional scaling indicate that the arsenic is associated with terrestrial sources and not munitions. This was not altogether surprising given that: (1) the chemical agents disposed of in this area supposedly did not contain arsenic, and (2) the disposal areas studied were under terrestrial influence or served as dredge spoil disposal sites. The sediment arsenic concentrations during this investigation ranged from <1.3 to 40mg/kg-dry weight with the lower concentrations typically found around control sites and munitions (not located in dredge disposal areas) and the higher values found at dredge disposal sites (with or without munitions). During the course of our investigation we did, however, discover that mercury appears to be loosely associated with munitions. Given that mercury contamination has been seen in about 20% of the munitions and ton containers of sulfur mustard, the association of mercury with chemical agents is not totally unexpected.