Effects of long-term dumping of harbor-dredged material on macrozoobenthos at four disposal sites along the Emilia-Romagna coast (Northern Adriatic Sea, Italy)

Management of dredged marine sediments in Southern France: main keys to large-scale beneficial re-use

Fifty million cubic meters of marine sediments are dredged each year in France in order to maintain harbor activities and sustain the economy of littoral territories. Because of anthropogenic activities in and around harbors, sediments can contain significant amounts of chemical and organic pollutants whose behavior during dredging must be addressed in order to avoid releasing risks for humans and the environment. French regulations come to govern the management of dredged sediments, considering them "safe" and possible to be dumped at sea or "contaminated" and needed to be treated on land as waste. In recent years, new constraints have been pushed toward the management of land. This management is, however, challenging as few channels are proposed to reuse marine sediments, and elimination appears to be economically and environmentally unsustainable. This study provides an overview of the technical and regulatory aspects related to dredged marine sediment management in France and aims to identify and discuss the limits of their valorization. Dredged sediments are mainly composed of particles with heterogeneous grain size, some being known for many applications such as building materials and growing media. However, several reasons have been put forward to explain why these particles are not reused when extracted from dredged sediments. Several technical, socio-economic, and regulatory obstacles explain the low demand for dredged sediments. This demand can be stimulated by government incentives and a good regulatory framework. National regulations could help streamline their reuse by removing their "waste" status and creating a regulated market for dredged sediment.

Multi-benthic size approach to unveil different environmental conditions in a Mediterranean harbor area (Ancona, Adriatic Sea, Italy)

Harbors are hubs of human activity and are subject to the continuous discharge and release of industrial, agricultural, and municipal waste and contaminants. Benthic organisms are largely known to reflect environmental conditions they live in. Despite meio- and macrofauna interacting within the benthic system, they are ecologically distinct components of the benthos and as such may not necessarily respond to environmental conditions and/or disturbances in the same way. However, in a few field studies the spatial patterns of meio- and macrofauna have been simultaneously compared. In the present study, we assess the response and patterns in the abundance, diversity, and distribution of the two benthic size classes to the different environmental conditions they live in (i.e., sediment concentrations of selected trace metals and polycyclic aromatic hydrocarbons (PAHs); organic matter contents and grain size) characterizing the Ancona Harbor (Adriatic Sea). Meio- and macrofauna provided partially similar types of information depending on the indices used (univariate measures or community structure/species composition) and the different 'response-to-stress'. The community structure (i.e., taxa composition) of both benthic size components clearly showed differences among sampling stations located from inside to outside the harbor, reflecting the marked environmental heterogeneity and disturbance typically characterizing these systems. Notwithstanding, the univariate measures (i.e., meio- and macrofauna total abundance, diversity indices and equitability) didn't show similar spatial patterns. Meiofauna were likely to be more sensitive to the effects of environmental features and contaminants than macrofauna. Overall, trace metals and PAHs affected the community composition of the two benthic components, but only the meiofauna abundance and diversity were related to the environmental variables considered (i.e., quantity and quality of organic matter). Our results pinpoint the importance of studying both meio- and macrofauna communities, which could provide greater insight into the processes affecting the investigated area and reveal different aspects of the benthic ecosystems in response to harbor conditions.

Water Turbidity and Suspended Particulate Matter Concentration at Dredged Material Dumping Sites in the Southern Baltic

Dredged material dumping is an activity that causes some of the greatest changes in coastal waters. It results in the need to regularly monitor the properties of seawater related to water quality. In this study, we present the first wide-ranging attempt to correlate seawater turbidity and suspended particulate matter (SPM) concentrations within dumping sites and adjacent waters on the basis of in situ measurements. In the years 2019-2020, we examined four dumping sites, namely Darłowo, Gdynia, Gdańsk, and DCT, located in Polish coastal waters of the Baltic Sea, in the course of four measurement campaigns conducted in the spring, summer, autumn, and winter. The measurements were conducted using a turbidity sensor to determine the turbidity, in formazin turbidity units (FTU), a spectrophotometer to determine the concentrations of nutrients (total phosphorus (P-tot), phosphate phosphorus (P-PO₄^-3), total nitrogen (N-tot), ammonium nitrogen (N-NH₄⁺), and nitrate nitrogen (N-NO₃^-)), as well as glass microfiber filters to determine the concentrations of SPM. The analysis of the relationship between the turbidity and SPM within the dumping sites in comparison to reference points showed that the dumping sites are very complex waters and that the issue must be approached locally. The highest turbidity values were registered in the spring, and they correlated linearly with the SPM concentrations (R² = 0.69). Moreover, we performed a statistical cluster analysis to illustrate the similarities between sampling points in the four dumpsites based on nutrient concentrations. We conclude that the influence of the dumping sites on the local bio-optical and chemical properties significantly exceeds their borders and spreads to the adjacent waters. Nutrient concentrations in many cases exceeded the legal policy limits.

Benthic impact assessment of a dredge sediment disposal in a dynamic resilient environment

The eastern part of the Bay of Seine (English Channel) is highly impacted by harbour activities and the dumping of dredged sediment by the port authorities of Le Havre (GPMH) and Rouen (GPMR). Sediment dredged by the GPMH (2-2.5 millions of m³ per year) has been disposed at the subtidal Octeville site since 1947. Since the 2000s, mainly fine sediment (80% of fine particles <63 μm) has been disposed using alternate mosaic boxes with limited thickness (0.2 to 0.6 m per box per year), preventing the accumulation of disposed sediment in some parts of the dumping site. During the period August 2016 to September 2017, an experimental study was set up to identify the spatio-temporal changes of the macrobenthos collected at ten stations on six dates: three stations where different volumes of sediments were dumped (from 41,000 to 186,000 m³), two stations located within the Octeville site but without dumping operations during the study and five stations outside the disposal site (northern and southern zones). The Taxonomic Richness, total abundance and abundances of the polychaete Owenia fusiformis show negative correlations with the volumes of deposited sediment, whereas use of the AMBI (AZTI's Marine Biotic Index) and B2OA (Benthic Opportunist Annelids Amphipods) indices does not allow us to distinguish the impacted zone. Our study shows that the impact of dumping remains local and the benthic habitats display a high degree of resilience with rapid recovery of the community after the cessation of disturbance. Recommendations on the future long-term strategy are proposed to improve assessment and minimise the impact of dumping sediment on this benthic habitat.

Long-term changes in the macrobenthic assemblages at a harbour sediment disposal site in the southern North Sea

This study focussed on the long-term, sediment-driven changes of macrobenthic assemblages in dredged harbour sediment from Rotterdam harbour disposed of in excavated sand extraction pits off the Dutch coast. Macrobenthic species and sediment grain size composition were studied in samples from two disposal sites and the surrounding environment over ten years after the cessation of disposal activities. There was a strong association between the sediment granulometry and the benthic assemblage composition. Shortly after the last discharge, the top layer of the sediments in the pits contained 20%-60% mud (particles <63 μm) and was colonised by benthic species typical for these sediments. The pit sediments and benthic assemblages contrasted strongly with the surrounding medium-coarse sediment, extremely low in mud (<0.01%). Over eight to ten years, the top layers of the disposal sites became significantly less muddy (ca. 5%-15% mud), and the benthic assemblages changed over this period from mud-favouring species dominated by annelids to species preferring fine sand with relatively low mud percentages dominated by molluscs. The two different disposal sites converged in sediment composition and benthic assemblages over the ten years of monitoring. The contrast with the medium-coarse sediments with very low mud percentages remained even after this period. The use of sand extraction pits as disposal sites for dredged harbour sediments may be seen as an economically sound beneficial use option in dredged material management, albeit with long-term ecological effects.

Effects of maintenance dredging on the macrofauna of the water column in a turbid estuary

Many human activities in or near aquatic habitats generate alterations in their environmental conditions, which could affect the organisms that inhabit them. Maintenance dredging of navigation channels in order to allow large ships access to inland ports is one such source of disturbance. In this study, by taking multiple approaches (immediate-, short- and medium term), we analysed the effects of a maintenance dredging operation on physiochemical variables and the early life stages of fish and other macrofauna groups present in two zones of the Guadalquivir estuary with different salinity ranges (poly- and mesohaline). Most physiochemical variables were homogenized in the water column immediately after the water mass passed by the dredger, including sediment resuspension. However, this process seemed to be transient as no significant increments in the depth-averaged levels of turbidity were observed in the short- and medium-terms. Instead, metal concentrations of Cr, Fe and Zn increased in the polyhaline station. Even so, these perturbations did not appear to be severe enough to influence the macrofauna. Still, organisms can suffer direct mechanical impacts of the trailer suction. Hyperbenthic species, like Pomatoshcistus spp. or decapods, tended to decrease slightly, while pelagic species such as Engraulis encrasicolus or mysids did not, indicating that benthic organisms are usually more susceptible to high entrainment. Nonetheless, the possible effects of this disturbance were of the same order or less than those of natural ones; therefore, organisms of the macrofauna could be well adapted to cope with them.

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.

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.

Soft-bottom community responses in a marine area influenced by recurrent dumping activities and freshwater discharges

The results of a 3 years monitoring program to assess the effects associated with recurrent dredged spoil disposal activity in a naturally stressed subtidal coastal area subjected to estuarine inputs are described. Changes observed through time in environmental and anthropogenic variables have been analyzed using cumulated sums and compared to macrobenthic community structure. Results revealed a scarce impact of the recurrent dumping activities, with faunal assemblages derived from the main "Tellina-venus community". The magnitude of estuarine influence appeared indeed greater on the soft-bottom community than the putative changes due to anthropogenic activities. Through a combination of high energetic conditions, structural changes were observed and ascribed to a flushing action of the highly channeled estuary. Finally, an exceptional flood was recorded over the monitoring period, resulting in a short-term spatial homogenization of the benthic community with an abundance burst of A. alba. Origins of this main new species are discussed.

Macrobenthic fouling assemblages and NIS success in a Mediterranean port: The role of use destination

Macrozoobenthic fouling assemblages were studied in the port area of Livorno, focusing on the occurrence of non-indigenous species (NIS). Sampling was carried out at ten sites characterised by different anthropic impacts related to their use destination. Among the 262 species identified, twenty-six were alien or cryptogenic, seventeen of which were new records for the study area, confirming the role of the port of Livorno as a hotspot of NIS introduction. Multivariate analyses highlighted a strong influence of the use destination on the diversity of macrozoobenthic communities. Even though the majority of transoceanic maritime traffic from and to Livorno pertains to the commercial harbour, the touristic harbour hosted the highest number of NIS, possibly because of secondary spread from other Mediterranean ports. The ALien Biotic IndEX (ALEX) identified all sites as high or good environmental status, but the large number of NIS detected suggests caution about their impact and further spread.

Effects of fish cage culture and suspended oyster culture on macrobenthic communities in Xiangshan Bay, a semi-enclosed subtropical bay in eastern China

The impacts of fish cage culture and suspended oyster culture on macrobenthic communities were investigated in Xiangshan Bay, China, on a seasonal basis from January to October of 2015. Samples were collected from a fish cage farm, a suspended oyster farm, and two corresponding reference sites. Two-way ANOVA results showed that species richness, abundance, biomass, and Shannon-Wiener diversity differed significantly between the four different investigated areas, and different seasons as well. Cluster analysis showed that macrobenthic community composition in the fish and oyster culture areas significantly differed from that in the reference sites, respectively. Trophic structure of macrobenthos in the fish and oyster culture areas mostly clustered together owing to higher abundance and biomass of surface-deposit feeders and carnivores. The macrobenthic communities and feeding guilds correlated highly with environmental factors, such as bottom water chlorophyll a and nutrients, as well as sediment total organic carbon. Although integrated multi-trophic aquaculture is regarded as a suitable approach to coordinate desirable economic, social, and environmentally sustainable outcomes, coastal ecosystems may suffer from large-scale nutrient enrichment due to aquaculture and other human activities, which should not be considered in isolation.

Quantitative Assessment of the Environmental Impacts of Dredging and Dumping Activities at Sea

The dumping of dredge materials often raises concerns about the release of pollutants to the marine environment. Wind data from the Global Forecast System (GFS) model was used to simulate the wind-wave propagation from offshore in a two-dimensional (2D) model during September and October 2016. The calibration and validation of the 2D model showed a high conformity in both the phases and amplitude between the observed and simulated data. The 2D mud transport simulation results of three scenarios showed that the concentration of suspended material in the third scenario tested (scenario 3) was greater than 0.004 kg/m3 in the low tide, spreading to a 9 km2 area, and in the high tide, the concentration was 0.004 kg/m3 in a 6 km2 area. Finally, the results of 2D particle tracking (PT) showed changes in the seabed due to the concentration of dredged material, and its dump (approximately 180 days) increased from 0.08 m to 0.16 m in 2.85 ha. In scenario 3, the element block moved quite far—approximately 2.9 km—from the dredge position. Therefore, the simulation results were qualified, as the dredging position situated far from the sea is significantly affected by the direction and velocity of wave-wind in the dredging position.

Effects of the installation of offshore pipelines on macrozoobenthic communities (northern and central Adriatic Sea)

Macrozoobenthos living around several pipelines placed at different depths and sediment types in the Western Adriatic Sea was investigated for three years after structures' deployment to detect possible effects due to their installation and presence. Three environmental habitats were considered based on the grain size (silty clay, clayey silt and sand). Samplings were taken within a radius of 100 m from the pipelines and at control sites. Multivariate and univariate analysis showed peculiarities of the three habitats due to the different sediment type, without differences between pipelines and controls inside each group. Silty clay and clayey silt communities appeared quite similar, being mainly represented by opportunistic species typical of the Adriatic coastal area. Benthic populations found at the offshore relict sand were characterized by a higher percentage of sensitive species. Independently of sediment typology, pipelines' installation seems to not affect the benthic populations that appear more influenced by environmental features.

Maintenance dredging impacts on a highly stressed estuary (Guadalquivir estuary): A BACI approach through oligohaline and polyhaline habitats

Understanding the effects of dredging in estuaries is a hard task due to the difficulty of implementing an adequate environmental diagnosis, as a consequence of the salinity gradient and anthropogenic disturbances. To assess the effects of maintenance dredging work on the Guadalquivir estuary (southwestern Spain), we used a Before-After-Control-Impact (BACI) approach to determine both direct and indirect effects in two salinity ranges. No effects were found on water and sediment physicochemical characteristics. The small impacts on dredged areas were followed by a rapid recovery of opportunistic species. The poor status of the benthos does not permit the detection of significant effects on macrofaunal community structure. The use of stable isotopes analysis to determine impacts on food web structure showed that changes over time seem to be explained by natural temporal variation rather than the dredging works. This paper emphasises the need to define proper management and conservation plans to improve the status of the benthic communities of the Guadalquivir estuary.

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.

Environmental assessment of contaminated marine sediments treated with solidification agents: Directions for improving environmental assessment guidelines

Treatment of dredged materials is a critical issue, since management and disposal of these products requires considerable investment of monetary resources, time, and space. The high concentration of pollutants in dredged materials, along with high water content and many fine particles make recycling these materials particularly difficult. In order to solve this problem, solidification/stabilization has been considered as a potentially viable solution for recycling dredged marine sediments. However, there are currently no guidelines that address potential biological and environmental impacts. To evaluate the stability of treated materials and their biological impacts, dredged marine sediments, which were polluted with heavy metals, were treated by solidification/stabilization using two different solidifying agents. To assess potential impacts, toxicity characteristic leaching procedures (TCLP, USEPA) and a bioassay (with the rotifer, Brachionus sp.) were performed with treated materials. In a TCLP test, we found that treatment with a solidification agent decreased the leaching concentration of heavy metals from sediment compared to the control. The rotifer bioassay showed no change in the survival rate during 24 h of exposure to both agents. However, survival differed between the two agents after 48 h of exposure. Screening physiological status using gene expression, showed that oxidative stress genes were significantly altered. These results suggest that more studies are needed to provide guidelines for deciding the usability of treated materials created by the solidification or stabilization of dredged materials.

Dangerous compounds in the dredged material from the sea - Assessment of the current approach to the evaluation of contaminations based on the data from the Polish coastal zone (the Baltic Sea)

It has been shown that the current approach to the assessment of contamination in the sediments obtained during the dredging works in the Baltic countries indicates the presence of "non-contaminated" dredged material. The concentration limits of heavy metals, Polycyclic Aromatic Hydrocarbons (PAHs), Polychlorinated Biphenyls (PCBs) have been exceeded only in 1% of the samples obtained during the dredging works (2005-2015) within the Polish coastal zone. After 2008, no contaminated sediments have been found. Also, in the remaining Baltic countries, sediments are very rarely contaminated. As a result of this assessment, the sediments can be stored in the sea or have a practical application. However, it has been questioned whether the large cost of determining the numerous chemical parameters is justified. It has been proposed to carry out simple screening tests. Following the preliminary screening, the decision on more detailed (and expensive) chemical tests of individual pollutants would be made.

Improving the monitoring of a dumping site in a dynamic environment. Example of the Octeville site (Bay of Seine, English Channel)

Dredged sediments have different physical and chemical characteristics compared with the sediments in place, which generates multiple effects on the environment. In this study, we show that the sampling strategy used to monitor the effects of dredge spoil deposition on the surrounding environment can lead to different interpretations. It appears that sediment sample replicates may or may not be necessary, depending on the studied area, the prevailing environmental forcings before sediment sampling and the combination of these two factors. The proposed modus operandi allows us to optimize both the confidence on the obtained results and the cost of the sediment studies (sampling and laboratory analyses). The results are based on the sediment fine fraction, which is considered as a key environmental component due, for example, to its strong association with the structure of benthic faunal communities as well as its role in the build-up of pollutants.

Limited impact of beach nourishment on macrofaunal recruitment/settlement in a site of community interest in coastal area of the Adriatic Sea (Mediterranean Sea)

Beach nourishment is a widely utilized solution to counteract the erosion of shorelines, and there is an active discussion on its possible consequences on coastal marine assemblages. We investigated the impact caused by a small-scale beach nourishment carried out in the Western Adriatic Sea on macrofaunal recruitment and post-settlement events. Artificial substrates were deployed in proximity of nourished and non-manipulated beaches and turbidity and sedimentation rates were measured. Our results indicate that sedimentation rates in the impacted site showed a different temporal change compared to the control sites, suggesting potential modifications due to the beach nourishment. The impact site was characterized by subtle changes in terms of polychaete abundance and community structure when compared to controls, possibly due to beach nourishment, although the role of other factors cannot be ruled out. We conclude that small-scale beach nourishments appear to be an eco-sustainable approach to contrast coastal erosion.

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.

Differential responses of marine communities to natural and anthropogenic changes

Responses of ecosystems to environmental changes vary greatly across habitats, organisms and observational scales. The Quaternary fossil record of the Po Basin demonstrates that marine communities of the northern Adriatic re-emerged unchanged following the most recent glaciation, which lasted approximately 100,000 years. The Late Pleistocene and Holocene interglacial ecosystems were both dominated by the same species, species turnover rates approximated predictions of resampling models of a homogeneous system, and comparable bathymetric gradients in species composition, sample-level diversity, dominance and specimen abundance were observed in both time intervals. The interglacial Adriatic ecosystems appear to have been impervious to natural climate change either owing to their persistence during those long-term perturbations or their resilient recovery during interglacial phases of climate oscillations. By contrast, present-day communities of the northern Adriatic differ notably from their Holocene counterparts. The recent ecosystem shift stands in contrast to the long-term endurance of interglacial communities in face of climate-driven environmental changes.

Spatio-temporal pattern of community development in dredged material used for habitat enhancement: A study case in a brackish lagoon

Dredged material is a potential resource for beneficial use for create/improve subtidal habitats. In a northwestern Adriatic lagoon, dredged sand was placed in inner areas with the management objective of improving the characteristics of the muddy areas being recharged. With this study we investigated the recolonization dynamics of benthic communities following the placement of dredged sand in a microtidal lagoon. The disposal of dredged sand had an immediate and negative effect on resident fauna. After an initial reduction, benthic communities followed different recovery pathways. One year after disposal, we recorded an almost complete recovery of the benthic invertebrates in terms of univariate parameters. Despite multivariate analyses still showed significantly different community structures, the trajectories of recovery for disposal areas converged towards the same basin of attraction of control areas. The ecological quality of sites, assessed with benthic indices, did not improve, thus no new beneficial habitat was created for macrobenthos.

Impacts of maintenance dredged material disposal on macrobenthic structure and secondary productivity

The results of a monitoring programme to assess the spatial impacts associated with ongoing dredged material disposal activity at a dispersive, coastal disposal site (southwest UK) are described. Benthic impacts were assessed using benthic community structure and secondary productivity estimates. Analyses of univariate indices (including secondary production) and multivariate community structure revealed differences between stations inside and those outside the disposal site were minimal. Generally, stations within and outside the disposal site were characterised by the same species. Regression models indicated that the variability in biological structure and secondary production was predominantly accounted for by natural variables (e.g., depth, sediment granulometry) with only a small amount of residual variability being due to contaminant variables. Thus, the elevated levels of certain contaminants in the vicinity of the disposal area were not sufficient to result in significant ecological or ecotoxicological changes. We ascribe such findings partly to the dispersive nature of the disposal site.

Monitoring the effects of disposal of fine sediments from maintenance dredging on suspended particulate matter concentration in the Belgian nearshore area (southern North Sea)

The impact of continuous disposal of fine-grained sediments from maintenance dredging works on the suspended particulate matter concentration in a shallow nearshore turbidity maximum was investigated during dredging experiment (port of Zeebrugge, southern North Sea). Before, during and after the experiment monitoring of SPM concentration using OBS and ADV altimetry was carried out at a location 5 km west of the disposal site. A statistical analysis, based on the concept of populations and sub-sampling, was applied to evaluate the effect. The data revealed that the SPM concentration near the bed was on average more than two times higher during the dredging experiment. The disposed material was mainly transported in the benthic layer and resulted in a long-term increase of SPM concentration and formation of fluid mud layers. The study shows that SPM concentration can be used as an indicator of environmental changes if representative time series are available.

Recovery from the impact of light reduction on the seagrass Amphibolis griffithii, insights for dredging management

A large-scale, manipulative experiment was conducted to examine the extent and rate of recovery of meadows of the temperate Australian seagrass, Amphibolis griffithii to different light-reduction scenarios typical of dredging operations, and to identify potential indicators of recovery from light reduction stress. Shade cloth was used to mimic different intensities, durations and start times of light reduction, and then was removed to assess the recovery. The meadow could recover from 3 months of light stress (5-18% ambient) following 10 months re-exposure to ambient light, even when up to 72% of leaf biomass was lost, much faster recovery rates than has previously been observed for large seagrasses. However, when the meadow had been shaded for 6-9 months and more than 82% of leaf biomass was lost, no recovery was detected up to 23 months after the light stress had ceased, consistent with other studies. Five potential indicators of recovery were recommended.

Ecological evaluation of an experimental beneficial use scheme for dredged sediment disposal in shallow tidal waters

An experiment was performed to test an alternative dredging strategy for the Westerschelde estuary. Clean sand dredged from the navigation channel was disposed seawards of an eroding intertidal flat in order to modify morphology and hydrodynamics, improving the multi-channel system with ecologically productive shallow water habitat. Five years of intensive monitoring revealed that part of the disposed sediment moved slowly towards the flat, increasing the very shallow subtidal and intertidal area, as planned. The sand in the impact zone became gradually finer after disposal, possibly due to reduced current velocities. Nevertheless, no changes in macrobenthic biomass, density, species richness and composition were detected in the subtidal zone, also demonstrating rapid macrobenthic recovery. In the intertidal zone, no ecological effects could be revealed superimposed on trends associated with long-term sediment fining. Thus, despite morphological success and absence of detected negative ecological impacts of the experiment, new beneficial habitat was not created.

A multi-criteria approach for the dumping of dredged material in the Thermaikos Gulf, Northern Greece

A multi-criteria approach was applied for the disposal into the sea of ∼1,100,000 m(3) of sediment, dredged from a coastal area in the northeastern part of the Thermaikos Gulf. This sediment (classified as muddy) is distributed vertically into two distinct Layers (A and B) with the thickness of the surficial sedimentary unit ranging from 7 to 54 cm. Its geochemistry reveals increased Cr and Ni concentrations, which may be attributed to natural enrichment through the erosion of the adjacent igneous and metamorphic rocks. In addition, a low to moderate contamination from urban-originated heavy metals, like Cu, Pb and Zn as well as from aliphatic and polycyclic hydrocarbons was identified for the upper Layer A. However, the limited proportion (5.5%) of the polluted Layer A in the total volume of the dredged material could not affect the good quality (assessed by the Sediment Quality Guidelines) of the bulk sediment. The identification of the optimum marine dumping site was based on (a) the physicochemical similarity (detected by the application of a cluster analysis) of the dredged material with the surficial deposits of potential dumping sites in the Outer Thermaikos Gulf, and (b) the consideration, based on previous studies, of various criteria related to the disposal area such as deep-water circulation, influence on living resources, impact on economical (aquaculture, fishing, navigation), recreational (fishing) and military activities.

Benthic ecosystem development in an artificial tidal flat constructed from dredged spoil

Dredged spoil (DS) was used as a silt and clay additive in the construction of artificial tidal flats from mountain sand (MS). As the ratio of DS in the sediment media increased, the number of emerging macrobenthos increased. The composition of the macrobenthic community was also affected by the addition of DS, and the changes might be dependent on the ratio of DS to MS. In addition, the macrobenthos in the artificial tidal flats was more abundant than that in the control tidal flat, which was constructed with natural tidal flat sediment. With a silt and clay content of 25%, polychaetes Ceratonereis erythraeensis and Capitella sp. and the gastropod Batillaria cumingii were dominant, whereas no bivalves were present. With less silt and clay (5% and 10%), the bivalves Ruditapes philippinarum and Musculista senhousia were observed in the artificial flats, while their numbers in the control tidal flat were lower.

Responses of a Northern Adriatic Ampelisca-Corbula community to seasonality and short-term hydrological changes in the Po river

During the 20th century, increased nutrient inflow has increased the frequency and intensity of eutrophication events in the North-western Adriatic Sea. More recently, evidence of a reduction in the Po river flow and a recovery of the benthic environment were reported. We examined the role played by Po river regime and seasonality in determining the temporal pattern of macrozoobenthos variation: samples were collected from a site located 10-12km off Cesenatico during two years from October 2004 to September 2006, when the mean Po discharge remained exceptionally low. 88 taxa were found, and the community was dominated by few species: Ampelisca diadema, Lumbrineris latreillii, Corbula gibba, Aricidea claudiae, Levinsenia gracilis and Nucula nucleus account for about 80% of total abundances. The density of these species exhibited a marked seasonal variability. Moreover, the total abundance and the density of the sensitive species, A. diadema, were negatively affected by several disturbance events (hypoxic conditions, frequent storms and an anomalous winter flood) that occurred between November 2005 and March 2006. The reduction of C. gibba and the increase of A. diadema densities observed in the investigated period, and verified recently by other authors could be related to the reduction in river inputs as a consequence of climatic changes.

A field experimental study on recolonization and succession of subtidal macrobenthic community in sediment contaminated with industrial wastes

A field experiment was carried out in Hong Kong to study the patterns of recolonization and succession of subtidal macrobenthos in defaunated sediment contaminated with industrial wastes and to determine the time required for benthic recovery in the industrial-contaminated sediment. A total of 50 species was found with an average of 172 animals/tray and 24 species/tray recorded one month after deployment. Initial colonizers were predominantly polychaetes (96 animals/tray, accounting for 55.7%) and gastropods (47 animals/tray, accounting for 27.2%). Abundance of macrobenthos increased quickly to a peak (505 animals/tray) after four months, declined afterwards, and increased again till the end of the experiment. Species number peaked (57 species/tray) in the same month as abundance did, and gradually declined thereafter. Abundance, species number and diversity were significantly lower in the industrial-contaminated sediment as compared to the controls during the early successional stages, indicating the harmful effects of industrial wastes on recolonization and succession of macrobenthos. Although no significant differences in community parameters between the industrial-contaminated and the control sediments were found after eleven months, significant difference in species composition still existed after fourteen months, showing a relatively long-term impact of industrial wastes on macrobenthic community structure.