Changes in maerl-associated macroalgal community dynamics as evidence of anthropogenic pressure.

BACKGROUND AND AIMS: Maerl-associated communities have received considerable attention due to their uniqueness, biodiversity and functional importance. Although the impacts of human activities are well documented for maerl-associated macrofauna, the spatio-temporal variations of macroalgae have comparatively been neglected, and the drivers that influence their dynamics are poorly known. We investigate the links between maerl-associated macroalgal communities, anthropogenic pressures and environmental conditions, and hypothesize that sites under human pressure would exhibit different dynamics when compared to reference sites. METHODS: To better understand community variation through space and time, four subtidal maerl beds under different pressures were consistently monitored over one year in the bay of Brest, Brittany, France. Both macroalgae community monitoring and environmental data were acquired through field sampling and available models. KEY RESULTS: Higher macroalgal biomass was observed within eutrophic sites, especially in summer (more than ten times higher than in the Unimpacted site), caused by free-living forms of opportunistic red macroalgae. The Dredged site also exhibited distinct macroalgal communities during summer from the Unimpacted site. Nutrient concentrations and seasonality proved to be key factors affecting the macroalgal community composition, although dredging and its effects on granulometry also had a strong influence. Over the long term, fewer than half of the species identified during historical surveys were found, indicating major temporal changes. CONCLUSIONS: Human pressures have strong impacts on maerl-associated macroalgal communities. Nutrient concentrations and dredging pressure appear as the main anthropogenic factors shaping maerl-associated macroalgal communities. Additionally, our results suggest historical changes in maerl-associated macroalgal communities over 25 years in response to changes in local human pressure management. This study suggests that maerl-associated macroalgal communities could be used as indicators of anthropogenically driven changes in this habitat.

Combining dredging with modified zeolite thin-layer capping to control nitrogen release from eutrophic lake sediment.

Dredging is widely used to control internal sediment nitrogen (N) pollution during eutrophic lake restoration. However, the effectiveness of dredging cannot be maintained for long periods during seasonal temperature variations. This study used modified zeolite (MZ) as a thin-layer capping material to enhance dredging efficiency during a year-long field sediment core incubation period. Our results showed that dredging alone more effectively reduced pore water N, N flux, and sediment N content than MZ capping but showed more dramatic changes during the warm seasons. The N flux in dredged sediment in summer was 1.8 and 2.5 times that in spring and autumn, respectively, indicating a drastic N regeneration process in the short term. In contrast, the combination method reduced the extra 10% pore water N, 22% N flux, and 8% sediment organic N content compared with dredging alone and maintained high stability during seasonal changes. The results indicated that the addition of MZ to the surface of dredged sediment not only enhanced the control effect of dredging by its adsorption capacity but may also smooth the N regeneration process via successive accumulation (in the channel of the material) and activation of bacteria for months, which was evidenced by the variation in microbial diversity in the MZ treatment. As a result, the combination of dredging with modified zeolite simultaneously enhanced the efficiency and stability of the single dredging method in controlling sediment N content and its release, exhibiting great prospects for long-term application in eutrophic lakes with severe pollution from internal N loading.

Microplastic in Dredged Sediments: From Databases to Strategic Responses.

Microplastics (MPs) accumulate in sediments, yet guidelines for evaluating MP risks in dredged sediments are lacking. The objective of this study was to review existing literature on MPs in sediments to improve fundamental knowledge of MP exposures and develop a publicly available database of MPs in sediments. Twelve percent of the reviewed papers (nine studies) included sediment core samples with MP concentrations generally decreasing with depth, peaking in the top 15 cm. The remaining papers evaluated surficial grab samples (0 to 15 cm depth) from various water bodies with MPs detected in almost every sample. Median MP concentrations (items/kg dry sediment) increased in this order: lakes and reservoirs (184), estuarine (263), Great Lakes nearshore areas and tributaries (290), riverine (410), nearshore marine areas (487), dredge activities (817), and harbors (948). Dredging of recurrent shoaling sediments could be expected to contain MPs at various depths with concentrations influenced by the time elapsed since the last dredging event. These results offer key insights into the presence and variability of MPs in dredged sediments, informing environmental monitoring and risk assessment strategies.

Ecotoxicity of marine sediments: Sampling and laboratory artifacts and their impacts on risk classification.

Assessing the ecotoxicological risk of marine sediments is now a critical factor in deciding how to treat dredged material in harbor and coastal areas. Although ecotoxicological analyses are routinely required by some regulatory agencies in Europe, laboratory skills necessary to perform them are often underestimated. According to the Italian Ministerial decree No. 173/2016, ecotoxicological tests are performed on the solid phase and elutriates, and the classification of sediment quality is defined using the "Weight of Evidence" (WOE) approach. However, the decree does not provide adequate information regarding the preparation techniques and laboratory skills. As result, a wide variability among laboratories occurs. An error in the classification of ecotoxicological risk has a negative impact on the whole environmental quality and/or the economy and management of the interested area. Thus, the main aim of this study was to determine if such variability can affect the ecotoxicological outcomes of tested species and WOE associated classification, producing different options for the management of dredged sediments. Four different sediment types were selected to assess the ecotoxicological responses and their changes as a function of variability of the following factors: a) the storage time laps (STL) for both the solid phase and the elutriates; b) the methods used to prepare the elutriates (centrifugation vs. filtration), and the conservation method used for the elutriates (freshly prepared vs. freezing). Results suggest a wide variability of ecotoxicological responses among the four sediment samples here considered, differentiated according to chemical pollution, grain-size texture, and macronutrient contents. The storage time laps significantly affect the physicochemical parameters and the ecotoxicity of both the solid phase test and elutriates. For the elutriates preparation, centrifugation is preferred to filtration to preserve a better representation of sediment heterogeneity. Freezing of elutriates does not seem to show any significant effects on the toxicity. Findings allow to define a weighted schedule of the storage time of sediments and elutriates useful for laboratories to scale analytical priority and strategies related to different sediment types.

Effects of sediment resuspension and changes in water nutrient concentrations on the remobilization of lead from contaminated sediments in Klity Creek, Thailand.

As Pb-containing sediments in Klity Creek have had negative impacts on the area for more than 20 years, the Supreme Court ordered the Pollution Control Department (PCD) of Thailand to remediate the site. In response to the court order, the PCD decided to reduce the contamination level by dredging the sediments of the creek. Therefore, this study is the first investigation to be conducted on the coupled effects of sediment resuspension caused by dredging and changes in water nutrient concentrations upon the remobilization of Pb from sediments into the water column. The Pb concentrations and speciation in both the water and sediments collected from upstream and downstream regions of the contaminated area were determined. The results showed that the total Pb concentrations in the water taken from all sampling sites in both the dry and wet seasons were lower than the national standard (50 µg/L), and a very low mobility index was found for Pb. The highest total Pb concentration in the sediments (6930 mg/kg) from the downstream site was 23.7- to 30.4-fold greater than those of the sediments collected from the upstream site. The predominant Pb species (organic and residual Pb fractions) in the sediments collected during the dry season were identified. However, carbonate- and Fe-Mn oxide-bound Pb fractions were mainly found in the sediments collected in the wet season. The diffusive gradients in thin films (DGT)-labile Pb concentrations, which reached 2.1 mg/L, indicated potential toxicity to aquatic organisms. A total of nine resuspension scenarios generalizing all changes in water nutrient concentrations in addition to sediment resuspension due to dredging were constructed. The results confirmed that sediment resuspension alone could remobilize Pb from the sediments into the water at levels from 0.06 to 16.9 µg/L. Sediment resuspension in water contaminated with 1 mg/L phosphate (PO43-) led to the dissolution of 28.4-73.0 µg/L Pb in the water column. Nitrate (NO3-) did not significantly remobilize Pb from the sediments into the water. The high ionic strength and activity coefficient of PO43- in the water were expected to cause the retention of dissolved Pb in the water and enhance the remobilization of Pb from the sediments due to the association of Pb with PO43- in the water.

[A case of corrosive digestive tract and lung injury caused by ingestion of pipeline dredging agent].

Ingestion of corrosive substances can severely burn the upper digestive tract leading to bleeding or perforation, and may even be life-threatening. Less commonly, damage to the trachea and bronchi is involved. In this paper, a case of corrosive digestive tract injury and lung injury after oral administration of pipeline dredging agent (the main components are hydroxide, sodium carbonate, sodium hypochlorite, etc.) was analyzed. After active rescue treatment, the patient died of massive hemoptysis. It is suggested that serious complications may occur after ingestion of corrosive substances. Timely diagnosis and reasonable medical management are needed to improve the level of recognition and treatment of such diseases.

The impact of mobile demersal fishing on carbon storage in seabed sediments.

Subtidal marine sediments are one of the planet's primary carbon stores and strongly influence the oceanic sink for atmospheric CO2 . By far the most widespread human activity occurring on the seabed is bottom trawling/dredging for fish and shellfish. A global first-order estimate suggested mobile demersal fishing activities may cause 0.16-0.4 Gt of organic carbon (OC) to be remineralized annually from seabed sediment carbon stores (Sala et al., 2021). There are, however, many uncertainties in this calculation. Here, we discuss the potential drivers of change in seabed sediment OC stores due to mobile demersal fishing activities and conduct a literature review, synthesizing studies where this interaction has been directly investigated. Under certain environmental settings, we hypothesize that mobile demersal fishing would reduce OC in seabed stores due to lower production of flora and fauna, the loss of fine flocculent material, increased sediment resuspension, mixing and transport and increased oxygen exposure. Reductions would be offset to varying extents by reduced faunal bioturbation and community respiration, increased off-shelf transport and increases in primary production from the resuspension of nutrients. Studies which directly investigated the impact of demersal fishing on OC stocks had mixed results. A finding of no significant effect was reported in 61% of 49 investigations; 29% reported lower OC due to fishing activities, with 10% reporting higher OC. In relation to remineralization rates within the seabed, four investigations reported that demersal fishing activities decreased remineralization, with three reporting higher remineralization rates. Patterns in the environmental and experimental characteristics between different outcomes were largely indistinct. More evidence is urgently needed to accurately quantify the impact of anthropogenic physical disturbance on seabed carbon in different environmental settings and to incorporate full evidence-based carbon considerations into global seabed management.

The desorption mechanism of dissolved organic matter on pollutants and the change of biodiversity during sediment dredging.

Sediment dredging is an effective means to control the endogenous pollution of lakes, which could significantly change the concentration and composition of organic matter, especially dissolved organic matter (DOM) in the lake. DOM is particularly important for the release of endogenous pollutants, which will inevitably bring an impact on aquatic biodiversity. Nevertheless, in recent research little attention has been paid to the desorption mechanism of DOM on pollutants and the change of biodiversity during dredging. This study investigated the physicochemical properties of DOM in the sediment by taking a sediment dredging project in Dianchi Lake in China for example. The correlations of DOM properties with the desorption behavior of nitrogen (N), phosphorus (P), cadmium (Cd), lead (Pb) and the biodiversity of aquatic organisms were analyzed. The results show that the aromaticity and humification of DOM were improved after dredging, and the high molecular weight DOM was degraded into low molecular weight substance. The desorption amount of N, P and heavy metals (Cd, Pb) were decreased as the pH values increased. Moreover, NH4+-N promoted the release of Pb2+ from DOM, while the release of PO43--P was inhibited. Correlation analysis shows that the physicochemical properties of DOM exactly affected the release of N, P, Cd and Pb. It was easier to desorb pollutants with low aromaticity and humification of DOM, leading to a decrease in the diversity of aquatic organisms. This study identified the desorption mechanism of endogenous pollutants in DOM and the ecological risk to aquatic organisms, providing a theoretical basis for the prevention and control of water pollution.

A Simple and Effective Method for Measuring the Density of Non-Newtonian Thickened Tailings Slurry during Hydraulic Transport.

The extension of the Zelazny Most tailings store facility (TSF), which is the largest in Europe, requires the transport of large amounts of tailings, e.g., from the central area of the TSF reservoir to the new southern extension (SE). In order to use the mature fine tailings deposits located under the clarified water in the TSF reservoir, which were thickened in the process of natural sedimentation, it was decided to choose suction dredgers that collect tailings a few meters from under the water surface. The dredgers, which are most commonly used for the extraction of sand or gravel, showed the ability to pump fine flotation tailings slurry in the conducted tests. However, in order to reduce the costs of the entire operation, it was necessary to control the density of the slurry. The article presents a prototype installation for measuring the efficiency of the solid phase of the "in situ" dredging process in real time. The installation was designed for the needs of dredging a deposit of tailings that were thickened in the natural sedimentation process, and which had a particle size of below 63 µm. The installation consists of a flow meter, a densimeter, and a section for measuring the head loss of the flow of the slurry. The applied methodology allows for the current assessment of the dredger's operating parameters, which translates into a more effective-in terms of process efficiency-management of the dredger's work.

Effect of dredging and capping with clean soil on the mitigation of algae-induced black blooms in Lake Taihu, China: A simulation study.

Sediment is an important source of matter that causes blackening and odor formation in a water body. The restoration of polluted sediment can suppress algae-induced black blooms to a certain degree. In this study, we compared the control effects of sediment dredging and capping with clean soil on algae-induced black blooms in Lake Taihu using indoor simulation experiments. In addition, we explored the driving effect of temperature on algae-induced black blooms using the method of gradual warming (18, 23, and 28 °C) during the experiment. No blackening of the water body was observed in the simulation stages I (18 °C) and II (23 °C), and the blackening and odor formation occurred within 3 d when the temperature increased to 28 °C in stage III, implying that high temperature was an important driving factor for algae-induced black blooms. Dredging and capping inhibited the blackening and odor formation to some extent, and the colorimetric values in the water columns were lower in the treatment groups than in the control group. At the end of the experiment, the colorimetric values of dredging and capping treatments were 56.5% and 96.7% of the colorimetric value of the control group, respectively. The control effect of dredging on the blackening elements, i.e., Fe2+ and S2- and the main odor forming compounds, i.e., dimethyl disulfide (DMDS) and dimethyl trisulfide (DMTS) was observed in stage II (11-20 d) and stage III (21-27 d), respectively, and the inhibition ability of dredging to suppress algal-induced black blooms was superior than that of capping with clean soil.

Mercury methylation upon coastal sediment resuspension: a worst-case approach under dark conditions.

Mercury behavior upon resuspension of sediments from two impacted areas of Guanabara Bay was evaluated to assess worst-case methylmercury (MeHg) responses, under dark experimental conditions to prevent demethylation by photolysis. Study areas include the Rio de Janeiro Harbor (RJH) and the chlor-alkali plant-affected Meriti River (MR) estuary. Total mercury (THg) and MeHg concentrations were determined along 24-h experiments of sediment resuspension in the bay water in dark conditions. Fine-grained Meriti River (MR) estuary sediments had 8 times higher MeHg initial concentrations than sandy Rio de Janeiro Harbor (RJH) sediments (3.4 ± 0.29 vs. 0.41 ± 0.1 ng g-1, respectively). Though THg contents were uncorrelated with resuspension time, statistically significant correlations of MeHg (rs = 0.78) and %MeHg in relation to THg (rs = 0.86) with resuspension time were observed for RJH sediments, indicating net methylation only for this study site. These positive correlation trends correspond to a 2.8 times MeHg concentration increase (ΔMeHg = 0.75 ng g-1) and 4.4 times increase in %MeHg (Δ%MeHg = 1.0%), after 24 h of resuspension. This suggests that assessments of factors affecting the MeHg spatial-temporal variability and associated toxicity risks can be limited in some sites if concentration changes due to sediment resuspension-redeposition processes are not considered. Therefore, the inclusion of MeHg evaluation before and after sediment resuspension events is recommendable for the improvement of dredging licensing and monitoring activities.

Assessing the Impacts of Dry Blasting on Fish Eggs in Adjacent Spawning Habitat.

Blasting used in construction of waterborne infrastructure may impact fish eggs in adjacent spawning habitats through introduction of mechanical vibrations as peak particle velocities (PPV). However, there are limited studies applying risk-based approaches to evaluate and mitigate these impacts. A navigation improvement project in the Soo Locks near the St. Marys Rapids provided an opportunity to evaluate existing data to inform blasting risks to fish eggs. To assess this risk, existing data were used to calculate species sensitivity distributions that were used to estimate a hazardous concentration for 5% of the salmon and trout species evaluated (HC5) and predicted no effect concentrations (PNEC). The HC5 ranged from 14.0 to 89.2 cm/s PPV, and the 'safe level' PNEC thresholds ranged from 2.8 to 17.8 cm/s PPV. This study provides a demonstration of how a risk-based approach can be effectively used to assess and manage dry blasting effects on underwater biota.

Statistical significance and its critics: practicing damaging science, or damaging scientific practice?

While the common procedure of statistical significance testing and its accompanying concept of p-values have long been surrounded by controversy, renewed concern has been triggered by the replication crisis in science. Many blame statistical significance tests themselves, and some regard them as sufficiently damaging to scientific practice as to warrant being abandoned. We take a contrary position, arguing that the central criticisms arise from misunderstanding and misusing the statistical tools, and that in fact the purported remedies themselves risk damaging science. We argue that banning the use of p-value thresholds in interpreting data does not diminish but rather exacerbates data-dredging and biasing selection effects. If an account cannot specify outcomes that will not be allowed to count as evidence for a claim-if all thresholds are abandoned-then there is no test of that claim. The contributions of this paper are: To explain the rival statistical philosophies underlying the ongoing controversy; To elucidate and reinterpret statistical significance tests, and explain how this reinterpretation ameliorates common misuses and misinterpretations; To argue why recent recommendations to replace, abandon, or retire statistical significance undermine a central function of statistics in science: to test whether observed patterns in the data are genuine or due to background variability.

Automated Sensing System for Real-Time Recognition of Trucks in River Dredging Areas Using Computer Vision and Convolutional Deep Learning.

Sand theft or illegal mining in river dredging areas has been a problem in recent decades. For this reason, increasing the use of artificial intelligence in dredging areas, building automated monitoring systems, and reducing human involvement can effectively deter crime and lighten the workload of security guards. In this investigation, a smart dredging construction site system was developed using automated techniques that were arranged to be suitable to various areas. The aim in the initial period of the smart dredging construction was to automate the audit work at the control point, which manages trucks in river dredging areas. Images of dump trucks entering the control point were captured using monitoring equipment in the construction area. The obtained images and the deep learning technique, YOLOv3, were used to detect the positions of the vehicle license plates. Framed images of the vehicle license plates were captured and were used as input in an image classification model, C-CNN-L3, to identify the number of characters on the license plate. Based on the classification results, the images of the vehicle license plates were transmitted to a text recognition model, R-CNN-L3, that corresponded to the characters of the license plate. Finally, the models of each stage were integrated into a real-time truck license plate recognition (TLPR) system; the single character recognition rate was 97.59%, the overall recognition rate was 93.73%, and the speed was 0.3271 s/image. The TLPR system reduces the labor force and time spent to identify the license plates, effectively reducing the probability of crime and increasing the transparency, automation, and efficiency of the frontline personnel's work. The TLPR is the first step toward an automated operation to manage trucks at the control point. The subsequent and ongoing development of system functions can advance dredging operations toward the goal of being a smart construction site. By intending to facilitate an intelligent and highly efficient management system of dredging-related departments by providing a vehicle LPR system, this paper forms a contribution to the current body of knowledge in the sense that it presents an objective approach for the TLPR system.

Red mud with other waste materials as artificial soil substitute and its effect on Sinapis alba.

Despite efforts to utilise bauxite residue, the amount of red mud stored in reservoirs is increasing. This paper aims to evaluate the potential of red mud and other sludge waste types as a soil substitute by monitoring plant development. Pot experiments were carried out testing two types of mixtures: dredging sludge from Lake Balaton mixed with garden soil and the sewage sludge and soil blend. These were then treated with red mud (15 and 30% w/w). The plants were under-, while the roots were more developed in the sewage sludge mix than the dredging sludge blend and the control soil. In the sewage amendment, the phosphorous content increased while the calcium content was lower than in the other soil types and the optimum. The metals uptake of the plants was a factor of the red mud quantity. Lead, nickel, titanium and silicon had elevated concentrations parallel to higher red mud content, but only the nickel exceeded the threshold of the Hungarian legislation. Silicon and titanium were beneficial for plant growth, compensating for the potentially toxic effects of lead and nickel. Results suggest that the red mud in a mixture with either sewage sludge or dredging sludge can act as catalysts for the growth rate of test plants, allowing their utilisation as secondary raw materials.

Can Sediments Contaminated by Mining be a Source of Mercury in the Coastal Environment Due to Dredging? Evidence from Thermo-Desorption and Chemical Speciation.

The sediments in the Gulf of Trieste (northern Adriatic Sea, Italy) are contaminated by mercury (Hg) due to historic mining which took place in Idrija (Slovenia). Despite many studies having been done regarding Hg, no information is available on the potential impact of dredging required along the main channel approaching the Port of Monfalcone. Sixteen surface sediment samples were collected along the channel to determine both total Hg concentration and chemical species using the thermo-desorption (TD) technique. Six samples were also chosen to apply a selective sequential extraction (SSE). The TD technique showed the maximum Hg release approximately at 260 and 335°C, corresponding to metacinnabar (ß-HgS) and cinnabar (α-HgS), respectively. The SSE demonstrated that Hg was mainly associated with poorly soluble or insoluble compounds (98.7%). A resuspension event over a limited period of time can be considered of negligible impact to the water column due to the scarce Hg mobility from sediments.

Changes in the Potential Activity of Nitrite Reducers and the Microbial Community Structure After Sediment Dredging and Plant Removal in the Empuriabrava FWS-CW.

In constructed wetlands (CW), denitrification usually accounts for > 60% of nitrogen removal and is supposedly affected by wetland management practices, such as dredging (and plant removal). These practices cause an impact in sediment properties and microbial communities living therein. We have quantified the effects of a sediment dredging event on dissimilatory nitrite reduction by analysing the structure and activities of the microbial community before and after the event. Potential rates for nitrate reduction to ammonia and denitrification were in accordance with changes in the physicochemical conditions. Denitrification was the predominant pathway for nitrite removal (> 60%) and eventually led to the complete removal of nitrate. On the contrary, dissimilatory nitrite reduction to ammonia (DNRA) increased from 5 to 18% after the dredging event. Both actual activities and abundances of 16S rRNA, nirK and nirS significantly decreased after sediment dredging. However, genetic potential for denitrification (qnirS + qnirK/q16S rRNA) remained unchanged. Analyses of the 16S rRNA gene sequences revealed the importance of vegetation in shaping microbial community structures, selecting specific phylotypes potentially contributing to the nitrogen cycle. Overall, we confirmed that sediment dredging and vegetation removal exerted a measurable effect on the microbial community, but not on potential nitrite + nitrate removal rates. According to redundancy analysis, nitrate concentration and pH were the main variables affecting sediment microbial communities in the Empuriabrava CWs. Our results highlight a high recovery of the functionality of an ecosystem service after a severe intervention and point to metabolic redundancy of denitrifiers. We are confident these results will be taken into account in future management strategies in CWs.

Dredging mitigates cyanobacterial bloom in eutrophic Lake Nanhu: Shifts in associations between the bacterioplankton community and sediment biogeochemistry.

Cyanobacterial blooms are a worldwide environmental problem, which is partly attributed to their access to excessive nitrogen (N) and phosphorus (P). Preventing the blooms by reducing N and P from internal inputs is viewed as a challenge. To evaluate the effects of dredging on cyanobacterial abundances and bacterioplankton communities, water and sediment samples were collected from eutrophic Lake Nanhu (Wuhan, China) before dredging (2017) and after dredging (2018). After dredging, significant decreases were observed for sediment nutrients (e.g., C, N, and P sources); C-, N-, P-, and S-cycling-related enzyme activity; N- and P-cycling-related gene abundance; microbial abundance; and dramatic changes were observed in the composition of the sediment microbial community. The release rates of nutrient including nitrogen, phosphorus, and organic matter decreased after dredging, and sediment biogeochemistry was closely correlated to nutrient release rates. Additionally, our observations and analyses indicated that the abundance and diversity of the bacterioplankton community decreased significantly, the composition and interaction of the bacterioplankton community dramatically changed, and the bacterioplankton community function (e.g., N, P-cycling-related enzymes and proteins) down regulated after dredging. Water and sediment physicochemical factors explained 72.28% variation in bacterioplankton community composition, and these physicochemical factors were significantly correlated with diversity, composition, and function of bacterioplankton community. Our findings emphasized that cyanobacterial blooms in freshwater ecosystems were closely correlated with noncyanobacterial bacterioplankton that were largely conserved at the phylum level, with Proteobacteria, Actinobacteria, and Bacteroidetes as the main taxa. To our knowledge, this is the first report clarifying the mechanism of cyanobacterial blooms mitigation by dredging, via changing the association between the bacterioplankton community and sediment biogeochemistry. Our findings are of significance and indicate that dredging is effective for mitigating cyanobacterial blooms.

Characterization of sediment toxicity in Shanghai Harbor using toxicity tests and digital gene expression analysis based on clams Ruditapes phillipinarum.

In the present study, chemical analysis of contaminants (three classes of organic pollutants and seven metals) and elutriate toxicity test were adopted to evaluate the potential environmental hazards of dredged sediment samples from five sites (SS1-5) along Huangpu River Channel (Shanghai Harbor, China). The metal Pb, Cu, Cr, Zn and the organic pollutants including total hexachlorocyclohexane (HCHs) and total dichlorodiphenyltrichloroethane (DDTs) in the five samples exceeded the threshold for effects level (TEL) to varying degrees. The probable effect concentration quotients (QPECm) of contaminants from the five dredged samples were all above 0.25, which means potential toxicity risks. Elutriate toxicity tests using medaka fish (Oryzias melastigma) and manila clam (Ruditapes philippinarum) showed that SS2 caused mortality to both species and SS1 caused mortality to fish. To explore the molecular biomarkers that may reflect the toxic effects, differential expressed genes were identified by RNA-Seq-based transcriptome profiling from the survived clams exposed to the two polluted elutriates (SS1, SS2). In clams exposed to SS1 and SS2 elutriate, 368 and 860 differential expressed genes (DEGs) were up-regulated, 199 and 1304 genes were down-regulated, respectively. Fourteen DEGs were selected from the enriched pathways that reflect cytotoxicity and responses to xenobiotics for the following quantitative real time PCR analysis. The transcriptomic profiling and the selected gene's expression patterns from clams exposed to SS1 and SS2 showed significant differences with the non-contaminated and control groups. Using the expression data of the selected gene battery in Factor Analysis allowed the discrimination between contaminated and non-contaminated sites and may reflect an influence gradient of sites. The development of the assay of these molecular biomarkers may provide a rapid and high-throughput tool for the quality assessment of the dredging sediments.

Characterising the geomorphological and physicochemical effects of water injection dredging on estuarine systems.

Dredging is a globally important aquatic system management activity, used for navigation improvement, contamination removal, aggregate production and/or flood risk mitigation. Despite widespread application, understanding of the environmental effects of some dredging types remains limited. Field campaigns in 2016 and 2017 in the River Parrett estuary, UK, therefore investigated the geomorphic and physicochemical effects of Water Injection Dredging (WID), a poorly studied hydrodynamic dredging technology. WID, applied to restore channel capacity for the maintenance of flood water conveyance in the tidal River Parrett, influenced surface elevations but not grain-size characteristics of dredged bed sediments. Topographic alterations due to the 2016 WID operation were short-lived, lasting less than 10 months, although benefits of the 2017 WID operation, in terms of volumetric change, outlasted the ≈12-month study period. Dredging had a significant impact on water physicochemistry (pH, dissolved oxygen, total suspended solids and turbidity) when comparing pre- and during-dredging conditions within the dredge reach, although time-series analysis found dredging effects were comparable in magnitude to tidal effects for some parameters. WID is typically targeted at the thalweg and not the banks, rendering the geomorphic signature of the method different to those of other, often more invasive dredging technologies (e.g. mechanical dredging methods). Further, thalweg not bankside dredging may have potential positive ecological implications, particularly where the majority of biomass is located within the channel margins, as in the tidal River Parrett. Collectively, data suggest WID can be an effective method for sediment dispersal within tidal systems although regular application may be required to maintain cross sectional areas, particularly where management precedes periods of low flows and/or high rates of sediment accumulation. In future, more work is required to better understand both the physical and ecological implications of WID as a flood risk management tool in estuaries and rivers.