Fine-grained Dredged Material Research Articles

Silicon pools, fluxes and the potential benefits of a silicon soil amendment in a nitrogen-enriched tidal marsh restoration

Tidal marshes are important sites of silicon (Si) transformation, where dissolved Si (DSi) taken up by macrophytic vegetation and algal species is converted to biogenic silica (BSi), which can accumulate in the soil, be recycled within the marsh, or be exported to adjacent coastal waters. The role of restored and created tidal marshes in these processes is not well understood, nor is the impact of nutrient enrichment at either the plant or ecosystem level. Here, Si fluxes were examined to develop a Si mass balance in a nitrogen (N)-enriched marsh created with fine-grained dredged material from the Chesapeake Bay, United States. In addition, the effectiveness of Si soil amendments to ameliorate the negative effects of excess nitrogen on Spartina alterniflora was examined through laboratory and field experiments. Silicon was exported to the estuary as DSi (49 g m−2 y−1) and BSi (35 g m−2y−1) in stoichiometric excess of nitrogen and phosphorus. Rapid recycling of Si within both marsh and the tidal creeks appeared to be important in the transformation of Si and export from the marsh. Enhanced macrophyte SiO2 tissue concentrations were observed in the field experiment, with end-of-season mean values of 2.20–2.69% SiO2 in controls and 2.49–3.24% SiO2 in amended plots, among the highest reported for S. alterniflora; however, improved plant fitness was not detected in either experiment. Thus, tidal marshes created with a fine-grained, N-rich dredged material appear to function as a rich source of Si to the restored marsh and local estuarine environment, an overlooked ecosystem service. Soil Si amendments, however, did not appear likely to alleviate N-induced stress in S. alterniflora.

Experimental sediment addition in salt-marsh management: Plant-soil carbon dynamics in southern New England

Thin Layer Placement (TLP) is an increasingly used management technique to promote coastal resilience to accelerated sea level rise, but it is unclear how differential thickness of dredged sediment application alters plant-soil carbon dynamics in northeastern Atlantic coast salt marshes. We initiated a field experiment in a microtidal Spartina alterniflora (smooth cordgrass) dominated salt marsh in Connecticut (USA) to examine how a silt-loam dredge applied at different thicknesses (low: +5 cm, medium: +10 cm, and high: +15 cm) altered biological and biogeochemical responses. Over two growing seasons we monitored plant responses (above and belowground biomass, stem height, stem density, leaf area) and soil-biogeochemical parameters (EC, pH, redox, NH4+, sulfides, C:N, decomposition, bulk density, carbon fluxes). We found adding 5–7 cm of dredged sediment promoted rapid revegetation, alleviated phytotoxic sulfides, enhanced CO2 uptake, and reduced CH4 emissions. Low treatments reached similar vegetation cover to controls after one growing season, though sediment treatments greater than 10-cm thick showed delayed growth. Low levels of sediment addition stimulated the highest root biomass in the underlying soil, promoting CO2 efflux, but this was offset by aboveground biomass productivity, promoting net CO2 uptake. Phytotoxic sulfides were reduced in all sediment addition treatments, but our data indicate that coastal managers aiming to promote rapid vegetative recovery while increasing elevation in the short term should target conservative depths (< 10 cm) when using fine-grained dredged material. Collectively, our work will guide wetland managers as they develop restoration specifications for perpetuating coastal marshes in the face of rising seas.

The Fate of Nitrogen in Dredged Material Used for Tidal Marsh Restoration

Tidal marsh restoration using dredged material is being undertaken in many coastal areas to replace lost habitat and ecosystem services due to tidal marsh loss. The fate of high levels of nitrogen (N) in fine-grained dredged material used as a substrate for marsh restoration is uncertain, but if exported tidally may cause subtidal habitat degradation. In this study, a mass balance was developed to characterize N fluxes in a two-year-old restored tidal marsh constructed with fine-grained dredged material at Poplar Island, MD, in Chesapeake Bay, and to evaluate the potential impact on the adjacent submersed aquatic vegetation (SAV) habitat. Denitrification and N accumulation in Spartina organic matter were identified as the major sinks (21.31 and 28.5 mg N m−2 d−1, respectively), while tidal export of TN was more modest (9.4 mg N m−2 d−1) and inorganic N export was low (1.59 mg N m−2 d−1). Internal cycling helped retain N within the marsh. Mineralization of N associated with labile organic matter in the dredged material was likely a large, but unquantified, source of N supporting robust plant growth and N exports. Exceedances of SAV water quality habitat requirements in the subtidal region adjacent to the marsh were driven by elevated Chesapeake Bay concentrations rather than enrichment by the marsh.

Inverse Infiltration Modeling of Dike Covers Made of Dredged Material Using PEST and AMALGAM

A variety of studies recently proved the applicability of different dried, fine-grained dredged materials as replacement material for erosion-resistant sea dike covers. In Rostock, Germany, a large-scale field experiment was conducted, in which different dredged materials were tested with regard to installation technology, stability, turf development, infiltration, and erosion resistance. The infiltration experiments to study the development of a seepage line in the dike body showed unexpected measurement results. Due to the high complexity of the problem, standard geo-hydraulic models proved to be unable to analyze these results. Therefore, different methods of inverse infiltration modeling were applied, such as the parameter estimation tool (PEST) and the AMALGAM algorithm. In the paper, the two approaches are compared and discussed. A sensitivity analysis proved the presumption of a non-linear model behavior for the infiltration problem and the Eigenvalue ratio indicates that the dike infiltration is an ill-posed problem. Although this complicates the inverse modeling (e.g., termination in local minima), parameter sets close to an optimum were found with both the PEST and the AMALGAM algorithms. Together with the field measurement data, this information supports the rating of the effective material properties of the applied dredged materials used as dike cover material.

Tidal Marsh Restoration at Poplar Island I: Transformation of Estuarine Sediments into Marsh Soils

Dredged materials from navigation channel maintenance represent a potentially valuable resource for wetland creation and restoration. In the northern Chesapeake Bay, fine-grained sediments from Baltimore Harbor approach channels are transported by barge southward for creation of wetlands on the site of an eroded island. High concentrations of ammonium, soluble reactive phosphorus, dissolved iron, and iron sulfide minerals in channel deposits are altered by the transport and drying of these materials prior to wetland development. The oxidation of iron sulfide minerals results in low pH, with the initiation of tidal inundation removing sulfuric acid from near-surface soil horizons and moderating the soil pH. Despite the loss of ammonium during dewatering and soil processing, the resultant soils retained high concentrations of dissolved and adsorbed ammonium. Iron-associated inorganic phosphorus represented a large pool of potentially labile phosphorus and along with the high ammonium, resulted in high nutrient concentrations for plant growth. Combined with results on plant growth presented elsewhere, these data suggest that fine-grained dredged materials from non-contaminated environments are well suited for the creation of tidal wetlands after placement and seasoning 1–2 years.

Tidal Marsh Restoration at Poplar Island: II. Elevation Trends, Vegetation Development, and Carbon Dynamics

In natural tidal marshes, nutrient fertilization stimulates complex responses, bringing into question the suitability of nutrient-rich dredged material as a substrate for tidal marsh restoration. We examined vegetation and elevation trends in the constructed tidal marshes at Poplar Island, Maryland where fine-grained dredged material (high nutrient) and locally dredged sand (low nutrient) were used as substrates. Macrophyte production was higher and root:shoot ratios lower in dredged material marshes. Measured vertical accretion was similar in dredged material (7.4 ± 0.6 mm y−1) and sand (6.4 ± 0.9 mm y−1) marshes, and is keeping pace with local sea-level rise. A detailed carbon budget was developed for one dredged material marsh to examine carbon dynamics under high nutrient availability. High annual macrophyte production combined with small exports via tidal exchange and methane emissions resulted in an annual carbon burial of 206 g C m−2 y−1, and calculated vertical accretion of 6.5 mm y−1 from organic matter. This is attributed to the contribution of organic matter from aboveground biomass due to protection from perimeter dikes constructed to contain dredged material during placement, reducing marsh exposure and organic matter export. With appropriate design and management, fine-grained, high-nutrient dredged material makes a suitable substrate for tidal marsh restoration.

20 years performance measurements of a landfill cover system with components constructed from pre-treated dredged sediments

The water balance and effectiveness of a landfill cover containing a liner from fine-grained dredged material (‘METHA-material’) and a drainage layer from sandy dredged material (‘METHA-sand’) from the Port of Hamburg (Northern Germany) was investigated for 20 years using two test fields (lysimeters), each 500 m2 in size. The layering within the standard design test field (FS) is identical to the layering of the cover on the landfill, whereas the alternative design test field (FA) was designed to provoke desiccation of the liner. The setup abstained from continuous side walls cutting through the liners in order to allow for material properties representative for the landfill cover, at the cost of possible minor lateral inflows or outflows, which were, however, considered negligible. By example of the lysimeter FA the risk of desiccation-induced failure of a liner from METHA-material under the given climate could be shown. In contrast, the discharges and hydro-chemical parameters measured for the lysimeter FS indicate continuous high efficiency of the liner until today. The average discharge below the liner was 14.9 mm/yr. The entire cover contributes to the good liner performance. Reason are (1) the low hydraulic conductivity of the liner (5 × 10−10 m/s) and its large thickness (1.5 m); (2) the increased stresses on the liner due to the 2.5 m thick overlaying cover; (3) the 1.0 m thick drainage layer from slowly-draining METHA-sand, allowing for a continuous nearly water-saturated fringe above the liner; and (4) the sufficient amount of plant available water in the recultivation layer.

Analysis of the coupled electro-osmotic and mechanical consolidation in clayey soils

Electrokinetic (EK) treatment is a possible attractive way to speed up the consolidation of fine-grained dredged sediments. The effectiveness of this method depends on the complex physical–chemical interaction between soil particles, interstitial fluid and pollutants. This paper presents the experimental laboratory results obtained by inducing mechanical and EK consolidation in a fine-grained dredged material. Then, a finite-difference numerical code implemented by the authors able to solve the large and small strain consolidation equations (Lassec1), including the electro-osmotic flow, is described along with the theoretical simplifications adopted and the calibration procedure required. The experimental results have been numerically simulated, showing the ability of Lassec1 to reproduce the coupled mechanical and electrical consolidation processes, highlighting that under very low stress levels it is necessary to take into account the highly non-linear soil behaviour, and thus the large strain theory is needed to obtain a reliable prediction of the consolidation process. With this aim, special laboratory devices are necessary for a good calibration of the permeability function and of the stress–strain relationship at very low stress levels.

New Experiences in Dike Construction with Soil-Ash Composites and Fine-Grained Dredged Materials

Abstract The supporting structure inside a coastal dike is often made of dredged non-uniform sand with good compaction properties. Due to the shortage of natural construction material for both coastal and river dikes and the surplus of different processed materials, new experiments were made with sand-ash mixtures and fine-grained dredged materials to replace both dike core and dike cover materials resulting in economical, environmentally friendly and sustainable dikes. Ash from EC Gdańsk and dredged sand from the Vistula river were mixed to form an engineering material used for dike construction. The optimum sand-ash composites were applied at a field test site to build a large-scale research dike. Fine-grained dredged materials from Germany were chosen to be applied in a second full-scale research dike in Rostock. All materials were investigated according to the standards for soil mechanical analysis. This includes basic soil properties, mechanical characteristics, such as grain-size distribution, compaction parameters, compressibility, shear strength, and water permeability. In the field, the infiltration of water into the dike body as well as the erosion resistance of the cover material against overflowing water was determined. Results of both laboratory and field testing are discussed in this paper. In conclusion, the mixing of bottom ash with mineral soil, such as relatively uniform dredged sand, fairly improves the geotechnical parameters of the composite, compared to the constituents. Depending on the composite, the materials may be suitable to build a dike core or an erosion-resistant dike cover.

Predicting geotechnical parameters of fine-grained dredged materials of the gulf of Izmit (NW Turkey) using the slump test method and index property correlations

2ABM Engineering Co., Izmit-Kocaeli, Turkey. Accepted 8 November, 2013 In this study, an attempt has been done to figure out the geotechnical properties of physically remolded dredged materials of the Gulf of Izmit located in NW Turkey, by using slump test method. For this aim, slum tests were conducted on dredged material specimens using open-ended polyvinyl chloride (PVC) cylinders of 10 cm diameter and height. Water content of the dredged material specimens was obtained in the laboratory using oven method. Bulk wet density, Atterberg limits and phase relations such as bulk unit weight, % solids by weight, void ratio, and engineering behavior properties such as Vane shear strength, and effective stress were determined. Later, the statistical correlations were conducted by regression analysis to obtain the relationships between water content and slump/cylinder height as well as other parameters such as wet bulk density, % solid by weight, void ratio, Vane shear strength and effective stress.

Case Studies of PSDDF for Phased Placement of Dredged Soils

Use of Terzaghi's one-dimensional consolidation theory is not suitable for consolidation of highly deformable soft clays such as dredged soils. To model this condition, it is necessary to consider non-linear finite strain consolidation behavior, i.e., changes in compressibility and permeability with increasing stress. A one-dimensional non-linear finite strain numerical model, Primary Consolidation, Secondary Compression, and Desiccation of Dredged Fill (PSDDF), has been used to predict the stress-dependent settlement of fine-grained dredged materials. In this paper, two case studies of using PSDDF are discussed to illustrate the applicability and accuracy of PSDDF. The first case study involves PSDDF simulations of laboratory-phased placement of a marine clay dredged from Busan, Korea. PSDDF results are in good agreement with the corresponding results of the laboratory large strain consolidation tests. The other involves estimating the service life of the Craney Island Dredged Material Management Area near Norfolk, Virginia, in the United States. The excellent agreement between measured and calculated values shows that PSDDF is a reliable tool for predicting settlement of dredged material.

Investigation of Dredged Materials in Combination with Geosynthetics Used in Dike Construction

In the project DredgDikes with partners from Poland and Germany different dredged materials from the South Baltic Sea region are investigated for their application in dike construction. Two large-scale experimental dikes have been built, one in Germany and one in Poland. Additionally, a large variety of laboratory tests and experiments have been performed and a considerable monitoring test programme will be followed. This paper contains a general description of the project as well as first results from a laboratory flume test, field investigations on seepage and the information about a planned climatic chamber experiment, all performed at the University of Rostock, where the focus is laid on fine-grained dredged materials in combination with geosynthetics solutions. The flume experiments showed a very high strength of the dredged materials samples with grass cover. The first seepage test at the large-scale test dike in Rostock showed good performance of the geosynthetic drainage solution applied as well as the stability of the dredged material with respect to rapid drawdown of the water level. The comparison of measurements inside the dike and a seepage model showed considerably higher hydraulic conductivity in the field compared to that determined in the laboratory, however still in the range suited for coastal dike cover materials. To investigate the cracking behaviour of the ripened fine-grained dredged material a climatic chamber experiment has been set up which is also discussed briefly.

Macrofaunal recolonisation following the intertidal placement of fine-grained dredged material

Dredged material is increasingly being regarded as a potential resource, and one of its many uses is to create and/or improve intertidal habitats (i.e. beneficial use). However, uncertainties over the longer-term environmental consequences of such schemes have, to date, limited the practice to small-scale applications in UK waters. This paper studies the macrofaunal recolonisation of fine-grained dredged material recharged concurrently at four adjacent recharge areas along the south-east coast of the UK in order to facilitate predictions regarding the recolonisation of comparable schemes and, thereby, to promote effective environmental management. During the 2-year study period, the four recharge areas were distinctly different in terms of their environmental characteristics, primarily wave exposure and bed level. These conditions resulted in different macrofaunal recolonisation rates and community structures. While the low-level, wave-sheltered area experienced rapid recolonisation, the process was delayed until 12 months post-recharge at the relatively wave-exposed areas. Bed level differences resulted in distinctly different communities in wave-sheltered areas but not under wave-exposed conditions. While we are unable to separate the effects of individual environmental variables on recolonisation, these results provide general conclusions as to the importance of environmental conditions on resulting macrofaunal communities.

Differential response of nematode colonist communities to the intertidal placement of dredged material

The use of fine-grained maintenance dredged material for habitat enhancement has increased in recent years, particularly recharge schemes which provide a means of combating the erosion of intertidal flats and saltmarsh. This article investigates the development of meiofaunal nematode communities following a natural experiment in 2003, when fine-grained dredged material was deposited concurrently at four adjacent intertidal recharge sites on the southeast coast of the United Kingdom. A 12-month survey of nematode assemblages was carried out to compare univariate, multivariate, allometric and functional attributes of colonist communities in relation to the different environmental conditions prevailing at the four sites. Developing assemblages were increasingly affected by the spatial differences in the elevation, consolidation and exposure of bed material. The results indicated that the colonisation sequence was the result of random settling of suspended nematodes, sequential reproduction and differential survival and reproductive success of colonising species. For the first time, this experiment provided insights into the development of adaptive and functional types of meiofaunal nematodes following the intertidal deposition of uncontaminated fine-grained dredged material. This, in turn, will contribute considerably to the development of ecological models of the evolution of the large-scale placement of muddy dredged material in the intertidal environment.

Settlement of Dredged and Contaminated Material Placement Areas. I: Theory and Use of Primary Consolidation, Secondary Compression, and Desiccation of Dredged Fill

A 1D nonlinear numerical model, Primary Consolidation, Secondary Compression, and Desiccation of Dredged Fill (PSDDF), is presented to predict the settlement of fine-grained dredged material and/or underlying compressible foundation materials that may be over-, under-, or normally consolidated. The three most important natural processes affecting the long-term settlement and thus service life of dredged material placement areas are primary consolidation, secondary compression, and desiccation. Nonlinear finite-strain consolidation theory is used to predict the settlement due to self-weight and surcharge-induced consolidation. The Cα ∕ Cc concept is used to predict the settlement from secondary compression, and an empirical desiccation model is used to describe the settlement from removal of water from confined dredged material by surface drying. This paper describes the modifications and improvements of PSDDF that present new functions and enhanced numerical efficiency. A companion paper describes the inp...

Macrofaunal recolonization on intertidal mudflats: effect of sediment organic and sand content

Following concerns over how differences in dredged material properties affects recovery following dredged material deposition on mudflats, a field manipulation experiment was conducted to investigate the effects of increased sediment organic content (from 0.9% to 2.8%) and sand content (from 12.0% to 47.0%) on macrofaunal recolonization and sediment properties on an intertidal mudflat, Crouch Estuary, Essex, UK. The manipulated sediments were placed in 1-m 2 plots, 10 cm deep, in a randomised block design and macrofauna and sediments sampled after 1 week, 1, 3, 6, and 12 months. The results suggested that while increased sand content had no discernible effect on sediment property changes, increased organic content resulted in marked reductions in redox potential at 1-, 2- and 4-cm sediment depths and increased shear strengths. These sediments exhibited a distinct ‘cracking’ appearance on their surfaces. Similarly, while macrofaunal recovery was only affected by increased sand content in the short-term (1 month), total numbers of individuals, number of species and diversity took longer to recover in sediments with increased organic contents. Recolonization proceeded via a gradual increase in the abundance of those taxa present in ambient sediments rather than via a distinct successional sequence. Recovery was species-specific with two species ( Hediste diversicolor (Müller) and Hydrobia ulvae (Pennant)) recovering to ambient levels within the first week of the experiment. Multivariate analyses indicated that the community assemblages of the low-organic content treatments had recovered after 12 months while those of the high-organic content treatments were still significantly different to those of the controls at the end of the experiment. We propose that the relatively rapid recovery and lack of successional sequence generally observed in all sediment types of this study can be explained by the opportunistic nature of the ambient assemblage and by the dispersive nature of the dominant species. Reduced sediments and/or increased shear strengths led to a slow recovery in high-organic content treatments. These results indicate that a careful consideration of the organic content of fine-grained dredged material must be made during the licensing process of beneficial use schemes.

Compressibility and Permeability Correlations for Fine-Grained Dredged Materials

New correlations are presented for the compressibility and permeability of normally consolidated, fine-grained, marine and riverine dredged materials that are based on the liquid limit alone. They are simpler, statistically stronger, and applicable over a wider range of effective stress and permeability than comparable, earlier correlations based on the liquid limit, plasticity index, and activity of fine-grained dredged materials, mine tailings, and similar soils. However, like the latter, they must be applied with caution to sandy materials and to materials with high organic contents or that contain atypical clays with fibrous particles.

Invertebrate recolonization of fine-grained beneficial use schemes: An example from the southeast coast of England

The disposal of maintenance dredged material con- stitutes one of the most important problems in coastal zone management. To minimise ecological impacts, a number of 'beneficial use' options have developed whereby the material is regarded as a potential resource and used to recharge or recreate intertidal habitats. This paper presents the results of a sampling programme to investigate the macrofaunal recovery rates, and the underlying mechanisms responsible for them, following a beneficial use scheme involving the placement of fine-grained dredged material on a salt marsh in southeast England. Three stations in the recharge area and three reference stations, located within the same salt marsh system, were selected. These stations were sampled prior to recharge (re- charge stations only) then 1 week, 3, 6, 12 and 18 months after the recharge. Sediment redox potentials (1, 2 and 4 cm sedi- ment depths) were also measured on each sampling occasion. The results indicated a rapid recolonization of the fauna typi- cal of the surrounding salt marsh channels. All univariate parameters had recovered after 3 months after the recharge. Active post-juvenile immigration is likely to have been the predominant recovery process. Multivariate data analysis re- vealed that the community structure of the recharge stations, however, did not progress towards those of the reference sites. Natural spatial variability in community structure at the scale of the recharge-reference station distance, and differences in eventual tidal elevations are factors responsible for these differences. The need to carefully assess reference site suit- ability in monitoring beneficial use schemes is discussed.

Emissions of porewater compounds and gases from the subaquatic sediment disposal site “rodewischhafen”, hamburg harbour

In the year 1993 a confined and unused harbour basin was used to store 290,000 m3 of fine-grained dredged material from Hamburg harbour. About 70% of the deposit surface was water covered. The edge areas were above the water table and covered with reed. Emissions of dissolved compounds into the groundwater, as well as surface gas emissions were measured from 1994 to 1996. As indicators for water fluxes from the deposit we used NH4+ and HCO3− because of their high concentrations in mud porewater in comparison to groundwater. The average concentrations of NH4+ and HCO3− in the porewater increased during 2 years from 85 to 250 mg NH4+ 1−1 and from 2.0 to 3.1 g HCO3− 1−1, while the groundwater samples showed constant values of 8 mg NH4+ 1−1 and 0.7 g HCO3− 1−1. Furthermore, the average gas emissions over the water surface were 3.2 g CH4 m−2 d−1 and 0.8 g CO2 m−2 d−1. In contrast, no methane and 3.0 g CO2 m−2 d−1 were emitted from land areas. The results indicated, that there were no significant emissions of mud porewater compounds into the groundwater but high CH4-emissions over the water covered surface of the mud deposit.

Emissions of porewater compounds and gases from the subaquatic sediment disposal site “Rodewischhafen”, Hamburg harbour

In the year 1993 a confined and unused harbour basin was used to store 290,000 m3 of fine-grained dredged material from Hamburg harbour. About 70% of the deposit surface was water covered. The edge areas were above the water table and covered with reed. Emissions of dissolved compounds into the groundwater, as well as surface gas emissions were measured from 1994 to 1996. As indicators for water fluxes from the deposit we used NH4+ and HCO3− because of their high concentrations in mud porewater in comparison to groundwater. The average concentrations of NH4+ and HCO3− in the porewater increased during 2 years from 85 to 250 mg NH4+ 1−1 and from 2.0 to 3.1 g HCO3− 1−, while the groundwater samples showed constant values of 8 mg NH4+ 1−1 and 0.7 g HCO3 1−1. Furthermore, the average gas emissions over the water surface were 3.2 g CH4 m−2 d−1 and 0.8 g CO2 m−2 d−1. In contrast, no methane and 3.0 g CO2 m−2 d−1 were emitted from land areas. The results indicated, that there were no significant emissions of mud porewater compounds into the groundwater but high CH4-emissions over the water covered surface of the mud deposit.