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Sediment resuspension may play a major role in sediment-water exchange of nutrients, matter and energy in coastal areas where waves and currents dominate sediment transport. Biogeochemical sediment properties regulate sediment erodibility, but there is only limited knowledge of how temporal variability in environmental variables is reflected in the resuspension potential, especially for subtidal habitats. Further, the significance of resuspension on nutrient fluxes in coastal environments has remained unclear as contradicting results have been reported. Here we quantified the temporal variation in resuspension potential metrics (erosion threshold (τc; N m−2) and erosion constant (me; g N−1 s−1)) and associated nutrient fluxes from three sites in the Hanko archipelago (Finland) using a core-based erosion device (EROMES). The sites were sampled bi-monthly from April to December. We also quantified the temporal variation in biogeochemical sediment properties at each site. The τc exhibited the clearest temporal pattern in muddy sediment, where the coefficient of variation (= 67) was two to three times higher than the mixed (= 29) and sandy (= 16) sediments. Dry bulk density was the best predictor for sediment erodibility at all sites explaining 26–46% of the temporal variation in τc despite its limited variability at sandier sites. In addition, temporal variations in the macrofaunal community were important predictors of muddy sediment erodibility and therefore community dynamics need to be considered in sediment transport studies. All sites were potential nutrient sources, yet the overall role of sediment resuspension on nutrient release from the sediments was small.

It is meaningful to investigate the impact of alien invasive plants on wetland sediment. Field experiments were conducted to study the impact of the alien invasive plant, Amaranthus retroflexus, on wetland sediment properties under two growth stages. The results showed that growth of A. retroflexus tended to increase moisture content, porosity, and could significantly decrease total nitrogen (TN) and nitrate (N-NO3ˉ) concentrations in sediment and ammonium (N-NH4+) concentration in interstitial water (p < 0.05). However, no obvious impact was observed on total phosphorus (TP) nor on N-NH4+ concentrations in sediment. There was a difference in impact of A. retroflexus on sediment properties under two growth stages. The plants with a longer growth stage significantly decreased loss on ignition in sediment and P-PO43ˉ concentration in interstitial water. There were also significant differences in N-NH4+ concentration in both sediment and interstitial water over the vertical profile of the plant. In the plant treatment with a longer growth stage, P-PO43ˉ concentration also showed significant differences over the vertical profile. Therefore, the growth of A. retroflexus can improve sediment physical and chemical properties, reducing N-NH4+ and P-PO43ˉ release from sediment to overlying water to some extent, thereby decreasing sediment nutrient loading.

11 pages, 7 figures, 3 tables, In this empirically-driven research, multibeam backscatter angular response analysis is presented, together with shallow electromagnetic data and groundtruthing, to examine its suitability as a proxy for sediment characterisation. Backscatter angular curves extracted from Kongsberg EM1002 sonar (95-98 kHz), acquired in the Malin Basin to the northwest of Ireland, have been selected as a case study. Standard angular backscatter features and newly derived curvature features are examined and cross compared. Exhaustive statistical analysis has been performed on the data to elucidate the complex relationship between multibeam backscatter and sediment properties. Subtle subsurface sediment property gradients across the basin identified by the conductivity system are also captured by the newly derived backscatter features. The results reveal that Near-range backscatter is better suited for subsurface sediment characterisation in soft, fine-grained sediments than far-range. Furthermore, the analysis has constrained the optimum interval for such characterisation to in-between 4° and 16° for the parameters of this study. A number of shape features (slope, first derivative, second derivative and Fourier-smoothed least-squares-fitted curvature) have been examined, and their suitability discussed, in terms of sediment characterisation and, in particular, as potential proxies for delineating the boundary between sand- or silt-dominated sediment facies. Nonetheless, curvature features are found to be independent from average angular backscatter response, but outperform both first and second derivatives when correlating with conductivity in the central part of this case-study with fine-grained homogeneous sediments, We wish to thank the Geological Survey of Ireland, the Integrated Mapping For the Sustainable Development of Ireland’s Marine Resources (INFOMAR) programme, the Petroleum Affairs Division (Ireland) and the Dublin Institute for Advanced Studies for funding this study. Research presented in this paper is supported by a Strategic Research Cluster grant (07/SRC/I1168) – StratAG, awarded to the National Centre of Geocomputation by Science Foundation Ireland under the National Development Plan. The survey data utilized in the research has been co-funded by the Geological Survey of Ireland and the Offshore Irish Petroleum Infrastructure Programme (PIP; Ref. No: IS05/16 Malin Basin EM)

The next generation of sediment quality guidelines (SQGs) requires better established causal links between the chronic exposure and effects of metals from both dissolved and dietary sources. The potential for dietary exposure from sediment metals to cause toxic effects to benthic invertebrates is strongly influenced by the metal-binding properties of the sediments. For relatively oxidized sediments, sublethal effects of copper to the epibenthic deposit-feeding amphipod, Melita plumulosa, and the benthic harpacticoid copepod, Nitocra spinipes, were investigated. Effects on reproduction were strongly influenced by the properties of the sediments and sediment-bound copper was found to be the major contribution to the toxicity. For sediments with the same total copper concentrations, effects were less for sediments with greater concentrations of fine particles (, This work was funded by the Marie Curie Actions under FP7 Programme through a IOF Marie Curie postdoc grant for O Campana.

The impacts of nutrients discharged from intensive shrimp farms on receiving waters and sediments in Indonesia are poorly understood. The main objective of this study was to evaluate the distribution of nutrients originating from an intensive shrimp farm in the adjacent waters and sediments. Samples were collected in February 2011 and August 2011 to represent wet and dry seasons respectively. Sampling involved collecting pond effluent from sluice channels during the shrimp harvest from three ponds. Samples of water and sediments in the bay were collected downstream of the farm outfall at varying distances to seaward. Harvest strategies consistently influenced variations in concentrations of solid nutrients only such as TOC, TSS and chlorophyll a rather than dissolved nutrients measured in the wet and dry seasons. Higher precipitation in the wet season diluted NO2-N, PO4 and TOC which resulted in lower concentrations of these nutrients. Nutrients originating from non-points sources represented 92 and 98% of annual amounts of N and P, respectively. In this study, spatial variations in concentrations of nutrients in waters and sediments were mostly observed in the dry season when shrimp farms were the main source of nutrients entering the bay. The incoming freshwater in the wet season not only transports nutrients, it also dilutes them in Hurun Bay resulting in lower salinity and concentrations of TAN, NO3-N and PO4 observed in the wet season. The hydrology of Hurun Bay affected distribution of nutrients in the sediment as shown by sparse distribution of nutrients in the sediments. Concentrations of nutrients discharged from harvested shrimp pond and in Hurun Bay waters exceeded the concentration thresholds set by the Indonesian Government for shrimp pond effluent and marine biota, respectively. Therefore, improvement in shrimp farm management, such as feeding strategies that reduce waste, become a critical issue at this study site. In addition, better wastewater treatment for non-point sources and shrimp farm effluent before their wastewaters are released to this bay are suggested. Thus, integrated pollution control policies are needed to safeguard water quality of Hurun Bay.

The macrobenthos of the subtidal, mesohaline zone of the Schelde Estuary (Belgium) was sampled in October 1996 and 1997 at 54 and 73 sampling locations respectively. Sediments ranged from silty to very coarse, with the dominant sediment type being silt (33% of all locations). Of the 35 macrobenthic species observed, only seven species occurred in more than 20% of the samples. The polychaete Heteromastus filiformis and Oligochaeta were most common. Multivariate techniques revealed three distinct communities, linked mainly with sedimentological factors: (1) a species-poor (nine species) community with a dominance of the amphipod Bathyporeia pilosa, a low mean abundance and biomass (86 ind m−2, 0.0189 g ash-free dry weight (AFDW) m−2), and a mean median grain size of 215±19 μm (fine sand); (2) a species-rich (22) community, with the small polychaete Polydora ligerica as indicator species, a relatively high mean abundance and biomass (2298 ind m−2, 1.395 g AFDW m−2, oysters excluded), a mean median grain size of 133±41 μm, and also the occurrence of sediments with hard substrates being characteristic for this community; (3) a community with an intermediate species richness (12), abundance and biomass (248 ind m−2, 0.249 g AFDW m−2), with H. filiformis and Oligochaeta as indicator species, and a median grain size of 76±9 μm. In the study area several typical brackish water species were observed (e.g. Polydora ligerica, Corophium lacustre, Gammarus salinus).Mean total abundance and biomass were very low, and the benthic communities appeared to be under stress, with a dominance of mainly small, subsurface deposit and surface deposit feeding opportunistic species. This is probably a combined effect of both natural physical and human-induced disturbance. Only sediments with hard substrates (e.g. rocks) seems to favour species richness, providing a shelter against physical disturbance.

Weak marine clay deposits are present in several regions of the world and they are imposing severe problems for structures founded in these deposits. The use of lime to improve the properties of these soft deposits is not new. In the present investigation, a test programme was carried out to study the migration of lime into the marine clay from the installed lime columns and lime slurry injected points. The formation of various cementation compounds due to soil-lime reactions were identified by X-ray diffraction studies and the attributed changes occurring in the engineering properties of the soil systems were studied. The test results indicate that a sufficient amount of lime is diffused into the soil systems with time and the presence of excessive sodium ions in sea water does not retard the effective penetration of lime into the soil. It is suggested that both the lime-column and lime-injection techniques can be conveniently used to improve the behaviour of soft marine clayey deposits. For weak marine clays under large depths of water, the lime-injection technique is better suited.

This paper describes apparatus, techniques and methods used by participants in MAST G6M project 4 (Cohesive Sediments) for determining cohesive sediment properties. This comparison of methods aims to stimulate a more general discussion on standardisation of techniques which will lead to characterisation of muds in terms of physical parameters. Such characterisation would allow inter-comparison of muds from different sources. Methods are given for sediment properties of grain size distribution, settling velocity and rheological parameters and for water-bed exchange properties of permeability, effective stress and critical shear stress for erosion and deposition. Accuracy and repeatability are discussed. A typical range of values is indicated for each of these parameters.