Marine Aggregates Research Articles

Particle-based modeling of aggregation and fragmentation processes: Fractal-like aggregates

The incorporation of particle inertia into the usual mean field theory for particle aggregation and fragmentation in fluid flows is still an unsolved problem. We therefore suggest an alternative approach that is based on the dynamics of individual inertial particles and apply this to study steady state particle size distributions in a 3D synthetic turbulent flow. We show how a fractal-like structure, typical of aggregates in natural systems, can be incorporated in an approximate way into the aggregation and fragmentation model by introducing effective densities and radii. We apply this model to the special case of marine aggregates in coastal areas and investigate numerically the impact of three different modes of fragmentation: large-scale splitting, where fragments have similar sizes, erosion, where one of the fragments is much smaller than the other and uniform fragmentation, where all sizes of fragments occur with the same probability. We find that the steady state particle size distribution depends strongly on the mode of fragmentation. The resulting size distribution for large-scale fragmentation is exponential. As some aggregate distributions found in published measurements share this latter characteristic, this may indicate that large-scale fragmentation is the primary mode of fragmentation in these cases.

Management of the marine environment: Integrating ecosystem services and societal benefits with the DPSIR framework in a systems approach

Ever increasing and diverse use of the marine environment is leading to human-induced changes in marine life, habitats and landscapes, making necessary the development of marine policy that considers all members of the user community and addresses current, multiple, interacting uses. Taking a systems approach incorporating an understanding of The Ecosystem Approach, we integrate the DPSIR framework with ecosystem services and societal benefits, and the focus this gives allows us to create a specific framework for supporting decision making in the marine environment. Based on a linking of these three concepts, we present a set of basic postulates for the management of the marine environment and emphasise that these postulates should hold for marine management to be achieved. We illustrate these concepts using two case studies: the management of marine aggregates extraction in UK waters and the management of marine biodiversity at Flamborough Head, UK.

Increasing evidence for the important role of Labyrinthulomycetes in marine ecosystems

This review summarizes increasing evidence for the role of Labyrithulomycetes in marine ecosystems gathered over the last six decades. It focuses on their diversity, habitats, biomass, productivity and overall role in food webs and remineralization. Earlier studies contributed enormously to the cultured diversity of Labyrinthulomycetes. In recent years, their uncultured diversity has been demonstrated in exotic environments like the deep sea and anoxic waters. These findings emphasize the need for novel culture methods to grow these organisms. Many species seem to be substrate-specific in their occurrence. Their commensalistic or mutualistic occurrence in marine invertebrates deserves attention. The biomass of Labyrinthulomycetes in the water column may often match or even exceed that of bacteria, although such occurrences seem to be seasonal. There is a major knowledge gap on their productivity and turnover in the water column. The high biomass and production of several degradative enzymes indicate their importance as remineralizers in the ocean. However, the mechanisms by which they overcome bacterial competition are not clear. It is likely that they occupy special niches, such as marine aggregates. One role of the Labyrinthulomycetes suggested in this review, based on preliminary experiments, is that of ‘left-over scavenging’, following bacterial growth.

The International Management of Marine Aggregates and its Relation to Maritime Archaeology

This article compares the marine element of the UK Aggregates Levy Sustainability Fund (ALSF) historic environment programme with other international management policies relating to heritage assets, in the context of the international marine aggregates industry. The article identifies by comparison the distinctive value of marine historic environment involvement in the ALSF alongside other forms of heritage management policy or practice currently applied in other nations that might be successfully applied in the UK in relation to marine heritage sites impacted by aggregate extraction. The article also identifies issues addressed by ALSF projects that have the potential for delivering 'added value' for other areas of marine planning and development, and promotes the international leadership role of the UK in the innovative management of marine heritage sites.

Ballast minerals and the sinking carbon flux in the ocean: carbon-specific respiration rates and sinking velocity of marine snow aggregates

Abstract. Recent observations have shown that fluxes of ballast minerals (calcium carbonate, opal, and lithogenic material) and organic carbon fluxes are closely correlated in the bathypelagic zones of the ocean. Hence it has been hypothesized that incorporation of biogenic minerals within marine aggregates could either protect the organic matter from decomposition and/or increase the sinking velocity via ballasting of the aggregates. Here we present the first combined data on size, sinking velocity, carbon-specific respiration rate, and composition measured directly in three aggregate types; Emiliania huxleyi aggregates (carbonate ballasted), Skeletonema costatum aggregates (opal ballasted), and aggregates made from a mix of both E. huxleyi and S. costatum (carbonate and opal ballasted). Overall average carbon-specific respiration rate was ~0.13 d−1 and did not vary with aggregate type and size. Ballasting from carbonate resulted in 2- to 2.5-fold higher sinking velocities than those of aggregates ballasted by opal. We compiled literature data on carbon-specific respiration rate and sinking velocity measured in aggregates of different composition and sources. Compiled carbon-specific respiration rates (including this study) vary between 0.08 d−1 and 0.20 d−1. Sinking velocity increases with increasing aggregate size within homogeneous sources of aggregates. When compared across different particle and aggregate sources, however, sinking velocity appeared to be independent of particle or aggregate size. The carbon-specific respiration rate per meter settled varied between 0.0002 m−1 and 0.0030 m−1, and decreased with increasing aggregate size. It was lower for calcite ballasted aggregates as compared to that of similar sized opal ballasted aggregates.

European marine aggregates resources: Origins, usage, prospecting and dredging techniques

Marine aggregates (sand and gravel) are important mineral resources and traded commodities 1 hen significance is bound to increase further due to increasing coastal,one development stricter environment regulation concerning land won aggregates and increasing demand for beach replenishment material Marine aggregate (MA) deposits can be differentiated into into and modern deposits 1 he former consist of sedimentary material deposited in the past and under different environmental sedimentary regimes than those existing presently (c g the gravel/sand deposits of the Pleistocene buried riser valleys of the northwestern european shelves) The latter are deposits which have been formed and corm oiled by the modern hydro and sediment dynamic conditions (e g the lineal sand banks of the southern North Sea) The present contribution reviews the current state of affairs in 9 representative European Member States concerning the prospecting and extraction (dredging) techniques as well as the levels of production and usage The review h is shown a mixed record as in some of the studied States marine aggregate production is an important and streamlined activity valet e us diet States base not yet des eloped efficient marine aggregate policies and industries It Is is also shown that although attempts hue been lately. made to coordinate the field the industry still faces problems which hinder Its sustainable development These include (amongst others) lack of standardisation of the idles ant information difficulties in the access to information non-coherent regulatory regimes and limited collaboration/coordination between the marine scientific research establishments and the marine aggregate industry These issues should be addressed as quickly as possible in older to exploit effectively this important mineral resource

Modelling the Effects of Sand Extraction, on Sediment Transport due to Tides, on the Kwinte Bank

In recent years, the exploitation of marine aggregates is increasing. As an example, on the Belgian continental shelf, one particular sandbank (the Kwinte Bank) is exploited extensively; this has led to the creation of a 5 m deep depression along its central part. In the present contribution, the influence of these bathymetric changes, on erosion and sedimentation patterns are studied, using numerical modelling, in order to obtain an initial impression of the effect of such intense sand extraction on the stability of the sandbank. Different numerical models are utilised. Twodimensional and three-dimensional hydrodynamic models have been used to derive currents, whilst third generation wave models have been used to simulate the waves. Two different models are presented, which calculate the total load sediment transport as a function of the local currents and waves. These models have been used to investigate the erosional and depositional patterns. The use of two different sediment transport models has some advantages, since the results of sediment transport models are still subject to some important uncertainties. The hydrodynamic model results are validated using ADCP current data, confirming the good performance of the models. Likewise the wave models provide good results, comparing their results with data from a buoy. The sediment transport model results were compared to the residual transport patterns, derived from the asymmetry of dunes. The results obtained seem to be in general agreement with these observations. The numerical models are used to simulate the response of the sediment transport to extensive sand extraction from the sandbank. One ‘worst-case’ scenario and two more realistic scenarios were simulated, whilst the effect of these bathymetric changes on sediment transport was studied. The results show that the intense sand extraction does not seem to influence extensively the stability of the sandbank, but that, as a consequence, there is less erosion and deposition. The model results show, for all of the scenarios, a small amount of deposition on the top of the sandbank; this could be an indication of a regeneration mechanism. A trench, created perpendicular to the crest of the sandbank, could be slowly refilled again. The time-scale of this regeneration and the influence of storms remain uncertain. Although the main emphasis of the paper relates to tidal forcing, a brief discussion is included on the influence of wave action, on sediment transport.

Climate Change and the Potential Spreading of Marine Mucilage and Microbial Pathogens in the Mediterranean Sea

BackgroundMarine snow (small amorphous aggregates with colloidal properties) is present in all oceans of the world. Surface water warming and the consequent increase of water column stability can favour the coalescence of marine snow into marine mucilage, large marine aggregates representing an ephemeral and extreme habitat. Marine mucilage characterize aquatic systems with altered environmental conditions.Methodology/Principal FindingsWe investigated, by means of molecular techniques, viruses and prokaryotes within the mucilage and in surrounding seawater to examine the potential of mucilage to host new microbial diversity and/or spread marine diseases. We found that marine mucilage contained a large and unexpectedly exclusive microbial biodiversity and hosted pathogenic species that were absent in surrounding seawater. We also investigated the relationship between climate change and the frequency of mucilage in the Mediterranean Sea over the last 200 years and found that the number of mucilage outbreaks increased almost exponentially in the last 20 years. The increasing frequency of mucilage outbreaks is closely associated with the temperature anomalies.Conclusions/SignificanceWe conclude that the spreading of mucilage in the Mediterranean Sea is linked to climate-driven sea surface warming. The mucilage can act as a controlling factor of microbial diversity across wide oceanic regions and could have the potential to act as a carrier of specific microorganisms, thereby increasing the spread of pathogenic bacteria.

Marine aggregates facilitate ingestion of nanoparticles by suspension-feeding bivalves

As the application of nanomaterials to science and technology grows, the need to understand any ecotoxicological effects becomes increasingly important. Recent studies on a few species of fishes and invertebrates have provided data which suggest that harmful effects are possible. The way in which nanoparticles are taken up by aquatic organisms, however, has been little studied. We examined uptake of nanoparticles by two species of suspension-feeding bivalves (mussels, Mytilus edulis; oysters, Crassostrea virginica), which capture individual particles <1 μm with a retention efficiency of <15%. Given this limitation, it would appear that nanoparticles could not be ingested in large numbers. During certain times of the year, however, >70% of suspended particles are incorporated within aggregates that are >100 μm in size. Therefore, we delivered bivalves fluorescently labeled, 100-nm polystyrene beads that were either (1) dispersed or (2) embedded within aggregates generated in the laboratory. Results indicate that aggregates significantly enhance the uptake of 100-nm particles. Nanoparticles had a longer gut retention time than 10-μm polystyrene beads suggesting that nanoparticles were transported to the digestive gland. Our data suggest a mechanism for significant nanoparticle ingestion, and have implications for toxicological effects and transfer of nanomaterials to higher trophic levels.

Effect of particulate aggregation in aquatic environments on the beam attenuation and its utility as a proxy for particulate mass

Marine aggregates, agglomerations of particles and dissolved materials, are an important particulate pool in aquatic environments, but their optical properties are not well understood. To improve understanding of the optical properties of aggregates, two related studies are presented. In the first, an in situ manipulation experiment is described, in which beam attenuation of undisturbed and sheared suspensions are compared. Results show that in the sheared treatment bulk particle size decreases and beam attenuation increases, consistent with the hypothesis that a significant fraction of mass in suspension is contained in fragile aggregates. Interestingly, the magnitude of increase in beam attenuation is less than expected if the aggregates are modeled as solid spheres. Motivated by this result, a second study is presented, in which marine aggregates are modeled to assess how the beam attenuation of aggregates differs from that of their constituent particles and from solid particles of the same mass. The model used is based on that of Latimer [Appl. Opt. 24, 3231 (1985)] and mass specific attenuation is compared with that based on homogeneous and solid particles, the standard model for aquatic particles. In the modeling we use recent research relating size and solid fraction of aquatic aggregates. In contrast with Mie theory, this model provides a rather size-insensitive mass specific attenuation for most relevant sizes. This insensitivity is consistent with the observations that mass specific beam-attenuation of marine particles is in the range 0.2-0.6m(2)/gr despite large variability in size distribution and composition across varied aquatic environments.

Role of microbial populations in the release of reduced iron to the water column from marine aggregates

The release of dissolved iron from artificial aggregates formed from oxic natural coastal water and senescent phytoplankton material was demonstrated under dark conditions. The rate of release was controlled by the amount of reducible Fe(III) available, and appears to be limited by the competing oxidation of Fe(II). Molecular (16S rRNA gene) analyses showed the bacterial community associated with the aggregates, originating from estuarine water, to be dominated by oxic heterorophs. However, it was possible to culture NO3- and Fe (III)-reducing bacteria from the artificial aggregates, and marine particles incubated with Fe(III) under anaerobic conditions contained microorganisms belonging to the genera Desulfovibrio and Marinobacter, bacteria known to reduce Fe(III). Whilst the precise mechanism of reduction is not clear, it is evident that marine aggregates can be a source of Fe(II), and thus ultimately iron in other forms, in coastal waters and most probably other natural water systems.

Marine Aggregates and Archaeology: a Golden Harvest?

The Aggregates Levy Sustainability Fund (ALSF) was introduced by the United Kingdom Government Department for Environment, Food and Rural Affairs as a two-year pilot scheme in April 2002. It is now expected to end in 2011. Since its inception, the marine part of the ALSF programme has delivered great benefits to the community because it has recognized that the baseline information to promote effective management of marine historic and natural environment resources is relatively poor, and the intrusive nature of marine aggregate extraction can represent a potential impact to heritage assets. This paper discusses the research undertaken under the behest of the ALSF in the UK, specifically in the marine historic environment, and how different marine environment stakeholders have been involved in this process of research, management and outreach to the benefit of all communities.

Does ocean acidification induce an upward flux of marine aggregates?

Abstract. The absorption of anthropogenic atmospheric carbon dioxide (CO2) by the ocean provokes its acidification. This acidification may alter several oceanic processes, including the export of biogenic carbon from the upper layer of the ocean, hence providing a feedback on rising atmospheric carbon concentrations. The effect of seawater acidification on transparent exopolymeric particles (TEP) driven aggregation and sedimentation processes were investigated by studying the interactions between latex beads and TEP precursors collected in the lagoon of New Caledonia. A suspension of TEP and beads was prepared and the formation of mixed aggregates was monitored as a function of pH under increasing turbulence intensities. The pH was controlled by addition of sulfuric acid. Aggregation and sedimentation processes driven by TEP were drastically reduced when the pH of seawater decreases within the expected limits imposed by increased anthropogenic CO2 emissions. In addition to the diminution of TEP sticking properties, the diminution of seawater pH led to a significant increase of the TEP pool, most likely due to swollen structures. A diminution of seawater pH by 0.2 units or more led to a stop or a reversal of the downward flux of particles. If applicable to oceanic conditions, the sedimentation of marine aggregates may slow down or even stop as the pH decreases, and the vertical flux of organic carbon may reverse. This would enhance both rising atmospheric carbon and ocean acidification.

Transparent exopolymer particles (TEP) from marine suspension feeders enhance particle aggregation

Transparent exopolymer particles (TEP) are known to form from dissolved precursors released by phytoplankton and bacteria. Many benthic suspension feeders also have been shown to produce significant amounts of TEP under field and laboratory conditions. Although TEP from phyto- plankton have been implicated in enhancing aggregation and sedimentation of suspended material, the role of TEP from suspension feeders in aggregate formation is still unknown. In order to deter- mine if TEP produced by suspension feeders enhance the formation of marine aggregates, organic matter from actively feeding blue mussels Mytilus edulis and sea vases Ciona intestinalis held in recirculating chambers was collected. Control water was collected from chambers without animals. Animal-conditioned and control water were then mixed with 1 of 2 non-sticky particles (silica-amino beads or diatomaceous earth). The suspensions were transferred to 250 ml bottles, which were placed on a roller table to generate aggregates. Particle aggregation was quantified by examining the size distribution of particles over time by means of an electronic particle counter (particles between 6 and 90 μm), and by counting large (greater than ca. 100 μm) aggregates under a microscope at the end of the experiment. We found that significantly more aggregates formed in the animal-conditioned water than in control water after 48 h, for both species and both kinds of added particles. The number of large aggregates that formed was related to TEP concentration, and not related to total or dissolved organic carbon. Our results suggest that suspension feeders produce significant quantities of TEP that can enhance particle aggregation.

The production of volatile iodocarbons by biogenic marine aggregates

We present the first reported measurements of volatile iodocarbon production by biogenic marine aggregates. Iodomethane (CH3I), iodoethane (C2H5I), 2‐iodopropane (CH3CHICH3), and 1‐iodopropane (CH3CH2CH2I) concentrations were determined in incubations of aggregates formed by concentrating the &gt;53 µm fraction of the plankton during a field campaign in the Celtic Sea. All four iodocarbons increased significantly in concentration in the aggregate incubations relative to filtered seawater controls. Maximum production rates ranged from 0.01 pmol L−1 h−1 for CH3CHICH3 to 0.31 pmol L−1 h−1 for C2H5I. Accompanying pheopigment and bacterial heterotrophic production suggest that the processes taking place on the aggregates studied were a good representation of those known to occur on natural marine particles. We also report iodocarbon production rates observed in natural marine aggregates, including a diatom mucilage collected in the Celtic Sea and phytodetritus sampled from Kongsfjord in the Arctic. Detrital particles could be hotspots of iodocarbon production in the marine environment.

The role of marine aggregates in the ingestion of picoplankton-size particles by suspension-feeding molluscs

Suspension-feeding molluscs are important members of coastal communities and a large body of literature focuses on their feeding processes, including the efficiency of particle capture. Some molluscs, such as bivalves, capture individual picoplankton cells (0.2–2.0 μm) with a retention efficiency of less than 50%, leading to the assumption that such particles are not an important food resource. Picoplankton, however, are often concentrated in particle aggregates of much larger size. This study investigates the ability of suspension feeders to ingest picoplankton-size particles (0.2–2.0 μm) bound in marine aggregates. We fed clams (Mercenaria mercenaria), mussels (Mytilus edulis), oysters (Crassostrea virginica), scallops (Argopecten irradians) and slipper snails (Crepidula fornicata) 1.0- and 0.5-μm fluorescent particles (either polystyrene beads or bacteria) that were (1) dispersed in seawater, or (2) embedded within laboratory-made aggregates. Dispersed 10-μm beads were also delivered so that feeding activity could be determined. Ingested fluorescent particles were recovered in feces or isolated digestive glands and quantified. Results indicate that aggregates significantly enhance the ingestion of 1.0- and 0.5-μm beads by all species of bivalves, and enhance the ingestion of bacteria (greatest cell dimension ca. 0.6 μm) by all suspension feeders examined. Differences among species in their ability to ingest aggregates and picoplankton-size particles, however, were evident. Compared to mussels and clams, scallops and oysters ingested fewer aggregates with 1.0-μm beads or bacteria, and slipper snails ingested the most dispersed beads and bacteria. These differences may be a consequence of variations in gill structure and mechanisms of particle processing. Our data demonstrate that suspension feeders can ingest picoplankton-size particles that are embedded within aggregates, and suggest that such constituent particles may be an important food resource.

Viruses, prokaryotes and biochemical composition of organic matter in different types of mucilage aggregates

It has been hypothesised that several microbial processes contribute to mucilage formation and transformation. However, to date, none of these mechanisms have been consistently tested using different types of mucilage. We investigated the biochemical composition and the microbial activities occurring in 9 different types of mucilage aggregates (macroflocs, stringers, cobwebs, ribbons, stringers/cobwebs clouds, big creamy surface layer, false bottoms and anoxic false bottoms) collected during summer 2000, 2002 and 2003 in the Adriatic Sea. Larger and aged aggregates, characterized by the accumulation of carbohydrate and a low lipid fraction, displayed significant biochemical differences when compared with younger aggregates. Prokaryote abundance, C production and extracellular enzymatic activities increased from small to medium-sized aggregates (corresponding approximately to mid life span) while they decreased in larger (and aged) aggregates. The highest prokaryotic C production and enzymatic activities were coupled with highest viral abundance. In mucilage displaying the highest viral abundance a reduced incorporation of enzymatically degraded C into prokaryote biomass was observed. This result suggests a potential involvement of viruses in the impairment of the microbial loop functioning in marine aggregates. Applying a multivariate analysis to the microbial variables, 3 stages of mucilage life span can be identified: (1) an early stage characterized by a large prokaryote colonization of the aggregate and DOM accumulation; (2) a mature stage characterized by a decreased capability of incorporating degraded C into prokaryote biomass and high viral abundance and (3) an aged stage characterized by the decrease in both viral and prokaryote abundance and prokaryote activity. These results provide new insights into the microbial ecology of marine aggregates and the processes influencing their life span.

Characteristics of Marine Aggregates in Shallow-water Ecosystems: Implications for Disease Ecology

Marine aggregates were evaluated for their potential role in the ecology of aquatic pathogens using underwater video surveys coupled with direct collection of aggregates in modified settling cones. Six locations, two each in New York, Connecticut, and Massachusetts, were surveyed over 8 months to explore differences in the characteristics of aggregates found in habitats populated by clams (Mercenaria mercenaria) and oysters (Crassostrea virginica). Microaggregate ( 500 μm) concentrations, but peak concentrations of macroaggregates and microaggregates, mean size of particles, and volume fraction of aggregated material varied among the six shallow-water habitats. Concentrations (colony-forming units per ml) of total heterotrophic bacteria (THB) and total mesophilic pathogenic bacteria (MPB) from samples of aggregates were significantly different among the four locations bordering Long Island Sound (LIS). The highest concentrations and enrichment factors in aggregates were observed in August for THB and in June for MPB. Significant correlations were detected for salinity and the concentrations and enrichment factors of THB in aggregates and for the concentrations and percentages of MPB in seawater samples. Significant correlations were also detected for temperature and the concentrations of MPB in aggregates and the enrichment factors for THB and MPB (marginal significance). Bacterial species identified in association with aggregates included: Vibrio cholerea, V. parahaemolyticus, V. vulnificus, V. alginolyticus, Aeromonas hydrophila, Pseudomonas aeruginosa, Escherichia coli, and Mycobacteria sp. These results have important implications for the way in which aquatic pathogens are collected, quantified, and monitored for risk-based surveillance in shallow-water ecosystems.

Urban Geology in Wales: 2 , Michael G Bassett, Valerie K Deisler &amp; Douglas Nichol , National Museum &amp; Galleries of Wales, Geological Series No. 24, 2005, ISBN: 0 7200 0563 9 (softback), List price: £18, 262 pp

Following within a year the first volume of a similar title (Nichol et al . 2004), Urban Geology in Wales: 2 balances coverage of the problems concerning redevelopment and regeneration of urban areas in formerly industrialized regions. This book presents a compilation of a further 31 papers concerning a wide variety of projects, arranged in three sections: ‘Urban Areas and Construction’, ‘Geohazards and Environmental Issues’ and ‘General Projects’, the latter ranging from wind farms through marine aggregates …

An application of sediment trend analysis to Carmarthen Bay, Bristol Channel

Abstract Carmarthen Bay is a large embayment on the northern coast of the Bristol Channel; a location that is exposed directly exposed to both Atlantic waves and a macro-tidal environment. Until recently this embayment was comparatively poorly described in terms of its sediment regime. In particular, limited data were available to identify sediment types and sediment exchanges with the offshore. The Bristol Channel is an active interest area for marine aggregate extraction, with the majority of licenses falling in Welsh Territorial Waters. To enable the Government View procedure on marine aggregate extraction in this area to develop with a more complete understanding a research project (Bristol Channel Marine Aggregates: Resource and Constraints, also commonly referred to as BCMA) was commissioned. This research project identified Carmarthen Bay as a strategic unit of the overall sediment regime, and defined a programme of primary research in this area to improve understanding of sediment exchanges. A key part of this research has been an application of sediment trend analysis (STA). This paper describes components of the STA technique, the rationale for its application, the survey design, results and subsequent interpretation of the information in the context of determining probable patterns of net sediment transport across Carmarthen Bay.