Sediment, water and biomass characteristics along gradients in Kongsfjorden, Svalbard

In contrast to numerous studies on the biomass of marine microphytobenthos from temperate coastal ecosystems, little is known from polar regions. Therefore, microphytobenthos biomass was measured at several coastal sites in Arctic Kongsfjorden (Spitsbergen) during the polar summer (June-August 2006). On sandy sediments, chla varied between 8 and 200 mg/m**2 and was related to water depth, current/wave exposure and geographical location. Biomass was rather independent of abiotic parameters such as sediment properties, salinity, temperature or light availability. At three stations, sediments at water depths of 3-4, 10, 15, 20 and 30 m were investigated to evaluate the effect of light availability on microalgae. Significant differences in distribution patterns of biomass in relation to deeper waters >10 m were found. The productive periods were not as distinct as phytoplankton blooms. Only at 3-4 m water depth at all three stations were two- to threefold increases of biomass measured during the investigation period. Hydrodynamic conditions seemed to be the driving force for differences in sediment colonisation by benthic microalgae. In spite of the extreme Arctic environmental conditions for algal growth, microphytobenthos biomass was comparable to marine temperate waters.

Settlement characteristics of quartz grains on certain sediment surface forms of tidal beaches along the Baltic and Wadden Sea

Sind in einem Sediment, das unter dem Einfluß einer Strömung abgelagert wurde, richtungsanzeigende Indikatoren vorhanden, so werden sie je nach den momentanen Bedingungen, die zur Zeit der Sedimentation herrschten, ein mehr oder weniger gutes Abbild der Strömungsverhältnisse liefern. Zahlreich sind Strömungsanzeiger organischen Ursprungs, wie z. B. Molluskenschalen u. a. Doch auch anorganische Partikel in Psephiten und Psammiten lassen häufig in ihrer Lagerung eine Abhängigkeit von der Strömungsrichtung erkennen: sie sind "geregelt". Die Autoren der verschiedenen Arbeiten, in denen Regelungen in klastischen Sedimenten untersucht wurden, gingen von der Tatsache aus, daß viele Sedimentpartikel statistisch gesehen keine Kugelform, sondern eine längliche Gestalt besitzen. Die langen Achsen dieser länglich geformten Sedimentkörner werden im folgenden als "Langachsen" bezeichnet. In Sanden sind es vor allem Quarzkörner von annähernd zylindrischer oder ellipsoidischer Form ("Langquarze"), die geeignet sind, durch die Lage ihrer Langachsen strömungsbedingte Regelungen anzuzeigen. Mit der Orientierung solcher Langquarze in marinen und fluviatilen Sanden haben sich bisher vorwiegend amerikanische Autoren befaßt. So untersuchten z. B. Dapples & Rominger (1945) die Sandsohle eines künstlichen Gerinnes. Sie stellten fest, daß die Hauptorientierungsrichtung der Langquarze mit der Strömungsrichtung des fließenden Wassers zusammenfiel. Dabei zeigte das spitze Ende tropfenförmiger ("polarer") Quarze stromab und das stumpfe Ende stromauf. Nanz (1955) maß die Langachsenrichtungen von Langquarzen in Sanden des nassen und trockenen Strandes von Texas und Florida und fand, daß sich diese Achsen vorwiegend parallel zur Auf- und Ablaufrichtung der Wellen und damit senkrecht zum Streichen der Strandlinie einregeln. Curray (1956 b) beobachtete die gleiche Regelung. Er wies ferner darauf hin, daß in Strandwällen und Strandhaken die bevorzugte Richtung der Langquarze senkrecht zum Streichen des Sedimentkörpers liegt. Zahlreiche weitere Autoren beschäftigten sich ebenfalls mit den Fragen der Langquarzregelung, so Schwarzacher (1951), Griffith & Rosenfeld (1953), Vollbrecht (1953), Rusnak (1956), Wendler (1956), Sriramadas (1957). Ganz allgemein war das Ergebnis aller dieser Untersuchungen, daß die aus einer Strömung abgelagerten Langquarze eine Regelung parallel zur Strömungsrichtung zeigen. Eigene Untersuchungen und Überlegungen ergaben, daß die bisher veröffentlichten Ergebnisse und die an sie angeschlossenen Vorstellungen z. T. bestätigt werden können, jedoch z. T. auch erheblich modifiziert werden müssen.

Sediment and ice characteristics at a buried ice-wedge system at Barrow

Barrow, the northernmost point in Alaska, is one of the most intensively studied areas in the Arctic. However, paleoenvironmental evidence is limited for northern Alaska for the Lateglacial-Holocene transition. For a regional paleoenvironmental reconstruction, we investigated a permafrost ice-wedge tunnel near Barrow, Alaska. The studied site was first excavated in the early 1960s and intercepts a buried ice-wedge system at 3-6 m depth below the surface. A multi-methodological approach was applied to this buried ice-wedge system and the enclosing sediments, which in their combination, give new insight into the Late Quaternary environmental and climate history. Results of geochronological, sedimentological, cryolithological, paleoecological, isotope geochemical and microbiological studies reflect different stages of mid to late Wisconsin (MW to LW), Allerod (AD), Younger Dryas (YD), Preboreal (PB), and Late Holocene paleoenvironmental evolution. The LW age of the site is indicated by AMS dates in the surrounding sediments of 21.7 kyr BP at the lateral contact of the ice-wedge system as well as 39.5 kyr BP below the ice-wedge system. It is only recently that in this region, stable isotope techniques have been employed, i.e. to characterize different types of ground ice. The stable isotope record (oxygen: d18O; hydrogen: dD) of two intersecting ice wedges suggests different phases of the northern Alaskan climate history from AD to PB, with radiocarbon dates from 12.4 to 9.9 kyr BP (ranging from 14.8 to 10.6 kyr cal BP). Stable isotope geochemistry of ice wedges reveals winter temperature variations of the Lateglacial-Holocene transition including a prominent YD cold period, clearly separated from the warmer AD and PB phases. YD is only weakly developed in summer temperature indicators (such as pollen) for the northern Alaska area, and by consequence, the YD cold stadial was here especially related to the winter season. This highlights that the combination of winter and summer indicators comprehensively describes the seasonality of climate-relevant processes in discrete time intervals. The stable isotope record for the Barrow buried ice-wedge system documents for the first time winter climate change at the Lateglacial-Holocene transition continuously and at relatively high (likely centennial) resolution.

High-Frequency Turbulence and Sediment Flux Measurements in an Upper Estuarine Zone

In natural estuaries, the predictions of scalar dispersion are rarely predicted accurately because of a lack of fundamental understanding of the turbulence structure in estuaries. Herein detailed turbulence field measurements were conducted continuously at high frequency for 50 hours in the upper zone of a small subtropical estuary with semi-diurnal tides. Acoustic Doppler velocimetry was deemed the most appropriate measurement technique for such shallow water depths (less than 0.4 m at low tides), and a thorough post-processing technique was applied. In addition, some experiments were conducted in laboratory under controlled conditions using water and soil samples collected in the estuary to test the relationship between acoustic backscatter strength and suspended sediment load. A striking feature of the field data set was the large fluctuations in all turbulence characteristics during the tidal cycle, including the suspended sediment flux. This feature was rarely documented.

Differences in benthic fauna and sediment among mangrove (Avicennia marina var. australasica) stands of different ages in New Zealand

Management of coastal environments requires understanding of ecological relationships among different habitats and their biotas. Changes in abundance and distribution of mangroves, like those of other coastal habitats, have generally been interpreted in terms of changes in biodiversity or fisheries resources within individual stands. In several parts of their range, anthropogenically increased inputs of sediment to estuaries have led to the spread of mangroves. There is, however, little information on the relative ecological properties, or conservational values, of stands of different ages. The faunal, floral and sedimentological properties of mangrove (Avicennia marina var. australasica) stands of two different ages in New Zealand has been compared. Older (>60 years) and younger (3-12 years) stands showed clear separation on the basis of environmental characteristics and benthic macrofauna. Numbers of faunal taxa were generally larger at younger sites, and numbers of individuals of several taxa were also larger at these sites. The total number of individuals was not different between the two age-classes, largely due to the presence of large numbers of the surface-living gastropod Potamopyrgus antipodarum at the older sites. It is hypothesized that as mangrove stands mature, the focus of faunal diversity may shift from the benthos to animals living on the mangrove plants themselves, such as insects and spiders, though these were not included in the present study. Differences in the faunas were coincident with differences in the nature of the sediment. Sediments in older stands were more compacted and contained more organic matter and leaf litter. Measurement of leaf chemistry suggested that mangrove plants in the younger stands were able to take up more N and P than those in the older stands. (C) 2003 Elsevier Science B.V. All rights reserved.

Defining habitat characteristics influencing the distribution, density and growth of Plaice (Pleuronectes Platessa) and Dab (Limanda Limanda) on west of Ireland nursery grounds

Plaice (Pleuronectes platessa, L.) and dab (Limanda limanda, L.) are among the most abundant flatfishes in the north-eastern Atlantic region and the dominant species in shallow coastal nursery grounds. With increasing pressures on commercial flatfish stocks in combination with changing coastal environments, better knowledge of population dynamics during all life stages is needed to evaluate variability in year-class strength and recruitment to the fishery. The aim of this research was to investigate the complex interplay of biotic and abiotic habitat components influencing the distribution, density and growth of plaice and dab during the vulnerable juvenile life stage and to gain insight in spatial and temporal differences in nursery habitat quality along the west coast of Ireland. Intraspecific variability in plaice diet was observed at different spatial scales and showed a link with condition, recent growth and morphology. This highlights the effect of food availability on habitat quality and the need to consider small scale variation when attempting to link habitat quality to feeding, growth and condition of juvenile flatfish. There was evidence of trophic, spatial and temporal resource partitioning between juvenile plaice and dab allowing the co-existence of morphologically similar species in nursery grounds. In the limited survey years there was no evidence that the carrying capacity of the studied nursery grounds was reached but spatial and interannual variations in fish growth indicated fluctuating environments in terms of food availability, predator densities, sediment features and physico-chemical conditions. Predation was the most important factor affecting habitat quality for juvenile plaice and dab with crab densities negatively correlated to fish condition whereas shrimp densities were negatively associated with densities of small-sized juveniles in spring. A comparison of proxies for fish growth showed the advantage of Fulton’s K for routine use whereas RNA:DNA ratios proved less powerful when short-term environmental fluctuations are lacking. This study illustrated how distinct sets of habitat features can drive spatial variation in density and condition of juvenile flatfish highlighting the value of studying both variables when modeling habitat requirements. The habitat models generated in this study also provide a powerful tool to predict potential climate and anthropogenic impacts on the distribution and condition of juveniles in flatfish nurseries. The need for effective coastal zone management was emphasized to ensure a sustainable use of coastal resources and successful flatfish recruitment to the fishery.

Runoff and sediment transport in a degraded area

Gully erosion occurs by the combined action of splash, sheetwash and rill-wash (interrill and rill erosion). These erosion processes have a great capacity for both sediment production and sediment transport. The objectives of this experiment were to evaluate hydrological and sediment transport in a degraded area, severely dissected by gullies; to assess the hydraulic flow characteristics and their aggregate transport capacity; and to measure the initial splash erosion rate. In the study area in Guarapuava, State of Paraná, Brazil (lat 25º 24' S; long 51º24' W; 1034 m asl), the soil was classified as Cambissolo Húmico alumínico, with the following particle-size composition: sand 0.116 kg kg-1; silt 0.180 kg kg-1; and clay 0.704 kg kg-1. The approach of this research was based on microcatchments formed in the ground, to study the hydrological response and sediment transport. A total of eight rill systems were simulated with dry and wet soil. An average rainfall of 33.7 ± 4.0 mm was produced for 35 to 54 min by a rainfall simulator. The equipment was installed, and a trough was placed at the end of the rill to collect sediments and water. During the simulation, the following variables were measured: time to runoff, time to ponding, time of recession, flow velocity, depth, ratio of the initial splash and grain size. The rainsplash of dry topsoil was more than twice as high as under moist conditions (5 g m-2 min-1 and 2 g m-2 min-1, respectively). The characteristics of the flow hydraulics indicate transition from laminar to turbulent flow [Re (Reynolds number) 1000-2000]. In addition, it was observed that a flow velocity of 0.12 m s-1 was the threshold for turbulent flow (Re > 2000), especially at the end of the rainfall simulation. The rill flow tended to be subcritical [Fr (Froude Number) < 1.0]. The variation in hydrological attributes (infiltration and runoff) was lower, while the sediment yield was variable. The erosion in the rill systems was characterized as limited transport, although the degraded area generated an average of 394 g m-2 of sediment in each simulation.

Insights into the Design and Characteristics of the Sedimentation Process at Multi-Barrel Culverts in Iowa, TR-596, 2010

The present study is an integral part of a broader study focused on the design and implementation of self-cleaning culverts, i.e., configurations that prevent the formation of sediment deposits after culvert construction or cleaning. Sediment deposition at culverts is influenced by many factors, including the size and characteristics of material of which the channel is composed, the hydraulic characteristics generated under different hydrology events, the culvert geometry design, channel transition design, and the vegetation around the channel. The multitude of combinations produced by this set of variables makes the investigation of practical situations a complex undertaking. In addition to the considerations above, the field and analytical observations have revealed flow complexities affecting the flow and sediment transport through culverts that further increase the dimensions of the investigation. The flow complexities investigated in this study entail: flow non-uniformity in the areas of transition to and from the culvert, flow unsteadiness due to the flood wave propagation through the channel, and the asynchronous correlation between the flow and sediment hydrographs resulting from storm events. To date, the literature contains no systematic studies on sediment transport through multi-box culverts or investigations on the adverse effects of sediment deposition at culverts. Moreover, there is limited knowledge about the non-uniform, unsteady sediment transport in channels of variable geometry. Furthermore, there are few readily useable (inexpensive and practical) numerical models that can reliably simulate flow and sediment transport in such complex situations. Given the current state of knowledge, the main goal of the present study is to investigate the above flow complexities in order to provide the needed insights for a series of ongoing culvert studies. The research was phased so that field observations were conducted first to understand the culvert behavior in Iowa landscape. Modeling through complementary hydraulic model and numerical experiments was subsequently carried out to gain the practical knowledge for the development of the self-cleaning culvert designs.

Ecosystem impacts of Alpine water intakes for hydropower: the challenge of sediment management

The natural flow hydrological characteristics (such as the magnitude, frequency, duration, timing, and rate of change of discharge) of Alpine streams, dominated by snowmelt and glacier melt, have been established for many years. More recently, the ecosystems that they sustain have been described and explained. However, natural Alpine flow regimes may be strongly modified by hydroelectric power production, which impacts upon both river discharge and sediment transfer, and hence on downstream flora and fauna. The impacts of barrages or dams have been well studied. However, there is a second type of flow regulation, associated with flow abstraction at intakes where the water is transferred laterally, either to another valley for storage, or at altitude within the same valley for eventual release downstream. Like barrages, such intakes also trap sediment, but because they are much smaller, they fill more frequently and so need to be flushed regularly. Downstream, while the flow regime is substantially modified, the delivery of sediment (notably coarser fractions) remains. The ecosystem impacts of such systems have been rarely considered. Through reviewing the state of our knowledge of Alpine ecosystems, we outline the key research questions that will need to be addressed in order to modify intake management so as to reduce downstream ecological impacts. Simply redesigning river flows to address sediment management will be ineffective because such redesign cannot restore a natural sediment regime and other approaches are likely to be required if stream ecology in such systems is to be improved.

An investigation of geological and geochemical characteristics of late-Quaternay sediments in the Georgian Bay Region, Southern Ontario

Core samples of postglacial sediments and sediment surface samples from Shepherd Lake on the Bruce Peninsula, Harts Lake on the Canadian Shield, and two cores from Georgian Bay (core P-l in the western deep part and core P-7 in the eastern shallow part) have been analyzed for pH, grain size distribution, water content, bulk density, loss on ignition at 4500C and 11000 C, major oxides (Si02 ,A1203,!FeO,MgO,CaO, Na20,K20,Ti02 ,MnO and P205) and trace elements (Ba,Zr,Sr,y,S, Zn,Cu,Ni,Ce and Rb). The sediment in Georgian Bay are generally fine grained (fine silt to very fine silty clay) and the grain size decreases from the Canadian Shield (core p-7) towards the Bruce Peninsula (core P-l) along the assumed direction of sediment transport. This trend coincides with a decrease in sorting coefficient and an increase in roundness. Other physical characteristics, such as water content, bulk density and loss on ignition are positively correlated with the composition of sediments and their compaction, as well as with the energy of the depositional environment. Analyses of sediment surface samples from Shepherd Lake and Harts Lake indicate the influence of bedrock and surficial deposits in the watershed on pH condition that is also influenced by the organic matter content and probably I ! I man's activities. Organic matter content increases significantly in the surface sediment in these small lakes as a result of either natural eutrophication or anthropogenic organic loading. The extremely high organic matter content in Shepherd Lake sediment indicates rapid natural eutrophication in this closed basin and high biological productivity during postglacial time, probably due to high nutrient levels and shallow depth. The chemical composition of the Canadian Shield bedrock is positively correlated with the chemical characteristics of predominantly inorganic lake sediments that were derived from the Shield rocks by glacial abrasion and by postglacial weathering and erosion of both bedrock and surficial deposits. High correlation coefficients were found between organic matter in lake sediments and major oxides (Si02,AI203,.~FeO, MgO,CaO,K20 and MnO) , as well as some trace elements (Ba,Y, S,Zn,Cu,Ni and Rb). The chemical composition of sediments in Harts Lake and core P-7 in Georgian Bay on the Canadian Shield differs from the chemistry of sediments in Shepherd Lake and core P-l in Georgian Bay on the Bruce Peninsula. The difference between cores P-l and P-7 is indicated by values of Si02 , AI203 ,:LFeo,Mgo,CaO,Ba,Zr,Sr,y and S, and also by the organic matter content. This study indicates that the processes of sediment transport, depositional environment, weathering of the rocks and surficial deposits in the watershed, as well as chemical composition of source rocks all affect the chemical characteristics of lake sediments. The stratigraphic changes and variations in lake sediment chemistry with regard to major oxides, trace elements, and organic matter content are probably related to the history of glacial and postglacial lake stages of the Georgian Bay Region and, therefore, the geochemical data can make a useful contribution to a better understanding of the Late-Quaternary history of the Great Lakes.

Textual characteristics of coarse sediments in selected streams of the Niagara Peninsula, Ontario

The streams flowing through the Niagara Escarpment are paved by coarse carbonate and sandstone sediments which have originated from the escarpment units and can be traced downstream from their source. Fifty-nine sediment samples were taken from five streams, over distances of 3,000 to 10,000 feet (915 to 3050 m), to determine downstream changes in sediment composition, textural characteristics and sorting. In addition, fluorometric velocity measurements were used in conjunction with measured -discharge and flow records to estimate the frequency of sediment movement. The frequency of sediments of a given lithology changes downstream in direct response to the outcrop position of the formations in the channels. Clasts derived from a single stratigraphic unit usually reach a maximum frequency within the first 1,000 feet (305 m) of transport. Sediments derived from formations at the top of waterfalls reach a modal frequency farther downstream than material originating at the base of waterfalls. Downstream variations in sediment size over the lengths of the study reaches reflect the changes in channel morphology and lithologic composition of the sediment samples. Linear regression analyses indicate that there is a decrease in the axial lengths between the intial and final samples and that the long axis decreases in length more rapidly than the intermediate, while the short axis remains almost constant. Carbonate sediments from coarse-grained, fossiliferous units - iii - are more variable in size than fine-grained dolostones and sandstones. The average sphericity for carbonates and sandstones increases from 0.65 to 0.67, while maximum projection sphericity remains nearly constant with an average value of 0.52. Pebble roundness increases more rapidly than either of the sphericity parameters and the sediments change from subrounded to rounded. The Hjulstrom diagram indicates that the velocities required to initiate transport of sediments with an average intermediate diameter of 10 cm range from 200 cm/s to 300 cm/s (6.6 ft./sec. to 9.8 ft./sec.). From the modal velocitydischarge relations, the flows corresponding to these velocities are greater than 3,500 cfs (99 m3s). These discharges occur less than 0.01 p~r cent (0.4 days) of the time and correspond to a discharge occurring during the spring flood.

Geochemical characteristics of surficial sediments in a tropical estuary, southwest India

Geochemical characteristics of surficial sediments in the Panangad region of Cochin estuary, the largest brackish-water humid ecosystem in the south-west coast of India, were analysed. Temporal variations in nutrient stoichiometry, seasonal characteristics of redox elements Fe and S, and the phosphorus geochemistry were employed for the purpose. The stoichiometric analysis pointed towards autochthonous origin of organic matter, possibility of nitrogen limitation, and allochthonous modification of redox conditions. Seasonal variations were not statistically significant for all the geochemical parameters, whereas significant spatial variations were observed with lower values at sandy stations, suggesting that the texture of the sediments is the main factor influencing the sediment geochemistry. Significant inter-relations between the geochemical parameters also suggest a common control mechanism. Based on these geochemical characteristics, the study region can be effectively categorized into two distinct zones, viz. (1) erosion and transportation and (2) deposition zones

Environmental Geochemistry of Core Sediment in the Cochin Estuary (CE), India

Distribution of toxic metal in the sediment core is an important area of research for environmental impact studies. Sediment cores were collected from two prominent region(C1 and C2) of CE and subjected to geochemical analysis to determine distribution of toxic metals (Cd, Co, Cr, Cu and Pb ), texture characteristics, total organic carbon (TOC) and CHNS. Statistical analysis was done to understand the interrelationship between the components. In the studied cores, metal contamination level was identified for Pb, Cu; Cr, in C1 and C2 respectively. The metal distribution depends on the granulometric factor, geogenic mineral components and anthropogenic input. Correlation analysis (CA) and Principal component(PCA) analysis also support these results

Limnological characteristics and zooplankton community structure of Mediterranean coastal lagoons undergoing restoration

Entre 1999 i 2003 es va desenvolupar un projecte Life de restauració a la maresma de La Pletera, afectada per un pla urbanització, i a la llacuna del Ter Vell, amb un elevat grau d'eutròfia (aiguamolls del Baix Ter, NE Península Ibèrica). L'objectiu d'aquesta tesi és establir el funcionament d'ambdós ecosistemes, analitzar-ne la problemàtica ambiental i avaluar els efectes de la restauració. A la maresma de la Pletera, es va analitzar el paper de la hidrologia en la composició i dinàmica dels nutrients i del zooplàncton en cinc llacunes, tres de les quals havien estat creades dins el projecte de restauració com a nous refugis per una espècie de peix amenaçada (Aphanius iberus). La hidrologia es va caracteritzar per un llarg període de confinament sense entrades d'aigua, interromput de manera irregular per inundacions puntuals. La dinàmica del nitrogen inorgànic es va relacionar amb les entrades d'aigua, mentre que la del fòsfor, del nitrogen total i de la matèria orgànica es va relacionar amb els processos d'acumulació i reciclatge intern durant el confinament. El zooplàncton es va analitzar mitjançant la combinació d'aproximacions taxonòmiques i de mides. L'estructura de mides de la comunitat es va veure més afectada per les interaccions tròfiques (depredació i competència) mentre que l'estructura taxonòmica va ser més sensible a factors abiòtics (nutrients). El ràpid creixement de la població A. iberus en les noves llacunes va suggerir que aquestes havien proporcionat l'hàbitat adequat per a l'espècie, almenys a curt termini. Les actuacions de restauració a la llacuna del Ter Vell es van centrar en la millora de la qualitat de l'aigua mitjançant (1) la construcció d'uns aiguamolls per depurar l'aigua d'entrada i (2) el dragat del sediment en diversos punts. Simultàniament a la restauració, però de forma independent, la gestió agrícola de l'aigua va reduir dràsticament el cabal d'entrada d'aigua dolça a la llacuna, provocant un canvi en el règim hídric. Es van analitzar els efectes a curt termini d'aquest canvi sobre la limnologia i el zooplàncton de la llacuna. Abans del canvi, la hidrologia era artificial ja que s'havia prolongat l'entrada d'aigua dolça d'acord amb la demanda agrícola, i per tant la llacuna presentava una elevada taxa de renovació de l'aigua i majors concentracions de nutrients. Després del canvi, la hidrologia va dependre més del clima, es van reduir les entrades d'aigua i es va allargar el període de confinament. La composició y dinàmica dels nutrients va tendir a assemblar-se a l'observada a les llacunes de la maresma, mentre que la comunitat del zooplàncton no ho va fer. L'estat ecològic de la llacuna va millorar després del canvi en el règim hídric.

Influence of particle characteristics and organic matter content on the bioavailability and bioaccumulation of pyrene by clams

Hydrophobic chemicals are known to associate with sediment particles including those from both suspended particulate matter and bottom deposits. The complex and variable composition of natural particles makes it very difficult therefore, to predict the bioavailability of sediment-bound contaminants. To overcome these problems we have previously devised a test system using artificial particles, with or without humic acids, for use as an experimental model of natural sediments. In the present work we have applied this experimental technique to investigate the bioavailability and bioaccumulation of pyrene by the freshwater fingernail clam Sphaerium corneum. The uptake and accumulation of pyrene in clams exposed to the chemical in the presence of a sample of natural sediment was also investigated. According to the results obtained, particle surface properties and organic matter content are the key factors for assessing the bioavailability and bioaccumulation of pyrene by clams. (C) 2002 Elsevier Science Ltd. All rights reserved.