The benthos of a perennially ice-covered Antarctic lake, Lake Hoare, contained three distinct 'signatures' of lipophilic pigments. Cyanobacterial mats found in the moat at the periphery of the lake were dominated by the carotenoid myxoxanthophyll; carotenoids: chlorophyll a ratios in this high light environment ranged from 3 to 6.8. Chlorophyll c and fucoxanthin, pigments typical of golden-brown algae, were found at 10 to 20 m depths where the benthos is aerobic. Anaerobic benthic sediments at 20 to 30 m depths were characterized by a third pigment signature dominated by a carotenoid, tentatively identified as alloxanthin from planktonic cryptomonads, and by phaeophytin b from senescent green algae. Pigments were not found associated with alternating organic and sediment layers. As microzooplankton grazers are absent from this closed system and transformation rates are reduced at low temperatures, the benthos beneath the lake ice appears to contain a record of past phytoplankton blooms undergoing decay.
Lake Hoare (77 degrees 38' S, 162 degrees 53' E) is a perennially ice-covered lake at the eastern end of Taylor Valley in southern Victoria Land, Antarctica. The environment of this lake is controlled by the relatively thick ice cover (3-5 m) which eliminates wind generated currents, restricts gas exchange and sediment deposition, and reduces light penetration. The ice cover is in turn largely controlled by the extreme seasonality of Antarctica and local climate. Lake Hoare and other dry valley lakes may be sensitive indicators of short term (< 100 yr) climatic and/or anthropogenic changes in the dry valleys since the onset of intensive exploration over 30 years ago. The time constants for turnover of the water column and lake ice are 50 and 10 years, respectively. The turnover time for atmospheric gases in the lake is 30-60 years. Therefore, the lake environment responds to changes on a 10-100 year timescale. Because the ice cover has a controlling influence on the lake (e.g. light penetration, gas content of water, and sediment deposition), it is probable that small changes in ice ablation, sediment loading on the ice cover, or glacial meltwater (or groundwater) inflow will affect ice cover dynamics and will have a major impact on the lake environment and biota.
The Phytomyxea ("plasmodiophorids") including both Plasmodiophorida and Phagomyxida is a monophyletic group of Eukaryotes composed of obligate biotrophic parasites of green plants, brown algae, diatoms and stramenopiles commonly found in many freshwater, soil and marine environments. However, most research on Phytomyxea has been restricted to plant pathogenic species with agricultural importance, thereby missing the huge ecological potential of this enigmatic group of parasites. Members of the Phytomyxea can induce changes in biomass in their hosts (e.g. hypertrophies of the host tissue) under suitable environmental conditions. Upon infection they alter the metabolism of their hosts, consequently changing the metabolic status of their host. This results in an altered chemical composition of the host tissue, which impacts the diversity of species which feed on the tissues of the infected host and on the zoospores produced by the parasites. Furthermore, significant amounts of nutrients derived from the hosts, both primary producers (plants and algae) and primary consumers (litter decomposers and plant parasites [Oomycetes]), can enter the food web at different trophic levels in form of zoospores and resting spores. Large numbers of zoospores and resting spores are produced which can be eaten by secondary and tertiary consumers, such as grazing zooplankton and metazoan filter-feeders. Therefore, these microbes can act as energy-rich nutrient resources which may significantly alter the trophic relationships in fresh water, soil and marine habitats. Based on the presented data, Phytomyxea can significantly contribute to the complexity and energy transfer within food webs.
Rhopalia of developing ephyrae were examined using the SEM and TEM at 24 h intervals following strobilation induction. Kinocilia are shorter in the ephyra stage than in polyps. A few ephyra-type kinocilia are found in rhopalia as early as 24 h after induction, before a distinct rhopalium is seen. By 72 h, the shorter kinocilia predominate and are almost as numerous as in ephyrae (120 h). Many of the kinocilia are associated with mechanoreceptor cells (MR) found in the rhopalia. These MR cells are compared to those reported for medusae. Although newly released ephyrae lack a touch plate, the MR cells in their rhopalia along with the statocyst and neuromuscular system apparently enable these organisms to detect and respond to gravity.
To examine temporal changes in a bacterial community, water samples were collected monthly for one year from five sites along a major use-reuse river, the Cuyahoga River, in northeastern Ohio (USA). Fluorescent in situ hybridization (FISH) was used to enumerate population sizes of two species of common bacteria, Pseudomonas putida and Acinetobacter calcoaceticus; FISH was also performed with a Domain Bacteria specific probe. In addition, the total bacteria (based on DAPI staining), colony forming units (on modified Nutrient agar) and coliforms were enumerated and supporting physical/chemical data were collected. Each variable examined exhibited a different seasonal pattern. Temporal changes in total number of bacteria and population size of P. putida were correlated with turbidity and precipitation suggesting that allochthonous sources and scouring of the benthos may be major contributors to these portions of the community. In contrast, the number of cells hybridizing the Domain Bacteria and A. calcoaceticus probes were correlated with temperature. Thus, different aspects of the bacterial community are potentially controlled by different factors and the role of allochthonous and autochthonous sources may vary among species.
Discriminating female mate preferences enhance the variance in reproductive success among males of a population and create a potential for sexual selection, which can account for trait evolution and diversification. Fish color patterns are among the prime targets of mate choice-driven sexual selection. Populations of the cichlid Tropheus from Lake Tanganyika display remarkable geographic color pattern variation, but the role of female choice in their rapid and rich phenotypic diversification is unclear. Males and females establish a pair bond prior to spawning monogamously, but as brood care is strictly maternal, female investment in reproduction is high and the operational sex ratio is male-biased. Therefore, variance in male reproductive success can accrue if individual males succeed repeatedly in securing a mate. To test this prediction in the red colored Tropheus moorii "Chimba", four pairs of males were presented to a series of females and female mate preferences were inferred from pairwise interactions. There was a significant difference in mating success between the males of each pair (P < 0.001 over all trials), as-with one exception-females shared preferences for the same males. Male courtship activity was strongly correlated with female choice. Our experiment suggests that female choice contributes to the variance in male reproductive success in the tested population.
Palaeoenvironments are reconstructed from the diatom flora of Holocene swamp and lacustrine sediments which lie in closed depressions of the Chad basin (Niger).
The geological and hydrological setting of the sedimentary profiles investigated is presented in section I. Three types of hydrological environments are considered: depressions which have been connected with L. Chad during the Holocene, small river-fed basins outside of the maximum extension of L. Chad, and depressions which have been mainly supplied by groundwater.
Methods used for palaeoecological reconstruction are discussed (section II) on the basis of the present-day distribution of diatom species and communities in the investigated zones. Attention is drawn to the diversity of the habitats in a given waterbody, and on the potential effects of seasonality and water stratification on the composition of diatom assemblages contained in the sediments. Because of the spatial and temporal changes in diatom communities, the sediment may integrate a mixture of communities with different ecological requirements. Thus, mean values of individual ecological variables deduced from a fossil assemblage are not sufficient to characterize a palaeoenvironment.
In section III, a classification of the palaeoenvironments is proposed. One attempts to distinguish the different communities contained in the fossil assemblages. The fossil communities are compared to diatom populations living today in the studied zones, or in other African sectors when no regional analogue has been found, and for which ecological conditions are known. This allows environmental characteristics to be inferred from sedimentary profiles. At a given time, the palaeosystems show the same ecological diversity as the modern ones.
The main status of the palaeoenvironmental evolution are then drawn for each stratigraphical profile (section IV), for an understanding of their causes. The major climatic tendancies affecting intertropical Africa have been chiefly responsible for the presence or absence of aquatic environments in the closed depressions. Superimposed to that, the diversity and the evolution of the individual palaeoecosystems have been controlled by local topographical and hydrological factors (origin of water, permeability of lake floor. . ). This is a common situation for waterbodies lying in tropical arid and semi-arid zones, and especially for palaeolakes associated to groundwater circulations. Therefore, palaeolimnological data can hardly serve as direct and accurate climatic indicators, if they are not corrected for the effects of local hydrology.
The longest vertical profile from the western basin of Taihu Lake ever taken was nearly 4 m (396 cm) in length and represented a time period of over 14000 years. The core was analyzed for the following proxies, magnetic susceptibility, organic carbon isotope, total organic carbon, total nitrogen, total pigments, saturated hydrocarbons, carbon 14, thermolytic hydrogen (the hydrogen index, HI) and foraminifera. Results from the west Taihu lake core indicate that ca. 14300–13400 a B.P., the lake was relatively shallow and the climate was likely to have been quite arid. From 13400 to 12400 a B.P., the environment became less arid and the depth of the water in Lake Taihu increased. Marine incursions occurred during this period as indicated by the presence of numerous marine foraminifera. From ca. 12400 to 10900 a B.P., the climate became wetter, warmer and more variable. A cold dry period occurred around ca. 11500 a B.P., causing the lake to become more shallow. From 10900 to 10000 a B.P., a warm and wet period reasserted itself and water depth again increased. A cold dry period reoccurred from 10000 to 9500 a B. P. From 9500 to 7200 a B.P., the climate was quite variable. By 7200–5700 a B.P., the climate again turned warmer and wetter. Some of the major sediment proxies used in this study changed dramatically at ca. 5050 a B.P., reflecting changes in material source and a probable interruption of sedimentation. The modern environment (4900 aB.P.-present) was characterized by a well oxidized sediment layer and thriving algae. The lake is presently very eutrophic and is characterized by cyanobacteria, primarily Microcystis aeruginosa, the dominant primary producer in the lake. This is the first study to use a variety of organic geochemical proxies to infer paleoenvironmental changes in Taihu Lake.
Marine sponges harbor dense microbial communities of exceptionally high diversity. Despite the complexity of sponge microbiota,
microbial communities in different sponges seem to be remarkably similar. In this study, we used a subset of a previously
established 454 amplicon pyrosequencing dataset (Schmitt and Taylor, unpublished data). Five Mediterranean sponges were chosen
including the model sponge Aplysina aerophoba to determine the extent of uniformity by defining (i) the core microbial community, consisting of bacteria found in all sponges,
(ii) the variable microbial community, consisting of bacteria found in 2–4 sponges, and (iii) the species-specific community,
consisting of bacteria found in only one sponge. Using the enormous sequencing depth of pyrosequencing the diversity in each
of the five sponges was extended to up to 15 different bacterial phyla per sponge with Proteobacteria and Chloroflexi being
most diverse in each of the five sponges. Similarity comparison of bacteria on phylum and phylotype level revealed most similar
communities in A. aerophoba and A. cavernicola and the most dissimilar community in Pseudocorticium jarrei. A surprising minimal core bacterial community was found when distribution of 97% operational taxonomic units (OTUs) was
analyzed. Core, variable, and species-specific communities were comprised of 2, 26, and 72% of all OTUs, respectively. This
indicates that each sponge contains a large set of unique bacteria and shares only few bacteria with other sponges. However,
host species-specific bacteria are probably still closely related to each other explaining the observed similarity among bacterial
communities in sponges.
Keywords454 amplicon pyrosequencing–Bacterial symbiont–Core microbiota–Microbial diversity–Sponge–Vertical transmission
A new method is described for the combined determination of -1,3-glucan and cell wall polysaccharides in diatoms, representing total cellular carbohydrate. The glucan is extracted by 0.05 mol l–1 H2SO4 at 60 C for 10 min, and the cell wall polysaccharides are subsequently hydrolyzed by 80% H2SO4 at 0–4 C for 20 h. Each carbohydrate fraction is determined by the phenol-sulphuric acid method. The method has been demonstrated for axenic cultures of the marine diatom Skeletonema costatum and natural marine phytoplankton populations dominated by diatoms. Cellular glucan and cell wall polysaccharides were determined with standard deviations of 1–3% and 2–5%, respectively.
We examined some characteristics of hydrolytic enzymes, especially β-1,3-glucanase, to obtain the information of cell wall lytic enzymes for rotifers.
Crude enzyme (ammonium sulfate fraction) of rotifers hydrolyzed starch, β-1,3-glucan, glycol chitin and CM-cellulose. Optimum pH for hydrolysis of starch and CM-cellulose was 6.5, and that for β-1,3 glucan and glycol chitin was pH 6.0. Pectic acid, xylan and agarose were not hydrolyzed at pH 3–10.
β-1,3 glucanase was purified about 73-fold from crude enzyme by ion-exchange chromatography and gel filtration. Optimum pH and temperature of the enzyme were 6 and 60 °C, respectively. The molecular weight of the enzyme was estimated about 260 kDa by gel filtration. The enzyme was inhibited by HgC12 and MnC12.
Nutrient and chlorophyll concentrations in Lake Newnan (27 km2, mean depth 1.5 m), Florida showed dramatic increases from 1991 to 1998. Historical data showed Lake Newnan never had sufficient aquatic macrophyte abundance for a shift in alternate stable states to account for increases in trophic state characteristics. External phosphorus and nitrogen loads from incoming streams were monitored from August 1997 to July 1998 to determine if external supplies of nutrients were responsible for increases in lake nutrient and chlorophyll concentrations. During the study period, external nutrient loading rates were not correlated to lake nutrient concentrations. Phosphorus and nitrogen models based on the external loading estimates predicted the lake total phosphorus and total nitrogen concentrations to be 370% and 680% less, respectively, than the observed lake total phosphorus and total nitrogen mean concentrations. Consequently, phosphorus and nitrogen exports were 280% and 540% greater, respectively, than stream input loading. Data during the study period revealed strong inverse relations between lake stage and total phosphorus (r=–0.78), total nitrogen (r=–0.71), and chlorophyll (r=–0.90) concentrations. Long-term data (1965–1998) also revealed inverse correlations (r=–0.48 to –0.52) between lake stage and total phosphorus, total nitrogen, and chlorophyll concentrations. Applying fundamental wave theory and using a bathymetric map, it is probable that as much as 70% of the lake bottom sediment could be subjected to resuspension 50% of the time when the lake stage falls below 19.9 m mean sea level (msl). Above a lake stage of 19.90 m msl, less than 20% of the lake bottom sediment can potentially be resuspended 50% of the time. A percent frequency distribution from 1991 to 1998 showed that over 30% of the lake stages fell below 19.9 m msl. However, from 1967 to 1990, only 8% of the lake stage values fell below 19.9 m msl. Increases in total phosphorus, total nitrogen and chlorophyll concentrations in Lake Newnan were likely caused by an increased probability of internal loading due to decreased lake levels, and not to external loading of phosphorus and nitrogen.
Benthic macroinvertebrates were sampled at six stations in the Athabasca River near Ft. Mackay, Alberta, during the 1977 open water season. Fluctuating discharge of the river effected changes in the nature of the sediments as well as the abundance and composition of invertebrate communities. During most of the summer, coarse sand was dominated by chironomids of the Harnischia complex and an undescribed Orthocladiinae. Stoneflies and mayflies invaded the coarse sand in autumn when decreasing discharge led to greater stability of the substrate. The invertebrate fauna of silt and mud resembled that of similar substrates in lakes. Bedrock supported communities similar to those of stony streams. The average abundances of invertebrates on sand and mud were similar but estimates from mud were somewhat more variable. These results are discussed with respect to substrate stability and compared with published records from other large rivers.
The monogonont Rotifera fauna of Lobo (Broa) reservoir (SP., Brazil), present in 12 samples collected on a single date during the cool season (26 August 1994), is listed and commented upon. In total, 102 species could be identified, three of which, Ascomorpha tundisii n.sp., Lecane broaensis n.sp. and Lepadella neglecta n.sp. are new to science. Lecane mitis Harring & Myers and Lepadella elongata Koste are redescribed. A note on the taxonomy of the Ascomorpha saltans-group is added.
The last few years have seen a dramatic growth in the use of 210Pb sediment dating. Despite this, considerable doubt still surrounds the nature of the processes by which 210Pb is deposited in lake sediments, and this has lead to a situation where there is a choice of dating models offering different interpretations of 210Pb data. In assessing 210Pb data it is therefore essential to first of all determine whether data is consistent with the assumptions of the dating model, and to then compare the 210Pb chronology with independent dating evidence. We have tested 210Pb data from a wide variety of sites, and our calculations indicate that the crs (constant rate of 210Pb supply) model provides a reasonably accurate chronology when the total 210Pb contents of cores from neighbouring locations are comparable.
The different species and infraspecific categories of the genus Brachionus, so far reported or described from India, are reviewed. Their distribution and taxonomic validity are discussed. Remarks are made on the ecology and epizoic nature of various species.
The physico-chemical habitat template of glacial streams in the Alps is characterized by distinct and predictable changes
between harsh and relatively benign periods. Spring and autumn were thought to be windows of favorable environmental conditions
conducive for periphyton development. Periphyton biomass (measured as chlorophyll a and ash-free dry mass) was quantified in five glacial and three non-glacial streams over an annual cycle. One glacial stream
was an outlet stream of a proglacial lake. In all glacial streams, seasonal patterns in periphyton were characterized by low
biomass during summer high flow when high turbidity and transport of coarse sediment prevailed. With the end of icemelt in
autumn, environmental conditions became more favorable and periphyton biomass increased. Biomass peaked between late September
and January. In spring, low flow, low turbidity, and a lack of coarse sediment transport were not paralleled by an increase
in periphyton biomass. In the non-glacial streams, seasonal periphyton patterns were similar to those of glacial streams,
but biomass was significantly higher. Glacier recession from climate change may shift water sources in glacier streams and
attenuate the glacial flow pulse. These changes could alter predicted periods of optimal periphyton development. The window
of opportunity for periphyton accrual will shift earlier and extend into autumn in channels that retain surface flows.
KeywordsAlpine-Algae-Primary production-Stream-Flow regime-Glacier-Ecological windows
Lake Plessa 107 is an example of the older, relatively small and often shallow mining lakes of Lusatia which only have groundwater inflow. From a morphological point of view, the lake should be polymictic with short stratified periods. But besides temperature, mixing is also determined by chemical gradients in the water column that can lead up to monomixis. The lake water shows an extreme acidification with high concentrations of calcium, iron, aluminium, manganese and sulphate. Despite low TIC and TP concentrations allowing only a low primary production in the pelagial within the oligotrophic range, anoxic conditions can occur during stratification because of Fe(II) oxidation and anoxic groundwater inflow. The phytoplankton is dominated by phytoflagellates. Chlorophyll concentrations follow a yearly pattern determined by temperature and light availability. The zooplankton consists of two rotifer species, ciliates and heliozoans. Sediment analyses show contrary depth gradients of Fe and P with a very high fraction of Fe in the upper sediment layers (up to 60% of DW) which decreases with depth. Probably due to groundwater inflow, at some sites substantial decreases in redox potential and conductivity can be observed with increasing sediment depth accompanied by increases of pH, DOC, DIC and DIP concentrations. No correlations have been found between the available phosphorus or carbon concentrations in the sediment porewater and the phytobenthic biomass. Euglena mutabilis(Euglenophyceae) and Pinnularia acoricola(Bacillariophyceae) are the dominant phytobenthic species. Lake Plessa 107 has a benthic food-web that consists of benthic algae, chironomids and corixids and a pelagic food-web which is composed of phytoflagellates, rotifers, ciliates and heliozoans. The two food-webs are not coupled because larger prey organisms such as crustaceans are missing.
The ionic product of 10750oxy-apatite has been calculated from data sets from the hard water rivers Rhine and Rhone. An overall value of 10–50 has been obtained, but this value has an uncertainty due to the uncertainty of the third ionisation constant of phosphoric acid. Implicitly it has been shown that these rivers are saturated with respect to 10750oxy-apatite and that thus calcium controls the solubility of o-phosphate.
Computer models can be helpful tools to provide abetter understanding of the mechanisms responsible forthe complex movements of cyanobacteria resulting fromchanges in buoyancy and mixing of the water column ina lake. Kromkamp & Walsby (1990) developed a verticalmigration model for Oscillatoria, that wasbased on the experimentally determinedrelationship between the rates of density change andphoton irradiance in this cyanobacterium. To adaptthis model to Microcystis, we determinedrelated changes in carbohydrate content in cultures ofMicrocystis. Samples were incubated at variousconstant values of photon irradiance and then placedin the dark. The changes in carbohydrate content ofthe cells during these incubations were investigated.The relationship between the ratio of carbohydrate toprotein and cell density in Microcystis wasestablished to permit conversion of the rates ofcarbohydrate change to rates of density change. Byplotting the calculated rates of density changeagainst the values of photon irradiance experiencedduring the incubations, an irradiance-response curveof density change was established. The curve showed adistinct maximum at 278 mol photons m-2s-1. At higher values of photon irradiance, therate of density change was strongly inhibited. Apositive linear correlation was found between celldensity and the rates of density decrease in the dark.The validity of the use of rate equations of densitychange, which are based on short-term incubations atconstant values of photon irradiance, to predictdensity changes in Microcystis in fluctuatinglight regimes was tested. This was accomplished bymeasuring the time course of change in carbohydratecontent of two continuous cultures of Microcystis, which were submitted to fluctuatinglight regimes, and comparing the results with thechanges in the carbohydrate contents of these culturespredicted by the rate equations of carbohydratechange. The results showed good agreement: the rateequations of density change were therefore introducedinto the model to simulate vertical migration of Microcystis. The model predicts that the maximummigration depth of Microcystis will increasewith colony size up to a maximum of 200 m radius.The effect of colony size on the net increase in celldensity during the light period was also investigatedwith the model. It predicts that small colonies havea higher net increase in cell density than largecolonies, but are inhibited at high photon irradiancesat the surface.
The results of water physico-chemical analyses and malacological data taken from a hundred stations belonging to five major French catchment areas have analysed using a factorial analysis of correspondences.First, a sequence of population descriptors and stations was obtained, corresponding with an increase of species richness and numbers.Second, 11 physico-chemical variables were projected as additional elements (non-active variables) in the plane F1-F2 of the previous analysis. Using the analyses of correspondences between the descriptors and the classes of each variable, it was possible to determine:
the classes of values which enable the optimum development of the molluscs;
the threshold value at which a variable becomes limiting and inhibits mollusc populations.
The results are summarized in Fig. 3 and followed by a discussion.
The type II microtrich sensilla on the lotic amphipod Gammarus pseudolimnaeus Bousfield enable it to control body orientation while swimming, as animals with their sensilla masked spent significantly more time swimming on their sides. These sensilla appear to be involved in the behavioural process that allows the animal to orient into the current (positive rheotaxis), as significantly fewer masked animals were able to turn into novel current flows compared with controls. The sensilla do not appear to play a role in detecting gravity. Results suggest that the sensilla transmit hydromechanical sensory information to the animal, and it is thought that the individual sensilla act in unison as a kinetic sensory organ. The sensilla are well adapted for such a hydromechanical role, as they would likely only be stimulated by currents hitting them broadside on. The sensilla are grouped, with each sensillum facing in a different direction, and the groups are located at appropriate positions for detecting current flows. The sensilla do not play a role in the detection of vibrations. Nor do they play a chemosensory role in the detection of food or predators; however, a role in conspecific chemodetection cannot be ruled out.
Individual homeostasis and genetic differentiation both contribute to the total distribution, in terms of salinity, of some marine euryhaline species (Battaglia 1957; Remane & Schlieper 1971). An assessment of the incidence of differentiation, however, is difficult. The dearth of examples may be artefactual, reflecting, as Battaglia (1967) suggests, ‘the paucity of marine forms …suitable for genetic investigations’, or may be a real phenomenon reflecting the relative contiguity of most marine-estuarine populations. At least on the latter ground inland saline waters would be expected to contain abundant material for study of differentiation. Distributed within the archipelago of salt lakes in western Victoria, Australia, are many populations of various species exposed to wide spatial differences and varied temporal instability in regard to salinity. Data relating to possible physiological diversification in a halobiont copepod found in many of these lakes are discussed here.
The present knowledge of the freshwater algal flora in the Indo-Malaysian North Australian region is reviewed. More than 4700
taxa have been recorded from this region. Desmids, diatoms and cyanobacteria are among the better studied groups of organisms,
while phytoflagellates have received very little attention. Phytoplankton communities in tropical lakes are generally similar
to summer communities of temperate lakes. In addition, there is a large number of typical tropical taxa, including pantropical
and regional endemic elements. Local endemism occurs in the old Tertiary lakes of the region. The composition of algal communities
changes markedly along an altitudinal gradient, and tropical taxa are gradually replaced by taxa characteristic for cool climatic
conditions. Biogeographical distribution patterns are exemplified for the desmids and diatoms. Among the more than 2680 desmids
recorded from the Indo-Malaysian North Australian region, about 800 have never been found elsewhere. Dispersal by migratory
birds and past climatic changes might explain distribution patterns. Because of incomplete taxonomy and a general lack of
understanding of the autoecology, distribution and speciation of freshwater algae, however, there remain serious obstacles
for detailed biogeographical analyses.
Radioecological field studies show that most of the 110m in contaminated freshwater ecosystems occurs in the sediment, which therefore represents a potential source of radioactive pollution. Laboratory experiments were carried out to quantify 110mAg uptake and retention by three species of bottom-dwelling organisms, a limicolous midge larva (Chironomus luridus), a benthic crustacea (Gammarus pulex) and an omnivorous fish (Cyprinus carpio), and to assess the potential incorporation of this radionuclide in freshwater food webs. The rate of contamination of each organism was described using a two-compartment model. Concentration factors (110mAg in organism: 110mAg in water) reached a maximum (1100 ww) in 30 and 60 d respectively for gammarid and midge larva. The concentration factor for Cyprinus carpio increased as a function of time to reach a maximum value of 106 after 180 d. 110mAg uptake from the sediment suggests a real possibility of direct transfer from this compartment to the three organisms. The maximum value of the transfer factor (110mAg in organism: 110Ag in sediment) was about 1.9, 0.17 and 0.022, for gammarid, midge larva and carp, respectively. The ingestion of contaminated gammarids and midge larvae by carp results in a 110mAg accumulation corresponding to a trophic transfer factor (110mAg in predator: 110mAg in prey) of 0.023 and 0.135, respectively. Comparison of the different factors that influence the 110mAg transfer suggests that water is the most important contamination vector. However, taking into account their 110mAg concentration, prey and sediment can lead to a greater level of contamination in consumer organisms than uptake from water.