Settling Particulate Matter Research Articles

Development of an in situ branched GDGT calibration in Lake 578, southern Greenland

Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are abundant in lake sediments and can potentially be used as proxies for evaluating past environmental conditions. The degree of methylation of brGDGTs has a strong relationship with the ambient temperature, and numerous brGDGT temperature reconstructions have been generated ranging from the tropics to high latitudes and over a variety of timescales. However, this proxy still requires calibration and validation in Arctic settings, which are among the most climatically sensitive regions on Earth. Here, we investigate Lake 578, a dimictic lake located in southern Greenland, and examine brGDGTs in a sediment core, surface sediments, catchment soils, and settling particulate matter (SPM). Our results suggest that sedimentary brGDGTs are mainly produced in the water column, and the SPM MBT′5ME (Methylation of Branched Tetraethers) values are significantly correlated with depth-integrated summer water temperature. Here, we provide the first lake water temperature-brGDGT calibration based on the MBT′5ME index, with an improved root mean square error (RMSE) of 0.52 °C. Like previous studies, we find that watershed soils differ in brGDGT distributions from those of the SPM or lake sediments, and we conclude that most brGDGT production in Lake 578 is occurring in situ. In the sediment core, we observe a significant cooling trend in the uppermost 7 cm, but this result is unrealistic because it conflicts with the instrumental temperature record from this region. This “core-top cooling” is associated with increasing relative abundances of brGDGT-IIa and IIIa, and with decreasing brGDGT-Ia, and we speculate that it may be driven by diagenetic effects or changing microbial communities in the sediment subsurface. The anomalous “core-top cooling” phenomenon, which is noted in numerous other published lacustrine brGDGT records, highlights the need for further studies of brGDGTs in modern and recent lake sediments. Constraining the source organisms of brGDGTs and better understanding the relationship between brGDGTs and environmental factors are essential, prior to their use in paleoclimate reconstructions.

Response of microalgae to large-seaweed cultivation as revealed by particulate organic matter from an integrated aquaculture off Nan'ao Island, South China

Large seaweed cultivation has proven an effective means to inhibit harmful microalgae at experimental scales and battle eutrophication in Chinese coastal waters, but essentially there is a lack of field-scale studies to explore the underlying mechanism. Here we present a 1.5-year-long time series of particulate organic matter (POM) and settling particulate matter (SPM) concentrations from an integrated aquaculture of Gracilaria lemaneiformis off the coast of Nan'ao Island, South China from April 2014 to August 2015. The microscopic examination and geochemical characteristics show that the POM mainly consisted of microalgae. The mean POM concentration increased 99.8%, 71.2%, 45.8% and 111.9% at the four sampling sites during the non-cultivation period, while decreased 25.5%, 17.3%, 12.2% and 20.3%, respectively, during the seaweed cultivation period. These results suggest that the large scale seaweed cultivation can remove excess nutrients and inhibit microalgal growth, thereby contributing to the improvement of coastal marine aquaculture environment.

Risk assessment and seasonal variation of heavy metals in settling particulate matter (SPM) from a typical southern Chinese mariculture base

Settling particulate matter (SPM) samples were collected monthly during a 21-month-long (April 2014 to December 2015) monitoring program from a fish cage and a large seaweed (Gracilaria lemaneiformis) cultivation in a typical mariculture base in eastern coast of Guangdong Province, South China. The concentrations of eight heavy metals (Pb, Cr, Ni, Cu, Zn, Co, V and Mn) showed a clear seasonality with relatively higher levels in the rainy season for most metals. In addition, five metals (Pb, Cr, Ni, Cu and Zn) showed slightly higher concentrations in the fish cage than in the large seaweed cultivation. A principal component analysis (PCA) further revealed that Ni, Cu and Zn were influenced by human activities, whereas the rest of the metals mainly by a combination of natural and anthropogenic factors. SPM in the two different mariculture areas had a 21% probability of toxicity based on the mean effects range-median quotient.

Tidal influence on particulate organic carbon export fluxes around a tall seamount

As tall seamounts may be ‘stepping stones’ for dispersion and migration of deep open ocean fauna, an improved understanding of the productivity at and food supply to such systems needs to be formed. Here, the 234Th/238U approach for tracing settling particulate matter was applied to Senghor Seamount – a tall sub-marine mountain near the tropical Cape Verde archipelago – in order to elucidate the effects of topographically-influenced physical flow regimes on the export flux of particulate organic carbon (POC) from the near-surface (topmost⩽100m) into deeper waters. The comparison of a suitable reference site and the seamount sites revealed that POC export at the seamount sites was ∼2–4 times higher than at the reference site. For three out of five seamount sites, the calculated POC export fluxes are likely to be underestimates. If this is taken into account, it can be concluded that POC export fluxes increase while the passing waters are advected around and over the seamount, with the highest export fluxes occurring on the downstream side of the seamount. This supports the view that biogeochemical and biological effects of tall seamounts in surface-ocean waters might be strongest at some downstream distance from, rather than centred around, the seamount summit. Based on measured (vessel-mounted ADCP) and modelled (regional flow field: AVISO; internal tides at Senghor: MITgcm) flow dynamics, it is proposed that tidally generated internal waves result in a ‘screen’ of increased rates of energy dissipation that runs across the seamount and leads to a combination of two factors that caused the increased POC export above the seamount: (1) sudden increased upward transport of nutrients into the euphotic zone, driving brief pulses of primary production of new particulate matter, followed by the particles’ export into deeper waters; and (2) pulses of increased shear-driven aggregation of smaller, slower-settling into larger, faster-settling particles. This study shows that, under certain conditions, there can be an effect of a tall seamount on aspects of surface-ocean biogeochemistry, with tidal dynamics playing a prominent role. It is speculated that these effects can control the spatiotemporal distribution of magnitude and nutritional quality of the flux of food particles to the benthic and benthic-pelagic communities at and near tall seamounts.

Dynamics of settling particulate matter during typhoon Muifa in Heini Bay, China

Settling particulate matter (SPM) is widely used to describe the sedimentary environment. We have investigated here the SPM collected with a time-series sediment trap in the Heini Bay, Weihai, Shandong Peninsula, China, during the super typhoon Muifa (August 2011, maximum wind speed 55 m/s). Meteorological and hydrological parameters were measured for 18 days. By analyzing the particle flux, grain size, and loss-on-ignition (organic matter content) of SPM we found dramatic changes in these parameters, induced by typhoon Muifa for about 6 days. With the arrival of typhoon, the daily SPM fluxes increased sharply to the maximum at 76.4 g/(m(2).d) on the first day and this increase is about 9 times of the normal value, and after 6 days the SPM decreased to the normal value gradually. Other parameters, such as grain size of SPM and organic matter also experienced similar changes. Using these SPM parameters, we divided the settling progress by cluster analysis into three phases: strong (for 3 days), weak (for 3 days), and zero typhoon impact.

Characteristics and flux of settling particulate matter in neritic waters: The southern Yellow Sea and the East China Sea

The typology and flux of settling particulate matter (SPM) were investigated based on sediment trap sampling at six typical stations in the Yellow Sea and the East China Sea. The settling particulate matter in the neritic seas was sorted into three categories, lithogenic particles, living organisms, and particle aggregates. The mass of individual organisms is an important portion of particulate matter in the neritic waters. The aggregates contain six types, mucus aggregates, fecal pellets, diatom aggregates, silicoflagellate aggregates, tintinnids, and miscellaneous aggregates, of which the silicoflagellate aggregates and tintinnids are the most abundant in the Yellow Sea and the East China Sea. High particle fluxes, such as 215 to 874 g m(-2). day(-1) SPM in the bottom layer, were found at three stations where the water was well mixed, and the maximum flux was detected in the boundary area between the Yellow Sea and the East China Sea, where a wide nepheloid layer was present. Hence, particle flux in neritic waters can be easily shifted by water turbulence. The net vertical flux (123 to 961 mg C day(-1)), the contribution of lateral advection to resuspension flux (5 to 76%), and the particulate organic carbon export ratio (18 to 60%) were estimated for the other three stations where the water was stratified. The highest values were all found in the upwelling area off the Zhejiang coast, suggesting that the area of high productivity provides a high net vertical flux of SPM. (C) 2010 Elsevier Ltd. All rights reserved.

Effects of calculation procedure and sampling site on trap method estimates of sediment resuspension in a shallow lake

AbstractResuspension estimates given by two different trap methods in a shallow lake were compared. The sensitivity of the methods to errors in estimates of gross sedimentation and organic fraction of trapped material was explored. The methods were label method, in which resuspension is estimated by determining the organic fraction of surface sediment, suspended seston and trapped material, and SPIM/SPM method, where the relationship between settling particulate inorganic matter (SPIM) and total settling particulate matter (SPM) is used. During the whole 111 day study period, according to the label method, at a sheltered station 1949 g m−2 dry weight of sediment was resuspended, whereas SPIM/SPM gave an estimate of 1815 g m−2. The difference in the estimates was probably due to mineralization loss of organic material in the traps during the two week exposure periods. Sensitivity analysis showed that of the two methods, the label method was more sensitive to variations in the organic content of trapped material. At a wind‐exposed station, the total amounts of resuspended matter given by the label method and by the SPIM/SPM method were 4966 g m−2 and 4971 g m−2, respectively. Due to wind effects, escape of trapped material took place, which caused underestimation of gross sedimentation and compensated the effects of mineralization loss to diminish the difference between the methods. Of the two methods, the SPIM/SPM method seems thus more suitable for lakes, where bacterial activity is high. If cyanobacterial blooms take place, the label method is probably more reliable, providing that the exposure time of sediment traps is kept adequately short.

PCBs, PCNs, PCDD/Fs, PAHs and Cl-PAHs in air and water particulate samples––patterns and variations

Methodology for the determination of biologically active polychlorinated biphenyls (PCBs), non- ortho PCBs, polychlorinated naphthalenes (PCNs), polychlorinated dibenzo- p-dioxins and dibenzofurans (PCDD/Fs), polycyclic aromatic hydrocarbons (PAHs) was used to investigate concentrations and patterns of certain chlorinated PAH (Cl-PAH) in source related samples using synthetic reference mixtures. Thus, in addition to the above mentioned compounds, mono-heptachlorosubstituted fluorenes, phenanthrenes/anthracenes and pyrenes/fluoranthenes (Cl-PAHs) were measured in vapour and particulate air samples from urban road tunnels, samples of settling particulate matter (SPM), and in bottom sediment samples from two point source locations (pulp and paper, and Mg-plant/Fe–Mn-smelter/chlor-alkali) and in the Baltic Sea. Concentrations in air samples followed: PAHs>PCBs>PCNs>non- ortho PCBs or Cl-PAHs>PCDD/Fs. SPM samples collected at increasing distance to the urban area of Stockholm showed: PAHs>PCBs>PCNs>PCDD/Fs>non- ortho PCBs or Cl-PAHs. For all compound groups there was a tenfold (Cl-PAHs fivefold) concentration decrease in SPM samples from highest levels in the urban water area to lowest levels at a distance of 26 km from city centre. PCB profiles of SPM showed similarities with combined profiles of Aroclor 1242 and 1254. PCN profiles of SPM showed similarities with combined profiles of Halowax 1099 and 1014. A correlation with concentration of all tested Cl-PAH and their corresponding parent PAH was found only for Cl-fluorene.

Anthropogenic trace metals in sediment and settling particulate matter on a high-energy continental shelf (Sydney, Australia)

The anthropogenic contribution of trace metals to settling particulate matter (SPM) and surficial sediments was determined on the high-energy continental shelf adjacent to Sydney, Australia. Settling particulate matter and surficial sediment was collected in the vicinity of a major sewage outfall and at five control sites on the middle shelf (80–100 m water depth). Sediment traps were deployed on 10 occasions for up to 2 weeks during the summer and winter of 1995 and SPM was analyzed for Ag, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn. Cobalt, Fe, Mn and Ni act conservatively in SPM and in sediments regionally and are used as normalizing elements to determine anthropogenic enrichment. Surficial sediments and SPM are enriched in Ag, Cr, Cu, Pb and Zn near a major ocean outfall and at four of the five control sites, although sewage particles contribute <5% of trace metals in the total sample. Silver is the most sensitive trace metal tracer for establishing the presence of sewage particulate matter. Sewage particulate matter flux near the outfall was estimated using a two endmember mixing model and is below 0.5 g m −2 day −1 during all deployment periods. The mean sewage particulate matter flux at sampling locations 30 km and 60 km north of the outfall are <0.13 g m −2 day −1 and <0.01 g m −2 day −1, respectively, indicating an efficient dispersal of anthropogenic material on this high energy continental shelf.

Cytotoxicity of settling particulate matter and sediments of the Neckar River (Germany) during a winter flood

AbstractTo investigate the cytotoxic and genotoxic potentials of settling particulate matter (SPM) carried by the Neckar River, a well‐studied model for a lock‐regulated river in central Europe, during a flood, acute cytotoxicity was investigated using the fibroblast‐like fish cell line RTG‐2 with the neutral red retention, the succinic acid dehydrogenase (MTT), and the lactatedehydro‐genase (LDH) release assays as well as microscopic inspection as endpoints. Genotoxicity of water, pore water, sediments, and SPM were assessed using the Ames test. Different extraction methods (Soxhlet extraction with solvents of variable polarity as well as a fluid/fluid extraction according to pH) in addition to a supplementation of biotests with S9 fractions from the liver of β‐naphthoflavone/phenobarbital‐induced rats allowed a further characterization of the biological damage. Both sediments and SPM extracts caused cytotoxic effects in RTG‐2 cells. Cytotoxicity was found to increase significantly with polarity of extracting solvents (NR50 = effective concentration for 50% cell death in the neutral red test: 80 [65], 100 [70], 180 [220], and 225 [270] mg/ml for ethanol, acetone, dichloromethane, and n‐hexane extracts, respectively, if measured with [without] S9 supplementation). Following extraction according to pH, cytotoxicity could be attributed mainly to neutral substances (NR50: 80 and 218 mg dry SPM/ml test medium for the neutral and the acid fractions, respectively), whereas the slightly acid and basic fractions already showed little or no cytotoxicity. Samples taken during the period of flood rise showed the highest cytotoxic activities. Cytotoxicity was significantly enhanced by the addition of S9 preparations. In contrast, no genotoxic activity was found in native surface waters, pore waters, and SPM.

In situ determination of PCB biodeposition by Mytilus edulis in a Baltic coastal ecosystem

Biodeposits of the blue mussel Mytilus edulis and pelagic and near-bed settling particulate matter were collected in situ over a 1 yr period in a coastal area of the Northern Baltic proper. The amo ...

Organic pollutant characterization and toxicity testing of settling particulate matter by nanoinjection in sea trout (Salmo trutta) eggs

A nanoinjection technique was used to expose sea trout (Salmo trutta) eggs to a toluene extract of settling particulate matter (SPM) and fractions thereof from the urban waters of Stockholm, Sweden. Total extract (unfractionated), fractions collected using fractionation on an open Florisil{reg_sign} column (F1-F4), high-performance liquid chromatography (HPLC) aminopropylsilica/2-(1-pyrenyl)ethyldimethylsiluted silica column (A1-A7 and A2/P1-P3), and recombined fractions of Florisil (F-Rec) and HPLC (A-Rec) were injected into fertilized sea trout eggs. Toxicity was evaluated on the basis of deformities at hatching and in larval stages and on the basis of larvae mortality. Chemical analysis, using gas chromatography-mass spectrometry, was performed on all HPLC fractions and indicated that major components of fractions A2/P1 and A3 through A7 were polycyclic aromatic hydrocarbons (PAHs) or their alkylated derivatives. Fraction A2/P2 contained non-ortho-chlorinated biphenyls, polychlorinated dibenzo-p-dioxins and dibenzofurans, and some Cl-substituted PAHs. Deformities at hatching were observed mainly in the larvae exposed to fraction A-Rec. F2 showed the highest effect on larvae mortality, and both F-Rec and A-Rec showed antagonistic mechanisms. The frequency of deformities in larvae was highest in fractions A2/P2, F4, and A-Rec. Fractions A2/P1 and F1, which partly contained similar substances, showed similar effects on deformity at hatching and larvae mortality; however,more » F1 showed no effect on larvae abnormality compared with A2/P1. This could have been due to antagonistic mechanisms acting in F1.« less

Occurrence, Sedimentation, and Spatial Variations of Organochlorine Contaminants in Settling Particulate Matter and Sediments in the Northern Part of the Baltic Sea

Sediment trap sampling of settling particulate matter (SPM) was carried out in remote coastal and offshore stations in the Bothnian Bay (BB) and the Bothnian Sea (BS) located in the northern Baltic Sea. This was done to investigate occurrence, composition profiles, sedimentation, and spatial differences of PCBs, HCHs, hexachlorobenzene, DDTs, chlordane compounds, and dieldrin. The contamination load at the coastal stations was compared to that of surface bottom sediments. At one coastal station, sediment samples were collected in two different seasons (autumn and spring) in order to compare seasonal variations. All compound groups were found in the SPM and sediment samples analyzed. The contaminant concentrations in SPM at the coastal stations ranged, on dry weight basis, from 0.41 to 8.6 ng/g for chlordanes and HCHs and at the offshore stations from 3.2 to 31 ng/g for hexachlorobenzene and PCBs. The levels in SPM at the offshore stations were 10 times higher (on the average) than the coastal stations, li...

Dioxin-like compounds in HPLC-fractionated extracts of marine samples from the east and west coast of Sweden: Bioassay- and instrumentally-derived TCDD equivalents

Lipophilic extracts of sediment, settling particulate matter (SPM) and blue mussel ( Mytilus edulis) samples, collected at coastal locations on the east and west coast of Sweden, were HPLC-separated into three fractions containing 1. monoaromatic/aliphatic, 2. diaromatic (e.g. polychlorinated biphenyls (PCBs), polychlorinated dibenzodioxins and polychlorinated dibenzofurans (PCDDs/Fs)), and 3. polyaromatic compounds (e.g. polycyclic aromatic hydrocarbons (PAHs)). The fractions were tested for dioxin-like effects using a sensitive bioassay, based on EROD-induction in cultured chicken embryo livers. The concentrations of PCDDs/Fs, PCBs and 15 PAHs in the samples were also determined. The polyaromatic fractions of the sediment samples were more potent as EROD-inducers than the diaromatic fractions. Only a small part of the EROD-induction caused by the polyaromatic fractions could be explained by the analysed PAHs in the samples, indicating presence of non-quantified polyaromatic EROD-inducing compounds in the samples. A greater pollution by EROD-inducing diaromatic and polyaromatic compounds on the east coast site than on the west coast site was seen. The filtration activities and faeces production of the mussels on the east coast experimental site increased the sedimentation of PCDDs/Fs, PCBs and PAHs. The described bioassay proved very useful in the assessment of dioxin-like compounds in both abiotic and biotic samples from the marine environment.

Toxic potencies of extracts of sediment and settling particulate matter collected in the recipient of a bleached pulp mill effluent before and after abandoning chlorine bleaching

Extracts of bottom sediment and settling particulate matter (SPM) samples collected in the recipient water body of a bleached pulp mill effluent were separated into three fractions: monoaromatic/aliphatic compounds, diaromatic compounds (e.g., polychlorinated biphenyls, polychlorinated dibenzo-p-dioxins, and polychlorinated dibenzofurans), and polyaromatic compounds (e.g., polycyclic aromatic hydrocarbons [PAHs]). The fractions were then tested for dioxinlike potency. The methods used for the assessment of dioxinlike potency were an in vitro assay, based on the induction of 7-ethoxyresorufin-O-deethylase (EROD) in chicken embryo livers, a test for EROD induction in ovo using chicken embryos, and an immunotoxicity test measuring inhibition of lymphoid cell development in cultured fetal mouse thymuses. The samples collected closest to the mill were the most potent. There was a time-dependent decrease in dioxinlike potency in the SPM samples collected near the mill, which coincided with the cessation of chlorine gas bleaching at the mill. The bioassays in general, and the in vitro chicken embryo liver bioassay in particular, proved useful in the assessment of dioxinlike compounds in the sediment and SPM samples. The polyaromatic fractions of the samples were generally more potent than the diaromatic fractions. Only a small part of the effects caused by the polyaromatic fractions could be explained by 15 analyzed PAHs, indicating the presence of unquantified polyaromatic compounds with dioxinlike effects. This investigation indicates that the cessation of chlorine bleaching in the pulp mill resulted in a reduced load of diaromatic dioxinlike compounds in the recipient water body.

Seasonal variability in phosphorus speciation and deposition in a calcareous, eutrophic lake

Settling particulate matter was collected in sediment traps from the major depositional basin of Onondaga Lake, a calcareous, eutrophic lake in Syracuse, New York, U.S.A. Sediment traps were deployed at three depths from July to November and for a brief period under ice cover in February to investigate both vertical and seasonal variations in sedimentation. A sequential chemical extraction (fractionation) method was applied to the collected material to quantify the following phosphorus (P) fractions, or forms: loosely bound-P (sorbed-P, CaCO 3 associated-P, and Fe and Al bound-P), extractable biogenic-P (easily degradable organic-P and biogenic inorganic poly phosphates), calcium mineral-P (e.g., apatite), and refractory organic-P. Extractable biogenic-P and refractory organic-P were strongly correlated, suggesting a common, autochthonous origin in plankton. Calcium mineral-P appears to be of terrigenous origin. A dramatic increase in the loosely bound-P content of the particulate matter was observed during fall turnover when dissolved Fe 2+, which had accumulated in the anoxic hypolimnion, mixed with the surface waters and oxidized with attendant adsorption of P. We estimate that the labile-, or exchangeable-P (i.e. loosely bound- and extractable biogenic-P forms) content of the settling particulates constitutes ~ 50% of the total P influx to the sediments over the period of study. The labile-P flux over the July–November study period was 11 mg P m −2 day −1 and the labile-P flux estimated from sediment traps deployed under ice cover was 6 mg P m −2 day −1. From these values the annual average labile-P flux to the sediments was estimated to be 9 mg P m −2 day −1, only slightly less than the estimated annual average sediment P release rate of 10 mg P m −2 day −1. This indicates that the sediments are approximately at steady state with respect to current external P loadings to the lake.

Impact of PAH outlets from an oil refinery on the receiving water area—Sediment trap fluxes and multivariate statistical analysis

PAH concentrations (15 compounds) in settling particulate matter (SPM) collected in the waters outside a petroleum refinery on the Swedish Baltic coast, and in samples of particulate and dissolved fractions in the wastewater from the refinery were determined. SPM concentrations varied between 550 and 4250 ng × g dw −1 and the corresponding calculated fluxes varied between 0.1 and 3.7 ng × cm −2 × day −1. Both concentrations and fluxes did not differ significantly from background coastal or offshore locations in the Baltic. PAH profiles of the SPM samples were compared with the wastewater samples and SPM samples from background areas in the Baltic, using pattern recognition techniques. This analysis showed that the SPM samples from the petroleum refinery displayed a PAH composition similar to that found in background reference sites in the Baltic, and that the SPM samples could not be connected to the wastewater samples from the refinery. This indicates that Nynas AB is not a significant source of PAHs to the waters in its immediate surroundings, i.e. the waters in the Nynäshamn area, and/or that the hydraulic residence time of the water outside the refinery is low. A budget calculation showed that the wastewater outlet from Nynas AB is only a minor contributor of the PAH load to the waters outside the refinery.

Toxic potencies of lipophilic extracts from sediments and settling particulate matter (SPM) collected in a PCB-contaminated river system

Sediments and settling particulate matter (SPM) were sampled in a polychlorinated biphenyl (PCB)-contaminated lake, Lake Jarnsjon, and in lakes located up-/and downstream from Lake Jarnsjon. The 7- ...

TOXIC POTENCIES OF LIPOPHILIC EXTRACTS FROM SEDIMENTS AND SETTLING PARTICULATE MATTER (SPM) COLLECTED IN A PCB-CONTAMINATED RIVER SYSTEM

Sediments and settling particulate matter (SPM) were sampled in a polychlorinated biphenyl (PCB)-contaminated lake, Lake Järnsjön, and in lakes located up-/and downstream from Lake Järnsjön. The 7-ethoxyresorufin O-deethylase (EROD)-inducing potencies of lipophilic extracts from sediment and SPM were investigated in organ cultures of chicken embryo livers (denoted in vitro chicken embryo liver bioassay). The extract from sediments collected in Lake Järnsjön had the greatest EROD-inducing potency of the extracts studied, and it also contained the highest concentrations of PCBs, polycyclic aromatic hydrocarbons (PAHs), and polychlorinated dibenzodioxins/furans (PCDDs/Fs). The non-ortho-chlorinated PCBs in the extracts were probably major contributors to the EROD induction noted. The EROD-inducing potency of sediment extract from the lake downstream Lake Järnsjön was higher than that of extract from the upstream lake. This indicates that EROD-inducing substances were transported from Lake Järnsjön sediment to the lake downstream. The extracts from Lake Järnsjön sediment and SPM were separated into three fractions containing aliphatic/monoaromatic, diaromatic, and polyaromatic compounds, respectively, which were tested in the in vitro chicken embryo liver bioassay. In all extracts, the aliphatic/monoaromatic fractions were low in EROD-inducing potency, while the polyaromatic fractions from SPM were more potent than their corresponding diaromatic fractions, indicating that they contained high concentrations of aromatic hydrocarbon (Ah) receptor ligands. Only a small part of the EROD induction caused by the polyaromatic fractions could be attributed to the 15 analyzed PAHs in the samples. The EROD-inducing potencies of the diaromatic fractions correlated quite well with their concentrations of PCDDs/Fs and PCBs. The in vitro chicken embryo liver bioassay detected low concentrations of EROD inducers in the extracts and therefore proved useful for estimating the contents of Ah receptor ligands in environmental samples.

A simple method to quantify sources of settling particles in lakes: Resuspension versus new sedimentation of material from planktonic production

A strong relationship (r &gt; 0.99) between settling particulate inorganic matter (SPIM) and total settling particulate matter (SPM) was observed in 315 samples from sedimentation traps in two Swedish lakes, Lake Erken and Lake Limmaren. This relationship can be used to distinguish between different sources of SPM in pelagic systems when the inflow of allochthonous particulate matter is negligible. It is possible to quantify the proportion of material from planktonic production as well as from sediment resuspension in the flux of settling or suspended particulate matter. Furthermore, fluxes of resuspended organic particles can be quantified and distinguished from fluxes of planktonic organic particles. Although Lake Erken and Lake Limmaren are quite different with respect to trophic level, lake surface area and water depth, the estimated proportion of resuspended particles in sedimentation traps was similar in both lakes. Resuspended particulate matter ranged from 35% of the total settling particulate matter up to 99%, with annual means of 83-94%. Moreover, for both lakes it was estimated that, even in epilimnetic traps, only 2046% (annual means) of the total organic settling particulate matter was from planktonic production, whereas 54-80% (annual means) was from sediment resuspension. This is likely to have important consequences for fluxes of nutrients and contaminants.