Top Sediment Layer Research Articles

LATE HOLOCENE PALYNOLOGICAL RECORD AND LANDSCAPE CHANGE FROM THE PIRAQUÊ-AÇU AND PIRAQUÊ-MIRIM ESTUARINE SYSTEM, ESPÍRITO SANTO, BRAZIL

The Piraque-Acu and Piraque-Mirim estuarine system (PAPMES) is located next to the Aracruz City (19˚ 57' S and 40˚ 9' W), Espirito Santo State, Brazil. Palynological analyses were conducted based on two sediment cores (PA20 and PM1). The main purpose of the present study was to recognize and interpret the vegetation dynamics in the region around the collection site in the last 2000 cal yrs BP. The sediment cores were subsampled at each 10 cm depth. The samples were submitted to standard palynological processes. The PA20 sediment core obtained the oldest age of 1758±68 cal yrs BP at a depth of approximately 105-cm. However, the PM1 sediment core obtained the oldest age of ≈2071±82 cal yrs BP at a depth of 95-cm. The comparative record of the sediment cores demonstrated that palynomorphs deposition were directly influenced by local water circulation. Pollen analysis indicated the striking presence of mangrove vegetation, which is mainly characterised by the Rhizophora pollen type. The other vegetation communities underwent little variation over the studied period. The top sediment layers of both sediment cores are characterized by the presence of exotic pollen grains of Eucalyptus , introduced by humans, and by the decrease of the original vegetation. doi: 10.12957/jse.2016.21878

Metabolic capacities of common carp (Cyprinus carpio) following combined exposures to copper and environmental hypoxia

In aquatic ecosystems, a decline in water O2 level is the main factor that can release heavy metal ions from top sediment layer. Therefore, hypoxia in turn, and in association with heavy metals might provide undesirable environment and impairs physiological functions of aquatic animals. To address this, metabolic capacities, including standard metabolic rate (SMR), maximum metabolic rate (MMR), aerobic scope (AS) and factorial aerobic scope (FAS) of common carp were determined following exposures to different levels of water-borne Cu2+ as well as hypoxia. Treatments for Cu2+ were included: 100% (acute), 50% (sub-lethal) and 10% (chronic) of LC50-96h for immediately, 24h and 7 days exposures respectively. Hypoxia treatments were assigned as acute for immediately, sub-lethal for 24h and chronic for 7 days. Combined effects of treatments were also considered as acute Cu2++hypoxia, sub-lethal Cu2++hypoxia and chronic Cu2++hypoxia. While SMR of carp was reduced by chronic hypoxia, significant (P<0.05) increase was observed during acute hypoxia, as compared with control. The MMR and AS were significantly reduced (P<0.05) following all hypoxia treatments. The acute and chronic Cu2+ treatments showed significant (P<0.05) increases in SMR and MMR values. All acute and sub-lethal combined treatments showed significant (P<0.05) reductions in SMR, MMR and AS values, whilst chronic combined treatments showed generally increasing trends for MMR and AS. PCrit was relatively reduced following all treatments except for acute and sub-lethal Cu2+-treated fish that showed higher value (P<0.05) and no change respectively. Although all Cu2+ treatments increased the number of mucus cell, hypoxia treatments did not show any remarkable differences when compared with control group. In general, the results of present study reveal that hypoxia acts as limiting stressor whilst Cu2+ do act as loading stressors in the case of common carp metabolism. The interactive exposures mostly showing a synergist effect in all metabolic capacities with an exception for chronic treatments.

HEAT FLUX AT THE WATER-SEDIMENT INTERFACE IN A SHALLOW LAKE

The results of long-term (2007–2013) year-round continuous temperature measurements in the near-bottom water and the top sediment layer of a small shallow lake are reported. The measurement technique using a bottom-mounted platform is described. Owing to the highly sensitive equipment used in the long-term water temperature measurements with a small time step (one minute) we managed to obtain fundamentally new information on heat transfer through the water-sediment interface throughout the year, including the periods of ice cover formation and destruction.

Seasonal patterns of bacterial communities in the coastal brackish sediments of the Gulf of Finland, Baltic Sea

Coastal areas are critical in mitigating the impact of nutrient runoffs and downstream eutrophication of aquatic ecosystems. In the Gulf of Finland, the easternmost sub-basin of the Baltic Sea, seasonal and long-term oxygen depletion at the surface of the sediment feeds back the eutrophication loop by promoting the release of nutrients locked in the sediment matrix. In order to understand how the bacterial community responds to the seasonal variations, we sequenced ribosomal gene fragments from the top sediment layer at two coastal sites in southern Finland in spring, summer and late autumn during two consecutive years. Analysis of the samples collected at a shallow (11 m) and deep site (33 m) revealed that the overall community composition was rather constant over time with an extensive collection of shared operational taxonomic units (OTU) between sites. The dominant taxa were related to organoheterotrophs and sulfate reducers and the variation in community structure was linked to the availability of organic matter in the surface sediment. Proteobacteria formed the most abundant and diverse group. The taxa characteristic of spring samples belonged primarily to Actinobacteria, possibly of fresh water origin and linked to humic carbon. Summer communities were characterized by an increase in the number of reads associated with heterotrophic bacteria such as Bacteroidetes which feed on labile organic matter from spring bloom. Taxa typical of autumn samples were linked to Cyanobacteria and other bloom-forming bacteria from the overlying water and to bacteria feeding on organic matter drifting from the phytal zone.

Particle sources and downward fluxes in the eastern Fram strait under the influence of the west Spitsbergen current

The carbon cycle of the Arctic Ocean is tightly regulated by land–atmosphere–cryosphere–ocean interactions. Characterizing these environmental exchanges and feedbacks is critical to facilitate projections of the carbon cycle under changing climate conditions. The environmental drivers of sinking particles including organic carbon (OC) to the deep-sea floor are investigated with four moorings including sediment traps and currentmeters at the Arctic gateway in the eastern Fram Strait, which is the area where warm anomalies are transported northwards to the Arctic. Particles fluxes were collected over one year (July 2010–July 2011) and have been analysed to obtain the content of the lithogenic fraction, calcium carbonate, OC and its stable isotopes, opal, and the grain size. Records of near bottom current speed and temperature along with satellite observations of sea ice extent and chlorophyll-a concentration have been used for evaluation of the environmental conditions.We found increased lithogenic fluxes (up to 9872mgm−2d−1) and coarsening grain size of settling particles in late winter–early spring. At the same time, intensifications of the northward flowing west Spitsbergen current (WSC) were recorded. The WSC was able to resuspend and transport northwards sediments that were deposited at the outlet of Storfjordrenna and on the upper slope west of Spitsbergen. The signal of recurrent winnowing of fine particles was also detected in the top layer of surface sediments. In addition, an increased arrival of sea ice transported ice rafted detritus (>414 detrital carbonate mineral grains larger than 1mm per m2) from the southern Spitsbergen coast along with terrestrial organic matter was observed beyond 1000m of water depth during winter months. Finally, the downward particle fluxes showed typical temporal variability of high latitudes, with high percentages of the biogenic compounds (opal, organic carbon and calcium carbonate) linked to the phytoplankton bloom in spring–summer. However, on an annual basis local planktonic production was a secondary source for the downward OC, since most of the OC was advected laterally by the WSC. Overall, these observations demonstrated the sensitivity of the downward flux of particles to environmental conditions such as hydrodynamics, sea ice rafting, and pelagic primary production. Future alteration of the patterns of natural drivers due to climate change is thus expected to cause major shifts in the downward flux of particles, including carbon, to the deep sea ecosystems.

Contribution of Methane Benthic and Atmospheric Fluxes of an Experimental Area (Sitka Stream)

Contributions of methane benthic fluxes and methane emissions to the total methane amount were studied during the summer season for two consecutive years. Considering the fact that methane is produced in great amount within hyporheic sediments, we have expected that both methane released by the benthic fluxes into the overlying water and methane emitted to the atmosphere should significantly affect the total methane budget of the stream water within the experimental area. In order to asses this assumption, we measured methane concentrations within the vertical sediment profile of a hyporheic zone, direct benthic methane fluxes by static chambers, methane concentrations in the surface water, and methane emissions into the atmosphere simultaneously. The methane concentrations in interstitial water tended sharply to increase with sediment depth (0.54–734.99 μmol L−1) and were strongly correlated with benthic fluxes (r = 0.88, p &lt; 0.05). We also found a considerable variability in the benthic methane fluxes (0–12.59 mmol m−2 day−1) and the spatial variability (0–71.43%) of the experimental area, suggesting that there may be various factors that affect the rate of benthic fluxes including methanotrophy in the top sediment layers. Generally, the contribution of benthic fluxes and methane emissions to the methane budgets of the experimental area was negligible (0.034 (0.45%) and 0.074 mol day−1 (0.98%), respectively).

English

Sediments play an important role in determining the quality of lakes, rivers and oceans as they can act as either a source or sink for pollutants. Once the input pollution is controlled, sediments as a secondary source of pollution can release the accumulated pollutants to overlying water.1 The organic matter content of sediments can also affect the structure of macroinvertebrate assemblages.2 To date, traditional sediments remediation methods include monitored natural recovery, in-situ treatment, and ex-situ treatment.3 The traditional methods are either expensive or not environmentally friendly, so it is crucial to find a cost-effective and environmentally friendly way to solve the contaminated sediments problem. Microbial fuel cell (MFC) technology is considered an environmentally friendly and promising approach for converting wastewater or solid waste into electricity.4–6 Recently, some studies have shown that sediment microbial fuel cell (SMFC) can alter the properties and enhance the removal of organic matter in sediment.7–9 Wang9 developed a three-dimensional floating biocathode to dispose river sediments, and concluded that the sediment organic matter content near the anode was removed by 29 %. Hong7 found that sediment organic matter around the electrodes became more humified, aromatic, and polydispersed, and had a higher average molecular weight, along with its partial degradation and electricity generation compared to that of the original sediment. Sajana10 studied the performance of SMFC by adding cellulose in freshwater and demonstrated effective cellulose degradation from aquaculture pond sediment and maintained the oxidized sediment top layer favourable for aquaculture. Zhou11 improved the SMFC performance by amendment of colloidal iron oxyhydroxide into sediments and concluded that high Fe(II) concentration in pore water of sediments led to high power production. Song12 found that the addition of biomass in appropriate proportions can enhance output power in SMFC. However, mass transfer limitations for electron donors to reach the anode and a low rate of oxygen reduction in cathodes were major limitations for power production.13 In freshwater environments, the maximum power densities in SMFC with felt graphite14 and carbon paper15 as cathode were 4 mW m–2 and 2 mW m–2 respectively. Song13 constructed SMFC with granule activated carbon cathode and stainless steel anode and obtained 3.5 mW m–2 maximum power density, and further increased to 11.2 mW m–2 by adding cellulose. Jiang16 built MFC with graphite fiber brush and enhanced TCOD removal rate from 11.3 % to 19.2 % for raw sludge. Removal and Changes of Sediment Organic Matter and Electricity Generation by Sediment Microbial Fuel Cells and Amorphous Ferric Hydroxide

The Effect of Water Level on The Effectiveness of Sediment Flushing

This research is focused on determining the effective flushing water level in pressure flushing activity at storage sedimen based on the hydraulic physical model test in the laboratory. The effective water level is the elevation of water level in sediment flushing which result in the highest concentration of sediment scours. Effective flushing water level is the elevation of water level near the top layer of sediment deposit which can trigger the erosion of the top layer of sediment so that it creates a maximum scours. That elevation is known as Effective Flushing Water Level (EFWL). This research was conducted in the laboratory using Wonogiri Reservoir prototype, with scale model of 1:66.67. The model operated without inflow, started from control water level (CWL) .and lowered gradually by operating the flushing gates. The gates were operated of a = 2.50 cm. The flushing implementation was repeated with variation of sediment thickness Hs=1.50; 3.00; 3.75 and 4.50 cm. The water level, sediment concentration, flushing discharge, and the flow velocity in the upstream of the gates were observed every 1.50 cm lowered of water level. Coal dust was used in this research to substitute sediment material. The result of this research is expected to be used as an initial consideration of effective sediment flushing in Wonogiri reservoir protoype in order to reduce the capacity loss of the reservoir due to sedimentation , or in other words to extend the life time plan of reservoir.

The impact of acid mine drainage on the methylmercury cycling at the sediment-water interface in Aha Reservoir, Guizhou, China.

The methylmercury (MeHg) cycling at water-sediment interface in an acid mine drainage (AMD)-polluted reservoir (Aha Reservoir) and a reference site (Hongfeng Reservoir) were investigated and compared. Both reservoirs are seasonal anoxic and alkaline. The concentrations of sulfate, sulfide, iron, and manganese in Aha Reservoir were enriched compared to the reference levels in Hongfeng reservoir due to the AMD input. It was found that the MeHg accumulation layer in Aha Reservoir transitioned from the top sediment layer in winter to the water-sediment interface in spring and then to the overlying water above sediment in summer. It supported the assumption that spring methylation activity may start in sediments and migrate into the water column with seasonal variation. The weaker methylation in sediment during spring and summer was caused by the excessive sulfide (∼15-20μM) that reduced the bioavailability of mercury, while sulfate reduction potential was in the optimal range for the methylation in the overlying water. This led to a transport flux of MeHg from water to sediment in spring and summer. In contrast, such inversion of MeHg accumulation layer did not occur in Hongfeng Reservoir. The sulfate reduction potential was in the optimal range for the methylation in top sediment, and dissolved MeHg was positively related to sulfide in pore water of Hongfeng Reservoir (r = 0.67, p < 0.001). This result suggested that accumulation of MeHg in lake water and cycling of MeHg at sediment-water interface associate with some sensitive environmental factors, such as sulfur.

Equilibrium and kinetic modeling of contaminant immobilization by activated carbon amended to sediments in the field

Addition of activated carbons (AC) to polluted sediments and soils is an attractive remediation technique aiming at reducing pore water concentrations of hydrophobic organic contaminants (HOCs). In this study, we present (pseudo-)equilibrium as well as kinetic parameters for sorption of a series of PAHs and PCBs to powdered and granular activated carbons (AC) after three different sediment treatments: sediment mixed with powdered AC (PAC), sediment mixed with granular AC (GAC), and addition of GAC followed by 2 d mixing and subsequent removal (‘sediment stripping’). Remediation efficiency was assessed by quantifying fluxes of PAHs towards SPME passive samplers inserted in the sediment top layer, which showed that the efficiency decreased in the order of PAC > GAC stripping > GAC addition. Sorption was very strong to PAC, with Log KAC (L/kg) values up to 10.5. Log KAC values for GAC ranged from 6.3–7.1 and 4.8–6.2 for PAHs and PCBs, respectively. Log KAC values for GAC in the stripped sediment were 7.4–8.6 and 5.8–7.7 for PAH and PCB. Apparent first order adsorption rate constants for GAC (kGAC) in the stripping scenario were calculated with a first-order kinetic model and ranged from 1.6 × 10−2 (PHE) to 1.7 × 10−5 d−1 (InP). Sorption affinity parameters did not change within 9 months post treatment, confirming the longer term effectiveness of AC in field applications for PAC and GAC.

Linking organic carbon sedimentation, burial efficiency, and long‐term accumulation in boreal lakes

AbstractCarbon (C) storage in lakes is now recognized as a significant sink of C at a global scale, but the pathways that lead to this storage remain poorly understood. In this study, we attempt to reconstruct and connect the processes that lead to long‐term C accumulation in boreal lakes. These include the rate of particulate organic C (POC) sedimentation in the water column and sediment metabolism operating at a temporal scale of weeks to months, organic C accumulation in the top sediment layers integrated over scales of tens of years, and long‐term organic C burial in lake sediment integrated over hundreds to thousands of years. The sinking POC flux was tenfold higher than the short‐term sediment C accumulation rates in all systems, and we found no direct relationship between this downward C flux and either the short‐term or long‐term C accumulation rates. However, the resulting C burial efficiency (which ranged from 5 to 62%) was strongly related to lake shape, which ultimately constrains the time freshly deposited material that is exposed to oxygen and thereby regulates the fraction of the carbon sinking flux that is mineralized back to the atmosphere or permanently buried in the sediments. Small and deep lakes act as more efficient C sinks than large and flat lakes. We also show that long‐term burial rates are nearly identical to current centennial‐scale accumulation rates and that therefore, little degradation occurs after a few decades. Sediment C storage tends to be small (&lt;5%) relative to lake C emissions, but that this balance is also strongly related to lake morphometry.

Natural Recovery and Planned Intervention in Coastal Wetlands: Venice Lagoon (Northern Adriatic Sea, Italy) as a Case Study

The goals of conservation and sustainable use of environmental ecosystems have increased the need for detailed knowledge of ecological evolution and responses to both anthropogenic pressures and recovery measures. The present study shows the effects of natural processes and planned intervention in terms of reducing nutrient inputs in a highly exploited coastal lagoon, describing its evolution over a 16-year period from the late 1980s (when eutrophication was at its peak) until 2003. Changes in nutrient and carbon concentrations in the top layer of sediments were investigated in parallel with macroalgal and seagrass biomass in the most anthropized basin of Venice Lagoon in four surveys conducted in accordance with the same protocols in 1987, 1993, 1998, and 2003. A pronounced reduction in trophic state (mainly total nitrogen, organic phosphorus, and organic carbon concentrations) and macroalgal biomass was recorded, together with the progressive expansion of seagrass meadows. General considerations are also made on the effects of Manila clam farming and the shift from illegal to managed clam farming.

Artificially evolved functional shell morphology of burrowing bivalves

The morphological evolution of bivalves is documented by a rich fossil record. It is believed that the shell shape and surface sculpture play an important role for the burrowing performance of endobenthic species. While detailed morphometric studies of bivalve shells have been done, there are almost no studies experimentally testing their dynamic properties. To investigate the functional morphology of the bivalve shell, we employed a synthetic methodology and built an experimental setup to simulate the burrowing process. Using an evolutionary algorithm and a printer that prints three dimensional (3D) objects, the first ever artificial evolution of a physical bivalve shell was performed. The result was a vertically flattened shell occupying only the top sediment layers. Insufficient control of the sediment was the major limitation of the setup and restricted the significance of the results. Nevertheless, it is demonstrated that systematic palaeontological research may substantially profit from synthetic methods. We suggest investigating functional morphologies not only by emulating the dynamical processes but also evolutionary pressure using evolutionary algorithms.

Characterization of the top sediment layer in coastal intertidal mudflats from medium-to-coarse resolution satellite imagery and field measurements

Intertidal sediments are critically important in controlling intertidal mudflat microphytobenthic primary productivity and the functioning of intertidal ecosystems. This paper demonstrates the possibility of deriving different intertidal sediment properties from coarse-to-medium resolution remote sensing imagery. Supervised and image based classification methods were used to map different substrate types based on the Spectral Angle Mapper (SAM) algorithm. The algorithm characterized different sediment properties from remote sensing data based on field collected and image-extracted endmembers. The results demonstrate that, different substrate types can be derived from coarse-to-medium resolution images using SAM algorithm. Supervised and image-based classification methods performed well in deriving intertidal sediment properties. From the results, sand sediments cover a wide area in extent than clay whereas Normalized Difference Vegetation Index (NDVI) validation results indicate that, clay sediments have higher NDVI values as compared to sand sediments. We conclude that, intertidal sediment properties can be successfully derived from coarse-to-medium resolution satellite imagery. Key words: Endmember, microphytobenthos, spectral signature, substrates, trios ramses, wadden sea.

Impact of high-density suspended oyster culture on benthic sediment characteristics

Benthic impacts that may ultimately result from further intensification of suspended oyster culture in eastern Canada were proactively investigated. Eastern oysters (Crassostrea virginica) were placed in experimental floating rafts (12.1m2) designed to hold densities 2–3 times higher than those presently found in floating bag operations. Experimental rafts were moored in shallow water (1–2m) at fixed positions where no aquaculture had been practiced. A biodeposition model predicted that the majority of feces released by suspended oysters would fall onto the seabed area directly beneath the rafts. However, field measurements over a 132d period indicated that the fecal deposition from the highly aggregated oysters was not reflected in higher organic sedimentation rates or seabed sulfide levels. Rather, the proportion of organic matter in the top sediment layer was significantly lower in samples collected underneath rafts (5.1±1.5%) than in samples taken at reference sites (10.5±3.2%). This same pattern was observed for control rafts holding shells only. It is suggested that the floating raft impacted local hydrodynamic processes, forcing water to move underneath the structure, thereby amplifying turbulence and resuspending low shear strength particles such as biodeposits.

Effect of presence of cellulose in the freshwater sediment on the performance of sediment microbial fuel cell

The performance of sediment microbial fuel cells (SMFCs) was evaluated in the presence of cellulose in the aquaculture pond sediment as 2% (w/w) in SMFC-2, 4% in SMFC-3 and without adding cellulose in SMFC-1. From aquaculture water, average chemical oxygen demand (COD) and total nitrogen (TN) removal efficiencies of 80.6±0.3% and 83.0±0.01% were obtained in SMFC-1, 88.2±0.5% and 89.6±0.8% in SMFC-2 and 83.1±0.3% and 64.5±1.6% in SMFC-3, respectively. During the complete experimental period, acetic acid was the only short chain fatty acid detected in all three SMFCs. Sediment organic matter removal in SMFC-1, SMFC-2 and SMFC-3 were 16%, 22% and 18.6%, respectively. SMFCs demonstrated effective cellulose degradation from aquaculture pond sediment and maintained the oxidized sediment top layer favourable for aquaculture.

Transport and Fate of Escherichia coli in Sediment Layer and Water Column of Basins on Active Construction Sites

<abstract> <bold><sc>Abstract.</sc></bold> The conventional method of controlling sediment-laden runoff on construction sites is the use of sediment basins. These basins slow the velocity of runoff and allow particles to settle from the water column before discharge to surface waters offsite. However, the sediment layers that accumulate in these best management practices may create a reservoir for potentially pathogenic bacteria. Deposited sediment is known to provide protection for bacteria; therefore, while these basins decrease sediment loadings to water bodies downstream, they may introduce harmful levels of pathogenic bacteria into these surface waters when resuspended during rain events. In addition to causing human health risks, these high bacteria levels alter the natural biological makeup of downstream ecosystems. This article describes the fate and transport of Escherichia coli in construction site sediment basins. Three sediment basins, located in Anderson, South Carolina, were sampled after rain events to explore trends in E. coli densities that exist among various sediment depths as well as inflow and outflow of basins. Results provide evidence to suggest that sediment basins are a reservoir for indicator bacteria. Data show that E. coli was most concentrated in the top layer of sediment, and high densities persisted for five to ten days. In addition, E. coli densities were higher in outflow than inflow. Consequently, high densities of bacteria may be routed to downstream waters. This research provides considerable evidence that the sediment layer in man-made construction basins can cause detrimental effects to surface waters. With this knowledge, better stormwater management practices may be developed with the goal of remediating impaired surface waters.

Post-depositional redistribution processes and their effects on middle rare earth element precipitation and the cerium anomaly in sediments in the South Korea Plateau, East Sea

We sampled two box-core sediments from the slope of the eastern South Korea Plateau (SKP) in the East Sea (Sea of Japan) at water depths of 1400 and 1700m. Two chemical fractions of extractable (hydroxylamine/acetic acid) and residual rare earth elements (REEs) together with Al, Ca, Fe, Mg, Mn, P, S, As, Mo, and U were analyzed to assess the post-depositional redistribution of REEs. Extractable Fe and Mn are noticeably abundant in the oxic topmost sediment layer (<3cm). However, some trace elements (e.g., S, As, Mo, U) are more abundant at depth, where redox conditions are different. Analysis of upper continental crust (UCC)-normalized (La/Gd)UCC, (La/Yb)UCC, and (Ce/Ce*)UCC revealed that the extractable REE is characterized by middle REE (MREE) enrichment and a positive cerium (Ce) anomaly, different from the case of the residual fraction which shows slight enrichment in light REEs (LREEs) with no Ce anomaly. The extractable MREEs seem to have been incorporated into high-Mg calcite during reductive dissolution of Fe oxyhydroxides. In the top sediment layer, the positive Ce anomaly is attributed to Ce oxide, which can be mobilized in deeper oxygen-poor environments and redistributed in the sediment column. In addition, differential concentrations of Ce and other LREEs in pore water appear to result in variable (Ce/Ce*)UCC ratios in the extractable fraction at depth.

Assessment of the distribution and risks of organochlorine pesticides in core sediments from areas of different human activity on Lake Baiyangdian, China

Burial characteristics and risks associated with 13 organochlorine pesticides (OCPs; α-HCH, β-HCH, γ-HCH, δ-HCH, p,p′-DDE, p,p′-DDD, p,p′-DDT, heptachlor, aldrin, dieldrin, endrin, α-endosulfan and β-endosulfan) in core sediments of Lake Baiyangdian were investigated. The core sediments were taken from areas of different anthropogenic activity along the lake. Concentrations of hexachlorocyclohexane (HCH), dichlorodiphenyltrichloroethane (DDT), heptachlor, aldrin, and endosulfan ranged from 0.64 to 2.72, nd (undetectable levels) to 2.79, 0.29 to 1.37, nd to 2.62, and nd to 1.76 ng g−1, respectively. Concentrations of OCPs in the core sediments exhibited the following spatial trend: Dongtianzhuang > Shaochedian > Zaolinzhuang. Concentrations in the surficial layer were also found to be greater than those in the bottom layer. OCPs were dominated by HCH. β-HCH was found in the greatest concentrations, indicating that the majority of HCH came from older inputs to the area. The ratio of DDT and its metabolites (DDD and DDE) also suggested a lack of recent inputs to the lake environment. The residues of heptachlor, aldrin, and endosulfan in core sediments indicated that cyclodienes were historically applied in the area. The OCP risk assessment, which was based on effect range low and threshold effect level values, suggested that the top layer of sediment in Dongtianzhuang cores had a relatively high toxicity to human health and the environment.

Bioindication of the state of deep-water areas in Petrozavodsk Bay, Lake Onega, by macrozoobenthos characteristics

Amphipods-oligochaetes index has been developed for the assessment of the state of macrozoobenthos in deep-water areas of Lake Onega. By the value of this index, bed areas of Petrozavodsk Bay, which are subject to the effect of municipal wastewaters, tank farm, rivers within the city boundaries, and the Shuya R., a large tributary of Lake Onega, show a high degree of transformation of zoobenthos community and highest pollution. The ratios of the major zoobenthos groups (amphipods and oligochaetes) in the central part of Petrozavodsk Bay and on its northern shore is at the natural level, but their abundance is dozens of times greater than that in background areas of Lake Onega. A reliable correlation was found to exist between the values of amphipods-oligochaetes index and the redox potential of the top layer of bottom sediments.