Purpose

This paper aims to elucidate urban development-induced processes affecting the sediment and the distribution of contaminating metals in a seasonal pond located in the highly populated Israeli Coastal Plain. The paper demonstrates how an integrated approach, including geochemical, sedimentological, geochronological, mathematical, historical, and geographical analyses, may decipher a complicated and dynamic metal pollution history in a sedimentary environment controlled by anthropogenic activity.

Materials and methods

Three short sediment cores were collected from the margins and center of a small urban pond (Dora, Netanya), located within the Israeli Coastal Plain. Profiles of grain size, organic matter (OM), trace metals (Pb, Zn, V, Ni, Cu, Cr and Co), Pb isotopic ratios, and ²¹⁰Pb activities (center and southern cores) were determined and a geochemical mixing model was employed (southern core). The watershed contour was calculated, and aerial photos and satellite images were examined.

Results and discussion

Construction activities in the watershed were chronologically associated with coarse sediment transport and deposition in the margins of the pond. The upper sandy layers were superimposed on layers rich in fine particles and OM, high concentrations of trace metals, and with Pb isotopic composition of more recent petrol. In the ²¹⁰Pb-dated southern core, deep metal-rich layers with petrol-related Pb isotopic ratios were inconsistent with metal emissions history. These findings point to mobility and migration of recent contamination metals through the coarse upper sediment layers and into deeper denser layers, confirmed also by a geochemical mixing model. Conversely, in the center of the pond, homogeneous fine particles were deposited with metal profiles consistent with regional emissions.

Conclusions

A small urban pond was found to provide an important case study for understanding heavy metal pollution records in highly populated regions. The margins of the pond depicted the surrounding urban development and the induced coarse sediment erosion, accompanied with post-depositional metal mobility. Due to the proximate developing residential areas, high metal concentrations accumulated in the margins, overshadowing regional atmospheric pollution levels recorded by sediment at the center of the pond.

Purpose

A study was carried out to evaluate the concentration of heavy metals (Pb, Cu, Cr, Cd, and Hg) and total petroleum hydrocarbons (TPH) in road-deposited sediments (RDS) from Tijuana, Mexico, and identify their possible sources.

Materials and methods

Thirty RDS samples were randomly collected during the dry season using a brush and dustpan and classified according to construction material, traffic intensity, and land use. Soil samples were collected from a nonurban area and their concentrations were used as background values. For TPH, the samples were quantified gravimetrically after Soxhlet extraction, whereas heavy metals were extracted by acid digestion and their concentrations were measured by atomic absorption spectrometry.

Results and discussion

The mean TPH concentrations for RDS were 4208 mg kg^?1 and ranged from 1186 to 9982 mg kg^?1. For heavy metals, mean concentrations were 31.8, 50.2, 17.1, 0.1, and 0.1 mg kg^?1 for Pb, Cu, Cr, Cd, and Hg, respectively. The Igeo results showed that RDS from Tijuana are moderately to strongly polluted with Pb and Cu and moderately polluted with Cr. Principal component analysis (PCA) showed that Pb, Cu, and Cr could have their origin in tire wear, brake pads, bearings, and bushings.

Conclusions

The findings of this study revealed that RDS from Tijuana are polluted with TPH and heavy metals and that their principal sources are anthropogenic activities.

Purpose

In spite of equal lithology, the local climate can affect soils’ geochemical characteristics. We investigated the dependence of heavy metal content on climatic factors according to a hierarchical nested analysis of variance design (ANOVA).

Materials and methods

We examined the heavy metal content in soils developed on the Upper Triassic dolomite at six locations situated at increasing distances from the Adriatic Sea towards inland. We tested the influence of the locations’ position, i.e. climate, vegetation cover, small-scale variability and analytical error. Co, Cr, Cu, Ni, Pb and Zn contents were determined by emission spectrometry.

Results and discussion

An initial increase in annual precipitation towards inland is followed by a steady decrease. Very high small-scale variability prevented statistically significant differences from being established at the location level due to the high variance components exhibited. However, the simpler one-way and non-parametric varieties of ANOVA confirmed significant differences in Co, Cr and Ni among locations. The differences are more pronounced in grassland soils where the Cu and Pb contents also differ between locations. There is a positive correlation among annual precipitation, Co, Cr and Ni, and it seems that the prevailing winds can also influence their content in soils.

Conclusions

The Co, Cr, Cu and Ni values are readily the highest in those locations with the greatest precipitation, possibly due to their resistance to leaching. The soils could be additionally enriched by an eolian contribution from the SW located outcropping flysch rocks. The established variability could be due to somewhat different dolomite composition. The reasons for the observed geochemical variability are complex and only partly due to climate.

Purpose

Investigations of geochemical characteristics of sediments of the Zrmanja River estuary were done in order to determine the natural and anthropogenic factors influencing sediment composition in this area. For that purpose, spatial and temporal distribution of major and trace elements in the sediments and surrounding soils was studied.

Materials and methods

Sediment and soil samples, including one marl sample, were collected at 28 locations. All samples were subjected to total digestion and subsequently analysed by high-resolution inductively coupled plasma mass spectrometry (HR-ICP-MS) for total concentration of 20 elements (Ag, Al, As, Be, Ca, Cd, Co, Cr, Cu, Fe, Li, Mn, Ni, Pb, Rb, Sb, Sn, Sr, Ti and Y). Obtained concentrations and their normalized counterparts were used for assessment of factors influencing sedimentation in the study area.

Results and discussion

The results of the analysis showed that the composition of sediments of the Zrmanja River estuary is primarily determined by the composition of bedrock, existing hydrodynamic conditions and the relative isolation of the studied basin. Nevertheless, anthropogenic influences were observed as well. The composition of the Zrmanja River sediments reflects the impact of the ex-alumina factory “Jadral” and transfer by wind of the material from its immediate surroundings to the water system of the Zrmanja River. In addition, sedimentation in the Zrmanja River was found to be influenced by the construction of reservoirs and the HE “Velebit”, hydroelectric power plant located in the Zrmanja watershed.

Conclusions

The geochemical composition of recent sediments of the Zrmanja River estuary is controlled primarily by natural factors, although the influence of anthropogenic activities is also evident.

Purpose

Cohesive sediment is able to flocculate and create flocs, which are larger than individual particles and less dense. The phenomenon of flocculation has an important role in sediment transport processes such as settling, deposition and erosion. In this study, laboratory experiments were performed to investigate the effect of key hydrodynamic parameters such as suspended sediment concentration and salinity on floc size and settling velocity. Results were compared with previous laboratory and field studies at different estuaries.

Materials and methods

Experimental tests were conducted in a 1-L glass beaker of 11-cm diameter using suspended sediment samples from the Severn Estuary. A particle image velocimetry system and image processing routine were used to measure the floc size distribution and settling velocity.

Results and discussion

The settling velocity was found to range from 0.2 to 1.2 mm s^?1. Settling velocity changed in the case of increasing suspended sediment concentration and was controlled by the salinity. The faster settling velocity occurred when sediment concentration is higher or the salinity is lower than 2.5. On the other hand, at salinities higher than 20, in addition to increasing SSC, it was found that the situation was reversed, i.e. the lower the sediment concentration, the faster the settling velocity.

Conclusions

Sediment flocculation is enhanced with increasing sediment concentration but not with increasing salinity.

Purpose

The low conductivity of sediments for mass and electron transport is the most severe limiting factor in sediment microbial fuel cells (SMFCs), so that sediment ameliorations yielded more remarkable effects than electrode improvements. The objective of this research was to enhance the electricity generation of SMFCs with amendments of biochar to freshwater sediments for conductivity enhancement.

Materials and methods

Laboratory-scale SMFCs were constructed and biochars were produced from coconut shells at different temperatures. Variations in the power output, electrode potential, internal resistance, total organic carbon (TOC) content, and microbial communities were measured.

Results and discussion

Amending with biochar reduced the charge transfer resistances of SMFCs and enriched the Firmicutes (mainly Fusibacter sp.) in the sediment, which improved the SMFC power generation by two- to tenfold and enhanced the TOC removal rate by 1.7- to fourfold relative to those without the amendment.

Conclusions

The results suggested that biochar amendment is a promising strategy to enhance SMFC power production, and the electrical conductivity of biochar should be considered important when interpreting the impact biochar has on the electrical performance of soil or freshwater sediment MFCs.

Purpose

The aims of the study were to evaluate the effect of combined sewer overflows (CSO) and storm water drains (SWD) on metal bioavailability in small urban streams in Prague and to evaluate levels of metals in water, sediment, and macroinvertebrates. The following working hypotheses were adopted: (a) sites dominantly affected by SWD are less polluted by metals, and (b) sites dominantly affected by SWD have higher bioavailability of metals.

Materials and methods

Physical and chemical parameters (pH, conductivity, NO₃-N, NH₄-N, COD, alkalinity, and water hardness) and concentrations of the metals Cu, Zn, Pb, Ni, and Cr were determined in samples of water and sediment at five to six sites on four target streams—Záti?ský Creek, Ko?íkovský Creek, Boti? Creek, and Rokytka Creek—three to five times per year during the period 2002–2004. The sites from all studied creeks were categorized into five groups according to the prevailing type of urban drainage impact. Macroinvertebrates were sampled and analyzed for metals at each site for a period of 1 month. The concentration patterns of metals were interpreted by partition coefficient (Kd), hazard quotient (HQ), cumulative criterion unit (CCU), and biota sediment accumulation factor (BSAF).

Results and discussion

Concentrations of metals in water as well as in sediment at sites receiving water from SWD were lower than at sites where creeks receive water from CSO, except for Pb. Concentrations of Cu, Zn, and Pb in sediment were higher at sites affected by CSO. Concentrations of metals in aquatic macroinvertebrates, expressed as BSAF, indicated higher values at sites affected by SWD. Frequencies of high BSAF (>1) were lower in CSO compared to SWD. This finding was explained by (a) a decrease of pH on SWD sites compared to the increase of pH on CSO sites during rain events, (b) a greater resuspension of sediment at SWD sites during rain events, and (c) an abundance of organic matter in CSO available for sorption of metals and a corresponding reduction of their bioavailability.

Conclusions

In the study area, the type of urban drainage affects the bioavailability of metals—while SWD increase metal bioavailability, CSO cause its decrease. The sediments in SWD sites do not indicate risk to the benthic community according to the applied environmental quality standards. Water and sediment in creeks affected by SWD are less polluted by metals. Both working hypotheses were therefore supported.

Purpose

The Three Gorges Dam project is one of the biggest projects in the world. The water level fluctuation zone (WLFZ) was created with impoundment. The purpose of the current study is to investigate the ecotoxicological potential of the sediment extracts from the WLFZ and propose future WLFZ monitoring for early detection of environmental changes brought about by pollution.

Materials and methods

The investigation was performed by using cell-based in vitro bioassays to determine acute cytotoxicity (neutral red retention assay) and mechanism-specific aryl hydrocarbon receptor (AhR)-mediated activity (7-ethoxyresorufin-O-deethylase (EROD) induction assay) of sediment extracts with rainbow trout (Oncorhynchus mykiss) liver cells (RTL-W1).

Results and discussion

Results showed that the cytotoxicity and AhR-mediated toxicity potential of the sediment extracts from the WLFZ in the Three Gorges Reservoir (TGR) were moderate of level compared with the ecotoxicity of sediments from other river systems. However, according to a sediment classification system in Germany, sediments from some individual sites in the WLFZ showed strong toxicity. Compared to the results from the Yangtze River in our previous study, more attention should be paid to the aryl hydrocarbon receptor inducers in the WLFZ in TGR.

Conclusions

The in vitro bioassays used in this study may serve as a valuable tool to predict the potential ecological hazards of the organic pollutants in the WLFZ to the aquatic organisms in some extent.

Purpose

Rivers feeding into the Loskop Dam, South Africa, pass through coal mining and heavily industrialised areas. Previous studies investigating mass mortalities of crocodile and fish in the river system, revealed the presence of organic compounds, including polycyclic aromatic hydrocarbons (PAHs), in their tissues.

Materials and methods

Samples were collected from nine sites within the dam in winter and summer. Liquid-liquid and microwave-assisted extraction was used for preconcentrating PAHs from water and sediment samples, respectively. Extracts were analysed by gas chromatography-mass spectrometry in the selected ion monitoring mode to determine the presence and levels of the 16 United States Environmental Protection Agency (US EPA)-priority PAHs.

Results and discussion

Significant levels of PAHs were found in both water and sediment samples. Concentrations were higher in sediments than in water, as well as in samples collected in winter. Levels of PAHs in sediments were generally higher than those reported by many researchers for other water bodies in industrialised areas. Zebrafish embryos were used to assess potential risks associated with the water and sediment, and to determine the effects of PAHs on aquatic life. Embryos, exposed to intact water and sediment samples, as well as to diluted sediment extracts, were monitored for 120 h post fertilisation. Sediment proved more toxic to zebrafish embryos than water, causing delayed embryo development and malformations.

Conclusions

These findings are alarming as they indicate that this water system is under stress. These findings can be typical of any water system situated in a coal mining and industrial region.

Purpose

Diffuse pollution emanating from metal mining-impacted sediment could serve as a barrier to achieving European Union Water Framework Directive and US Clean Water Act requirements. UK climate projections (UKCP09) predict increases in rainfall and aridity that will influence river stage alternately exposing and submersing contaminated riverbank sediment. Research focuses on the environmental contaminant dissolved Zn and investigates patterns of release, key geochemical mechanisms controlling Zn mobilisation and the environmental risk of sediment subjected to these perturbations.

Materials and methods

Using two laboratory mesocosm experiments, metal mining-contaminated sediment was subjected to alternate wet and dry sequences of different duration and frequency. The first experiment was run to determine the influence of submersion and exposure of contaminated sediment on releases of Zn and to establish environmental risk. The second experiment utilised diffusional equilibration in thin film (DET) to observe the patterns of Zn release, with depth, in the sediment. Pore water chemical analysis at the sediment-water interface enabled elucidation of key geochemical mechanisms of control of Zn mobilisation.

Results and discussion

Patterns of Zn release were found to be different, depending on the length of wet and dry period. High concentrations of dissolved Zn were released at the start of a flood for runs with longer dry periods. A buildup of soluble Zn sulphate minerals over long dry periods followed by dissolution on first flood wetting was a key geochemical mechanism controlling Zn release. For longer wet runs, increases in dissolved Mn and Zn were observed over the flood period. Key geochemical mechanisms controlling Zn mobilisation for these runs were: (i) reductive dissolution of Mn (hydr)oxides and release of partitioned Zn over prolonged flood periods followed by (ii) oxidation and precipitation of Mn (hydr)oxides and sorption of Zn on exposure to atmospheric conditions.

Conclusions

Mesocosm experiments were a first step in understanding the effects of UK climate projections on the riverbank environment. Contaminated sediment was found to pose a significant environmental risk in response to hydrological perturbations. The ‘transient’ nature of dissolved Zn release could make identifying the exact sources of pollution a challenge; therefore, further field studies are advised to monitor contaminant releases under a range of hydrological conditions and account for complex hydrology at mining sites.

Purpose

The present study deals with the geochemical fractions of Pb, Cd, Zn, Cu and As present on profiles using chemical simple extraction process. This work was conducted on Portman Bay, located in the SE Spain and strongly affected by mining activities.

Materials and methods

Four simple extractions were applied to selected samples in order to evaluate the potential mobility of metals. X-ray diffraction (XRD) was applied to the characterisation of samples and the residues remaining after each extraction, providing additional information about the sediment phases carrying the elements studied.

Results and discussion

The results obtained after the extractions suggested that the highest potentially toxic element (PTE) content was obtained in the oxidising medium. The mineralogical composition is an important factor that should be taken into account in the evaluation of PTE mobility, firstly because the mineral phases react differently in the proposed situations depending on their chemical nature, and secondly, because the presence of a particular phase depends on the degree of weathering.

Conclusions

The evaluation of PTE mobility and mineralogical composition under different environmental conditions may be very important in the execution of restoration projects which could involve dredging and mobilisation of materials.

Purpose

Using Ells River, Alberta, Canada bed sediments, this study aims to determine (1) the erosion, transport, and deposition characteristics of cohesive bottom sediments, and (2) the influence of the microbial community in this regard.

Materials and methods

A 2-m annular flume was used to generate bed shear to assess cohesive sediment dynamics for eroded beds with consolidation/biostabilization periods of 1, 3, and 7 days. Additional optical particle sizing, image analysis, densitometry, and microbial analysis were employed to further the analysis with respect to bed erosion and eroded floc characteristics.

Results and discussion

Sediment dynamics can influence the benthic and planktonic community health within aquatic systems. The critical bed shear stress for erosion increased from 0.05 to 0.19 Pa (for 1- to 7-day runs). Consolidation (dry density) increased with time and depth and eroded biofilm biomass was observed to increase with time. The community structure of the eroded sediment did not change with time suggesting a stable well-established and highly selected community. Hydrocarbon-degrading bacteria were present within the microbial consortium. The sediment was highly hydrophobic (96 %) due to a high natural oil content which likely had a profound effect on sediment dynamics, flocculation, and sediment cohesion. Eroded sediment settled poorly, which will result in the long-range transport of associated contaminants.

Conclusions

The Ells River possesses some unique properties which should be considered when assessing contaminant source, fate, and effect. The most significant of these are small floc size, the hydrophobicity of the sediment, and the biological community as these were found to be influential in both the erosion and flocculation processes. It is important that any management strategies and operational assessments of reclamation strategies that may have implication on river health incorporate the sediment compartments (SS and bed sediment), biology, and the energy dynamics within the system in order to better predict the downstream flux of sediments.

Objective

The concentration gradients of solid Al, Fe, Mn, Zn, Cd, Pb, Cr and Ni in freshly formed concretions and in older concretions preserved in the sediment were evaluated in a millimetre resolution scale. These results provide a better understanding of the complex biogeochemical processes in the root-sediment system and elucidate the potentialities of marshes in the restoration of contaminated aquatic systems.

Methods

Tens (soll das vielleicht tonnes/tons heißen) of freshly formed concretions and preserved concretions were collected in the Rosário salt marsh. Each tubular structure and involving sediments were scraped in concentric layers of 2-mm thickness to form two sets of composite samples. The elemental composition of concretion and sediment samples were determined by atomic absorption spectrometry.

Results and Discussion

The sediment involving the concretions contained ～0.5 mmol g^-1 Fe, but concentrations increased towards the root up to 3.4 mmol g^-1 in 3-mm interval. Manganese, Zn, Cd and Pb exhibited similar radial distribution in both preserved and freshly formed concretions indicating that these metals remain in those structures with the age. Chromium and Ni showed a different pattern being lower in concretions with respect to involving sediments, and consequently, concretions do not act as a barrier for these elements. The estimated amount of Zn (59 tons), Pb (5 tons) and Cd (0.4 tons) retained in the concretions all over the Rosario salt marsh highlights the importance of these structures in sequestering metals.

Conclusions and Outlook

The sequestering may be particularly relevant in salt marshes located near urban and industrial zones, being areas working as a natural remediation system and contributing for the detoxification of aquatic environments and the well-being of coastal resources.

Purpose

The Almadén mining district has suffered long-term extraction activity, and this has left significant areas of decommissioned mining liabilities. Nowadays, the uncontrolled runoff and related erosion and transport of trace metal-enriched soils and sediments affect the whole freshwater ecosystem. The goal of this study was to distinguish geogenic from mining-related sources of trace metals in freshwater sediments, to understand their dispersion in the watershed, and, finally, to evaluate the potential environmental implications for future corrective plans.

Materials and methods

Freshwater surface sediment samples were collected from ten points along the main streams of the watershed (nine inside the mining district and one control point outside the district). Sediments were air dried and analyzed by different standard methods for pH, total major and trace element concentrations, total organic carbon, and grain size. In addition to the determination of the enrichment factor, a multi-statistical approach was applied involving discriminant analysis, Student’s t test, and Mann-Whitney U analysis.

Results and discussion

Sediments inside the district contained high levels of major and trace elements with respect to the control point. The predominance of fine fractions in these sediment samples appears to be one of the most important factors that affects trace metal concentrations. Among the trace elements, not only Hg but also As, Pb, and Zn are discriminative geochemical markers, thus allowing the identification of the different mining sources and their individual or combined impact throughout the district. Furthermore, the high enrichment factors obtained for As, Hg, Pb, and Zn with respect to the local background values highlight the persistent and severe impact from the decommissioned mines on the freshwater surficial sediments and their potential geoavailable risk for aquatic organisms.

Conclusions

The geochemistry of freshwater sediments alone demonstrates that different contamination sources are recognizable within the mining district and these can be related to the specific decommissioned mines. In addition, the discrete sources can be clearly distinguished on the basis of the statistical analysis of the geochemical data. Despite the closure of the mines, stream sediments are still the main repository of trace metals within the district, and they are therefore a potential threat to the freshwater ecosystem.

Purpose

A monitoring investigation undertaken along the River Ibach, northwest Switzerland over the winter 2012/2013, found that riparian areas recently supporting the invasive plant Himalayan Balsam (HB) recorded significantly higher erosion rates than nearby uninvaded areas. This communication sythesises the latest findings about the influence of HB on sedimentation processes, again, from the Ibach, but also from a second river system in southwest UK.

Materials and methods

Erosion pins, a micro-profile bridge and a digital caliper were used to measure changes in soil surface profile (SSP) at selected riparian areas supporting HB plants along both rivers. Values were statistically compared against equivalent data recorded from nearby reference areas supporting mixed perennial vegetation. A comparison of source and sediment geochemistry was also undertaken on soil from HB-invaded and uninvaded floodplain areas along the Ibach, to assess the potential for identifying the extent to which either group acts as a sediment source.

Results and discussion

Erosion pin data indicate that soil loss from HB-colonised areas was significantly greater than soil loss from reference areas in two out of the four periods at the River Ibach site, and in two out of three measurement periods at the River Taw site. Colonisation of new HB sites may initially occur by hydrochorous processes, but HB plants may increase colonisation potential by trapping additional fine sediment and organic matter, including viable HB seeds. Geochemical results from the Ibach suggest that high inputs of suspended sediment originate from sources close to the river channel, but HB-invaded floodplain sources have geochemical properties that are most similar to suspended river sediment.

Conclusions

The findings from both rivers led us to rethink our original hypothesis; that HB promotes soil erosion, to an amended hypothesis in which HB may be associated with areas where high erosion is sometimes recorded. Whilst initial colonisation may be due to hydrochorous processes, as HB becomes increasingly established, the displacement of perennial vegetation increases the risk of erosion during the winter period when live HB plants are absent. Preliminary geochemical findings of floodplain soils supporting different vegetation types along the Ibach tentatively suggest that at least some material originating from HB sites may enter the watercourse.

Purpose

This study used multi-element signatures of stream sediments to assess both natural and human-induced impact on fluvial system in the River Neretva delta receiving environment over time. The river basin actually comprises several sub-catchments, and the geochemical features of major elements, trace metals radiometric and mineralogical characterisation of river bed sediments were used to assist the interpretation of the environment of deposition and its subsequent modifications caused by various anthropogenic pressures within the river basin.

Materials and methods

Five sites were chosen for sediment sampling at key locations within the study area with assumed undisturbed, continuous sedimentation process. At each of the sites, three representative cores were taken by scuba divers. Sample sites were selected in order to reflect the influence of different sub-catchments they belong to and the land-use pattern of the surrounding area. Samples were analysed for pH, redox-potential, granulometry, mineralogy, thermogravimetry, major and trace element concentrations and radionuclide activities. The univariate and multivariate statistics were applied. The geochemical normalisation of data was done using Al, the procedure based on calculation of the regression line of the metal on the normaliser followed by testing the ratios metal/normaliser on all data-points.

Results and discussion

All studied sediments are classified as silt, ranging from clayey silt to silt and sandy silt. Mineralogically, the sediments were dominated by carbonates and quartz. The chemical contaminant data are generally of good quality, mostly below guideline levels. Sedimentation rates were estimated using vertical distribution of ¹³⁷Cs activities. Normalisation of TMs done by using Al shows strong R ² _adj values for the regressions of Al and V, Al and Cr, and Al and Ni. However, Al cannot fairly explain the fluctuation of the concentrations of Cd, Cu, Pb and Zn in sediment cores from all of the sampling sites. Generally, inorganic scavengers such as clay minerals followed by Fe and Mn oxides and S (pyrite and gypsum) seem to be dominant factors controlling TMs in studied sediments.

Conclusions

Although the River Neretva delta occupies a rather small area, the geochemical features of major and trace elements and ¹³⁷Cs activities show complex sediment provenances. Each of the sampling sites reflect exactly different effects of anthropogenic intervention that particularly refer to the changes in river morphology and ecology, along with the altered flow regimes within the catchment on sediment loads and quality.

Purpose

Wood extractives in sediments originating from the wood industry may interfere with benthic biota in aquatic environments. The research area was the Äänekoski watercourse in Central Finland, which has been affected by the chemical wood industry for over a century. The goal was to determine the dissolution potency of resin acids (RAs) and their derivative, retene, in the sediment, and their current vertical and spatial stratification to assess the load due to potential erosion.

Materials and methods

Sediments were collected from two upstream reference sites and three lake-like basins, located as far as 33 km downstream from the mills. The dissolution potency was studied by two different agitation times and temperatures from sediment-water (1+4 v/v) elutriates. The vertical distribution of extractives was determined from the uppermost 20 cm of sediment. Using spatial interpolation, the distribution of extractives was estimated from two upper sediment layers (0–2 and 2–5 cm) downstream from the source. According to the interpolation, the total amount of dehydroabietic (DHAA) and isopimaric acids (IPA) were calculated as kg/ha in the whole sediment area.

Results and discussion

The total concentration of RAs in the surface sediment reached up to 168 µg/g dw, and they were found to desorb to water up to 77 µg/l. The concentrations of retene were low both in the sediment (<51 µg/g dw) and elutriate (<0.53 µg/l). Spatial interpolation showed that the highest calculated amounts of the most abundant RAs were in Kuhnamo basin, in the sediment layer 2–5 cm; the estimated amount of DHAA and IPA were approximately 440 and 85 kg/ha, respectively.

Conclusions

Disturbances may change the exposure situation, causing desorption of sediment-associated compounds in levels that may be harmful to aquatic animals. The amount of desorption varies depending on the concentration of contaminants in sediment, the nature of disturbance, and the sediment organic carbon content. Low retene concentrations can be explained by oxic conditions and low abundance of RAs in the sediments.

Purpose

This study aimed at evaluating the acute effects of arsenic and zinc to the warmwater aquatic oligochaete Branchiura sowerbyi. Relative sensitivity with the coldwater species Tubifex tubifex was compared. Implications for the use of B. sowerbyi in the risk assessment of sediments in the tropics are discussed.

Materials and methods

Water-only (96 h) and sediment (14 days) toxicity tests were conducted with both species evaluating a concentration series of arsenic and zinc. The tests were conducted considering the environmental conditions in the natural habitat of T. tubifex (predominantly temperate) and B. sowerbyi (predominantly tropical). Both lethal and sublethal endpoints (autotomy of the posterior body parts, abnormal behavior and appearance) were determined in the tests. The lethal (LC₁₀ and LC₅₀) and effect (EC₁₀ and EC₅₀) concentrations were also determined to assess metal sensitivity for both species.

Results and discussion

Both test species were more sensitive to Zn than As in water-only tests, which is in agreement with previous studies evaluating the toxicity of these metals to aquatic oligochaetes. Sublethal effects were generally noted at concentrations lower than those leading to mortality. The warmwater oligochaete B. sowerbyi was more sensitive to both metals tested than the coldwater species T. tubifex.

Conclusions

Study findings support the need for using indigenous tropical species in risk assessments in the tropics. In addition, sublethal effect parameters should be included in toxicity testing with aquatic oligochaetes.

Purpose

The objective of this work is to better understand the role that biological mediation plays in the behaviour of fine sediments. This research is supported by developments in ecological theory recognising organisms as “ecosystem engineers” and associated discussion of “niche construction”, suggesting an evolutionary role for habitat modification by biological action. In addition, there is acknowledgement from engineering disciplines that something is missing from fine sediment transport predictions.

Materials and methods

Advances in technology continue to improve our ability to examine the small-scale 2D processes with large-scale effects in natural environments. Advanced molecular tools can be combined with state-of-the-art field and laboratory techniques to allow the discrimination of microbial biodiversity and the examination of their metabolic contribution to ecosystem function. This in turn can be related to highly resolved measurements and visualisation of flow dynamics.

Results and discussion

Recent laboratory and field work have led to a paradigm shift whereby hydraulic research has to embrace biology and biogeochemistry to unravel the highly complex issues around on fine sediment dynamics. Examples are provided illustrating traditional and more recent approaches including using multiple stressors in fully factorial designs in both the laboratory and the field to highlight the complexity of the interaction between biology and sediment dynamics in time and space. The next phase is likely to rely on advances in molecular analysis, metagenomics and metabolomics, to assess the functional role of microbial assemblages in sediment behaviour, including the nature and rate of polymer production by bacteria, the mechanism of their influence on sediment behaviour.

Conclusions

To fully understand how aquatic habitats will adjust to environmental change and to support the provision of various ecosystem services, we require a holistic approach. We must consider all aspects that control the distribution of sediment and the erosion-transport-deposition-consolidation cycle including biological and chemical processes, not just the physical. In particular, the role of microbial assemblages is now recognised as a significant factor deserving greater attention across disciplines.

Purpose

We determined the relationship of a planktonic algal bloom with spatial and temporal changes in sediment bacterial communities in a eutrophic urban river in the Taihu Basin, China.

Materials and methods

Surface sediments from different locations on the river, including with and without an algal bloom, were collected monthly for 1 year. Sediment bacterial communities were assessed by sequencing 16S rRNA gene amplicons using an Illumina MiSeq.

Results and discussion

There were distinct spatial and temporal changes in sediment bacterial community structure. Significant decrease in the Shannon diversity corresponded with the peak chlorophyll a (Chl a) concentration. Proteobacteria, Chloroflexi, and Bacteroidetes were the dominant phyla throughout the year; however, their relative abundances changed seasonally. At the time of peak Chl a concentrations, Proteobacteria and Bacteroidetes comprised a greater proportion of the bacterial community. Bacterial community structure also varied spatially at the operational taxonomic unit (OTU) level according to canonical correspondence analysis (CCA), especially in locations with an algal bloom compared with those without an algal bloom. There were positive correlations between multiple bacterial genera and Chl a content, suggesting the potential for facilitative relationships between phytoplankton and bacteria. Based on the CCA, water temperature, NH₄ ⁺-N, TN, NO₃ ^?-N, and TP in the sediment and Chl a contents in the water column were significantly correlated with sediment bacterial community structure (P < 0.05).

Conclusions

Planktonic algal blooms may influence sediment bacterial community structure at all taxonomic levels in urban rivers. This work emphasizes the need for more comprehensive studies regarding the impact of planktonic algal blooms on sediment bacterial communities.