Abiotic Compartments Research Articles

Feedbacks between Vegetation, Surface Structures and Hydrology during Initial Development of the Artificial Catchment ‘Chicken Creek’

Our investigations at the artificial catchment ‘Chicken Creek’ in Lusatia/Germany aim to disentangle and understand the feedback mechanisms and interrelationships of processes and their co-development with spatial and temporal structures and patterns by studying this initial, probably less complex ecosystem. Intensive measurements were carried out in the catchment with regard to the development of surface structures, hydrological patterns, and vegetation dynamics.During the first seven years, considerable changes within the catchment were observed. Both internal and external factors could be identified as driving forces for the formation of structures and patterns in the artificial catchment. Initial structures formed by the construction process and initial substrate characteristics were decisive for the distribution and flow of water. External factors like episodic events triggered erosion and dissection during this initial phase, promoted by the low vegetation cover and the unconsolidated sandy substrate.The transformation of the initial geo-system into areas with evolving terrestrial or aquatic characteristics and from a very episodic to a more permanent stream network and discharge, together with the observed vegetation dynamics increased site diversity and heterogeneity with respect to water and nutrient availability and transformation processes compared to the more homogenous conditions at point zero.The processes and feedback mechanisms in the initial development of a new landscape may deviate in rates, intensity and dominance from those known from mature ecosystems. It is therefore crucial to understand these early phases of ecosystem development and to disentangle the increasingly complex interactions between the evolving terrestrial and aquatic, biotic and abiotic compartments of the system. Artificially created catchments could be a suitable tool to study these initial developments at the landscape scale under known, designed and defined boundary conditions.

Monitoring the formation of structures and patterns during initial development of an artificial catchment

The objective of this paper is to present observations, results from monitoring measurements, and preliminary conclusions about the development of patterns and structures during the first 5years of development of an artificial catchment starting from point zero. We discuss the high relevance of initial system traits and external events for the system development and draw conclusions for further research. These investigations as part of a Collaborative Research Center, aim to disentangle and understand the feedback mechanisms and interrelationships of processes and their co-development with spatial and temporal structures and patterns by studying an initial, probably less complex ecosystem. Therefore, intensive measurements were carried out in the catchment with regard to the development of surface structures, hydrological patterns, vegetation dynamics, water chemistry, and element budgets. During the first 5years, considerable changes within the catchment were observed. Both internal and external factors could be identified as driving forces for the formation of structures and patterns in the artificial catchment. Initial structures formed by the construction process and initial substrate characteristics were decisive for the distribution and flow of water. External factors like episodic events triggered erosion and dissection during this initial phase, promoted by the low vegetation cover, and the unconsolidated sandy substrate. The transformation of the initial geosystem into areas with evolving terrestrial or aquatic characteristics and from a very episodic to a more permanent stream network and discharge, together with the observed vegetation dynamics increased site diversity and heterogeneity with respect to water and nutrient availability and transformation processes compared with the more homogenous conditions at point zero. The processes and feedback mechanisms in the initial development of a new landscape may deviate in rates, intensity, and dominance from those known from mature ecosystems. It is therefore crucial to understand these early phases of ecosystem development and to disentangle the increasingly complex interactions between the evolving terrestrial and aquatic, biotic, and abiotic compartments of the system. Long-term monitoring of initial ecosystems may provide important data and parameters on processes and the crucial role of spatial and temporal structures and patterns to solve these problems. Artificially created catchments could be a suitable tool to study these initial developments at the landscape scale under known, designed, and defined boundary conditions.

Concentration of arsenic in water, sediments and fish species from naturally contaminated rivers

Arsenic (As) may occur in surface freshwater ecosystems as a consequence of both natural contamination and anthropogenic activities. In this paper, As concentrations in muscle samples of 10 fish species, sediments and surface water from three naturally contaminated rivers in a central region of Argentina are reported. The study area is one of the largest regions in the world with high As concentrations in groundwater. However, information of As in freshwater ecosystems and associated biota is scarce. An extensive spatial variability of As concentrations in water and sediments of sampled ecosystems was observed. Geochemical indices indicated that sediments ranged from mostly unpolluted to strongly polluted. The concentration of As in sediments averaged 6.58μg/g ranging from 0.23 to 59.53μg/g. Arsenic in sediments barely followed (r=0.361; p=0.118) the level of contamination of water. All rivers showed high concentrations of As in surface waters, ranging from 55 to 195μg/L. The average concentration of As in fish was 1.76μg/g. The level of contamination with As differed significantly between species. Moreover, the level of bioaccumulation of As in fish species related to the concentration of As in water and sediments also differed between species. Whilst some fish species seemed to be able to regulate the uptake of this metalloid, the concentration of As in the large catfish Rhamdia quelen mostly followed the concentration of As in abiotic compartments. The erratic pattern of As concentrations in fish and sediments regardless of the invariable high levels in surface waters suggests the existence of complex biogeochemical processes behind the distribution patterns of As in these naturally contaminated ecosystems.

Protocol for Ecological Risk Assessment in Aquatic Environment Considering the Jacuí River Environmental Monitoring Program , São Jerônimo (RS)

The contribution of this work is to present protocol for ecological risk assessment in an aquatic environment using data derived from environmental monitoring programs. The location focused by this study was a segment of the Jacuí River, in the town of São Jerônimo – RS, Brazil, which was assessed by applying an environmental monitoring program. The line of evidence recorded from the abiotic compartments surface water and sediments was considered an explanatory variable. The chemical evidence stemmed from the presence of Hg, Pb and Zn, while the ecotoxicological evidence resulted from aquatic toxicity tests using Ceriodaphinia dubia for surface water and Hyalella azteca for sediments. The biological evidence from the Shannon-Weaver index, species richness, equitability and numerical density data in zooplanktonic and benthonic communities was considered the response variable. The ecological risk (Low, Medium, and High) was characterized by the association with environmental quality (Great, Warning, and Critical), established by the lines of evidence recorded. The results have shown that it is possible to use environmental monitoring programs to evaluate of ecological risk assessment, if they have chemical and ecotoxicological data required by environmental laws, and monitoring data of resident biota.

Integrating Field Analyses with Laboratory Exposures to Assess Ecosystems Health

In this article, we present studies that were established to assess the state of the environment as it pertains to the presence of polycyclic aromatic compounds (PAC) and to fulfill the goal of the Department of Fisheries and Oceans, Canada's Oceans Strategy “to ensure healthy, safe and prosperous oceans for the benefit of current and future generations of Canadians.” Analyses of parental and alkylated polycyclic aromatic hydrocarbons (PAH) and dibenzothiophene derivatives in offshore biota were needed as background data prior to the construction of oil rigs in Eastern Canada. Later, the quality of biotic and abiotic compartments in proximity to raw sewage effluents was investigated. In addition, chemistry-based studies were integrated with time, toxicology endpoints, to determine the impact associated with the body burden of three invertebrate species. Bioaccumulation and biotransformation was pursued in laboratory-exposed finfish, amphipods, and snails. Measurements of toxicity emphasized the link between the avoidance response of amphipods and/or snails exposed to harbor sediments, PAH, pyrene (PY) and 1-hydroxypyrene to the body burden of the animals. The research proved that: (1) finfish bioaccumulate and biotransform PAC; (2) amphipods Corophium volutator only accumulate PAC; (3) snails and whelks bioaccumulate and biotransform PAC; (4) PAH are good markers of other harbor contaminants; (5) bioaccumulation of PAC >1,000 times lower than levels explaining narcosis is linked to the avoidance response of amphipods to harbor sediments; (6) disturbance in the balance between the biotransformation and bioaccumulation of PY is observed in stressed snails; (7) biotransformation of xenobiotics is weaker during the reproductive season of snails; and finally (8) relationship between body burden and behavioral effects in organisms needs more research.

Environment protection: The current challenge in radioecology

Radioecology, a multifaceted scientific discipline which addresses environmental issues relevant to radioprotection, has for a long time been focused on environmental transfers through the environment to feed the needs of human radioprotection. This quite anthropocentric initial scope is now moving to a more ecocentric view capable of assessing ecological risk mediated by ionising radiation. The central issue consists in reaching an ability to understand the effects of radiation on the environment components, from individual organisms up to populations of species and ecosystems, together with their interaction with the abiotic compartments. Dominated by operational goals, the system of radiological protection of the environment which is under development emphasises a concept based upon reference organisms supported by traditional toxicological data on individual organisms. Whilst there are immediate advantages to this approach (pragmatism, consistency with other approaches in use for man and biota), there are also clear limitations which need to be acknowledged and further considered. The most important probably is to rely on effects data gathered almost exclusively for individual organisms to meet protection goals which are usually set at population and ecosystem levels. Overcoming this limitation leads to scientific and methodological approaches featuring the ecosystem concept.

Hexabromocyclododecane: Current Understanding of Chemistry, Environmental Fate and Toxicology and Implications for Global Management

Hexabromocyclododecane (HBCD) is a globally produced brominated flame retardant (BFR) used primarily as an additive FR in polystyrene and textile products and has been the subject of intensified research, monitoring and regulatory interest over the past decade. HBCD is currently being evaluated under the Stockholm Convention on Persistent Organic Pollutants. HBCD is hydrophobic (i.e., has low water solubility) and thus partitions to organic phases in the aquatic environment (e.g., lipids, suspended solids). It is ubiquitous in the global environment with monitoring data generally exhibiting the expected relationship between proximity to known sources and levels; however, temporal trends are not consistent. Estimated degradation half-lives, together with data in abiotic compartments and long-range transport potential indicate HBCD may be sufficiently persistent and distributed to be of global concern. The detection of HBCD in biota in the Arctic and in source regions and available bioaccumulation data also support the case for regulatory scrutiny. Toxicity testing has detected reproductive, developmental and behavioral effects in animals where exposures are sufficient. Recent toxicological advances include a better mechanistic understanding of how HBCD can interfere with the hypothalamic-pituitary-thyroid axis, affect normal development, and impact the central nervous system; however, levels in biota in remote locations are below known effects thresholds. For many regulatory criteria, there are substantial uncertainties that reduce confidence in evaluations and thereby confound management decision-making based on currently available information.

PBDEs and methoxylated analogues in sediment cores from two Michigan, USA, inland lakes

Polybrominated diphenyl ethers (PBDEs) have been widely studied in sediments from the North American Great Lakes; however, no studies have been conducted of occurrences of methoxylated (MeO-) PBDEs in abiotic compartments in this region. In the present study, 23 tri- to hepta-PBDEs and 12 MeO-PBDEs were analyzed in dated sediment cores collected from two inland lakes (White Lake and Muskegon Lake) in Michigan, USA. Concentrations of Σ(23) PBDEs ranged from 3.9 × 10(-1) to 2.4 × 10(0) and from 9.8 × 10(-1) to 3.9 × 10(0) ng/g dry weight in White Lake and Muskegon Lake, respectively. The historical trends of tri- to hepta-PBDEs in the two lakes were different, possibly because of different input and remediation histories. The tri- to hepta-PBDE profiles were similar in the two lakes, with BDE-47 as the predominant congener, followed by BDE-99 and BDE-183. A different temporal trend for BDE-183 was found compared with other PBDEs, which is consistent with debromination of high-brominated PBDEs during sedimentation and aging. Methoxylated-PBDEs were detected only in Muskegon Lake (3.6 × 10(-3) to 1.2 × 10(-1) ng/g dry wt). Methoxylated PBDEs showed different temporal trends compared with tri- to hepta-PBDEs. The differences in patterns of concentrations of MeO-PBDEs in the two lakes might be due to different aquatic communities in each lake. The occurrences of MeO-PBDEs could be the major source of hydroxylated-polybrominated diphenyl ethers (OH-PBDEs) observed in organisms collected in these freshwater systems.

Distribution and partitioning of aliphatic hydrocarbons and polycyclic aromatic hydrocarbons between water, suspended particulate matter, and sediment in harbours of the West coastal of the Gulf of Tunis (Tunisia)

Harbours of La Goulette, Rades and Sidi Bou Said are considered as the principal largest and most important port in the Gulf of Tunis characterised by a direct influence of different activities (sailing, industry and fishing) to the Mediterranean Sea. Due to their social and economic impact, a comprehensive assessment of the spatial distribution and partitioning of 24 polycyclic aromatic hydrocarbons (PAHs) and 18 aliphatic hydrocarbons (AHs) in summer and in winter among overlying water, suspended particulate matter (SPM) and surface sediments is essential. Distribution of hydrophobic organic contaminants in abiotic compartments is important for describing their transfer and fate in aquatic ecosystems and to identify the potential danger due to mobilization of contaminants produced by managing of the same sediments. Total organic carbon (TOC) contents range between 4.3% and 6.5%, with an average value of 5.9% in summer, and between 2.3% and 9.6%, with an average value of 6.1% in winter. The average concentrations of ΣPAH in winter and in summer were respectively 703.1 ng L⁻¹ and 378.4 ng L⁻¹ in seawater, 4599.1 ng g⁻¹ and 3114 ng g⁻¹ in SPM, and 1507.6 ng g⁻¹ dw (dry weight) and 1294.6 ng g⁻¹ dw in surface sediment. For ΣAH the average concentrations in winter and in summer were respectively 701 ng L⁻¹ and 741.7 ng L⁻¹ in seawater, 6743.5 ng g⁻¹ and 6282.9 ng g⁻¹ in SPM, and 4971.3 ng g⁻¹ and 4588.1 ng g⁻¹ in surface sediment. Higher PAH and AH concentrations were observed in SPM than in surface sediment. SPM and water were dominated by PAH with low molecular weight, while for sediment low and high molecular weight PAHs were present. PAH and AH fingerprint ratios, such as pristane to phytane (Pr/Ph), phenanthrene to anthracene (Phe/An) and fluoranthene to pyrene (Fl/Py), suggest that hydrocarbons in all harbours may originate from both pyrolytic and petrogenic sources derived from discharge of untreated sewage and wastewater or from direct input by ship traffic in the area. The results showed significant difference (ANOVA, p < 0.05) for hydrocarbon mean concentrations between all harbours studied and between different matrixes.

Balanced Fates of Pyrene and 1-Hydroxypyrene in Snails, Ilyanassa Obsoleta, and Spiked Sediments

Eastern mud snails were exposed to pyrene (PY) and 1-hydroxypyrene (PYOH) spiked individually in sediment. Animals were examined for the bioaccumulation of parent compound and the presence of biotransformation products in soft tissue extracts after 3 days of exposure. Single and double oxidation products along with sulphate conjugates were detected in animals from both exposures, with traces of mono-glucuronide. The major phase I and II products were 1-hydroxypyrene (PYOH) and pyrene-1- sulphate (PYOS). Biotransformation was more efficient at low levels of PY or PYOH exposure and bioaccumulation more substantial at higher dose. Phase I oxidation was more efficient in fall exposed snails and phase II conjugation in the summer. Stressed animals were seen in the fall and analyzed separately from healthy ones. Their level of abundant metabolites was thrice that of non-stressed snails. The present data can be compared to a published study where snails were exposed to spiked food that was consumed within minutes. In that earlier work, stressed snails were associated with five times the level of metabolites than unaffected animals. Therefore, a longer contaminants' uptake time led to observing a lower excess of metabolites in soft tissues of impacted snails. PYOH degraded more readily in the snails' native sediments than PY, with intermediates in the catabolism of the compound detectable in sediments 3 days after spiking the media. This study demonstrates the importance of investigating the balance of fates of PAC in biotic and abiotic compartments in order to understand the state of the environment.

Formation, occurrence, significance, and analysis of organoselenium and organotellurium compounds in the environment.

Among all environmentally-relevant trace elements, selenium has one of the most diverse organic chemistries. It is also one of the few trace elements that may biomagnify in food chains under certain conditions. Yet, the exact chemical forms of selenium involved in the uptake into organisms and transfer to higher trophic levels, as well as the biochemical mechanisms that lead to their subsequent metabolism in organisms, are still not well understood. This is in part due to the analytical challenges associated with measuring the myriad of discrete Se species occurring in organisms. While there are generalized concepts of selenium metabolism, there is a lack of conclusive analytical evidence supporting the existence of many postulated intermediates. Likewise, there is a disconnect between the major selenium species encountered in abiotic compartments (waters, soils, and sediment), and those found in organisms, which renders the qualitative and quantitative description of the bioaccumulation process uncertain. Here, we summarize the knowledge on important selenium and tellurium species in all environmental compartments, and identify gaps and uncertainties in the existing body of knowledge, with emphasis on problems associated with past and current analytical methodology.

The cold‐water coral community as hotspot of carbon cycling on continental margins: A food‐web analysis from Rockall Bank (northeast Atlantic)

We present a quantitative food‐web analysis of the cold‐water coral community, i.e., the assembly of living corals, dead coral branches and sediment beneath, associated with the reef‐building Lophelia pertusa on the giant carbonate mounds at ~800‐m depth at Rockall Bank. Carbon flows, 140 flows among 20 biotic and abiotic compartments, were reconstructed using linear inverse modeling by merging data on biomass, on‐board respiration, δ15N values, and literature constraints on assimilation and growth efficiencies. The carbon flux to the coral community was 75.1 mmol C m−2 d−1 and was partitioned among (phyto)detritus (81%) and zooplankton (19%). Carbon ingestion by the living coral was only 9% of the carbon ingestion by the whole community and was portioned among (phyto)detritus (72%) and zooplankton (28%). Carbon cycling in the community was dominated by suspension‐ and filter‐feeding macrofauna associated with dead coral branches. Sediment traps mounted on a bottom lander trapped 0.77 mmol C m−2 d−1 (annual average), which is almost two orders of magnitude lower than total carbon ingestion (75.1) and respiration (57.3 mmol C m−2 d−1) by the coral community. This discrepancy is explained in two ways: the coral community intercepts organic matter that would otherwise not settle on the seafloor, and through their action as ecosystem engineers, the increased turbulence generated by the coral framework and organic‐matter depletion in the boundary layer augment the influx to the coral community. A comparison of macrofaunal biomass and respiration data with soft sediments reveals that coral communities are hot spots of biomass and carbon cycling along continental margins.

Efeitos antrópicos sobre concentrações de metais alcalinos na região da microbacia do Arroio Araçá, Canoas - Rio Grande do Sul

This work presents alterations in the concentrations of alkaline metals sodium, lithium and potassium, in abiotic compartments, at Araca stream micro-basin, located in Canoas, RS. Its spring is located in a low populational density region and crosses an elevated environmental impacted urban area. Its final course crosses an agricultural area. Samples of atmospheric particulates, macrophites, water and sediments were analyzed. High concentrations of alkaline metals, related with draining of rice fields or with the ground type, as well as correlations among its concentrations with regional activities were verified. Tripogandra diuretica has shown bioaccumulation compatible with their concentrations on waters.

Assessing the risks of persistent organic pollutants to top predators: A review of approaches

Accurate risk assessment of secondary poisoning by persistent organic pollutants (POPs) in top predators is possible but requires multidisciplinary input from wildlife ecology, ecotoxicology, and analytical chemistry. Because of the transfer of POPs up the food chain, traditional approaches to exposure assessment based on POPs in abiotic compartments or organisms low in the food chain can make the assessment of risk to top predators complicated. For more direct, accurate, and site-specific methods of assessing the risks of secondary poisoning of top predator by POPs, we classify 2 main approaches: diet based and tissue based. Exposure assessment via the diet-based approach requires samples of the predator's diet and measured concentrations in the prey items, realistic estimates of dietary composition, and ingestion rates. The even more direct, tissue-based approach uses measured POP concentrations in tissues of top predators to determine internal exposure coupled with tissue-based effect concentrations (or biological responses measured via biomarkers) to determine risk. The advantage of these methods is that uncertain estimates of POPs transfer to top predators from lower trophic levels are avoided. In practice, the availability of dose-response data and internal exposure-response relationships for POPs in top predators is limited, so these may have to be extrapolated from surrogate species. In this paper we illustrate and evaluate the potential of diet-based and tissue-based risk assessment approaches with case studies and demonstrate that appropriate methodologies significantly reduce the uncertainty in risk assessments of POPs.

Modelling carbon and nutrient cycling in a simulated pond system at Ranchi

Mathematical modelling of ecosystems requires a considerable amount of knowledge about the subsystems functioning within the broad framework, and the various rate processes and transfer coefficients that control the dynamic aspects. A detailed analysis of the transfer rates and budget of inorganic carbon and nutrients in a simulated pond was conducted for assessment, and comparison with aquatic bodies that undergo cultural eutrophication. In these systems, the processes are complicated by a variety of inputs. Such inputs interfere with the assessment of lake background conditions and water quality. We used the compartmental model of biogeochemical cycling and a mathematical model designed by our group to calculate transfer rates of inorganic carbon and nutrients through various processes. The major external variables or forcing functions considered were light and temperature, while the state variables included the biotic and the abiotic compartments. The major processes studied were: photosynthesis, respiration and decomposition that play an important part in balancing the nutrient content of the system and maintain a dynamic equilibrium. The aquatic system depicted a perfect cycling of carbon while the nitrates and phosphates resonated in tune with the metabolic rhythm of the biota. The study illustrates the use of our mathematical model in determining the various rate processes of the biota, and for the development of compartmental models for analysis and management of systems through process optimization.

Environmental Crime Investigation in Arroio do Meio, Rio Grande do Sul, Brazil: Tannery and Shoe Factory Waste Landfill Case Study

In Brazil, the criminal prosecution is defined by laws as well as crimes, including crimes against the environment, which cannot exist without being previously stated by law. Pollution is defined as a crime when it reaches levels that may damage or are already damaging human health. Investigation of environmental crimes, especially pollution crimes, requires environmental forensics' knowledge to provide accurate scientific evidence. The present case study was carried out in an area under suspicion of potential pollution situation—a landfill site containing hazardous waste of tannery and shoe factories, located in Arroio do Meio, Rio Grande do Sul, Brazil. The work methodology, adapted from the traditional crime scene examination, included the detailed description of the area. Further examinations were the quantification and characterization of the probable pollution source; gathering data from preexisting analyses in biotic and abiotic environmental compartments; and sampling and analyses of animal tissues, water, and sediments. Despite Cr being known as the major pollutant in tannery wastes, the analyses in environmental media pointed no significant Cr contamination in the area. The pollution crime by health endangerment can be defined if any discharge from substances increases environmental concentrations of elements or substances above limits regulated in legislation to protect human health. Evidence for this is provided by groundwater analyses where Pb, a well known toxic metal, appeared in concentrations above those defined as maximum concentration allowed by the potable water regulation.

Testing an ecological model for transmission of Salmonella enterica in swine production ecosystems using genotyping data

An ecological model for transmission of Salmonella enterica in swine production ecosystems was developed, identifying host species, environmental reservoirs, and temporal, spatial, and functional (i.e., stage of production) dimensions. It was hypothesized that transmission was most likely within spatial and functional compartments, between hosts of the same species and abiotic compartments of the same type. Eighteen swine production systems in Illinois, USA, were sampled in four collection cycles (1998, 1999, 2000, 2003). There were 11,873 samples collected, including feces from swine and other mammals and birds, and samples from insects, pen floors, boots, feed, and water. The 460 Salmonella isolates obtained were genotyped using repetitive sequence PCR with three primers—REP, BOX, and ERIC. All isolates from 2000 and 2003 were serotyped, as well as a subsample from 1998 and 1998. Genetic relatedness was estimated from the similarity of fragmentation patterns after gel electrophoresis of PCR products. Cluster analysis identified genetically related isolates. Linking of isolates in tight clusters (similarity ≥85%) was viewed as evidence for transmission. Five farms had a sufficient number of tight clusters for hypothesis testing. The factors most differentiating isolates genetically were farm of origin and time of sampling. Isolates were also differentiated genetically by site, building, room, and pen. There was no consistent association of genotype with stage of production or host/environment reservoir. Serotype analysis confirmed that Salmonella lineages were differentiated by visit and site. Thus, Salmonella transmission was primarily over short distances, i.e., within the same pen or room, with some transmission between rooms and buildings on the same site, but with limited transmission between sites. Transmission was observed across a variety of ecological niches represented by different host species and environmental reservoirs. Genetic differences over time reflected multiple introductions into the ecosystem of different Salmonella genotypes, as well as evolutionary changes within lineages. Intervention strategies to reduce Salmonella prevalence within swine production ecosystems would be best targeted at maintaining spatial barriers to transmission, whereas intervention targeted at specific biological hosts or environmental reservoirs is less likely to be effective.

Partitioning characteristics of PAHs between sediment and water in a shallow lake

Distribution of hydrophobic organic contaminants in abiotic compartments is essential for describing their transfer and fate in aquatic ecosystems. Taihu Lake is the third largest freshwater lake in China. Water quality of Taihu Lake has deteriorated greatly during the last decades and has threatened the water supply. The aim of the present study was to investigate the partitioning of polycyclic aromatic hydrocarbons (PAHs) among overlying water, suspended particulate matter (SPM), sediments, and pore water in Meiliang Bay, Taihu Lake and to provide useful information for the ecological engineering in this area. Overlying water and surface sediment were sampled from six sites in Meiliang Bay, Taihu Lake, China. Within 72 h of sampling, sediments were centrifuged to obtain the pore water. Overlying water samples were filtered to separate dissolved and SPM samples. After extraction, samples were purified following a clean-up procedure. PAH fraction was obtained by elution with a mixture of hexane: DCM (7:3, V/V) and analyzed by GC/MS. PAHs concentrations in overlying water varied from 37.5 ng/L to 183.5 ng/L. Concentrations of PAHs in pore water were higher than those in overlying water. The total concentrations of 16 priority PAHs in sediments ranged from 2091.8 ng/g-dw to 4094.4 ng/g-dw. PAHs concentrations on SPM were decreased with suspended solid concentrations (SSC). Total PAHs concentrations on SPM varied in the range of 3369.6 ng/g-dw to 7531.1 ng/g-dw. The partition coefficients between sediment and overlying water (log K oc) for PAHs with log K ow<5 were positively correlated with their octanol-water partition coefficients (log K ow) (n=39, r=0.79, p<0.0001). Partition coefficients between sediment and pore water (log K oc′) for all PAHs were also significantly correlated with their log K ow values (n=48, r=0.82, p<0.0001). In general, PAHs derived from combustion sources tend to bind strongly to soot particles in natural sediment. Consequentially, K oc values observed in the natural environment could be orders of magnitude higher than those predicted by linear correlation relationships under laboratory conditions. In the present study, the ratio of log K oc values to log K ow values falls consistently above 1, indicating that the sediment soot carbon in the bay was more attractive for PAHs than n-octanol. The log K oc′ was also higher than that predicted under laboratory conditions, suggesting that the measured pore water PAH concentrations were lower than those predicted. That is to say, not all the sediment PAHs can be available to partition rapidly into sediment pore waters. A variation in soot content is a possible reason. Furthermore, concentrations of PAHs on SPM were higher than those in sediments. The compositions of PAHs on SPM and in sediments were similar, indicating the importance of re-suspension process of sediments in the partitioning process of the shallow lake. The results indicated the equilibrium partitioning model could be used to predict PAHs distribution in various phases of a shallow lake in the stagnation period, but re-suspension processes should be considered to modify the relationship between log K ocs and log K ows. Concentration, particle size and composition of resuspended particles could affect the relationship between log K ocs and log K ows. Further work should be done under field conditions, especially where a steady thermodynamic equilibrium state could be assumed.

Evidence for higher biomagnification factors of lower chlorinated PCBs in cultivated seabass

Thirty three PCB congeners were analyzed in three size classes of seabass (Dicentrarchus labrax), from a semi-intensive fish farm, in food and in abiotic compartment. Water and suspended particulated matter (SPM) showed higher concentrations of lower chlorinated PCBs, whereas fish tissues and food showed higher concentrations of CB153 and CB138. In order to examine the influence of different inputs to seabass contamination, bioaccumulation factors (BAF), biota-suspended particulate matter bioaccumulation factors (BSMAF) and biomagnification factors (BMF) were calculated. In general, the log BAF and log BSMAF showed good correlations with log K(ow), for congeners with log K(ow)>6.1. In three fish size classes, PCB congeners with log K(ow)<6.1 were found at concentrations higher than what was expected based on the BAF calculated for the more hydrophobic congeners, suggesting a different contribution of sources. The application of a mass balance model for accumulation of some congeners in seabass estimated concentrations in fish 3- to 38-fold higher than the measured values, probably by overestimating gill absorption. The model was applied with other scenarios in order to maximize uptake from food, which may have a significant influence in accumulation, and not only from diet pellets. Its contribution to fish contamination for highly chlorinated PCBs may reach a maximum of 54-64%, and for lower chlorinated PCBs its contribution is lower than 20%. In this work it was proved that to reduce fish contamination the quality of the water should be controlled.

The fate of bacterial carbon in an intertidal sediment: Modeling an in situ isotope tracer experiment

We report the results of an integrated modeling and in situ isotope tracer experiment study examining the fate of bacterial carbon in an intertidal sediment. 13C-glucose was injected into the upper 10 cm of an intertidal sediment, which successfully tagged the bacterial community as evidenced by 13C enrichment of bacterial specific polar-lipid-derived fatty acids. Over a period of 4.5 months, 13C enrichment was monitored in sediment organic carbon, bacteria, meiobenthos, macrobenthos, and dissolved inorganic carbon. A mechanistic model accurately simulated label transfer among the biotic and abiotic compartments and was used to derive bacterial production and the loss processes grazing, mortality, respiration, and exchange. Bacterial production averaged 67 mmol C m-2 d-1, of which 8% was lost from the sediment by exchange processes, 3% was grazed by meiobenthos and 24% by macrobenthos. The primary fate of bacterial production was mortality (65%) and the released bacterial carbon was recycled back to dissolved organic carbon, resulting in recycling of carbon within the dissolved organic carbon-bacteria loop. Bacterial respiration was the main loss process from this loop. Although a significant fraction of bacterial carbon production was grazed, our results show that bacterial carbon is primarily a sink of organic carbon in the food web of intertidal sediments.