Use of a food web model to evaluate the factors responsible for high PCB fish concentrations in Lake Ellasjøen, a high Arctic Lake

Background, aim, and scope

Lake Ellasjøen, located in the Norwegian high arctic, contains the highest concentrations of polychlorinated biphenyls (PCBs) ever recorded in fish and sediment from high arctic lakes, and concentrations are more than 10 times greater than in nearby Lake Øyangen. These elevated concentrations in Ellasjøen have been previously attributed, in part, to contaminant loadings from seabirds that use Ellasjøen, but not Øyangen, as a resting area. However, other factors, such as food web structure, organism growth rate, weight, lipid content, lake morphology, and nutrient inputs from the seabird guano, also differ between the two systems. The aim of this study is to evaluate the relative influence of these factors as explanatory variables for the higher PCB fish concentrations in Ellasjøen compared with Øyangen, using both a food web model and empirical data.

Methods

The model is based on previously developed models but parameterized for Lakes Ellasjøen and Øyangen using measured data wherever possible. The model was applied to five representative PCB congeners (PCB 105, 118, 138, 153, and 180) using measured sediment and water concentrations as input data and evaluated with previously collected food web data.

Results

Modeled concentrations are within a factor of two of measured concentrations in 60% and 40% of the cases in Lakes Ellasjøen and Øyangen, respectively, and within a factor of 10 in 100% of the cases in both lakes. In many cases, this is comparable to the variability associated with the data as well as the efficacy of the predictions of other food web model applications.

Discussion

We next used the model to quantify the relative importance of five major differences between Ellasjøen and Øyangen by replacing variables representing each of these factors in the Ellasjøen model with those from Øyangen, in separate simulations. The model predicts that the elevated PCB concentrations in Ellasjøen water and sediment account for 49%–58% of differences in modeled fish PCB concentrations between lakes. These elevated sediment and, to a lesser extent, water concentrations in Ellasjøen are due to PCB loadings from seabird guano. However, sediment–water fugacity ratios of PCBs are consistently greater in Ellasjøen compared with Øyangen, which suggests that internal lake processes also contribute to differences in sediment and water concentrations. We hypothesize that the nutrients associated with guano influence sediment–water fugacity ratios of PCBs by increasing the stock of pelagic algae. As both these algae and the guano settle, their organic carbon content is degraded faster than PCBs, which causes an extra magnification step in Ellasjøen before these detrital particles are consumed by benthic organisms, which are in turn consumed by fish. The model predicts that the remaining ～50% of the differences in PCB concentrations observed between the fish of these lakes are due to other subtle differences in their food web structures.

Conclusions

In conclusion, based on the results of a food web model, we found that the most dominant factors influencing the higher PCB fish concentrations in Lake Ellasjøen compared with Øyangen are the higher sediment and water concentrations in Ellasjøen, caused by seabird guano. Together, sediment and water are predicted to account for 49%–58% of differences in fish concentrations between lakes. Although seabird guano provides a source of nutrients to the lake, in addition to contaminants, empirical data and indirect model results suggest that nutrients are not leading to decreased bioaccumulation, in contrast to what has been observed in temperate, pelagic food webs.

Recommendations and perspectives

The results of this study emphasize the importance of considering even small differences in food web structure when comparing bioaccumulation in two lakes; although the food web structures of Ellasjøen and Øyangen differ only slightly, the model predicts that these differences account for most of the remaining ～50% of the differences in PCB fish concentrations between the two lakes. This study further demonstrates the utility of food web models as we were able to predict and tease apart the influence of various factors responsible for the elevated concentrations in the fish from Lake Ellasjøen, which would have been difficult using the field data alone.     

Long-range atmospheric transport of three toxaphene congeners across Europe. Modeling by chained single-box FATEMOD program

Background, aims, and scope  Since toxaphene (polychlorocamphene, polychloropinene, or strobane) mixtures were applied for massive insecticide use in the 1960s to replace the use of DDT, some of their congeners have been found at high latitudes far away from the usage areas. Especially polychlorinated bornanes have demonstrated dominating congeners transported by air up to the Arctic areas. Environmental fate modeling has been applied to monitor this phenomenon using parallel zones of atmosphere around the globe as interconnected environments. These zones, shown in many meteorological maps, however, may not be the best way to configure atmospheric transport in air trajectories. The latter could also be covered by connecting a chain of simple model boxes. We aim to study this alternative approach by modeling the trajectory chain using catchment boxes of our FATEMOD model. Polychlorobornanes analyzed in biota of the Barents Sea offered one case to study this modeling alternative, while toxaphene has been and partly still is used massively at southern East Europe and around rivers flowing to the Aral Sea. Materials and methods  Pure model substances of three polychlorobornanes (toxaphene congeners P26, P50, and P62) were synthesized, their environmentally important thermal properties measured by differential scanning calorimetry, as evaluated from literature data, and their temperature dependences estimated by the QSPR programs VPLEST, WATSOLU, and TDLKOW. The evaluated property parameters were used to model their atmospheric long-range transport from toxaphene heavy usage areas in Ukraine and Aral/SyrDarja/AmuDarja region areas, through East Europe and Northern Norway (Finnmarken) to the Barents Sea. The time period used for the emission model was June 1997. Usual weather conditions in June were applied in the model, which was constructed by chaining FATEMOD model boxes of the catchment’s areas along assumed maximal air flow trajectories. Analysis of the three chlorobornanes in toxaphene mixtures function as a basis for the estimates of emission levels caused by its usage. High estimate (A) was taken from contents in a Western product chlorocamphene and low estimate (B) from mean contents in Russian polychloroterpene products to achieve modeled water concentrations. Bioaccumulation to analyzed lipid of aquatic biota at the target region was estimated by using statistical calculation for persistent organic pollutants in literature. Results  The results from model runs A and B (high and low emission estimate) for levels in sea biota were compared to analysis results of samples taken in August 1997 at Barents Sea. The model results (ng g⁻¹ lw): 4–95 in lipid of planktovores and 7–150 in lipid of piscivores, were in fair agreement with the analysis results from August 1997: 21–31 in Themisto libellula (chatka), 26–42 in Boreocadus saida (Polar cod), and 5–27 in Gadus morhua (cod) liver. Discussion  The modeling results indicate that the application of chained simple multimedia catchment boxes on predicted trajectory is a useful method for estimation of volatile airborne persistent chemical exposures to biota in remote areas. For hazard assessment of these pollutants, their properties, especially temperature dependences, must be estimated by a reasonable accuracy. That can be achieved by using measurements in laboratory with pure model compounds and estimation of properties by thermodynamic QSPR methods. The property parameters can be validated by comparing their values at an environmental temperature range with measured or QSPR-estimated values derived by independent methods. The chained box method used for long-range air transport modeling can be more suitable than global parallel zones modeling used earlier, provided that the main airflow trajectories and properties of transported pollutants are predictable enough. Conclusions  Long-range air transport modeling of persistent, especially photo-resistant organic compounds using a chain of joint simple boxes of catchment’s environments is a feasible method to predict concentrations of pollutants at the target area. This is justified from model results compared with analytical measurements in Barents Sea biota in August 1997: three of six modeled values were high and the other three low compared to the analysis results. The order of magnitude level was similar in both modeled (planktovore and piscivore) and observed (chatka and polar cod) values of lipid samples. The obtained results were too limited to firm validation but are sufficient to justify feasibility of the method, which prompts one to perform more studies on this modeling system. Recommendations and perspectives  For assessment of the risk of environmental damages, chemical fate determination is an essential tool for chemical control, e.g., for EU following the REACH rules. The present conclusion of applicability of the chained single-box multimedia modeling can be validated by further studies using analyses of emissions and target biota in various other cases. To achieve useful results, fate models built with databases having automatic steps for most calculations and outputs accessible to all chemical control professionals are essential. Our FATEMOD program catchments at environments and compound properties listed in the database represent a feasible tool for local, regional, and, according our present test results, for global exposure predictions. As an extended use of model, emission estimates can be achieved by reversed modeling from analysis results of samples corresponding to the target area. This article is dedicated to the memory of Professor Alexander B Terentiev (who passed away in November 2006), our true friend. With his Institute of Organo-Element Compounds, Russian Academy of Science, Moscow, he was an important main organizer of the six joint Finnish–Russian seminars (every third year since 1989) on the field (‘Chemistry and Ecology of Organo-Element Compounds’). He prompted us especially to search properties and environmental fates for various polyhalogen compounds. We remember him for his friendly character and great sense of humor.     

CO_2 Emission Induced by Urban Household Consumption in China

Household consumption is one of the important factors that induce COL emission. Based on input-output model, this article calculated the intensity of CO2 emission of different income groups and seven provinces in China, and then estimated total CO2 emission induced by urban household consumption from 1995 to 2004 in China based on statistic data of household living expenditure. The results show that CO2 emission per capita induced by household consumption had increased from 1583 to 2498 kg CO2 during 1995-2004. The ratio of consumption-induced CO2 emission to total CO2 emission had risen from 19% to 30% in the past decade. Indirect CO2 emission accounted for an important part of the consumption-induced emission, the ratio of indirect emission to consumption-induced emission had risen from 69% to 79% during the same period. A significant difference in consumption-induced CO2 emission across different income groups and different regions has been observed. COs emission per capita of higher income groups and developed regions increased faster than that of lower income groups and developing regions. Changing lifestyle has driven significant increase in CO2 emission. Especially, increases in private transport expenditure （for example, vehicle expenditure） and house building expenditure are key driving factors of growth in consumption-induced COL emission. There are big differences in the amount of CO2 emission induced by change in lifestyle across different income groups and provinces. It can be expected that lower income households and developing regions will increase consumption to improve their livings with income growth in the future, which may induce much more CO2 emission. A reasonable level of CO2 emission is necessary to satisfy human needs and to improve living standard, but a noticeable fact is that CO2 emission per capita induced by household consumption in developed areas of China had reached a quite high level. Adjustment in lifestyle towards a low-carbon society is in urgent need.     

The Sustainable Development of ICTs in China： An Empirical Study of Small and Medium-Sized Enterprises

The wide application of new information and communication technologies （ICTs） has been argued to be critical to business success of small and medium-sized enterprises （SMEs）, especially to those in the developing countries. Drawing upon existing literature, this article will examine the determinants of ICTs application in SMEs in China based on data collected from interviews with top managers and/or owners of 70 SMEs. We identify 20 factors affecting ICTs application in SMEs in China and divide them into four broad categories, namely pressures, firm specific factors, technical factors and local milieu. We also pay special attention to the Chinese business environment affecting ICTs application. Our analysis shows that local ICT infrastructure, external pressures from competitors and ICT knowledge of employees are the determinants of Internet application by SMEs, while product characteristics and market target are important factors of e-commerce adoption.     

Monte Carlo analysis of field water flow comparing uni- and bimodal effective hydraulic parameters for structured soil

Soil structure critically affects the hydrological behaviour of soils. In this paper, we examined the impact of areal heterogeneity of hydraulic properties of a structured soil on soil ensemble behaviour for various soil water flow processes with different top boundary conditions (redistribution and drainage plus evaporation and infiltration). Using a numerical solution of the Richards' equation in a stochastic framework, the ensemble characteristics and flow dynamics were studied for drying and wetting processes observed during a time interval of ten days when a series of relatively intense rainfall events occurred. The effects of using unimodal and bimodal interpretative models of hydraulic properties on the ensemble hydrological behaviour of the soil were illustrated by comparing predictions to mean water contents measured over time in several sites at field scale. Although the differences between unimodal and bimodal fitting are not significant in terms of goodness of fit, the differences in process predictions are considerable with the bimodal soil simulating water content measurements much better than unimodal soil. We also investigated the relative contribution of the soil variability of each parameter on the variance of the water contents obtained as the main output of the stochastic simulations. The variability of the structural parameter, weighting the two pore space fractions in the bimodal interpretative model, has the largest contribution to water content variance. The contribution of each parameter depends only partly on the coefficient of variation, much more on the sensitivity of the model to the parameters and on the flow process being observed. We observed that the contribution of the retention parameters to uncertainty increases during drainage processes; the opposite occurs with the hydraulic conductivity parameters.     

Incorporating layer- and local-scale heterogeneities in numerical simulation of unsaturated flow and tracer transport

This study characterizes layer- and local-scale heterogeneities in hydraulic parameters (i.e., matrix permeability and porosity) and investigates the relative effect of layer- and local-scale heterogeneities on the uncertainty assessment of unsaturated flow and tracer transport in the unsaturated zone of Yucca Mountain, USA. The layer-scale heterogeneity is specific to hydrogeologic layers with layerwise properties, while the local-scale heterogeneity refers to the spatial variation of hydraulic properties within a layer. A Monte Carlo method is used to estimate mean, variance, and 5th, and 95th percentiles for the quantities of interest (e.g., matrix saturation and normalized cumulative mass arrival). Model simulations of unsaturated flow are evaluated by comparing the simulated and observed matrix saturations. Local-scale heterogeneity is examined by comparing the results of this study with those of the previous study that only considers layer-scale heterogeneity. We find that local-scale heterogeneity significantly increases predictive uncertainty in the percolation fluxes and tracer plumes, whereas the mean predictions are only slightly affected by the local-scale heterogeneity. The mean travel time of the conservative and reactive tracers to the water table in the early stage increases significantly due to the local-scale heterogeneity, while the influence of local-scale heterogeneity on travel time gradually decreases over time. Layer-scale heterogeneity is more important than local-scale heterogeneity for simulating overall tracer travel time, suggesting that it would be more cost-effective to reduce the layer-scale parameter uncertainty in order to reduce predictive uncertainty in tracer transport.     

Cation exchange in a glacial till drumlin at a road salt storage facility

At a former wood preservation plant severely contaminated with coal tar oil, in situ bulk attenuation and biodegradation rate constants for several monoaromatic (BTEX) and polyaromatic hydrocarbons (PAH) were determined using (1) classical first order decay models, (2) Michaelis–Menten degradation kinetics (MM), and (3) stable carbon isotopes, for o-xylene and naphthalene. The first order bulk attenuation rate constant for o-xylene was calculated to be 0.0025 d^− 1 and a novel stable isotope-based first order model, which also accounted for the respective redox conditions, resulted in a slightly smaller biodegradation rate constant of 0.0019 d^− 1. Based on MM-kinetics, the o-xylene concentration decreased with a maximum rate of k_max = 0.1 µg/L/d. The bulk attenuation rate constant of naphthalene retrieved from the classical first order decay model was 0.0038 d^− 1. The stable isotope-based biodegradation rate constant of 0.0027 d^− 1 was smaller in the reduced zone, while residual naphthalene in the oxic part of the plume further downgradient was degraded at a higher rate of 0.0038 d^− 1. With MM-kinetics a maximum degradation rate of k_max = 12 µg/L/d was determined. Although best fits were obtained by MM-kinetics, we consider the carbon stable isotope-based approach more appropriate as it is specific for biodegradation (not overall attenuation) and at the same time accounts for the dominant electron-accepting process. For o-xylene a field based isotope enrichment factor ε_field of − 1.4 could be determined using the Rayleigh model, which closely matched values from laboratory studies of o-xylene degradation under sulfate-reducing conditions.     

Model evaluation of the phytoextraction potential of heavy metal hyperaccumulators and non-hyperaccumulators

Evaluation of the remediation ability of zinc/cadmium in hyper- and non-hyperaccumulator plant species through greenhouse studies is limited. To bridge the gap between greenhouse studies and field applications for phytoextraction, we used published data to examine the partitioning of heavy metals between plants and soil (defined as the bioconcentration factor). We compared the remediation ability of the Zn/Cd hyperaccumulators Thlaspi caerulescens and Arabidopsis halleri and the non-hyperaccumulators Nicotiana tabacum and Brassica juncea using a hierarchical linear model (HLM). A recursive algorithm was then used to evaluate how many harvest cycles were required to clean a contaminated site to meet Taiwan Environmental Protection Agency regulations. Despite the high bioconcentration factor of both hyperaccumulators, metal removal was still limited because of the plants' small biomass. Simulation with N. tabacum and the Cadmium model suggests further study and development of plants with high biomass and improved phytoextraction potential for use in environmental cleanup.     

湖岸缓冲带反硝化作用的研究进展

反硝化作用是湖岸缓冲带去除硝酸盐的重要途径。湖岸缓冲带是联系陆地与湖泊生态系的纽带,不仅为许多动植物提供适宜生境,而且通过反硝化作用能去除地下水中的硝酸盐,提高湖泊水质。概述不同检测反硝化速率的方法,并对比各种方法的优点与缺点。阐述反硝化作用的影响因素：厌氧环境、有机碳、湖岸坡度、缓冲带坡度、pH与温度、硝酸盐浓度。介绍反硝化速率模型的研究开发状况。最后,提出了目前国内外反硝化研究中存在的不足及发展方向。     

新型转式垃圾焚烧过程中脱氯脱硫机理的研究

为了探讨有机垃圾焚烧过程钙基添加剂对HCl,SO_x生成特性的影响,分别在自行设计的中空水冷转式垃圾焚烧炉和固定床加热炉中进行了一系列的实验,研究结果表明新型转式焚烧炉具有强化传热传质特性,能提高HCl、SO_x的脱除率,可抑制有害气体的生成;同时也研究了 HCl,SO₂气体同时存在时,钙基添加剂对脱氯脱硫效率的影响规律。