Toward enhanced subsurface intervention methods using chaotic advection

Many intervention activities in the terrestrial subsurface involve the need to recover/emplace distributions of scalar quantities (e.g. dissolved phase concentrations or heat) from/in volumes of saturated porous media. These scalars can be targeted by pump-and-treat methods or by amendment technologies. Application examples include in-situ leaching for metals, recovery of dissolved contaminant plumes, or utilizing heat energy in geothermal reservoirs. While conventional pumping methods work reasonably well, costs associated with maintaining pumping schedules are high and improvements in efficiency would be welcome. In this paper we discuss how transient switching of the pressure at different wells can intimately control subsurface flow, generating a range of "programmed" flows with various beneficial characteristics. Some programs produce chaotic flows which accelerate mixing, while others create encapsulating flows which can isolate fluid zones for lengthy periods. In a simplified model of an aquifer subject to balanced pumping, chaotic flow topologies have been predicted theoretically and verified experimentally using Hele-Shaw cells. Here, a survey of the key characteristics of chaotic advection is presented. Mathematical methods are used to show how these characteristics may translate into practical situations involving regional flows and heterogeneity. The results are robust to perturbations, and withstand significant aquifer heterogeneity. It is proposed that chaotic advection may form the basis of new efficient technologies for groundwater interventions.     

Orientation of plaice (Pleuronectes platessa) in the open sea: evidence for the use of external directional clues

We studied the orientation of plaice (Pleuronectes platessa L.) in the open sea (Southern Bight of the North Sea) during May and June of 1979 and 1980, using continuous, on-line data from 6 fish equipped with transponding acoustic compass tags. During the day, fish swimming in midwater did not maintain their heading. At night, the same fish maintained their heading in a way that was consistent with active orientation to some external directional clue, but inconsistent with the use of an inertial guidance system. We believe this to be the first analysis to demonstrate the use of external guidance clues by fish in the open sea. Because fish were able to maintain a consistent heading in midwater by night, in the apparent absence of both visual and tactile clues, the external reference is likely to be geophysical. Possible clues include the electrical field generated by the flow of sea water through the geomagnetic field and the earth's magnetic field itself.     

Freshwater leeches (Hirudinea) as a screening tool for detecting organic contaminants in the environment

In earlier work, we found that leeches from an industrially polluted creek bioaccumulated chlorophenols to much higher concentrations than other resident benthic invertebrates and fish. We suggested that leeches may have significant potential as biomonitors for these and other organic contaminants in the environment. In this study, we compared the bioaccumulation and depuration of 16 organic compounds, including eight chlorophenols (CPs), lindane, DDT and four derivatives, benzothiazole (BT) and 2-(Methylthio)benzothiazole (MMBT) for three species of leeches. Dina dubia had the highest bioaccumulation capacity for most contaminants, but residues persisted longest in Erpobdella punctata. Helobdella stagnalis appeared capable of degrading some compounds. Half lives of CPs, DDT and DDT derivatives were generally longer than one month. In contrast, half lives were only 1 day for lindane, 1–2.5 days for MMBT and 7 days for BT despite very high initial tissue concentrations of the latter two compounds. Bioconcentration factors for contaminants in leeches were higher than those reported for other aquatic organisms. Half lives for lindane, DDT and DDT derivatives were consistent with the literature for other organisms, but half lives for CPs were much longer. The results suggest that leeches would be excellent biomonitors of both continuous and intermittent contamination of a waterway with CPs and DDT, as they retain these compounds for long periods after exposure. Their usefulness as a screening tool for lindane and benzothiazoles would be limited to chronically contaminated environments.     

Lake sediments record sensitivity of two hydrologically closed upland lakes in Mexico to human impact

We provide evidence of rapid, recent environmental change in two lakes in the highlands of central Mexico. Multiple sediment cores were obtained from Lago de Zirahuén (Michoacán) and Laguna de Juanacatlán (Jalisco). Analysis of diatom assemblages, magnetic susceptibility, and metal concentrations was carried out, with the chronology provided by 210Pb dating, 14C dating, and tephrochronology. There is evidence of catchment disturbance during the colonial period in both basins, but the most striking feature at both sites is the rapid change in diatom assemblages during the last 20 y, indicating the onset of eutrophication. Limnological data from Lago de Zirahuén support this interpretation, although none are available from Laguna de Juanacatlán. Paleolimnology is a powerful tool in tracking recent change, particularly in the absence of regular limnological monitoring programs. These lakes appear to be highly sensitive to changes in catchment exploitation, which must be considered in future drainage basin management.     

Characteristics and source attribution of PM2.5 during 2016 G20 Summit in Hangzhou: Efficacy of radical measures to reduce source emissions

A field campaign was conducted to study the PM_2.5 and atmospheric gases and aerosol's components to evaluate the efficacy of radical measures implemented by the Chinese government to improve air quality during the 2016 G20 Summit in Hangzhou China. The lower level of PM_2.5 (32.48 ± 11.03 µg/m³) observed during the control period compared to pre-control and post-control periods showed that PM_2.5 was alleviated by control policies. Based on the mass concentrations of particulate components, the emissions of PM_2.5 from local sources including fossil fuel, coal combustion, industry and construction were effectively reduced, but non-exhaust emission was not reduced as effectively as expected. The accumulation of SNA (SO₄^2?, NO₃^?, NH₄⁺) was observed during the control period, due to the favourable synoptic weather conditions for photochemical reactions and heterogeneous hydrolysis. Because of transboundary transport during the control period, air masses from remote areas contributed significantly to local PM_2.5. Although, secondary organic carbon (OC_sec) exhibited more sensitivity than primary organic carbon (OC_pri) to control measures, and the increased nitrogen oxidation ratio (NOR) implied the regional transport of aged secondary aerosols to the study area. Overall, the results from various approaches revealed that local pollution sources were kept under control, indicating that the implementation of mitigation measures were helpful in improving the air quality of Hangzhou during G20 summit. To reduce ambient levels of PM_2.5 further in Hangzhou, regional control policies may have to be taken so as to reduce the impact of long-range transport of air masses from inland China.     

A farewell to Dr Thomas Knacker (* 29.04.1951 – ? 30.10.2011): scientific contributions and personal memories

Background

The bioaccumulation potential of chemical substances is commonly determined in flow-through fish tests according to the Organization for Economic Cooperation and Development (OECD) technical guideline (TG) 305, aiming at the determination of bioconcentration factors (BCF). Investigations on aquatic organisms have shown a significant positive correlation between the accumulation of a chemical and the lipid content of organisms. Residue levels can thus differ between individuals, species, and size groups depending on their lipid content. BCF values can be normalized by lipid content; however, this requires the use of appropriate extraction techniques to ensure the complete extraction of total lipids from fish/tissue samples. The OECD TG 305 is currently under revision. A literature review was carried out to select preferred methods which shall be included in the updated OECD TG 305 along with a sampling schedule for lipid measurement in fish.

Results

An overview and appraisal of a broad range of lipid extraction methods is presented. Extraction procedures applied in bioaccumulation studies described in the literature and procedures currently used for such studies by governmental, academic, and industrial labs are surveyed. Possible impacts of unsuitable extraction techniques on lipid normalized BCF results were assessed. Default values for BCF normalization commonly used in bioaccumulation studies are described. The effect of differences in residue distribution over different organs and/or lipids on the normalization of BCF values is discussed.

Conclusions

A broad range of procedures for lipid extraction are available. However, only the use of suitable extraction techniques guarantees the complete extraction of total lipids from fish samples in bioaccumulation studies which is required to ensure the correct lipid normalization of BCF values. Preferred methods for inclusion in the updated OECD 305 test guideline as well as a standard schedule for lipid measurements are suggested.