Shouyun Hu

Magnetic responses to acidification in Lake Yangzonghai, SW China

Abstract A short core of 33 cm length was obtained from lacustrine sediments of Lake Yangzonghai, Yunnan Province, China. A power plant, built in 1960 is located close to the northeast corner of the lake, and black burned coal ashes can be found within the uppermost 12 cm of the sediments. The age frame of the core was determined based on 137 Cs and 210 Pb analyses. Magnetic, biological and geochemical analyses were performed on the sediments and magnetic parameters were also determined from the source material of the power plant. The burned coal ash, collected directly from the power plant, is strongly magnetic, and its main magnetic content is magnetite. However, magnetic susceptibility and anhysteretic remanence of the sediment core is much lower and shows some evident fluctuations above 12 cm, corresponding to the time when the power plant was built. Ostracoda show a similar pattern, with a lower concentration at the top and a higher one below. However, some certain diatom species, which only can survive in acid water environment, show the reverse pattern. Element contents such as Al, a sensitive indicator for acidification, decrease above the 10 cm level. Based on all these data, it can be concluded that the water of the lake was acidified after the power plant was built, which caused dissolution of magnetic particles, and resulted in the decrease of magnetic concentration at the top of the core. This work demonstrates that magnetic response towards environmental pollution can be in different ways, i.e. not only by an enhancement of magnetic concentration.

Traffic-Related Pollutants in Roadside Soils of Different Countries in Europe and Asia

We investigated the magnetic and chemical properties of the roadside soil samples collected from five European and Asian countries. Spots in which cars slowed down and/or accelerated due to the traffic organization (speed limits, junctions, and traffic lights) were selected for sampling. Apart from the Zabrze site (Poland), the magnetic susceptibility and heavy metal contents decreased with increasing distance from the road edge. The highest mass-specific magnetic susceptibility values (χ) were observed in the samples collected from Mumbai (India) and Zabrze (Poland). Moreover, the high contents of Fe, Ni, Mn, and Co were observed in Mumbai, whereas in Zabrze, all the examined elements demonstrated high contents, except for Co. Analyses revealed that magnetite was the main magnetic mineral in the roadside soil samples. The high correlation coefficients (ru2009=u20090.87) between the magnetic susceptibility values and the total Fe content demonstrated that Fe occurred mainly as ferrimagnetic particles of technogenic origin resulting from traffic emissions. The traffic origin of the pollutants was also confirmed by the increased contents of the typically anthropogenic metals (Pb, Zn, Cd, and Cu) and a good correlation (ru2009=u20090.83) between the Ti and Mo contents, which do not occur in natural associations. The ratio between particular polycyclic aromatic hydrocarbons (PAHs) and high content of PAHs typical for car exhaust also implied traffic as their main source.

Atmospheric pollution history at Linfen (China) uncovered by magnetic and chemical parameters of sediments from a water reservoir

We studied magnetic and chemical parameters of sediments from sediments of a water reservoir at Linfen (China) in order to quantitatively reconstruct the atmospheric pollution history in this region. The results show that the main magnetic phases are magnetite and maghemite originating from the surrounding catchment and from anthropogenic activities, and there is a significant positive relationship between magnetic concentration parameters and heavy metals concentrations, indicating that magnetic proxies can be used to monitor the anthropogenic pollution. In order to uncover the atmospheric pollution history, we combined the known events of environmental improvement with variations of magnetic susceptibility (χ) and heavy metals along the cores to obtain a detailed chronological framework. In addition, air comprehensive pollution index (ACPI) was reconstructed from regression equation among magnetic and chemical parameters as well as atmospheric monitoring data. Based on these results, the atmospheric pollution history was successfully reconstructed.

Incursion of sea water into Gucheng Lake detected by magnetic, biologic and chemical data

Abstract Magnetic, biological and chemical studies were performed on lacustrine deposits from Gucheng Lake, Jiangsu Province, China. Magnetite and haematite are identified along the entire profile. It is not clear whether magnetite or/and ferrimagnetic iron sulfide (likely greigite) predominates above a striking boundary at 12.0 m, expressed by higher susceptibility (χ) and remanence values. Low NRM intensities above 12.0 m correlate to lower P factors ( χ max χ min ) and shallow inclinations of χmin, possibly indicating some disturbing remanence acquisition processes. Pollen, diatom, pigment and TOC analyses reveal that the early Holocene warming (started at the 13.7 m) led to a pulsative sea water incursion at 12.0 m. This incursion resulted in a period of brackish water, which favours the authigenesis of magnetite or ferrimagnetic iron sulphide, resulting in higher magnetic susceptibility and remanences values. Progressive freshing water occurred between 6.0 and 4.0 m. NRM changes correlate with these environmental trends. Magnetic changes above 2.5 m seems to be a result of human-driven deforestation and cultivation, as evidenced from pollen studies and lithological observations. Our results show that pollen and pigment assemblages directly reflect palaeoclimatic changes, whereas magnetic properties and diatoms respond primarily to the changes of hydrology and the limnology of Gucheng Lake.

A preliminary magnetic study on lacustrine sediments from Zoigê Basin, eastern Tibetan Plateau, China: Magnetostratigraphy and environmental implications

Abstract A preliminary magnetic study was conducted on Core RM (310 m long), drilled in the Zoige Basin (33 °57′N, 102 °21′E), on the eastern Tibetan Plateau. Greigite in SD state exists as a main magnetic contributor along the whole core. In addition, magnetite and haematite are detected between 160-45 m. NRM directions show a complex record with many apparent changes in inclination, for which greigite or the remanence acquisition process may be responsible. Nevertheless, the Matuyama/Brunhes boundary and, possibly, the Blake Event are identified. Between 310 and 160 m (as well as between 45 and 4.5 m), predominant anoxic conditions favour the formation of greigite, leading to higher susceptibility (χ) and remanence peaks. However, higher carbonate content during dry periods in these zones, may dilute the concentration of magnetic minerals, resulting in lower values of magnetic parameters. Between 160 and 45 m, weak oxic conditions preserve detrital magnetic minerals. The increasing χ background in this zone may indicate changes in the concentration of magnetite and haematite related to the uplift of the Tibetan Plateau, while higher χ peaks may indicate fluctuations to anoxic conditions, which enhance greigite concentration.

Remanence acquisition and its alteration on sediments

Previous palaeomagnetic work shows that the mechanism of remanence acquisition on sediments is very complicated. Different magnetizing processes under different conditions may produce some anomalous magnetic signals which have nothing to do with the changes of the geomagnetic field and are difficult to explain.The depositional remanent magnetization (DRM) may produce an inclination error and a bedding error, while postdepositional remanent magnetization (PDRM) may result in a time delay between the magnetic and sedimentary ages. When there are some different magnetic phases with different lock-in depths in the sediments, it is difficult to judge the depth of the reversal or excursion, or even the artificial magnetic signal may be produced. Even if there is only one magnetic phase in the sediment, the recorded magnetic signals may also be different if the lock-in depth is changed comparative to the lasting period of one reversal or excursion. Demagnetization may also change the primary magnetic records and the changes of water content may result in the displacement of magnetic boundary. The so-called “unstable core”, representing subtle changes in mineralogy into and out of a self-reversal region or a viscous magnetization region, gives a complicated palaeornagnetic record with many apparent changes in the palaeomagnetic direction. Moreover, some physical disturbances, such as biodisturbance, deformation, drilling processes and drying effects, may result in the remanence alteration. Some palaeomagnetic investigations demonstrate that good magnetic signals are invariably achieved on homogenous mud or clay sediments, but the worse signals on inhomogeneous profiles, especially on sandy layers.

Magnetic properties and particle-size analysis of dust-storm samples collected in Lanzhou and Sydney

Measurements of magnetic properties and particle size were carried out for dust-storm samples collected from Sydney (Australia) on 23 September 2009 and from Lanzhou (China) on April 2010. The results show that the magnetic mineral content of the Lanzhou sample is much higher than that of the Sydney sample. Magnetite, maghemite and possibly hematite occur in the Lanzhou sample. In addition to these minerals, there is also goethite in the Sydney sample. The magnetic grainsize of the Sydney sample is finer than that of the Lanzhou sample. These magnetic property differences are probably related to the source materials and anthropogenic particles. As to particle-size distribution, the Sydney sample shows a wide and flat curve with four peaks, while the Lanzhou sample displays a narrow curve with three peaks. The multi-peak particle-size distribution curves for the dust-storm samples indicate that there are multiple dust sources. Furthermore, a comparison of particle size between the Lanzhou storm sample and Jiuzhoutai loess/paleosol samples was also carried out. The results show that an increase in the 1–10 µm component and decrease in the 10–20 µm component of the loess/paleosol samples are mainly caused by pedogenic process (i.e. physical and chemical weathering of unstable minerals), while the increase in the 0.02–1 µm component is principally attributed to the formation of new minerals and the weathering of unstable minerals. The similarity of particle-size distribution curves between dust-storm and loess/paleosol samples implies that modern storm events are a good analogue for eolian processes operating in the Quaternary Period when loess/paleosol layers formed.

An economic passive sampling method to detect particulate pollutants using magnetic measurements

Identifying particulate matter (PM) emitted from industrial processes into the atmosphere is an important issue in environmental research. This paper presents a passive sampling method using simple artificial samplers that maintains the advantage of bio-monitoring, but overcomes some of its disadvantages. The samplers were tested in a heavily polluted area (Linfen, China) and compared to results from leaf samples. Spatial variations of magnetic susceptibility from artificial passive samplers and leaf samples show very similar patterns. Scanning electron microscopy suggests that the collected PM are mostly in the range of 2-25 μm; frequent occurrence of spherical shape indicates industrial combustion dominates PM emission. Magnetic properties around power plants show different features than other plants. This sampling method provides a suitable and economic tool for semi-quantifying temporal and spatial distribution of air quality; they can be installed in a regular grid and calibrate the weight of PM.

Comparative study on magnetic minerals of tidal flat deposits from different sediment sources in Jiangsu coast, Eastern China

Understanding the sources of sediments deposited in tidal flats is critical for reconstructing the evolution of coastal regions impacted by large rivers. Environmental magnetism can be an effective tool to track sediment sources and analyze the sediment properties. We evaluate several magnetic parameters from the tidal flat sediments along the Jiangsu coast. The results show that the sediments of Liandao Island have the lowest values of magnetic susceptibility (χ), anhysteretic remanent magnetization (ARM) and saturation isothermal remanence magnetization (SIRM). In addition to these, the values of χ, ARM and SIRM display a generally increasing trend from the north to the south along the Jiangsu coast. The strong relations between χ, ARM and SIRM show that the changes of magnetization of the tidal flat sediments mainly reflect the changes of concentration rather than those in grain sizes of magnetic particles. The main magnetic phase is magnetite, with a small amount of hematite. The strong relationship between χ and the 2-16 μm grain-size fraction suggests that magnetite is enriched in the finer silt fraction. The sediment sources is the main factor that influences the magnetic properties of the tidal flat sediments from the Jiangsu coast. Combined with the previous studies, the results indicate that the tidal flat sediments of Liandao Island were mainly derived from the nearshore rock weathering. The Yellow River is the dominant supplier for the north of Dafeng, while the Yangtze River is the dominant supplier for the south of Rudong. The coast between Dafeng and Rudong is a transition zone influenced by both rivers. This study provides a basis against which possible future variations in sediment composition resulting from catchment changes can be assessed.

Responses of magnetic properties to heavy metal pollution recorded by lacustrine sediments from the Lugu Lake, Southwest China

Environmental magnetism, which is rapid, sensitive, economical, and non-destructive, has been used to assess heavy metal pollution in lake sediments based on the relationships between magnetic properties and heavy metal concentrations. We conducted a systematic environmental magnetic and heavy metal study of the sediments of the core LGS from Lugu Lake in Southwest China. The results show that the concentration-related magnetic parameters (χ, χARM, and SIRM) in the core LGS showed an increasing trend from bottom to top. The results of rock magnetism indicated that the dominant magnetic particles were magnetite. Two sources of magnetic minerals can be distinguished by the correlations of χ vs. χfd% and χ vs. χARM/χ: the surrounding catchment and anthropogenic activities. In addition, Pearson correlation analysis and principal component analysis showed that the concentration-dependent magnetic parameters have significant correlations with heavy metal (Al, Ti, Fe, Cr, Ni, Cu, Zn, and Cd) concentrations as well as the Tomlinson pollution load index (PLI), indicating that there are essential linkages of sources, deposition, and migration between magnetic particles and heavy metals. Based on previously reported 137Cs and 210Pb data, the historical trends of heavy metal pollution in Lugu Lake were successfully reconstructed, and the causes of heavy metal pollution were mainly agricultural practices and atmospheric metal depositions from anthropogenic sources. The significant correlations between magnetic parameters, heavy metals, and the PLI indicate that magnetic parameters can potentially be used as an index of heavy metal pollution in lacustrine deposits.