John F. Boyle

Inorganic Geochemical Methods in Palaeolimnology

Inorganic geochemical analysis of sediment has played a central role in palaeolimnology since its establishment as a research field. This chapter outlines methods that can be applied, explores the issues affecting reliability of interpretations, and refers readers to the appropriate literature. A distinction is made between inorganic geochemical palaeolimnology and inorganic geochemistry in general. While sharing many techniques and information sources, the two subjects differ fundamentally in purpose. Inorganic geochemistry aims to understand the chemical properties of the natural world, and the behaviour of chemical substances within it. Geochemical palaeolimnology uses such information to describe and quantify the environment. Furthermore, whereas palaeolimnological analysis is about lake, catchment or even landscape scale processes, geochemistry often considers minute scales. This contrast in scale has lead to conflicting interpretations. Geochemists working with laboratory experiments, and studying speciation and small-scale mobility, emphasize complexity. Palaeolimnologists, on the other hand, tend to look at large scale phenomena, and often find consistent patterns, even where a full geochemical understanding is lacking. The two disciplines should not be seen as separate. Inorganic geochemistry feeds into geochemical palaeolimnology because it is important to have a good understanding of the behaviour of the elements being measured. Conversely, palaeolimnological data can help to constrain geochemical models. Nevertheless, the contrasts in purpose and scale must be kept firmly in mind. A further distinction is made between organic and inorganic methods. For many inorganic elements, behaviour is highly dependent upon organic substances, and the two topics cannot be treated in isolation. Rather, inorganic methods must include a basic evaluation of organic components.

Rapid elemental analysis of sediment samples by isotope source XRF

Energy dispersive isotope-source X-ray fluorescence (XRF) analysers are little used in academic environmental research, in spite of being ideally suited to a number of tasks. In this paper an XRF method is tested by measuring a wide range of environmental materials of known elemental composition. Precision, accuracy and detection limits are presented.Using isotope-source X-ray fluorescence analysis, the total concentrations of Si, Ti, Ca, K, Fe, Mn, Cl, S, Nb, Ni, Pb, Rb, Sr, Zn and Zr can be determined in soils and sediments at a rate of >70 samples per day. The combination of speed and accuracy makes the technique ideal for three classes of application within environmental research. First, in sediments and soils that are highly heterogeneous, reliable characterisation is more dependent upon the number of samples measured than on measurement precision or accuracy. Under these circumstances the method is sufficiently accurate to be used alone. This is also the case where there is high and wide ranging contamination of sediment or soil by Pb and Zn. Second, major elements (Si, Ti, Fe, Ca, K and S) can be measured with sufficient accuracy in sediments and soils to aid the interpretation of other sediment chemical analyses. Third, the technique is ideal for the rapid screening of sediment or soil, allowing effective targeting of samples for more time consuming or expensive analyses. The XRF method presented here offers rapid, non-destructive total elemental analysis of sediments and soils that is sufficiently accurate to be useful in environmental research.

Detecting atmospheric pollution in surface soils using magnetic measurements: a reappraisal using an England and Wales database.

Industrial activity such as burning of fossil fuels produces magnetically enhanced particulates. These particulates consist of coarse-grained multidomain and stable single domain magnetic minerals. Two threshold values of low field magnetic susceptibility (chi(LF)) and frequency dependent susceptibility percentage (chi(FD)%) discriminate ferrimagnetic minerals of these sizes and can act as a tracer of magnetic pollution. Application of the thresholds to a magnetic topsoil data set (n=5656 across England and Wales) revealed 637 samples potentially dominated by pollution particulates. The magnetic parameters of these samples display a negative correlation with distance to urban areas and positive correlations with metals associated with anthropogenic activity (Cu, Pb, and Zn). Results of experimentation with threshold values and modelling of magnetic anomalies suggest that regional factors such as geology and potential for pedogenic secondary magnetic enhancement should be considered when setting threshold values.

Sedimentary evidence for changes in the pollution status of Taihu in the Jiangsu region of eastern China

As part of a study using lake sediments to determine the extent and causes of human impacts to lakes along an east–west transect following the Yangtse River, sediment cores were taken from Taihu in eastern China. Previous studies have focussed on the impacts of direct inputs of pollutants from municipal and industrial wastewater but little work has been undertaken on trends in atmospheric deposition from the many industrial sources surrounding the lake. Analysis of the Taihu sediment cores for atmospheric pollutant indicators such as trace metals, magnetic parameters and spheroidal carbonaceous particles (SCPs) show the lake has become increasingly contaminated over the last 40–50 years. Sediment levels of atmospherically deposited pollutants are currently similar to some of the more contaminated lakes in Europe. Further, sediment nitrogen, phosphorus and geochemical analyses confirm the dramatic increase in eutrophication at the site and periods of recent soil erosion in the catchment.

Lake-sediment evidence for local and remote sources of atmospherically deposited pollutants on Svalbard

Twenty-one lakes along the west coast of Svalbard were cored between 28 July and 14 August 1995. Five cores were 210Pb dated and analysed for spheroidal carbonaceous particles (SCPs), indicators of deposition from fossil-fuel combustion sources, and trace metals. Surface and pre-industrial levels of five cores were analysed for 10 polychlorinated biphenyl (PCB) isomers and 16 polycyclic aromatic hydrocarbon (PAH) compounds, whilst all 21 surface sediments were analysed for SCPs. Temporal and spatial trends in the atmospheric deposition of pollutants were identified. Whilst temporal patterns of deposited pollutants may have been truncated due to concentrations falling below the limits of detection, spatial patterns showed elevated levels of SCP, PAH, PCB, and possibly Pb within 60–70 km of Isfjord. Tenndammen (U), the closest site to Longyearbyen, showed the highest levels of contamination for all pollutants. Differences in the deposition patterns of PAH and PCB are thought to be due to local sources of PAH from coal combustion whilst PCB sources are remote. It is concluded that the impact from atmospheric deposition on Svalbard is due to a combination of spatially limited local sources superimposed on a broad-scale, long-range pattern.

Association between magnetic properties and element concentrations of Liverpool street dust and its implications

Ninety-seven street dust samples were collected in a sampling period and 19 sites were revisited. Comparison between 97 sites and 19 revisited sites, using t-test and one-way analysis of variance (ANOVA), suggests that representative magnetic properties, and mean values of some element concentrations and the organic matter content may be obtained with a small number of samples from a sampling period of one or several days. Correlation analysis and factor analysis were applied to investigate associations between magnetic properties and between magnetic properties and element concentrations. The results suggest mixed contributions of magnetic material from urban and natural sources, probably mainly urban sources. Finally, this study may suggest a possible approach for source identification of magnetic material in pollution studies.

Redox remobilization and the heavy metal record in lake sediments: a modelling approach

The issue of whether heavy metal concentration profiles in lake sediments are vulnerable to redox mediated post-burial alteration stubbornly refuses to go away. Such behaviour is well-known in iron and manganese, due to great contrasts in the solubility of the reduced and oxidized chemical forms. A numbers of trace elements that also exhibit more than one oxidation state in lake sediments have also been shown to undergo diffusive migration in response to redox gradients (e.g., As, Co, Cr, V). What remains unclear is whether elements like Cd, Cu, Pb and Zn, that have only one stable oxidation state in sediments, are also subject to alteration. This paper reviews existing evidence and presents a model, based on current knowledge, to constrain the likely effects. It is concluded that some migration is likely, but that this is only significant at extremely low sediment mass accumulation rates. The formulation of the model highlights the need for further information about the physical form of iron and manganese oxyhydroxides in lake sediments.

Sediment heavy metal record in Lake Baikal: natural and antrhopogenic sources

Geochemical analysis of six radiometrically dated short cores of recent sediment from Lake Baikal shows clear evidence of enhanced Pb supply. However, the sediment concentration increases are very small; the average Pb concentration rises from a baseline value of 10.9 μg g-1 to a peak value of only 14.8 μg g-1. In contrast to the more polluted lakes commonly studied in Europe and North America, variation in Pb concentration is far more strongly influenced by natural variation than by pollution. In sediment deposited over the last 150–200 years 73% of the variance in the sediment Pb concentration can be accounted for by variation in bulk composition of the sediment, and by atmospheric pollution. Factors influencing Pb concentrations over this time period are, in order of decreasing average importance (fraction of total variance explained), catchment supply (indicated by 226Ra activity variation) (43%), anthropogenic Pb emissions (24%), and dilution by ferromanganese hydroxides (6%). On longer (1000s of years) time scales dilution by biogenic silica is probably more important.The recent enhanced supply of catchment Pb correlates with accelerating accumulation rates, indicating a link with enhanced erosion. Anthropogenic sources dominate only in the southern basin, where local fossil-fuel burning industry is situated. The evidence for a local industrial source for the Pb pollution is strengthened by the high correlation between the inventories for Pb and for spheroidal carbonaceous particles. The absence of detectable anthropogenic Pb enrichment in the northern part of the lake suggests that long-distance Pb pollution is small compared with the local natural supply.

Storage and distribution of trace metals and spheroidal carbonaceous particles (SCPs) from atmospheric deposition in the catchment peats of Lochnagar, Scotland

Lochnagar is a remote mountain lake to the south-east of the Cairngorm region in Scotland. Its catchment receives anthropogenic trace metals solely from atmospheric deposition. Ten peat cores were taken from the catchment and analysis confirmed that they have been contaminated by trace metals. The peats have an high affinity for trace metals and this results in metal accumulation in the surface peat layers. The formation of trace metal sulphides may also reduce remobilisation. In this way, trace metals derived from atmospheric deposition have been scavenged and accumulated. In contaminated peat layers, 77.4% Hg, 89.6% Pb, 93.4% Cu, 72.4% Zn and 86.5% Cd of the total stored are from anthropogenic sources. The accumulated trace metals in the peats can potentially influence the lake system through erosion. Spheroidal carbonaceous particle (SCP) profiles were used to date the peat cores. By referring to the SCP profiles in the peats and comparing these with the trace metal profiles in the lake sediments, the mobility of trace metals in the catchment peats is confirmed.

Association between the organic matter content and magnetic properties in street dust, Liverpool, UK

The organic matter content of street dust in Liverpool, UK, is measured for five particle size fraction and bulk samples. The content decreases significantly with increasing size for fractions 300 μm. The magnetic measurements indicate that the dominant magnetic component is multidomain grains of ferrimagnetic minerals and that superparamagnetic and stable single domain ferrimagnetic grains and non-ferrimagnetic minerals are present in small magnetic concentrations. There is a close association between the organic matter content and frequency-dependent susceptibility (χFD percentage), with a significant correlation for 63-μm fraction and <1000-μm bulk samples. The ratio χARM/SIRM shows a highly significant correlation with the organic matter content for <150-μm fraction samples. This study suggests that simple, rapid, and non-destructive magnetic measurements could provide useful information about source apportionment of organic matter in street dust.