Timo Tarvainen

The problem of defining geochemical baselines. A case study of selected elements and geological materials in Finland

Abstract Although the term ‘geochemical baseline’ appears in the international geochemical mapping programmes IGCP 259 and 360, it has never been well defined. Several considerations relevant to such a definition are discussed. A geochemical baseline for an element refers to its natural variations in concentration in the surficial environment. Geochemical baselines were studied in Finland by comparing results from regional geochemical mapping programmes based on samples of till, clay and organic stream sediment. The geochemical background changes regionally with the basic geology and locally with the type and genesis of the overburden. Baseline concentrations depend on sample material collected, grain size and extraction method. In Finland, concentrations of potentially harmful elements tend to be higher in fine-grained marine and lacustrine sediments than in glacial till. Concentrations are also systematically higher in the

Baselines of certain bioavailable and total heavy metal concentrations in Finland

Abstract “Total” (hot aqua regia extraction) and “bioavailable” (acid ammonium acetate EDTA extraction) heavy metal concentrations were measured for 90 basal till samples in Finland. The study covers the whole country. The “total” natural concentrations of several heavy metals in many places exceed the Finnish guideline or limit values designated for contaminated land. The “bioavailable” concentrations are usually only 1–5% of the “total” concentrations. The correlations between “total” and “bioavailable” concentrations were significant for Cr (Pearsons correlation coefficient 0.455∗∗, N=87), Cu (0.452∗∗, N=89), Ni (0.216∗, N=89), Pb (0.325∗∗, N=89), V (0.613∗∗, N=90) and Zn (0.569∗∗, N=89). ∗∗ Signifies that the correlation is significant at the 0.01 level, and ∗ signifies that it is significant at the 0.05 level.

Sources of trace metals in streams and headwater lakes in Finland

Distributions of Mn, Zn, Cu, Ni, Cr, Pb, As, and Cd in Finnish surface waters were studied by comparing two data sets: samples from 154 headwater lakes collected by the Water and Environment Administration in 1992 and samples from 1165 headwater streams collected during the environmental geochemical mapping program of the Geological Survey of Finland in 1990. It was expected that headwater lakes with catchments smaller than 1 km2 and high lake percentage (ratio of lake area to catchment size) would be more influenced by atmospheric trace metal deposition than the streams, with average catchment size of 30 km2.The lakes with highest arsenic concentrations lie in an area with greenstones and arsenic-rich black schists. The same lakes have high copper concentrations, which evidently are derived from the Cu-rich greenstones of the catchment. The high copper concentrations of streams and lakes in the industrialized region of the southwest coast are due to several anthropogenic sources.The highest concentrations of chromium occur in brown stream and lake waters rich in humic matter, while manganese and zinc concentrations, which are controlled by acidity, tend to be elevated in low-pH waters. The high nickel concentrations in lakes in southwestern Finland probably are due to anthropogenic input, while Ni anomalies in stream and lake water in eastern Finland are correlated with high Ni contents of glacial till. The lead concentrations in lakes are mainly of airborne anthropogenic origin.The pattern of atmospheric deposition is reflected in the concentrations of Cd, As, Cu, Zn, and Ni in headwater lakes, but land-use, the natural distribution of metals in the overburden, water acidity, and the amount of humic substances influence the distribution of trace metals in both lakes and streams. Thus the trace metal distribution in headwater lakes cannot be used alone to estimate the contribution of anthropogenic atmospheric deposition to metal anomalies in Finnish surface waters.

Baltic soil survey: total concentrations of major and selected trace elements in arable soils from 10 countries around the Baltic Sea

Agricultural soils were collected from 10 European countries over a 1,800,000 km2 area surrounding the Baltic Sea. The sampling density was 1 site/2500 km2. Two samples were taken at each site: topsoil 0-25 cm (ploughing layer, Ap-horizon) and subsoil (bottom samples, usually B- or C-horizon) at an approximate depth of 50-75 cm, well below the ploughed layer. The samples were analysed for total element concentrations of 41 elements by WD-XRF. Analytical results for both layers are quite comparable. Large differences between element concentrations and variations can be observed for most elements when the different countries are compared. The Nordic countries show considerably higher concentrations and variations for quite a number of elements [Al, Fe, (Mg, P), Ti, Ba, Sc, Sr, V] in their agricultural soils. This is an expression of geology, the relatively younger age of the soils here and of the climatic conditions (reduced weathering rates). Regional geochemical maps demonstrate that geology overwhelmingly dominates the total concentration of chemical elements as observed in the agricultural soils. The three (four) large tectonic units (Caledonian mountain chain, Fennoscandian Shield and the northern and southern eastern European Platform) composing this area are all reflected in the regional maps.

Interpolation methods for geochemical maps : a comparative study using arsenic data from European stream waters

A geochemical map of As in water from the FOREGS Geochemical Atlas of Europe, performed using the Alkemia interpolation method based on moving weighted median (MWM), and a comparable map prepared by kriging are compared with an As map prepared with a new multifractal inverse distance weighted (MIDW) interpolation method using GeoDas™ software. The colour scale classification of the MIDW interpolated map of As is based on the concentration–area (C-A) fractal method which allows images to be subdivided into components representing specific features on the ground related, for example, to geology. Conventional techniques, such as MWM and kriging, are shown to smooth out the local variability of the geochemical data. The problem is most serious in maps prepared by kriging which erroneously show large areas of Europe to have high levels of As in water. On the other hand, MIDW creates a geochemical map in which information about the local data structure is retained. This is essential in distinguishing anomalies from background values. The information provided by background and anomaly maps, using the MIDW and fractal filtering methods, are shown to give more reliable upper limits of background values.

The geochemical correlation between coarse and fine fractions of till in southern Finland

Since the 1950s, the <0.06 mm fraction of till samples has been sieved off and analysed, for purposes of mapping the geochemistry of Finland. The primary objective of the mapping was reconnaissance, regional and local scale exploration. The data are now stored and readily available from the relational ALKEMIA databases at the Geological Survey of Finland (GSF). Data on the natural distribution of nutrients, base cations and trace metals are also important for addressing environmental issues. However, a coarser fraction (< 2 mm) has been preferred in several environmental studies. To evaluate the usefulness of the old data in modern environmental studies, the element concentrations in the fine and coarse fractions of 618 till samples from southern Finland were compared using four data sets: 1. analyses based on total dissolution of the fine till fraction, as published in the Geochemical Atlas of Finland; 2. aqua regia soluble concentrations of the fine till fraction; 3. analyses based on total dissolution of the coarse till fraction; and 4. aqua regia soluble concentrations of elements in the coarse till fraction. The total concentrations of Na, Ca and K in the coarse till fraction reflected well the chemical composition of the underlying bedrock, while the distribution of the same elements in the fine fraction was ambiguous. By contrast, the concentrations of trace elements in the two fractions correlated well, although the concentrations were higher in the fine fraction. With the aid of linear relationship functions, the analytical results from the fine fraction of till can be used to estimate the natural distribution of trace elements in the coarser till fraction.

Weathering release of heavy metals from soil in comparison to deposition, litterfall and leaching fluxes in a remote, boreal coniferous forest

Soil weathering release rates of Cd, Cu, Ni, Pb and Zn were determined at 4 plots in a forested catchment located in eastern Finland. The rates are compared with atmospheric deposition, litterfall and leaching fluxes at two of the plots. The soils were Haplic Podzols and developed in glaciofluvial deposits or glacial till having sandy loam to loamy sand fine-earth (<2 mm) textures. The bedrock in the area consists of granodiorites. Total concentrations of heavy metals in the <2 mm fraction of the parent material were determined from a mixed acid (HF and HClO4) digestion using ICP–MS. Weathering rates were calculated assuming that the molar ratio of heavy metal to base cation (Ca+Mg) weathering rates (previously determined by the Zr depletion method) equalled the molar ratio of heavy metal to base cation concentrations in the parent material. The mean weathering release rates were 8.3 μmol m−2 a−1 for Zn, 5.2 for Ni, 4.3 for Cu, 1.5 for Pb, and 0.011 for Cd. These rates were similar to the deposition, litterfall, and leaching fluxes for each metal. Weathering is therefore an important process in the heavy metal biogeochemistry of boreal, forest ecosystems.

The distribution of uranium over Europe: Geological and environmental significance

Abstract The variation of baseline levels of uranium in soil and stream sediments over Europe is described, based on new data prepared by the Forum of European Geological Surveys (FOREGS). The samples have been collected and analysed according to the protocols established for the International Union of Geological Sciences/International Association of Geochemistry and Cosmochemistry (IUGS/IAGC) Working Group on Global Geochemical Baselines. The baseline levels of U vary between 0·21 to 53 mg kg-1 in topsoils, 0·19 to 30 mg kg-1 in subsoils and < 1 to 59 mg kg-1 in stream sediments. There is generally good agreement between the levels of U in the three sample types, and the median concentration in all three media is approximately 2 mg kg-1. The most anomalous baseline levels occur over the Variscan orogen, especially areas into which late postorogenic radiothermal high heat production (HHP) granites were emplaced. Spiderdiagrams based on trace element levels and rare earth element (REE) plots, confirm the association between the highest U anomalies and evolved radiothermal granites. High values are also associated with parts of the Alpine terrain especially in Slovenia, where there are historical U workings, and Southern Italy, where high values of U reflect contemporary volcanism. In contrast, much of the Caledonides of North West Europe and the Precambrian of the Baltic Shield and East European craton and its overlying sedimentary cover have very low values, generally < 4 mg kg-1. The results suggest that the main concern for the environment and human health from U, and the Th and K with which it is generally associated, is the naturally occurring total gamma radiation and radon potential associated with radiothermal granites. This is likely to be especially important where the granites are mineralised and have been worked historically, for example in the North West of the Iberian Peninsula where U and its decay products are likely to be more dispersed in the surface environment. The study also indicates the value of multielement data in distinguishing between anthropogenic and naturally occurring anomalies.

Visualization of geochemical data on maps at the Geological Survey of Finland

Abstract Software for presentation of geochemical data on maps has been integrated into a user-friendly package, ALKEMIA, at the Geological Survey of Finland (GSF). ALKEMIA contains procedures for generating dot maps, colour surface maps, shaded relief maps, and vector images, and for interpolating and smoothing irregularly gridded data. Combining dots and colour surfaces provides a means of visually integrating up to three variables on a map, revealing the spatial relationships between them. The methods employed are described in detail, particularly the moving weighted median, which has been widely used at the GSF for interpolating and smoothing geochemical and other numerical data. Several geochemical and oncological atlases and series of maps have been produced with these methods.

Geochemical mapping and databases in Finland

Abstract Regional geochemical maps in Finland have been produced from many different programmes. The scale of sampling, the material collected and the analytical methods used varied according to the aim of the study. The entire country was covered at a reconnaissance scale using glacial till, groundwater, surface water and organic stream sediments as sampling media. Glacial till was sampled throughout the country at a regional scale. Local scale mapping and detailed geochemical studies are carried out in selected areas. The main analytical methods have been ICP-AES and ICP-MS, but other methods were used when necessary. In assaying solid material, both total decomposition and strong acid (aqua regia) leaching were used. The results are stored in ALKEMIA, a database developed in the geochemistry department of the Geological Survey of Finland. The data are available as tabulated ASCII files and as digital image files on diskettes, or as various types of symbol and colour maps from desired areas or map sheets. Two examples of the application of geochemical mapping data in prospecting and in environmental research are presented. Indications of the presence of gold and multiple-sulphide ore deposits have been the most useful results obtained from a prospecting standpoint. On the environmental side, reconnaissance scale geochemical mapping data gave more reliable information on the base cation concentration than bedrock maps, making them particularly valuable in devising an acidification assessment model.