Pertti Lahermo

Geochemistry and origin of saline groundwaters in the Fennoscandian Shield

Chemical and isotopic analyses of water from drill holes and mines throughout the Fennoscandian Shield show that distinct layers of groundwater are present. An upper layer of fresh groundwater is underlain by several sharply differentiated saline layers, which may differ in salinity, relative abundance of solutes, and O, H, Sr and S isotope signature. Saline groundwater can be classified into four major groups based on geochemistry and presumed origin. Brackish and saline waters from 50–200 m depth in coastal areas around the Baltic Sea exhibit distinct marine chemical and isotopic fingerprints, modified by reactions with host rocks. These waters represent relict Holocene seawater. Inland, three types of saline groundwater are observed: an uppermost layer of brackish and saline water from 300–900 m depth; saline water and brines from 1000–2000 m depth; and superdeep brines which have been observed to a depth of at least 11 km in the drill hole on the Kola Peninsula, U.S.S.R. Electrical and seismic studies in shield areas suggest that such brines are commonly present at even greater depths. The salinity of all inland groundwaters is attributed predominantly to water-rock interaction. The main solutes are Cl, Ca, Na and Mg in varying proportions, depending on the host rock lithology. The abundance of dissolved gases increases with depth but varies from site to site. The main gas components are N2, CH4 (up to 87 vol.%) and locally H2. The δ13C value for methane is highly variable (−25 to −46%), and it is suggested that hydrothermal or metamorphic gases trapped within the surrounding rocks are the most obvious source of CH4. The uppermost saline water has meteoric oxygen-hydrogen isotopic compositions, whereas values from deeper water plot above the meteoric water line, indicating considerably longer mean residence time and effective low temperature equilibration with host rocks. Geochemical and isotopic results from some localities demonstrate that the upper saline water cannot have been formed through simple mixing between fresh water and deep brines but rather is of independent origin. The source of water itself has not been satisfactorily verified although superdeep brines at least may contain a significant proportion of relict Precambrian hydrothermal or metamorphic fluids.

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.

ARSENIC AND OTHER TOXIC ELEMENTAL CONTAMINATION OF GROUNDWATER, SURFACE WATER AND SOIL IN BANGLADESH AND ITS POSSIBLE EFFECTS ON HUMAN HEALTH

The problems of contamination caused by arsenic (As) and other toxic metals in groundwater, surface water and soils in the Bengal basin of Bangladesh have been studied. Altogether 10 groundwater, seven surface water and 31 soil samples were collected from arsenic-affected areas and analysed chemically. The geologic and anthropogenic sources of As and other toxic metals are discussed in this paper. The chemical results show that the mean As concentrations in groundwater in the Char Ruppur (0.253 mg As L−1), Rajarampur (1.955 mg As L−1) and Shamta areas (0.996 mg As L−1) greatly exceed the WHO recommended value, which is 0.01 mg As L−1. The concentrations of As in groundwater are very high compared to those in surface water and in surface soil in the three (As-affected) areas studied. This indicates that the source of As in groundwater could be bedrock. The relatively high concentrations of Cr, Cu, Ni, Pb and Zn in surface water, compared to world typical value, are due to the solubility of metal ions, organometalic complexes, coprecipitation or co-existance with the colloidal clay fraction. In the soil, the elevated concentrations of As, Cr, Cu, Ni, Pb and Zn are due to their strong affinity to organic matter, hydrous oxides of Fe and Mn, and clay minerals.

The impact of selenium fertilisation on the distribution of selenium in rivers in Finland

Abstract Finland is a country covered by thin layers of glacial deposits, mainly till, on top of Precambrian igneous and metamorphic rocks. The environment is characterised by low selenium (Se) concentrations. To improve the Se intake of the population, Se-supplemented fertilisers have been used nationwide since 1985. This raises the possibility of undesirable environmental effects of the operation. The present study, the first one dealing with Se concentration of stream waters and stream sediments in Finland, throws light on the mobilisation of Se in the environment. The median Se concentrations (range) in stream waters and stream sediments were 67.5 ng 1 −1 (32–180 ng 1 −1 ) and 258 μg kg −1 (29–3940 μg kg −1 ), respectively. There was a highly significant correlation between the Se concentration of stream waters and sediments ( r =0.313, P n =204). The rainfall-related seasonal variations of the Se concentrations in stream water exceeded 100%. The stream water Se concentrations decreased from 1991 to 1992, possibly as the result of a reduction in the amount of Se added to fertilisers since 1991. The stream water Se concentrations correlated with those in well water and with cultivated field area per community. About 8.5% of the Se in stream waters was in particulate form. The fractions of the total Se in humic substances (36%) and selenate (35.7%) dominated the Se species of stream waters, while selenite comprised only 9.6% of the total Se. Cultivation and the use of Se-supplemented fertilisers may have temporarily increased the Se concentrations in headwater stream and river waters in Finland.

The national atmospheric deposition program

A total number of 1165 stream water and 1172 lake water samples were collected in two different projects in the autumns of 1990 and 1987, respectively. The sampling points in streams were determined to include a drainage area of ca 30 km2. The lakes were selected to represent the lakes in the size range of 0.01–10 km2. The anions have different distributions in the stream and lake water data sets. Stream waters are dominated by HCO3 (median value 200 μeq/l), which comprises over half of the anion sum. Organic anions and sulphates are of the same order of magnitude (ca 70 μeq/l), respectively, followed by chloride (40 μeq/l) and nitrate (ca 30 μeq/l). In lakes, sulphate (85 μeq/l) and organic anion (76 μeq/l) concentrations are higher than those of bicarbonate (64 μeq/l). Chloride concentrations in lakes are comparable to those of the streams (28 μeq/l), but nitrate (1 μeq/l) and fluoride contents (< 1 μeq/l) are very minor. The median concentrations of the main cations appear in the same successive order of magnitude in both stream and lake water data sets: Ca > Mg > Na > K > Al > H. The total amounts of cations (medians) in lake waters and streams are 260 and 450 μeq/l, respectively. The hydrogeochemical maps compiled for this study show elevated concentrations in coastal areas for most of the elements particularly in stream waters, which have a more uniform sampling network grid all over the country. In many cases, the same areal pattern is discernible in lake waters, although there are only a few lakes along the coast as the selection was targeted mainly on the upland areas with a higher lake density. These circumstances result in pronounced differences in the distribution of the concentrations. Small lakes show high individuality even in adjacent hydrological systems reflecting the different hydrographical conditions and soil and bedrock types of their catchments. The larger lakes with extensive catchment areas and higher amounts of dissolved solids have higher buffer capacity than small lakes. Therefore, the chemistry of larger lakes is more compatible with that of streams.

Hydrogeochemistry and sensitivity to acidification of streamwaters in crystalline areas of northern Fennoscandia

About 6,400 water samples were collected from small catchments in northern Finland and Norway above 66° N latitude as a part of the Nordkalott Project carried out jointly by the Geological Surveys of Finland, Norway, and Sweden. Electrical conductivity (EC) was measured in situ and Ca, Mg, Sr, Ba, Na, K, Si, Fe, Mn, Al, and Zn concentrations were determined from filtered and acidified samples by the ICAP method. The relative abundance of mafic, ultramafic, and carbonate rock components in the catchments is the most influential factor controlling the EC values and the main cation concentrations (Ca, Mg, Sr). These components also determine the HCO3 alkalinity or acid-neutralizing capacity (ANC) of streamwater. In the northern coastal belt, Na is derived largely from airborne sea salts, but in the southwestern corner of the research area it may be derived partly from relict sea salts in sediments. The concentrations of Na, K, and Si do not depend solely on the lithological environment. Fe and, to a lesser extent, Mn and Al occur in the highest abundances in the low-lying, intensely paludified southern part of the area, suggesting that these metals tend to go into solution and are transported in complexed forms with dissolved and colloidic humic matter. The areal distribution patterns of the main cations (Ca, Mg, Sr) and of some heavy metals (Fe, Mn) in streamwater are fairly consistent with those of till and minerogenic stream sediments, although, in a statistical approach, only a few significant correlation coefficients were established.

Radiogenic elements in Finnish soils and groundwaters

Abstract In Finland, U and Rn concentrations in groundwaters are highest in the south of the country in bedrock composed of granites or migmatites with abundant granite or pegmatite veins. The areal distribution patterns of U and Rn in groundwater from bedrock are consistent with U and Th anomalies in the fine fraction of till and with the external gamma dose rate measured on the ground surface. The U and Rn concentrations in groundwater from bedrock are only moderately correlated; hence the elevated U contents do not imply abundant Rn contents. Both elements are practically independent of other dissolved components. The exception is the moderate correlation between U and HCO 3 suggesting the occurrence of U-rich carbonates as fracture-coating minerals. In a few areas with U and Rn anomalies, the exceptionally high Rn concentrations in ambient house air pose a considerable health risk, particularly in detached houses founded on pervious sand and gravel deposits. Regardless of the potential health risk no radiological recommendations for U and Rn concentrations in potable water have been officially set in Finland.

Atmospheric sulfur deposition and streamwater quality in Finland

The correlation between sulfate concentrations in Finnish headwater streams and atmospheric sulfate deposition has been studied by using data from the streamwater chemistry in August–September 1990 and computed S deposition from the anthropogenic emissions. The sulfate concentrations and acidity in water are interpolated and smoothed into a deposition model grid. These data are compared with geological and pedogeochemical (glacial till) background information. The areas where the streamwater SO4 concentrations are mainly controlled by either anthropogenic S deposition or sulfur in till is estimated by applying the fuzzy Gustafsson-Kessel algorithm, which provides a soft clustering suitable for overlapping control factors. Residual areas can be well explained by the SO4-rich Littorina clay deposits. The higher overall background SO4 concentrations in streams in south Finland compared with central and northern Finland are an indisputable consequence of the heavier S deposition load in the south. However, anthropogenic sulfur deposition has a clear correlation with the sulfates in streamwaters only in northeastern Lapland impacted by the large industrial emissions in the Kola Peninsula. The secondary sulfide and sulfate minerals of marine Littorina sediments are dominating sources in the broad coastal belts, as are the primary sulfide minerals locally in the Pori-Vammala area, at the eastern end of the main sulfide ore belt between Lake Ladoga and the Gulf of Bothnia, in the Outokumpu area, and in the Peräpohja and central Lapland schist belts. Consequently, in addition to the anthropogenic deposition, there are natural sources of sulfur which cause acidity of streamwaters.

MINERALOGICAL, GEOCHEMICAL, AND MICROBIOLOGICAL ASPECTS OF IRON DEPOSITION FROM GROUNDWATER

Iron is readily soluble constituent in groundwater and the solubility is further increased by its chelation with organic matter. Iron, and minor elements such as Mn, are undesirable in water supply systems as they cause problems of taste, odour, and discolouration, and clogging and deposition in the screens and pipelines which eventually leads to corrosive conditions. The removal of iron can be accomplished by a sequential treatment involving oxidation, settling, and filtration with various modifications but, as well as the high cost of the treatment, incomplete iron removal and associated problems are frequently encountered.

Environmental factors affecting the acid neutralization capacity of Finnish glacial till deposits

A batch titration method for acid neutralization buffer capacity (ANC) was used to monitor the stage of leaching and resistance to acid precipitation of surficial deposits. Four till profiles, including podzol horizons, were sampled at different geographical, climatological and environmental sites in Finland. The fresh samples (<0.7mm) were air dried (25°C), homogenized and then equilibrated at increasing acidity (0, 0.66, 3.33, 6.66 and 10.00 mM·1‐1 of H2SO4) in capped polyethylene tubes. After centrifugation and measurement of the pH in the tubes, the contents of leached elements were analysed using colorimetric methods for Fe(II), Al and Si, and flame‐AAS methods for other elements (K, Ca, Fe, Mn and Zn). A sequential extraction procedure at different time intervals was used for Fe oxides. The results indicate that the ANC is strongly affected by the environmental geochemistry of iron. The leaching of Fe from bedrock and sediments accompanied by seasonal and biogeochemical cycles, and rprecipitation of...