work, humus samples for chemical analysis were collected in the counties of Nord-Trondelag, Oppland, and Buskerud (Fig. 1) during the period. 1960---1964.
Geoderma, 16 (1976) 317--325
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© Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands
R E G I O N A L DISTRIBUTION OF HALOGENS IN NORWEGIAN F O R E S T SOILS
J. L/~G and E. STEINNES
Department of Soil Science, Agricultural University of Norway, ~s-NLH (Norway) Institute for Atomenergy, Isotope Laboratories, Kjeller (Norway) (Received January 26, 1976; accepted June 3, 1976)
ABSTRACT L~g, J. and Steinnes, E., 1976. Regional distribution of halogens in Norwegian forest soils. Geoderma, 16: 317--325. Regional distribution of chlorine, bromine, and iodine in humus layers of Norwegian forest soils has been studied by means of neutron activation analysis. The halogen concentrations show a rapid decrease at increasing distances from the ocean, indicating that the supply of these elements to the soil is mainly through precipitation. Strong correlations between Cl and exchangeable Na ÷ and Mg2+, indicate atmospheric input to soils for these two cations as well.
INTRODUCTION
Discussions related to the chemical composition of soils have most often been based on the composition and properties of soil-forming rocks. For a long time the influence of the chemical composition o f precipitation on the soil chemistry was to a great extent neglected. One of the first to realize the significance of atmospheric inputs of chemical elements to soils seems to have been V. M. Goldschmidt. In his posthumous t e x t b o o k (Goldschmidt, 1954, p. 590) he points out that the supply through atmospheric precipitation is an important process in the cycle of the halogens, as well as sulphate, sodium, magnesium and some potassium. As this process goes on year by year and adds these substances to the uppermost soil horizons, it must, according to Goldschmidt's opinion, be a very important process in the evolution of soils, especially in coastal regions. More recent authors have expressed somewhat different views in this matter. According to Eriksson (1960) the amount of chlorine supplied to the rivers by natural processes represents predominantly oceanic constituents carried into the continents by the atmosphere. Correns (1956), on the other hand, in an extensive treatment of the geochemistry of the halogens, admits that a pDrtion of the halogens found in soil is contributed by rain water but concludes on the basis of available research that the major
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share of the halogens in soils comes from rock weathering. In the survey by Vinogradov (1959) the significance of atmospheric inputs to soils is clearly emphasized in the case of iodine and to a lesser extent of bromine. During the last two decades, a large-scale investigation of forest soils in Norway has been carried out by the Agricultural University of Norway and the National Forest Survey. The programme of this investigation includes registration of important properties of soil material and soil profiles in most of the productive forest areas of the country. Besides the field registration work, humus samples for chemical analysis were collected in the counties of Nord-Trondelag, Oppland, and Buskerud (Fig. 1) during the period 1960---1964. About 3,000 samples were collected in the three counties. As will be explained later, this material offered a unique opportunity to study the influence of elements supplied through precipitation on the chemical composition of soils. An investigation of the exchangeable cations, Na ÷, Mg2÷, and Ca2+, in these soils (L~g, 1968b) indicated a geographical distribution pattern showing good correspondence with observations on the chemical composition of the
Fig. 1. Sampled areas in Norway.
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precipitation. The cations, Na ÷ and Mg2÷, which are abundant in sea water, were f o u n d to be enriched relative to Ca 2÷ by a factor about 5 in podzol soils from the coastal districts of Nord-TrSndelag as compared to softs from central eastern Norway. This evidence of the importance of airborne supply with regard to the c o n t e n t of exchangeable cations in the soils led the present authors to focus attentian on the halogens, in which case there might also be reasons to assume distinct trends in regional distribution, because of the well-known association of these elements with the marine environment. EXPERIMENTAL
Collection of samples The humus samples were obtained from sample plots of 78.5 m 2 or 100 m 2 , regularly distributed in forest areas with an annual normal production exceeding 0.12 m3/1,000 m 2. The samples were taken from the central part of the humus layer if its thickness was 10 cm or less; in cases of thicker humus layers the depth of sampling was 5--10 cm. At least ten separate portions were collected at spots regularly distributed over the sample plot and mixed thoroughly to form one sample for analysis. The total number of samples taken in the general programme was about 1,000 in each of the counties of Nord-Tr6ndelag, Oppland, and Buskerud. For the present investigation, every fifth sample was taken for analysis. In all three counties, the collected samples predominantly represent Podzol profiles.
Determination of chlorine, bromine, and iodine The samples were subjected to neutron activation analysis t%r the determination of chlorine, bromine, and iodine. The fourth member of the halogen group, fluorine, could not easily be determined simultaneously with the available facilities. As the analytical m e t h o d used has been described in detail elsewhere (L~ig and Steinnes, 1972) only a brief account will be given here. Samples of 100--200 mg were irradiated for 5 min in the JEEP-II reactor (Kjeller, Norway) at a thermal neutron flux of 1 . 5 . 1 0 'a n cm -2 s -1, together with a halogen standard solution. The analyses were based on the radionuclides asC1 (t'A = 37.2 min), 8°Br (tlA = 17.6 min), and 12sI (tl/2 = 25.0 min), and a ~/-spectrometer based on a Ge(Li) solid-state detector was used for the activity measurement. For a great number of samples a radiochemical separation had to be carried out in order to remove interfering activities before ~/-spectrometry measurement. The reproducibility of the analyses, including possible inhomogeneous distribution of Halogens within the sample, was of the order of + 5%.
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SOME GEOGRAPHICAL AND METEOROLOGICAL F E A T U R E S OF S O U T H E R N NORWAY
Before presenting the data, some geographical and meteorological features of the investigated areas are described as relevant to the subsequent discussion. Fig. 1 shows a map of Norway up to a latitude of 65°N, including the forest areas sampled for the present investigation. Nord-TrSndelag is an area without large variability in topography and climate. Only small areas close to the Swedish border reach altitudes higher than 900 m. The climate ranges from a coastal to a slightly more continental type. A certain decrease in mean annual precipitation takes place from areas close to the coast (about 1,200 mm} to areas near the Swedish border (about 700 mm). The air-line distance between coast and border is about 150 km, on average. The precipitation is predominantly supplied through westerly winds. The region of eastern Norway, in which the Oppland and Buskerud counties occur, has a continental-type climate, except for areas close to Oslo fjord. The area is shielded by high mountain chains to the north and west, for which reason the precipitation is to a great extent carried by southern winds. This means that the precipitation falling in the northern part of this area may originate from air masses which have moved quite a long distance after having had contact with the ocean. The mean annual precipitation is about 600 mm in large parts of the area. In the districts along the Oslo fjord it is somewhat higher whereas in the northwestern valleys it is as low as 300 mm in some places. The districts in which the forest soil samples were obtained thus differ considerably in the amounts of precipitation and in distance from the sea. Otherwise, the properties of the Nord-Tr6ndelag soils appear to be similar to those of Oppland and Buskerud (L~ig, 1962, 1965, 1968a). The soil samples therefore seem well suited for studies of regional differences in the supply of chemical constituents to the soil through precipitation. RESULTS AND DISCUSSION
The contents of C1, Br, and I were determined in about 700 humus samples, all of which had been previously analyzed for other characteristics such as pH, loss on ignition, and exchangeable cations. For convenience of discussion, the data from the present study have been divided into 29 sub-groups on a geographical basis, each group comprising 15--30 samples. The location corresponding to each sub-group is indicated in Fig. 1. The numerical order of these sub-areas within each of two major areas has been so arranged as to indicate a decreasing influence of the marine environment as estimated from geographical and meteorological factors. The mean values for the concentrations of C1, Br, and I in the various subgroups of soil, are given in Table I. The C1/Br, Cl/I and Br/I ratios are also
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