relation between till geochemistry and the occurrence ... - Arkisto.gsf.fi

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Geological Survey of Finland, Special Paper 9 Pertti Hari, Alf Björklund, Hannu Rita and Anneli Ylimartimo samples are from a depth of 1-2 m, which is well below the sai1 horizon in this area. After drying, < 0.06 mm fraction was sieved from the samples and leached at + 80°C for 1 h in 7N aqua regia. An extract was analyzed by induction-coupled plasma atomic emission spectrometry (ICP). An index was developed based on knowledge of the effects of acid deposition on soil properties and tree nutrition . The values of the variables describing the concentrations of K, Mg, Ca, Al, Fe, and Mn were standardized. The first principal component coefficients of these variables were roughly equal. This supported the choice of equal weights in the definition of the index, which we here call the GEI (Geochemical Environmental Index): (K + Mg + Ca)-(Al + Fe + Mn). We use this index to describe the geochemical properties of till. Unfortunately, there is no systematic inventory of the area of damage by scleroderris canker in Finland; the available records are sporadic and often based on subjective observations. To obtain a more quantitative picture of the frequency of scleroderris canker an experimental survey was ar- ranged in July, 1986, in southern Finland in the above-mentioned 100 kmx 300 km area. The method was to involve a quick-survey to estimate the disease intensity near by the geochemical survey points. The most severely damaged young pine stand not more than in the 0.5 km neighborhood of each geochemical sampling point was chosen. In each standthe proportion of all trees having 1) recovered crowns with one or more changes of a leading shoot, 2) crowns with recent browning of shoots, and 3) dead crowns was measured. The sum of the values of these three response variables was then calculated for each stand to describe the long-term situation of damage occurrence. We use this sum as a disease index. The 80 pine stands surveyed were ranked according to the value of the GEI, and 20 stands with the lowest and 20 stands with the highest GEI values were chosen for the comparison. Owing to the strong skewness of the distribution of the disease index these two chosen pine-stand-groups were compared using the Mann-Whitney U-test. RESULTS AND DISCUSSION It has been normal practice to predict the geochemistry of glacial overburden on the basis of the known geology of the bedrock. Accordingly, predictions of the acidification sensitivity of soil in an area have been made on the basis of bedrockgeological maps (Kommitten Miljö 1982, Shilts 1981). Recent geochemical maps over large regions - e.g. maps of the Nordkalott project (Be~lviken et al. 1986), maps of the Geochemical Atlas of Finland, and maps of the Geological Survey of Finland - show that the areal distribution of the aqua-regia extractable contents of most elements correlates with the main bedrock units only to a limited extent. The reason for the disagreement and the source of increased contents unrelated to bedrock geology has not yet been explained. Björklund (1988a, b), who pointed out this feature, suggests a relation between past hydrothermal processes, with related alteration and metal enrichment in the bedrock, and an increase in the mobile phases of elements in the overlying glacial drift. He suggests that deep salt groundwater and ascending geogas may play an important role in the transport and enrichment of the mobile phase of elements in overburden. The pine stands in the lowest quartile of the GEI value had a higher disease index mean than the pine stands in the highest quartile. We used the Mann-Whitney U-procedure to test the hypothesis of equal means and were able to reject it with the p-value of 3.15 %. Areas susceptible to scleroderris canker can thus be predicted using the GEI (Figs. 2 and 3). Figure 2 shows a color image of the moving median (Björklund & Gustavsson, 1987) for GEI based on the data of the Geochemical Atlas of Finland. The color image of the moving median of GEI in Fig. 3 is based on the denser sampling grid of the Geological Survey of Finland. Because there is no systematic inventory of the area damaged by scleroderris canker in Finland the compatibility of the damaged area with the prediction in the Figs. 2 and 3 cannot be tested. The disease frequency has been recorded very sporadically and the records are often based on subjective observations. A more detailed, long-term survey of the damage by scleroderris canker in Finland is needed. The results of the present study give support to the hypothesis that till geochemistry and the occurrence of scleroderris canker are related to each
Geological Survey of Finland, Special Paper 9 Relation between till geochemistry and the occurrence of scleroderris canker in Finland b GEOCHEMISTRY OF TILL -62 pm + - Aqua Regia leach --i Fig. 2. The moving median for GEI, (K + Mg + Ca)-(Mn + Fe + Al), based on the data of the Geochemical Atlas of Finland.
Page 1 and 2: Environmental geochemistry in north
Page 3: Fig. 1. The study area measuring 10
Page 7: Geological Survey of Finland, Speci

relation between till geochemistry and the occurrence ... - Arkisto.gsf.fi

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