Geographic Trends in the Accumulation of Heavy Metals in Mosses and Forest Litters in Karelia

Heavy metals (HMs) are considered to be among priority technogenic pollutants. To solve ecological problems related to the environmental effects of HMs in the Russian North, it is necessary to make a detailed inventory of their contents in natural objects in different areas with regard to the diversity of climatic and soil-geochemical conditions and the degree of industrial development in these areas. It is known that mosses are informative indicators of aerotechnogenic environmen-tal pollution. Forest litters are important as the struc-tures retaining and accumulating various pollutants. The contents of HMs in the soil depends on the distance from local pollution sources and, to a large extent, on the pattern of pollutant transfer in the upper layers of the atmosphere. An important role belongs to region-specific natural factors, i.e., local climate, relief, vege-tation, and soils.

The Republic of Karelia is located on the Baltic shield, which forms the northwestern part of the Russian platform. The vast area of the republic (117300 km 2 )

extends from the north to the south for 672 km; hence, the climate, geological structure, hydrographic net-work, soils, and vegetation in different parts of the republic are heterogeneous.

The climate in Karelia is relatively mild, with a long mild winter and a short cool summer; considerable cloudiness, high humidity, and changeable weather are characteristic of all seasons. The prevailing form of atmospheric circulation over the territory of Karelia is the western transfer of air masses. The formation of precipitation is also accounted for by moisture evapo-rated from the White Sea and numerous lakes and bogs, which cover one-third of the Karelian territory. Vegeta-tion has a considerable effect on the migration of sub-stances. In Karelia, coniferous forests are the dominant type of vegetation.

The spectrum of possible sources of technogenic HM pollution in Karelia is wide. There are 10284 sources of industrial emissions into the atmosphere, and most of them are concentrated in the cities of Petrozavodsk, Segezha, Kostomuksha, and Kondo-poga. The total amount of emissions from large indus-trial enterprises of these cities reaches 128600 tons per year. A complex combination of technogenic factors and natural geochemical conditions in Karelia deter-mines the pattern of HM distribution over its territory. In this work, we studied green mosses (Pleurozium schreberi, Hylocomium splendens) and forest litters. The former indicate the state of the atmosphere over a relatively short period of time (approximately three years), and the chemical composition of the latter reflects the impact of long-term industrial pollution (over more than ten years). The chemical analysis of mosses and litters can provide information about the sources, ranges, and extents of environmental pollu-tion, as well as reveal major pollutants. Our studies were performed by internationally accepted methods (Atmospheric Heavy Metal…, 1996).

Samples of green mosses and forest litters were taken from test plots of the bioindication network cov-ering the entire Karelian territory. The contents of iron, manganese, chromium, copper, nickel, zinc, cobalt, lead, and cadmium in the samples were determined by atomic absorption spectrometry.

We also estimated the effects of climatic parameters (wind rose, precipitation rate) on the distribution of aerotechnogenic pollutants containing HMs over the territory of the republic. The data on each of eight wind directions recorded by the Karelian hydrometeorologi-cal observatory (N, S, W, E, NE, NW, SE, SW) was assessed quantitatively with respect to wind stability, i.e., the frequency of its occurrence as a percentage of the total number of observations (without calm winds). Taking into account wind directions in winter and sum-mer and different weather patterns in the cold or warm periods of the year, the parameters of stability were averaged. Thus, we distinguished cold winters with lit-tle snow from warm, snowy winters and cold, rainy summers from warm, dry summers.

To estimate the correctness of grouping (homogene-ity within each group and heterogeneity of different groups), stepwise discriminant analysis was used. Its results confirmed that all five groups were identified correctly: they proved to be internally homogeneous and did not overlap with one another. The main dis-criminators (major pollutants) in forming regional groups with respect to the pollution of mosses are nickel, cobalt, chromium, and cadmium. According to their significance for group formation, they can be arranged in the following series: Co > Cr > Ni > Cd. In the case of forest litters, the main discriminators arranged in the same order are as follows: Fe > Mn > Pb > Zn.

The results of pairwise comparisons of the regional groups in the three-factor spaces with respect to HM contents in mosses and forest litters (Table 3) demon-strated that differences were significant only for groups I and II, especially concerning the contents of cad-mium. In the second group (Segezhskii and Med-vezh’egorskii raions), differences between HM accu-mulation in mosses and forest litters were significant for the majority of elements (especially for copper) and nonsignificant for zinc and iron.

Thus, we revealed the existence of geographic trends in the distribution of pollutants over the Karelian territory and their accumulation in mosses and forest litters.