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

Key words: heavy metals, accumulation, mosses, litters, Karelia, multivariate statistical analysis.

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.

We developed an original approach to the analysis of HM distribution over the Karelian territory with respect to each individual element and their combinations, Geographic Trends in the Accumulation of Heavy Metals in Mosses and Forest Litters in Karelia which allowed us to assess the structure of their emis-sion from different sources. This approach involves the combined use of the methods of multivariate statistical analysis in the following sequence: stepwise regression analysis is used for selecting the most efficient climatic indices for each element; factor analysis, for assessing the structure of HM distribution with respect to combi-nations of elements; and stepwise discriminant analy-sis, for estimating the correctness of results obtained at the preceding stages. Another reason for using factor analysis is that HMs are distributed over the territory in certain combinations, rather than individually. Our results confirmed this fact (see below).

Regression analysis was used for assessing HM accumulation in mosses and forest litters with regard to the effects of most significant climatic indices on each element (Table 1). The results showed that precipitation generally has a weak effect on HM distribution; we can note only a slight influence of this parameter on the deposition of copper, nickel, and cadmium. Westerly winds bring to the Karelian territory mainly cobalt, lead, chromium, and manganese; east-erly winds, zinc and lead; northerly winds, zinc and nickel; and southerly winds, chromium and lead. The input of lead depends on winds to the greatest extent. The westerly winds are responsible for the distribution of a broader spectrum of HMs. The regression analysis of HM distribution and accumulation in green mosses and litters produced similar results. By factorizing the matrices of correlation between the values of pollutant distribution in mosses and forest litters, calculated by regression equations, we identified three factors (F1 , F2 , and F3) accounting for 80.0 and 77.1% of the total variance for mosses and litters, respectively. Each factor reflects one aspect of the inter-nal structure of HM combinations formed upon their distribution over the territory of Karelia (Table 2). Mosses.By F1 , the combination of Zn, Cr, Co, and Pb is distinguished (high positive loads). Factor F2, by high positive loads, reflects the distribution of the com-bination of copper and manganese over the territory. High negative loads may be used for tracing pollution with lead and cadmium, with the prevalence of the lat-ter. By F3, the combination of iron and nickel is distin-guished (high positive loads); a small negative load indicates the distribution of cobalt over the territory. Forest litters.By F1, the combination of manga-nese, cobalt, iron, and copper (with the prevalence of manganese) is distinguished (high positive loads). F2 indicates the distribution of iron, cadmium, zinc, and chromium, with the prevalence of iron (high positive loads). By F3, the combination of copper and cadmium (with the prevalence of copper) is distinguished (high positive loads).

According to the pattern of object distribution (the proximity of their coordinates in a three-dimensional space), five groups of administrative districts (raions) (I–V) were distinguished, which correspond to the areas where mosses and forest litters were polluted with HM combinations accounted for by each of the three factors:

(I) Loukhskii, Kaleval’skii, Kemskii, Muezerskii, Belomorskii raions and the city of Kostomuksha; pol-lutants: nickel, copper, manganese, and iron in mosses; cadmium, iron, chromium, zinc, copper, and nickel for litters.

(II) Segezhskii and Medvezh’egorskii raions; pol-lutants: copper, cobalt, chromium, lead, zinc, cadmium, and manganese in mosses; cobalt, nickel, cadmium, zinc, iron, and lead in litters.

(III) Pitkyarantskii, Sortaval’skii, Lakhdenpokhskii, and Suoyarvskii raions; pollutants: nickel, cobalt, chro-mium, lead, cadmium, zinc, and iron in mosses; cad-mium, nickel, and lead in litters.

(IV) Pryazhinskii, Kondopozhskii, Olonetskii, Pri-onezhskii, and Vepskii raions; pollutants: cobalt, lead, and cadmium in mosses; cobalt, manganese, copper,

iron, lead, and nickel in litters. (V) Pudozhskii raion; pollutants: chromium, lead, cobalt, zinc, copper, and manganese in mosses; iron, cadmium, copper, chromium, zinc, cobalt, and manga-nese in litters.

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.

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