Phytoremediation capacity of hybrid aspen at sites affected by industry and agriculture.

Fast-growing Populus spp. are well-acknowledged to restore contaminated soils from heavy metals in industrial areas. Thus far, there is no knowledge about the phytoremediation capacity of Populus spp. plantations in hemiboreal Estonia conditions to restore industrially polluted areas. The objective of this study was to assess the soil contamination rate of heavy metals (As, Cd, Co, Cr, Cu, Fe, Mn, Mo, Ni, Pb and Zn) and their uptake by mature hybrid aspen (Populus tremula × Populus tremuloides Michx.) in plantations in different industrial pollution areas (e.g. cement factory, oil shale mining). For the reference, industrially polluted plantations were compared with the low pollution area hybrid aspen plantation on former agricultural soil, which was influenced by fertilization and liming before afforestation. Twenty-one years after afforestation, soil samples were collected from the 0-10 cm topsoil layer. Aboveground biomass sampling was performed for bark and stem wood by ingrowth cores to separate wood formed during early (1-10 years) and late (11-21 years) stand development. Two decades after the afforestation of industrially polluted areas, the heavy metal concentrations in the soil were higher than the reference plantation and the standard reference for unpolluted soils in most cases. The highest concentrations of heavy metals in woody biomass were in the oil shale quarry spoil; because of poor growth, the accumulated pools in aboveground biomass were low. Cd differed from other metals and accumulated less in wood and more in bark. The concentration of heavy metals (Cd, Cr, Cu, Fe, Mn, Ni and Zn) was higher in the first decade of stand formation (1-10 years) than in the last 10 years (11-21 years). High pools of heavy metals were accumulated in aboveground biomass in the reference plantation, indicating the considerable removal of heavy metal residues from the previous fertilization and liming source with harvest. Two decades of afforestation with hybrid aspen is too short for complete ecosystem restoration from heavy metals in industrially polluted areas.

Re-vegetation processes in cutaway peat production fields in Estonia in relation to peat quality and water regime.

Eighty-one cutaway peat production fields with a total area of about 9000 ha exist and were studied in Estonia in 2005-2015. Only a very small number of the fields (seven) have been restored-either afforested or used for growing berries. The re-vegetation of Estonian cutaway peat production fields is mainly the result of natural processes, which are generally very slow due to an unfavourable water regime or a too thin remaining peat layer. The fields are mostly covered by cotton grass and birches. Often sparse vegetation covers 15-20% of a peat field, but some fields have turned into heaths or grasslands with plant coverage up to 60%. However, due to changes in environmental (mainly hydrological) conditions and peat characteristics (mainly peat type), these areas can also be new niches for several species. A number of moss species new to or rare in Estonia, e.g. Pohlia elongata, Ephemerum serratum, Campylopus introflexus and Bryum oblongum, were recorded.

Effect of wood ash on leaf and shoot anatomy, photosynthesis and carbohydrate concentrations in birch on a cutaway peatland.

Trees in cutaway peatland are growing in difficult conditions. Fertilization with nutrient-rich wood ash helps improve growth conditions. Photosynthesis and carbohydrate concentration along leaf anatomy were studied on plots treated with 10 and 5 t ha(-1) wood ash (WA10 and WA5) and on untreated (Control) plot to explain the physiological background of the differences in tree growth. The leaves from WA10 had the largest leaf area, total thickness, the thickest mesophyll and also significantly larger average values of all anatomical parameters of the shoots. The photosynthetic assimilation was significantly higher on treated plots at 200 and 400 ppm CO2 levels. In leaves on the treated plots, the sucrose concentration was lower while that of starch was higher than in trees on untreated soil. The differences in the maximum photosynthesis were relatively small. At unit ground, the leaf area provided for a wood ash-treated tree an efficient surface for CO2 assimilation, light interception and some starch storage during the growing period.

Monitoring of heavy metals uptake and allocation in Pinus sylvestris organs in alkalised soil.

The concentration of heavy metals in soil and in Scots pine (Pinus sylvestris) organs growing on a pH gradient from 4.0 to 7.9 of soil at different distances from a cement plant was monitored. Emission for over 40 years of alkaline dust (pH 12.3-12.6) into the atmosphere in North Estonia had resulted in alkalisation and elevated concentration of total heavy metals in upper layers of the soil (0-30 cm), which was considerable even 10 years after the dust pollution stopped. Monitoring showed that the accumulation and allocation of heavy metals varied between the stem, shoots and needles and differed from the trees in the unpolluted area, depending more on the mobility of elements and the pH than element concentrations in the alkaline soil. A strong negative correlation was found between the soil pH and Mn, Zn and Cd concentrations in different tree organs. Compared to the unpolluted area, Pb was present in relatively higher concentrations in all organs but Cr, Fe and Cu in needles and shoots. The concentrations of Mn and Cd were much lower than control in all organs of trees in alkalised soil. The height increment and density of needles on shoots were predominantly in negative correlation with the pH of soil.

Short-term responses of soil chemistry, needle macronutrients and tree growth to clinker dust and fertiliser in a stand of Scots pine.

Waste management of clinker dust by spreading it on forest soil was studied in a 25-year-old Scots pine stand on acidic sandy soil. Clinker dust (0.5 kg m⁻²), fertiliser (N, P, K, Mg, 0.05 kg m⁻²; N 190 kg ha⁻¹) and untreated soil were applied on 120-m² plots in four replicates. The fertiliser was included to confirm the nutrient limitation in the stand. Clinker dust increased the soil pH by 1.2 units relative to the pH of 4.6 in the untreated soil by the second year. Soil K and Mg concentrations were larger in the dust and fertiliser treatments. Nutrient diagnostics indicated that needles of untreated trees were deficient in N and K. Fertiliser treatment indicated that the growth of trees was limited by N, since the fertiliser tended to increase needle K, N, N/P, needle dry mass and diameters of stem and shoots. By an auxiliary dataset, no effects of the dust and fertiliser on possible excess of the micronutrient Mn were observed. Clinker dust increased needle K concentration, but due to the N limitation, there was no increase in the growth of stems, branches, shoots and needles. It was concluded that in plots of 120 m² application of clinker dust at a rate of 0.5 kg m⁻² was safe for the 21-year-old Scots pine stand in this trial on an acid nutrient-poor sandy soil during 4 years after the treatment.

Assessment of growth and stemwood quality of Scots pine on territory influenced by alkaline industrial dust.

Long-term influence of alkaline dust (pH 12.3-12.7) pollution emitted over 40 years from a cement plant in Estonia was the reason of alkalisation (pH 6.7-7.9) and high concentrations of K, Ca and Mg in the soil of affected territories. Although dust emission has diminished during the last 10 years, the imbalances in nutrition substrate and their influence on the growth of trees are notable up to now. The study of morphological and physical properties of 70-80-year-old Scots pine (Pinus sylvestris L.) crown, stems and stemwood from three different air pollution zones showed serious deviations in comparison with a relatively healthy forest in an unpolluted area. The specimens from polluted trees, if compared to reference site, showed significantly smaller height growth, radial increment and width of annual rings of sapwood. In heartwood wider annual rings were found in polluted areas. In the period of heartwood formation the dust pollution level emitted from the plant was relatively modest and cement dust, which contains elements necessary for mineral nutrition of trees, may have acted as fertiliser. The moisture content in sapwood and heartwood, especially in the upper layers of stems, was lower in the polluted area than in reference site trees. Regression analysis revealed a strong dependence between latewood percentage and sapwood or heartwood in stems of Scots pine in all sample plots.

The radial increment and stemwood element concentrations of Scots pine in the area influenced by the Narva power plants in Northeast Estonia.

In the northeastern part of Estonia, near the town of Narva, there are two large oil shale fueled power plants, Baltic PP and Estonian PP. On burning oil shale the main atmospheric pollutants are fly ash, sulphur oxides and nitrogen oxides. The radial increment was measured and concentrations of Ca and Cu were estimated in the stemwood of Scots pine (Pinus sylvestris L.) from four sites in the influence area of the Narva power plants. Increment cores were taken also from two sites in an unpolluted area located 112 and 120 km northwest from the Estonian PP. The stands selected for investigation were similar as to their edaphic conditions and forest survey indicators (75- to 80-year-old (Oxalis-) Myrtillus-type pine stands of 0.7-0.8 density and of quality class II). The strongest effect of air pollution on radial increment was observed on the sampling site in the direction of dominating winds at a distance of 22 km to northeast from the Estonian PP. Using the annual rings, the core samples were divided into five-year sections (1945-1949; 1950-1954 etc.). The concentration of Ca increased and that of Cu decreased from the youngest, outermost annual rings towards the centre of the stem. High concentrations of Ca and Cu in stemwood in 1970-1974 may be due to the launching of the Estonian PP in 1969 in addition to the Baltic PP, which has operated since 1959.

Impact of emission from oil shale fueled power plants on the growth and foliar elemental concentrations of Scots pine in Estonia.

To study the impact of air pollution on the growth and elemental composition of conifers, 5 sample plots were established at different distances and directions from the Estonian Power Plant (Northeast Estonia) in 1999-2000. The selected stands were 75-80(85)-yr-old parts (0.05 ha) of (Oxalis)-Myrtillus site type forest of 0.7-0.8 density. The soils of all sample plots were Gleyic Podzols (Lkg) on sands. The several times higher Ca concentration in the humus horizon of the sample plot NE from the Estonian PP is caused by the prevailing westerly and southerly winds which carry more pollutants NE from the power plant than to SSW. To ascertain the effect of power plants on the growth of Scots pine (Pinus sylvestris L.), the length growth of the needles and shoots formed in 1997-2000, dry weight of 100 needles, and density of needles on the shoots were measured. As compared to the control, the strongest inhibition of growth was revealed in the sample plots situated 22 km north-east and 17 km south-west from the Estonian Power Plant. As compared to control, the needles of trees growing on sample plots closer to the power plant showed higher contents of Ca, S and Zn. The content of Mg in needles increased with distance from the pollution source. Current year needles had higher contents of Cu and Zn than older needles. Today the amounts of fly ash emitted from Narva power plants are fallen. Long-term fly ash emission has caused changes in the measurements of morphological parameters and chemical composition of needles.