**4. Pollution of soils in protected areas**

phosphorus and potassium may cause alteration in nutrient uptake because of their less efficient retranslocation in polluted stands [67]. Due to the high level of calcium in the soil, the leaves in both control and damaged trees had a great amount of calcium. A more pronounced tendency for calcium and magnesium accumulation in polluted region was found in the leaves of *C. australis*, despite of the antagonistic effect of calcium on magnesium uptake. Among the elements, the greatest accumulation was established for calcium (from 3.5 to 7 times higher than the control) and phosphorus (on average 2 times over the control). The higher magnesium level in damaged leaves of *C. australis* could be explained with an increased exchange of magnesium in polluted soils. The lower nutrients content in polluted leaves, especially of potassium and phosphorus, was due to the inhibition of total functional activity in damaged trees. The decreased concentration of potassium, known to play an important role in water regime regulation, might be regarded as an indicator for a water misbalance in polluted leaves [68]. Some specificity was found in the accumulation of separate micronutrients and heavy metals among the species. The most pronounced difference between damaged and control trees were found in copper, manganese, zinc and lead concentrations. Remarkable copper accumulation was observed in the leaves of *C. australis*. Severe manganese accumulation was found in polluted leaves both of *Fr. americana* and *C. australis*. According to some authors, manganese toxicity might be a significant constraint for the health of forests on disturbed soils [69]. The accumulation of zinc was higher in polluted leaves of *Fr. americana*. Cadmium was accumulated mostly in the leaves of afflicted*C. australis* trees and exceeded the levels of toxicity [22]. The greater amount of soluble manganese is favourable to iron availability. In polluted stands, iron was accumulated extremely by *Fr. americana* and moderately by the leaves of *C. australis*. Complex changes in chemical composition, disturbed balance of nutrient elements and increase in the content of heavy metals accompanied decline processes [68]. An uptake of heavy metals by plants occurs together with nutrients through the roots or directly through leaves. The entry of elements through the leaves is more significant for the pollution ones. The slightly alkaline reaction of soil in Devnya region does not create a large amount of easily accessible for the plants forms of heavy metals. Therefore, the accumulation of heavy metals in the leaves might be mainly due to the deposition of air pollutants. Zinc, being an essential element to the plant metalloenzymes, is translocated extensively and its uptake is dependent on metal concentration in extractable fraction in soil as well [70, 71]. The response of vegetation to pollutants depends on the degree of pollutant loading. At low pollutant loads, vegetation can act as a sink for pollutants, and no or minimal physiological alteration occurs [39]. In our study, such role may play *C. australis*. The content of copper, cadmium and especially lead in the leaves of *C. australis* exceeded the excessive values for tree vegetation and can be regarded as damaging [17]. Although the heavy metals are mostly below the critical levels of decreased growth, they may threaten tree vegetation in the region. Hence, the area studied was with slight to moderate heavy metal contamination. The accumulation levels obtained are air and soil orientated [72, 73]. The examined species accumulated mainly lead, copper, zinc and

148 Soil Contamination - Current Consequences and Further Solutions

In conclusion, each of these pollutants can be suggested as an indicator for the influence of industrial emission on the soil of the region. Changes in foliar element concentrations, howev‐

manganese.

The content of heavy metals and other pollutants in soils from the territories of national and nature parks in the country is poorly studied. With the exception of soils from Strandzha Nature Park, their territories are not subject to monitoring within the national forest ecosystem monitoring network. Due to the large mapping areas, steep terrains and difficult access, some authors apply the landscape ecological approach, which allows to specify relatively homoge‐ neous landscape units in relation to selected criteria [74–77]. They are accepted as a represen‐ tative sample and serve for conducting different scientific studies, including assessment of soil pollution.

*Central Balkan National Park* was established in 1991 in order to protect self‐regulating ecosys‐ tems and is characterized by exceptional biodiversity, communities and habitats of rare and endangered species. The park occupies the highest part of the Balkan Mountains and has a total area of 72,021.07 ha, being the second largest national park in Bulgaria. Some authors reported pollution of soils and plants in pastures with copper, arsenic, lead and cadmium, as well as leaves of *Fagus silvatica* [78]. Natural soil enrichment with cadmium was determined in some areas [79, 80].

Analysis of the park landscape structure was performed in 2015 [81, 82], and 71 relatively homogenous territorial units in relation to the soil‐forming rocks and terrain were established within the "forest" landscape category. Analysis of soils and plants was performed using a representative sample—"landscape formed on schists". The soil is Regosols with 20 cm soil depth. Soil material in the layer 10–20 cm showed enrichment of soil‐forming rocks with copper, arsenic and cadmium (see **Table 5**). The amounts of Cu and Cd in the litter repeatedly exceeded the toxic levels determined for forests in Europe [22], 20 and 3.5 mg kg−1, respectively.


**Table 5.** Content of heavy metals and arsenic in soils from the area of the Central Balkan National Park.

The content of heavy metals and arsenic in *Pinus sylvestris* needles was also analysed at the same site (**Table 6**).


**Table 6.** Content of heavy metals in *Pinus sylvestris* needles from the area of Central Balkan National Park.

Repeatedly increased copper content was determined in comparison with the established variation limits of these elements within the ICP Forests [41]. The exceedances of manganese and cadmium were relatively low.

*Bulgarka Nature Park* is adjacent to the Central Balkan National Park. The park is located on the northern slopes of the central part of the Balkan range, occupying a total area of 21,772.163 ha. Environmental pollution risk in landscapes formed by alpine pastures, due to the soil enrich‐ ment with heavy metals, was determined on the park territory [79]. The maximum measured values of lead in soils reached 497 mg kg−1 and of arsenic—112 mg kg−1. These values were determined at the pasture of the Malusha locality. The following herbaceous plants were identified as strongly lead‐accumulating plants: *Holcus lanatus* (29.29 mg kg−1), *Thymus sp.* (42.32 mg kg−1), *Viola tricolor* (9.81 mg kg−1), etc. Arsenic‐accumulating plants are *Viola dacica* (3.1 mg kg−1), *Rubus idaeus* (2.9 mg kg−1), *Fragaria vesca* (1.5 mg kg−1), etc. [83].

The studies of heavy metal content in soils and plants of *Pirin National Park* are also very limited. The park was created in 1962 in order to preserve the natural character of the ecosystems and landscapes along with their plant and animal communities and habitats. The park territory, occupying 40,356.0 ha, has not been differentiated into appropriate landscape units yet. In order to study the soil pollution in 2015, the authors carried out a research on representative for the area soil units (see **Table 7**).


**Table 7.** Heavy metal content in soils from the territory of the Pirin National Park.

Only cadmium content can be assessed as excessive in accordance with the criteria on forest soils [22].

*Strandzha Nature Park* is the only park in the country with a developed national forest ecosystem monitoring network. The park was established in 1995, occupying an area of 116,054.21 ha, and is aimed at long‐term preservation of the unique nature of the drainage basins of the Veleka and Rezovska rivers. The studies of heavy metal content for the period 1987–2008, carried out at 11 sample plots, indicated the absence of pollution or natural soil enrichment. The average values of Cu, Pb and Zn in *Luvisols* and *Alisols* for the period 2009–2015 (see **Table 8**) also confirmed this tendency.


**Table 8.** Heavy metal content in soils from the territory of the Strandzha Nature Park.

Single studies carried out in the Uzunbodzhak biosphere reserve, located on the territory of the Strandzha Nature Park, also confirmed the absence of soil pollution [84].
