Landscape-Geochemical Approach for Evaluation of the Iskar River Basin State in the Western Balkan Mountain (Bulgaria)

Zornitza Cholakova Sofia University “St. Kliment Ohridski”, Faculty of Geology and Geography, Department of Landscape Ecology and Environmental Protection Sofia, BULGARIA

Abstract

This paper aims at representing the pollution with heavy metals (Cu, Pb, Zn, Cd, Mn, Ni, Cr, Co) of the channel sediments of the Iskar River basin and its tributaries within the borders of the Balkan Mountain. Part of the river course after the no-longer functioning metallurgical factory has several times higher concentrations of Cu, Zn, Рb, Сd and Mn than the permissible concentration levels (PCL) for river waters. Due to the lack of PCL for the channel sediments, they are compared with the PCL of the soils, as well as with the average values of the content of researched microelements form other river basins in the country. The Iskar River valley has the following geochemical specialization determined by the concentration coefficient: (Кс): Cd (Кс = 9), Zn (6.86), Cu (6.85), Pb (5.02), Mn (1.19). The geochemical specialization of the Iskar River tributaries in the West Stara Planina Mountain is more different: Pb (13.36), Cu (4.48), Zn (4.46), Ni (1.85), Mn (≈1).

Keywords: landscape-geochemical system, river basin, channel sediments, heavy metals, concentration coefficient.

Introduction

The landscape-geochemical variety of each territory is determined by many factors. The basic ones among them are athmo-, litho-, hydro-, pedo-, phyto-, and technogeochemical factors. The last group plays a leading role in the occurrence of the geochemical processes and the differentiation of the chemical elements at the contemporary stage of nature complexes’ development. In order to evaluate the impact of these factors, each landscape component should be researched in detail, and the internal and external relations within the borders of the whole landscape-geochemical system should be analyzed. The channel sediments are an element of the complex system of aqua landscapes. They are characterized by varied lithological, grain-size and geochemical content and possess the highest degree of information about polluting substances in the water of rivers, lakes, artificial lakes, seas, etc. The main reason for that is the subordinate position of the aqua landscapes in the landscape-geochemical structure of each territory with regard to the main migration flows of the chemical elements and their compounds. The channel sediments formed as a result of the mechanical and chemical sedimentation of the soluble and insoluble particles contained in the water represent natural environment for the accumulation of heavy metals as well. The different migration capability of the latter, which also depends on the physicochemical properties of the water, leads to significant differences in the degree of their accumulation in the channel sediments in each particular part of the river course.

Object of research

The Iskar river basin in the West Stara Planina (Balkan) mountain covers an area of around 1000 km2 and drains parts of Sofiiska, Murgash, Golema, Mala, Ponor, Koznitsa, Rzhana and Vrachanska Mountain. The Iskar river has formed in Stara Planina Mountain the longest and most inhabited gorge in Bulgaria. In the course of 76 km the river depicts an impressive gorge with maximum depth of incision to 900-1000 m and the slope of the river channel varies from 1 to 5 ‰. Here the river receives a number of tributaries, the biggest of which are Svidnitsa (4.5 km), Dalbochitsa (8.8 km), Iskretska reka (21 km), Proboinitsa (13 km), Ochinska reka (6.5 km) and Zlatitsa (8.8 km) from the left tributaries and Romchanska river (4.8 km), Batuliiksa river (37.5 km), Gradeshnitsa (5.3 km), Redinska river (9 km), Treskavets (8.5 km), Lakatnishka river (8 km), Gabrovnitsa (21 km), Razhanska river (8.6 km), Dzherniovitsa (10 km) and Voinova river (9.3 km) from the right tributaries. The mean annual runoff of the Iskar river (for the period of 1955/56 - 1984/85) at Kurilo, before entering the gorge, is 24.7 m3/s and at Rebarkovo, after exiting the gorge, is 40.8 m3/s (Hristova, 1992). The module of the runoff on average is around 15 l/s per 1 km2. Within the year, the maximum of the runoff is in early spring, in March (Kurilo – 31.1 m3/s, and Rebarkovo – 60.4 m3/s). The minimum is in August (Kurilo – 16.2 m3/s, and Rebarkovo – 21.4 m3/s). The runoff distribution is an important indicator with regard to the processes of transportation and sedimentation of the channel sediments. In the periods of high water, an increase of the water turbidity is observed as well as a transportation of bigger fraction materials on long distances, withdrawing and returning to the water stream of already deposited sediments in the river channel. In low water the accumulation processes activate as well as sorting of materials in the different parts of the river channel.

The long-term mean turbidity at Kurilo is 1149 g/m3 (for a period of 20 years), while at Rebarkovo it is 281 g/m3 (for a period of 12 years). The considerably higher values of turbidity at Kurilo result from the technogenic impact of the industrial enterprises in Sofia and of the numerous pits for extraction of inert materials. The turbidity distribution within the year is identical of that of the runoff and has its maximum in the early spring months and its minimum at the end of the summer (Limnology of the Bulgarian Danube Tributaries, 1994).

Methods of research

This report presents part of the results of a complex landscape-geochemical research of the Iskar river basin within the river gorge in the Stara Planina Mountain. It aims at presenting the geochemical migration and differentiation of eight chemical elements – heavy metals (Cu, Zn, Pb, Cd, Mn, Ni, Co, Cr) in the channel sediments of the main river and its tributaries, as well as at revealing the main geochemical associations of the leading elements in the polluted and in the relatively less affected by the technogenic impact parts of the basin.

In order to disclose the concentration and distribution of the heavy metals, the method for sampling channel sediments of Saet (1982), Batoyan (1983), Penin (1989), Saet et al (1990), Kasimov, Penin (1991) has been used. The samples have been gathered from the bank sections of the river channel along the stream from the entrance into the gorge at Kurilo quarter of the town of Novi Iskar to the village of Lyuti Brod.

The sampling has been done in periods of low water (September). It has been carried out in places situated immediately before and after the very sources, as well as before and after the confluence of the main tributaries. Seven of these tributaries have been sampled. The number of sampling points depends on the size of the respective river basin. The comparison and determination of the geochemical associations, which characterize the basins of the main river Iskar and its tributaries, is made with the help of the concentration coefficient (Kc). It represents the ratio between the mean content of a given chemical element in the channel sediments of the researched river basin and the mean content of the same element in the channel sediments in the background river basins in Bulgaria.

Results and discussion

The research of pollutants’ contents in the sediments of Bulgarian rivers is not carried on regularly. Within the Iskar river catchment in the Iskar gorge sampling was made in different locations in 1993 (Penin, Krastev, 1996), 1996-1997 (Evaluation…,1997), 1998-1999 (Evaluation…,1998). A detailed investigation of the contents of heavy metals in the Iskar river channel sediments and its tributaries in the Iskar gorge is made in the period 1999-2002. Some of the already published results (Cholakova, 2002, 2004) show again that the main river is polluted with Cd, Pb, Zn and Cu. The values of these elements are many times higher than their mean values in the earth crust (Vinogradov, 1962) and higher than their mean values in background and technogenic river basins in Bulgaria (Penin 2000, 2003 and table 1).

Table 1. Average content of heavy metals (mg/kg) in the channel sediments of the Iskar river and its tributaries in Stara Planina Mountain, background and technogenic regions in Bulgaria (Penin, 2003).

Tributaries in Background Technogenic The Iskar The Iskar River, Stara Planina Regions in Regions in River, 1999 2001 Mountain Bulgaria Bulgarias

Cu 249 308.6 201.7 45 217 Zn 586 645.3 419.3 94 155 Pb 125.5 119.2 334 25 102 Cr 58.6 55 59.4 64 74 Ni 27 33.7 51.9 28 35 Co 13.6 14.6 15.5 17 37 Mn 925 871.8 766.8 777 972 Cd 9 5.2 1 1 1.9

The data show that in 2001 the channel sediments of the Iskar river contained on average 1.24 times more Cu, 1.1 times more Zn, 1.25 times more Ni and 1.07 times more Co in comparison with 1999. The content of Cd has decreased 1.73 times, of Cr and Mn – 1.06 times, of Pb – 1.05 times (fig. 1).

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Figure 1. Average content of heavy metals in channel sediments of the Iskar River

The chemical content of the bottom sediments for both years does not change substantially with the exception of the almost double decrease of Cd concentration. The difference in the contents of some heavy metals in separate sampling locations is better seen in the downstream. For instance, sample locations in the beginning of the gorge (at the village of Romcha, the village of Lukovo and others) indicate higher concentrations of the elements Cu, Zn, Pb, Cr, Ni (at Romcha) and for Cu, Zn, Pb, Cr, Ni, Co, Mn (at Lukovo) in 2001 compared to 1999. Only Cd has kept (at Romcha) and even decreased its content almost two times (at Lukovo). It is as a result of the release of non-purified waters form the purifying station in Sofia. This additional burdening of the river basin is observed farther in the downstream – Cu and Pb until the sampling location at the village of Tserovo, Zn and Ni – till Bov railway station. The rest of the elements show small or no increase of their concentrations.

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0 Iskar River - Iskar River - Iskar River - Iskar River - Iskar River - Iskar River - Iskar River - Iskar River - Iskar River - the bridge at after the after the Svoge, at the bridge at Lakatnik, before the bridge after Lyuti Romcha Batuliiska Dalbochtsa the garbage Bov station after the Eliseyna Ltd. after Zverino brod river river dump Preboinitsa confluence confluence river confluence

Figure 2. Content of Cu in the channel sediments in the sampling points downstream the Iskar river in Stara Planina mountain

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Figure 4. Content of Pb in the channel sediments in the sampling points downstream the Iskar river in Stara Planina mountain

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Figure 5. Content of Cd in the channel sediments in the sampling points downstream the Iskar river in Stara Planina mountain 2000

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Figure 6. Content of Mn in the channel sediments in the sampling points downstream the Iskar river in Stara Planina mountain

With relation to the tributaries (the data show the mean content of the researched heavy metals in the channel sediments of Batuliiska river, Dalbochitsa river, Redinska river, Iskretska river, Treskavets river, Gabrovnitsa river, Dzherniovitsa river) high concentrations have got the elements Cu, Zn, Pb, Ni, Mn. These elements accumulate additionally in the sediments of the main river as a result of varied anthropogenic impact. It should be noted that some of the tributaries are also subject of such impact and it cannot be assumed that their mean contents are entirely background ones with regard to the main river.

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Cu background regions 300 technogenic regions mg/kg tributaries in Stara planina

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0 r. Batuliiska r. Dalbochitsa r. Redinska r. Iskretska r. Treskavets r. Gabrovnitsa r. Dzherniyovitsa

Figure 7. Content of Cu in the channel sediments of the bigger tributaries of the Iskar river in Stara Planina mountain The Stara Planina tributaries of the Iskar river have on average higher concentrations of Cu in their sediments (Fig. 7) than the rivers from background regions in Bulgaria. The Treskavets and Dzherniovitsa rivers form catchments on territories with raised natural content of this element in the rocks and soils. Additional factor, which can explain the high content of Cu in the sediments of the Treskavets river is the exploitation of the Izdremets mine in the 60s and 70s of the past century. The increase of Cu content in the channel sediments of the main river after the confuence of this tributary marks the second peak in the line of concentrations in fig. 2.

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Zn background regions 600 technogenic regions mg/kg tributaries in Stara planina

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0 r. Batuliiska r. Dalbochitsa r. Redinska r. Iskretska r. Treskavetz r. Gabrovnitsa r. Dzherniyovitsa

Figure 8. Content of Zn in the channel sediments of the bigger tributaries of the Iskar river in Stara Planina mountain

The natural background for the content of Zn in the region of the Iskar gorge has been increased 2.5-4.5 times compared to other catchments in Bulgaria. Two of the rivers from the researched catchment – Dalbochitsa and Dzherniovitsa, contain in their channel sediments two times more Zn than the mean value for the region (fig. 8). The high concentration of Zn in the waters of Dalbochitsa probably owes to an anthropogenic impact, as there are no substantial zinc lithogeochemical anomalies in its catchment. The high concentrations can be traced in the sediments downstream the Iskar river to the town of Svoge (fig. 3). Passing by Zverino, the Dzherniovutsa river receives pollutants of inorganic and organic origin. It is very probable that the high concentration of Zn in the sediments before its confluence with the Iskar river, is a result of the stronger anthropogenization of the region. 1600

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Pb background regions 800 technogenic regions mg/kg tributaries in Stara planina

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Figure 9. Content of Pb in the channel sediments of the bigger tributaries of the Iskar river in Stara Planina mountain

Another element, which distinguishes the Iskar River catchment in Stara Planina mountain from the rest catchments in Bulgaria, is lead (Pb). The sediments in the tributaries of the main river contain on average between 3 and 13 times more Pb than the technogenic and background basins in the country. The Treskavets river stands out among them. Its concentrations are higher in its upper course. The river springs from the foot of the peak Izdremets and drains the territory of a mine, which was exploited from the beginning of the 50s till the end of the 60s in the 20th century mainly for lead and less for zinc, silver etc. At the same time in the lower course of the river additional technogenic impact causes the Christo Botev mine at Bov railway station. A weak increase in the concentration of Pb in the channel sediments is observed after the confluence of Treskavets with the Iskar river (fig. 4).

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0 r. Batuliiska r. Dalbochitsa r. Redinska r. Iskretska r. Treskavetz r. Gabrovnitsa r. Dzherniyovitsa

Figure 10. Content of Ni in the channel sediments of the bigger tributaries of the Iskar river in Stara Planina mountain

Nickel (Ni) is the fourth microelement, which characterizes the geochemical condition of the tributaries of the Iskar river in Stara Planina mountain. Compared to the background and technogenic river basins in Bulgaria, the sediments in the tributary catchments contain 1.5-2 times more Ni (table 1). Mostly the catchments of Batuliiska river, Dalbochitsa river, Gabrovnitsa river and Redinska river have a specialization with regard to this metal. The main reason is probably the lithogeochemical impact of the rock base in these regions. The highest content of Ni in the channel sediments of the main river is registered after the confluence of Batuliiska river with the Iskar river, but the mean contents for the whole river valley do not exceed or are close to the ones of background and technogenic river basins in Bulgaria. In contrast to the tributaries, Ni is not one of the main specializing elements in geochemical respect for the channel sediments of the Iskar river.

The mean value of manganese (Mn) for the tributary catchments is close to the one of background basins in the country. Batuliikska river, Dalbochitsa river and Gabrovnitsa river have a higher concentration of Mn in the channel sediments. Sofiiska Planina mountain is a territory with anomalous content of Mn in the rocks and soils, which reflects on the geochemical characteristics of the sediments of the Batuliiska river, which forms the left part of its basin on this territory. A similar geochemical anomaly is established in the rocks and soils of Mala Planina mountain, where the basin of the river Dalbochitsa is formed.

The elements Co and Cr have contents close to or lower than the mean for the catchment in the sediments of most of the Iskar river tributaries or background regions in the country. The water catchment of Batuliiska River stands out strongest with higher concentration levels of Cr in its sediments compared to other catchments in technogenic regions in the country, and concentrations of Co above the mean for the Iskar River catchment in Stara Planina Mountain and background river basins in the country.

The content of Cd in the river sediments of almost all tributaries is 1 or <1 mg/kg which indicates their background character (table 1). The source for the high concentrations of this element in the sediments of the main river is outside the territory of these water catchments.

Conclusions: The channel sediments of the rivers in the Iskar river catchment in the West Stara Planina mountain have higher contents of the heavy metals Cu, Pb, Zn, Cd, Mn, Ni compared to other basins in Bulgaria. With regard to the main pollutants, the Iskar River valley has the following geochemical specialization determined by the concentration coefficient (Кс): Cd (Кс = 9), Zn (6.86), Cu (6.85), Pb (5.02), Mn (1.19).

The geochemical specialization of the Iskar river tributaries in the West Stara Planina mountain is more different: Pb (13.36), Cu (4.48), Zn (4.46), Ni (1.85), Mn (≈1).

The geochemical condition of the Iskar river basin in the researched region with regard to the heavy metals results from the long lasting complex impact of natural (litho-, hydro-, pedogeochemical) and technogenic factors. The differences in the associations of pollutants between the main river and its tributaries indicate the leading importance of the technogenic impact of various character and localization for this basin. The high concentrations of the major pollutants at the “entrance” and at the “exit” of the river system justify its categorization as medium to strongly anthropogenized.

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