Holocene and Recent Alluvial Sediments in River Basin (Northwestern ) and Anthropogenic Impact Assessment

Dora Angelova Geological Institute, Bulgarian Academy of Sciences, , Bulgaria email: [email protected]

Abstract

The catchment basin of Ogosta river takes an area of 3,110 sq km. It involves well developed river system of 40 feeders inclusive. In the region of Stara Planina mountain and the Fore Balkan the rivers are with narrow beds but in some places form large valleys. In the lowland these rivers form wide floodplain terraces and strongly meandering river beds. The thickness of Holocene and recent alluvial sediments varies into wide ranges (from 1 m up to 40 m), as well as the sedimentation environment is changeable, too. The floodplain terraces width varies from 1 m to 2 km. The alluvial sediments in the Ogosta river basin are subjected to strongest anthropogenic alterations as a result of the urbanization, agricultural activities, mining industry, etc. Ninety four recent terrains strongly polluted with substandard substances in soil and water as a result of the anthropogenization. Some of the terrains are so strongly polluted with heavy metals and arsenic that they are defined as non- reclaimable. Generally, the pollution came in the period 1964-1979 from mining and flotation plants, which are located in Ogosta river upstream. Heavy metals and arsenic transportation is realized by river water during the high water, and their accumulation in alluvium comes in low water periods. The strong intensification of living style and agriculture, especially in the second half of 20th century also increased the alluvium pollution with chemical substances, living and construction waists. The poly- functional usage of alluvial sediments from the floodplain terraces of rivers from Ogosta river basin extremely reduced their quality. In the last years this necessitates fulfillment of extensive and integral studies and monitoring, which to the present remain still incomplete. The work presented makes assessment of Holocene alluvial sediments, natural and anthropogenic impacts and their stability.

Keywords: Holocene, sediments, anthropogenic pollution, Ogosta river, Northwestern Bulgaria.

Introduction

The Ogosta river basin covers an area of 3,110 sq km. The Ogosta river itself springs from the West Stara Planina mountain. It is characterized with well-developed river system, which involves about 40 bigger feeders. The Ogosta river length exceeds 144 km. It runs into the Danube river. The bigger feeders of Ogosta river are as follows: Dagodelska Ogosta river (average annual water flow of 2.10 m3/s), Barziya river (1.95 m3/s) and river (1.81 m3/s). In the region of Stara Planina mountain and the Fore Balkan the rivers are with narrow beds but in some places form large valleys. In the Danube lowland these rivers form wide floodplain terraces and strongly meandering river beds. The floodplain terraces width varies from 1 m to 2 km. The thickness of Holocene and recent alluvial sediments varies into wide ranges (from 1 m up to 40 m), as well as the sedimentation environment is changeable, too. These sediments had been studied by Mishev (1959), Stoilov (1970), Angelova (2001), etc. The alluvial sediments in the Ogosta river basin are subjected to strongest anthropogenic alterations as a result of the urbanization, agricultural activities, mining industry, etc. Some of the terrains are so strongly polluted with heavy metals and arsenic that they are defined as non- reclaimable (Kotsev, Yokova, 2002; Kotsev et al., 2005). Ninety-four recent terrains strongly polluted with substandard substances in soil and water as a result of the anthropogenization (Tsatchev et al., 1973). The poly-functional usage of alluvial sediments from the floodplain terraces of rivers from Ogosta river basin extremely reduced their quality. The work presented makes assessment of Holocene alluvial sediments, natural and anthropogenic impacts and their stability.

Brief notes about the geology and tectonic of Ogosta river basin

The territory of Ogosta river basin represents a variegated puzzle of strongly deformed and several times eroded Caledonian, Hercynian and Alpine structures being in autochthonous and allochthonous position. The tectonic structures are built by sequences various by age (from Paleozoic to Quaternary) and lithological types’ rocks deposited in different geodynamic environments. The main lithological

BALWOIS 2008 – Ohrid, Republic of Macedonia – 27, 31 May 2008 1/7 types subjected to erosion and denudation and building the floodplain terraces of most of the rivers from Ogosta river basin are as follows: phyllites, marbles, schists, basic volcanites, granitoids, dolomites, siltstones, shales, breccias-conglomerates, marls, sandstones, clays, quartz, etc.

The geological-tectonic evolution within the studied territory of Northwestern Bulgaria resulted in the forming and discovery of various mineral resources – metal, non-metal and fuels.

The ore deposits are formed under conditions of collision. They are tied to the horst structures. The main ore minerals are: pyrite, arsenopyrite, sphalerite, galena, scheelite, native gold, electrum, silver and silver sulfosalts. The erosion, denudation and accumulation processes cause concentration of significant quantities of heavy metals in the alluvial sediments.

From the non-metal deposits of local importance are clays at Chiren and , sands at Bukovets, Rogozen, Banitsa, Montana, etc., and pebble at Montana, Byala Slatina and Butan village.

Holocene and recent alluvial sediments

The Holocene and recent alluvial sediments build both higher and lower floodplain terraces as well as the river bed (Figures 1 and 2) and have the marks of morphodynamic development of morphostructural units (Angelova, 2001).

Figure 1. Geological map of the Quaternary sediments in the watershed of Ogosta river in the Danubian plain (after the Geological map of Bulgaria, 1:100,000 scale, map sheets and Byala Slatina, Filipov et al., 1989, 1993, with amendments): 1-4 Holocene: 1 – alluvium; 2 – proluvium; 3 – gravitation formations and sediments; 4 – diluvium; 5-9 Pleistocene: 5 – alluvium covered with loess; 6 – sandy loess; 7 – typical loess; 8 – clayey loess; 9 – loess-like clays; 10-11 Plio-Pleistocene: 10 – Red clay formation; 11 – Covering gravel formation; 12 – Pre-Quaternary rock complexes. The pie diagrams show the percentage of clay, silt and sand into the loess varieties.

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Figure 2. Geological map of the Quaternary sediments in the Ogosta river basin in the Fore Balkan and the Stara Planina mountain (after the Geological map of Bulgaria, 1:100,000 scale, map sheet Montana, Filipov et al., 1993, with amendments): 1 – Pre-Quaternary rock complexes; 2 – Plio- Pleistocene covering gravel formation; 3-5 Pleistocene-Holocene: 3 – diluvium; 4 – proluvium; 5 – gravitation formations and sediments; 6 – Pleistocene-Holocene alluvium.

Within the mountain and foreland morphotectonic units the Ogosta river and its feeders flow into their erosional beds. In the places where terrace deposits are preserved they represent roughly processed boulders up to 40 cm in diameter, chaotically deposited in the riverbed facies. In the valley extensions the boulders become finer to medium size (up to 10-12 cm) cobble, as thin intercalations and lenses of sands are observed, too. The thickness of alluvial sediments exceeds 10 m. The river terraces width changes depending on the pliability of lithological varieties. The particles’ content is quite different.

In the Danube lowland (Moesian hilly-plateau-like lowland) the alluvial deposits come predominantly into flood facies. The gravel of the riverbed facies in the Kozloduy lowland lies directly on the Pliocene clays. Its thickness is about 6 m, as at the base the particles are bigger and well rounded, while at the top they become smaller, cemented with sandy-clayey cement. Above them 12 m of brown-yellow compact clayey sands are deposited. The total thickness of alluvial sediments amounts to 19 m. The following fauna has been determined there: Theodoxus transversalis Pfeif., Lithoglyphus sp. Pfeif., Amphimelania holandri Ferr. and Fagita acicularis Ferr. These findings define the Holocene age of the sediments (after Koyumdzhieva, National Geofund).

The Ogosta river flood terrace is about 1-2 km wide. The differentiation of lower and higher floodplain terraces is provisional one due to the gradual and undistinguished transition between them. The

BALWOIS 2008 – Ohrid, Republic of Macedonia – 27, 31 May 2008 3/7 section penetrated in well N152 at Gromshin village is 11.5 m thick. The lower boundary to the marls is erosional one. At the base of the section fine-grained sands 1.5 thick are deposited. They are covered with 1 m thick gravel, which is followed upward by yellow fine to medium grained cross- bedded sands up to 2 m thick. The top of the section is built by 6 m thick gravel with intergranular space filled up with coarse-grained sand. The gravel particles are well rounded as the sizes vary from 1-2 cm to 7-8 cm. The particles are presented by various rock types but the quartz predominates. The top 1 m cover consists of dark grey compact soil-like clays. Alluvial loess and clay, 2.0-2.5 m thick, superpose the profile from Lehchevo village to the north (wells NN 58 and 75), as their thickness increases northward. The thickness of gravel deposited at the base of the section of well N29 drilled between Nivyanin and Komarevo villages is 3 m, as it lies on the eroded surface of grey marly clay. The gravel is poorly cemented with clayey-sandy cement. The gravel particles are small (1-2 cm size), semi-rounded to well rounded, consisting predominantly of limestone and quartz. The gravel is covered with gray- brown compact fat clay up to 3 m thick. The sand and clay portions in alluvium increase to the north, while the gravel portions decrease (well N72 at Krushovitsa village).

The alluvium from the flood terraces of the Danube, Ogosta and Skat rivers becomes mixed in the river mouths.

Paleobotanic remains of cultural plants (Triticum monococcum L., Triticum dicoccum Schrank, Triticum sp. and Hordeum sp.) of Neolithic age (VII-VI centuries BC) have been found in the alluvial deposits from the regions of historic settlements at Gradeshnitsa village, as well as ligneous and frutescent species had been determined, too (Corylus avellana L. and Quercus sp.). The cultural plants remains (Hordeum vulgare L. var nudum, Hordeum vulgare L. polistichum) found at Krivodol village date back to Eneolithic age (V-IV centuries BC) and the ligneous and frutescent species also (Quercus sp., Quercus pubescens Villd., Pinus sp., Ulmus campestris L., Ulmus sp.) (Lisitsina and Filipovich, 1980) (Figure 3).

Figure 3. Map of paleofloral and paleofaunistic remains in Quaternary sediments of Ogosta river basin: a-b Paleoflora: a – Neolithic; b – Eneolithic; c-d Plaeofauna: c – mammalian; d – aves. Sites: 1 – Gradeshnitsa; 2. Krivodol; 3. .

BALWOIS 2008 – Ohrid, Republic of Macedonia – 27, 31 May 2008 4/7 Anthropogenic alterations of alluvial sediments

The studied region comes into territory with the oldest human habitat specified so far in Europe. In Suhi Pech (Kozarnika) cave are found broken human bones dated 1.8 mil years (Sirakov, unpublished data). The oldest preserved morphostructural changes of floodplain terraces in Ogosta river basin are tied to the mining and ore-dressing activities there.

In the alluvial sediments of Ogosta river and its feeders is followed ancient mining for gold and silver from Thracian times – 1000 years BC (Georgiev, 1987). The cobbles piled perpendicularly to the recent riverbed in the region of , Govezhda, Dalgi Del, along river at Gaganitsa, Kotenovtsi villages, at Varshets along Varshetska river are especially impressive. Only in the region of Sredogriv village the ancient Thracians cradled more than 6 mil m3 of pebble and sand, and in the terrace of Dalgodelska Ogosta at Bukov Brod – more than 20 mil m3 (Georgiev, 1987). Native silver had been mined there together with the gold mining. The placer gold production had been intensified in the period VI – I century BC. From Ogosta river and its feeders in the period 1974-1992 are produced 9,125.1 mil m3 alluvial sediments with gold content of 74.3 mg/m3 and 678 kg Au metal (Dimitrov, 1998). After 1992 the placer gold mining activities are privatized and they are not under the state control.

From the floodplain terraces of the rivers belonging to the Ogosta river basin are mined clays (Chiren and Byala Slatina), sands (Bukovets, Rogozen, Banitsa, Montana, etc.) and pebbles (Montana, Byala Slatina and Butan) for local construction needs. The number of illegally developed quarries and rubble quarries, as well as the lack of reclamation increased latterly. The rubble quarries abandoned transform into marshes and technogenic lakes.

The structures that accompany the mining activity in the region of Chiprovtsi are piles and slimers. These are the main pollutants for the alluvial sediments. The contaminations became generally in the period 1964-1979. The transfer of heavy metals and arsenic had been realized in high water periods, and their accumulation in the alluvial soils became at low water periods.

Significant pollutions of the alluvial soils on the lower and higher river terraces are determined within the studied territory. The most sizable ones are fixed in the land of Gavril Genovo village at about 2 km over the mouth of Dalgodelska Ogosta river into Ogosta river, and in the Oreshaka site near Gorno Tserovene village as well. The main source of pollution is the mine locates in the region of Chiprovtsi town. Polymetals and uranium are mined and floatated there. The elements predominating in the polluted soils are as follows: As, Pb, Mn, Cu, Zn and Cd (Table 1).

Table 1. Contents of Pb, As, Mn and Fe (mg/kg) (after Kotsev and Dzhokova, 2002)

Studied soils in Depth of Pb As Mn Fe sampling (cm) Gorno Tserovene village 0-10 311 8871 11536 73350 Oreshaka site 10-24 343 11895 18186 97400 24-45 180 371 8055 44550 45-60 171 242 6881 42000 90-110 107 81 - - 120-160 84 76 879 28800 180-190 100 444 2550 33600 Gavril Genovo village 0-13 456 2840 9300 60000 25-48 838 15100 25000 127000 55-67 1381 2500 64500 197000 Gaganitsa village 0 27 37 799 25750 0-10 26 33 1249 28500 10-20 25 27 - - 20-40 22 22 - - 40-66 21 27 698 35600 66-69 24 19 - - 69-94 29 17 1497 36000 94-97 19 19 - -

BALWOIS 2008 – Ohrid, Republic of Macedonia – 27, 31 May 2008 5/7 As the table demonstrates the quantity of As, Pb, Fe and Mn in the soils of Oreshaka site exceeds significantly the contents of the same elements in the soils of unaffected territories along the valleys of the other feeders (Zlatitsa river at Gaganitsa village). In the table is seen also the different distribution of the metals within the soil profile. The contents of As, Pb, Fe and Mn exceed several times the background content and reach correspondingly 300-400, 150, 3 and 5-6 times. The contents of As and Pb show an exceeding of accumulations in the lower layers also, as they reach and pollute the groundwater. The quantity of heavy elements distributed in the polluted soil near Gavril Genovo village increases in depth and reaches up to very high values in the middle and in the lower part of the soil profile. All these accumulations and their accelerated migration, besides the “hot points” (Figure 4), polluted also to various extents the air, the water and the vegetation, and resulted in complications of human and animal health.

Figure 4. Map of the “hot points” within the Ogosta river basin: 1 – Montana dam; 2 – site of established technogenic alterations of alluvial soils.

A part of the unprofitable mining enterprises was closed, as a result of the economic changes, performed now in Bulgaria, and the equalization of Bulgarian ecological standards to the standards of European Union (EU). According to the EU standards for the Ogosta river basin is established that the pH over the studied territory is 5.2-7.1 now, and it should be in the range of 6-7; according to the EU standards the Pb content should vary between 50 and 300 mg/kg, but now within the studied region it is sizably increased (up to 1381 mg/kg). The same is referred to the rest of the heavy metals contents.

A part of the area under cultivation (within the studied territory it is defined as soils of high degree of soil fertility) have disturbed or completely destructed economic significance, as a result of the mining activities. All these necessitated the starting of the soils reclamation. The reclamation is carried out through engineering, melioration, agriculture, forestry, etc. activities, taking in consideration the

BALWOIS 2008 – Ohrid, Republic of Macedonia – 27, 31 May 2008 6/7 studies performed on the Quaternary sediments and their stratigraphic sequences, too, and the landscapes peculiarities within the studied territory as well.

An important role for the strong anthropogenic alterations of the alluvial sediments plays the agricultural activity. The most typical alterations here are tied to the artificial terracing, making of anti- erosional terraces, irrigation and drainage channels and riverbeds corrections. The presence of dams of artificial micro-lakes affects additionally the river flow distribution and the basin system transformation, and hence the deposition of recent alluvial sediments. The average annual river flow distribution of Ogosta river before its run into the Danube river amounts to 25.40 m3/s, and of Skat river it is 0.86 m3/s. The floods in Ogosta river basin are quite frequent – in the region of both towns and Montana these come 6 to 8 times per year, and for the rest regions – 3 to 6 times annually. The intensity of the drifting solids flow in the spring part of Dalgodelska Ogosta river exceeds 1000 t/year/km2, close to Montana town it varies from 201 to 400 t/year/km2, in the lower course of Ogosta river from Vladimirovo village northward to the Danube river – from 51 to 120 t/year/km2 and for the basin of Skat river and rest parts – from 0 to 50 t/year/km2 (In: Physical , p. 262).

The recent accumulative processes are developed in the river beds and sides. Floating sands are formed and they have the marks of hydrodynamic changes and represent inertia river structures. Such structures are followed along Ogosta river after Hayredin.

Conclusion

The Holocene alluvial sediments in Ogosta river basin are subjected to strong anthropogenization from ancient times to the present days. As a result of the urbanization, agricultural activities, mining industry, etc. strong pollution with substandard substances in the alluvial sediments of 94 recent terrains is observed. In the last years this necessitates fulfillment of extensive and integral studies and monitoring, which to the present remain still incomplete. Because of the important role of this region in the transport communications of EU it should be paid greater attention to the entire geological section of Holocene sediments in Northwestern Bulgaria.

References Angelova, D., 2001. Quaternary geology, geomorphology and tectonics in the Ogosta river system of the Danubian plain (Bulgaria). – Bulletin of the Geological Society of Greece, vol. 34, 1, 55-60. Cheshitev, G., L. Filipov, eds., 1992. Explanatory note to the Geological map of Bulgaria in 100,000 scale, map sheet Kozloduy, S., Geology and Geophysics Corp., 34 p. (in Bulgarian) Dimitrov, R., 1998. Gold deposits in Bulgaria. – Mining and geology, 4, 2-6 (in Bulgarian) Filipov, L., ed., 1995. Explanatory note to the Geological map of Bulgaria in 100,000 scale, map sheet Montana, S., Geology and Geophysics Corp., 109 p. (in Bulgarian) Filipov, L., ed., 1995. Explanatory note to the Geological map of Bulgaria in 100,000 scale, map sheet Byala Slatina, S., Geology and Geophysics Corp., 85 p. (in Bulgarian) Georgiev, G., 1987. Metal and non-metalliferrous resources in the time of the Thracians. – Publishing house of Bulgarian Academy of Science, Sofia, 134 p. (in Bulgarian) Kotsev, Ts., M. Yokova, 2002. Distribution of As, Pb, Fe and Mn with depth of polluted alluvial soils from the valley of Ogosta river. – Proceedings of the International scientific conference in memoriam of Prof. Dimitar Yaranov, Varna, 348-354 (in Bulgarian) Kotsev, Ts., Z. Cholakova, T. Popova, K. Chakalov, 2005. As and Pb forms in the contaminated soils of the Ogosta river valley affected by mining activities. – Problems of geography, Bulgarian Academy of Science, 1-2, 55-63 (in Bulgarian) Lisitsina, G., L. Filipovich, 1980. Palaeoethnobotanical findings in the Balkan peninsula. – Studia Praehistorica, Bulgarian Academy of Science, 4, 5-90, (in Russian) Mishev, K., 1959. Geomorphological studies of the Danubian lowland between the rivers Vidbol and Ogosta. – Bulletin of the Institute of Geography, Bulgarian Academy of Science, vol. 4, 27-83 (in Bulgarian) Stoilov, D., 1970. Gomorphological assessment of the relief in relation with the construction of Mihaylovgrad dam. – Bulletin of Bulgarian Geographic Society, 10, 51-63 (in Bulgarian) Tsatchev, Ts., K. Ivanov, D. Petchinov, 1973. Polluted rivers in Bulgaria with suspended matter. – Publishing house of Bulgarian Academy of Science, Sofia, 120 p. (in Bulgarian).

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