sediments and hyporheic water in the middle part of the river pose an ecological threat ... Key words: Iskar River, heavy metals, water quality, bottom sediments.
Ecological Engineering and Environmental Protection, Vol.1, 2008 Iskar River: heavy metals in waters, sediments and hyporheic zone D. Parvanov, Topalova,Y., Kenderov, L. ABSTRACT: This paper is one part of the complex studies and intends to provide the background for explaining the spatial differentiation of macroinvertebrate and microbial community settled in the Iskar River. The study has been conducted along the whole river course. Total amount of Cu, Zn, Pb, Mn and Fe in three key sub-ecosystems (surface water, hyporheic water and sediments) has been assessed. Comparing the present content of heavy metals in the surface waters and sediments with previous gathered data, a decrease in the concentrations of these elements was found with the exception of lead content, which shows a serious increase. The investigations show that the most significant linear correlation is the one between iron and manganese. Taking into consideration the obtained data it can be concluded that heavy metal content in sediments and hyporheic water in the middle part of the river pose an ecological threat to the local environment.
Key words: Iskar River, heavy metals, water quality, bottom sediments
1. Introduction The Iskar River as one of the largest rivers in Bulgaria is exposed to impact inflows of different kinds of pollutants. The river itself and some tributaries are used as sewages receivers (municipal and industrial waters). This is the reason of high degree of pollution of surface water and sediments [18]. Water pollution by heavy metals as a result of human activities is causing serious ecological problems almost in all parts of the world. This process has a particular importance because of the role played by river waters in the circulation of toxic chemical components between different parts of the environment, including the biota [15]. This situation is aggravated by the lack of natural elimination processes for metals. Data concerning the contents of heavy metals in the surface water of the Iskar River can be found in papers by Stoianov,S [19]. There are also papers concerning studies on heavy metals content in river sediments [17; 5; 20;], and their ecotoxicological impact [8; 7; 9;]. However the former investigations were carried out in disparate reaches of the river course and were usually concentrated in one part of the lotic ecosystem (surface water or sediments). The time distance of the cited papers, relatively small number of them concerning the level of heavy metals in surface water, and the lack of data regarding the microcomponents content of river sediments and hyporheic zone were the main reason for undertaking studies presented here.
2. Study area The study was carried out in the Iskar River in western Bulgaria. This is the longest river on bulgarian territory with a length of 368 km. The total catchment’s area of its basin is 8648 km2. The water samples were collected at 8 sites (Fig.1). Study sites have different characteristics because of the variety of their spatial localization in the river course (Table.1). However features of the river bed were almost the same in all 8 study sites - stony bottom, covered by a layer of small to medium gravel. Some of the sites have a description in relation to regular monitoring studies (Table.2).
Ecological Engineering and Environmental Protection, Vol.1, 2008 Table.1 Sampling design: localization and characteristics of sampling sites. Stations
Site 1 (confluence point) Site 2 (Dragoshinovo) Site 3 (above Iskar reservoir) Site 4 (Lesnovska outflow ) Site 5 ( Novi Iskar) Site 6 (Prokopanik) Site 7 (Eliseina) Site 8 (Orehovitza)
Surfac Hyporheic Sediment Remarks e water water sample sample sample + + Mountainous part of the river, negligible loading of sewage +
+
+
+
+
Mountainous part of the river, loading of minicipal and agricultural sewage Effluents from Samokov and outflow from Palakaria river
+
+
+
Industrial and municipal wastes from Sofia region
+
+
+
+
+
+
+
+
+
+
+
Mixed contamination of industrial, agricultural and municipal wastes Mining waters, industrial and municipal waste from Novi Iskar Mining waters, combined with small quantity municipal waste Predominantly agricultural wastes
Table.2 Chemical status of working surface water chemical points [21] (mod.-moderate)
Chemical status of working surface water chemical points Description between Samokov and reservoir Iskar site 2 and site 3 town Novi Iskar – site 5 Rebarkovo – close to site 7 Orehovitza – site 8 level of polution for the different points Index level class status
1999 good
2000 mod.
2001 mod.
2002 good
2003 good
poor good good
poor mod. good
poor mod. good
mod mod. mod.
poor mod. mod.
1 high
2 good
3 mod.
4 poor
5 bad
Ecological Engineering and Environmental Protection, Vol.1, 2008 Fig.1 Map of the study area and location of the sampling sites ( 1-8 ) Gigen
Site 8 Orehovitza
Koinare
Reseletz Mezdra Eliseina
Roman
Site 7 Svoge Leskovska
Iskretzka
Site 6 Prokopanik
Novi Iskar
Site 5 Site 4
Sofia
Lesnovska
Isk ar
Site 3 ак а П ал
рия
re
se r
vo i
r
Site 2 Dragoshinovo
Site 1 rni I e h C
r ska
Beli Iskar
Beli Iskar
Ecological Engineering and Environmental Protection, Vol.1, 2008 3. Materials and methods The studies of heavy metals contents were conducted in May 2005 and they concerned the following elements: copper, lead, zinc, manganese and iron. The hyporheic water samples were taken with a Bou-Rouch pump (35 cm depth) [2]. Samples of the surface sediment (sampled to a depth of 5 cm) were randomly taken using a plastic corer (10 cm diameter). Sediment samples were transported to the laboratory, air dried for 48 hours and grounded in a planetary mill. The total amount of heavy metals was determined after their mineralization according to the ISO 14 000 standards. Atomic absorption spectrometry (AAS) was applied. Correspondingly pH was measured (BDS 17.1.4.27-80). Basing on an analysis of the linear correlations of investigated parameters the relationship between heavy metals and their effect on metal transport was considered. Excel and SygmaStat were used for all data analyses.
4. Results 4.1 . Heavy metal content in waters (surface and hyporheic zone) and sediments. The concentration of investigated heavy metals was several times higher in hyporheic waters than the one in surface waters. According to the available data the most contaminated sites were connected with Eliseina industrial plants and Lesnovska River (site №4 and № 7). The situation was critical especially in surface waters at the site № 4 when the concentration of heavy metals had а maximum values (fig.2). In sediments the situation was different - at site №5 and №6 the concentration of heavy metals was higher. Taking into account the extreme values in surface waters the concentration of Fe differed most of all (standard deviation = 0.397; values: 0.151-1.47 mg/l). The concentrations of the other metals vary slightly. In hyporheic waters variations in the river length were much wider. This concerned especially Cu and Mn (standard deviation = 1.92 and 1.46 respectively; values: 0.054-5.954 and 0.85-4.65 mg/l respectively). In river sediments the most variable were again Cu and Mn (with values: 41-322.11 mg/kg and 435.67-699.93 mg/kg respectively) pH values were relatively stable and vary between 7-8.5. This showed that the chemical process of migration among different parts of the lotic environment had low rates. (fig.3) Fig.2 Content of heavy metals in the Iskar River a) In surface waters
0.06
c) In sediments
Hyporheic waters
Sediments concentartion mg\l
Cu
concentartion mg\l
Surface waters
b) In hyporheic waters
0.05 0.04 0.03 0.02 0.01 0 1 2 3 4 5 6 7 8 station
350 300 250 200 150 100 50 0 1 2 3 4 5 6 7 8 station
Pb
0.06
concentartion mg\l
concentartion mg\l
Ecological Engineering and Environmental Protection, Vol.1, 2008 0.05 0.04 0.03 0.02 0.01 0
350 300 250 200 150 100 50 0
Zn
1 2 3 4 5 6 7 8 station
0.3
concentartion mg\l
concentartion mg\l
1 2 3 4 5 6 7 8 station
0.25 0.2 0.15 0.1 0.05 0
350 300 250 200 150 100 50 0 1 2 3 4 5 6 7 8 station
0.3
concentartion mg\l
Mn
concentartion mg\l
1 2 3 4 5 6 7 8 station
0.25 0.2 0.15 0.1 0.05 0
800 600 400 200 0 1 2 3 4 5 6 7 8 station
2
concentartion mg\l
Fe
concentartion mg\l
1 2 3 4 5 6 7 8 station
1.5 1 0.5 0 1 2 3 4 5 6 7 8 station
surface water hyporheic water sediments pH
s t a t i on
9 8.5 8 7.5 7 6.5 6
1
600 400 200 0 1 2 3 4 5 6 7 8 station
Fig.3 pH values
pH
800
2
3
4 5 station
6
7
8
Ecological Engineering and Environmental Protection, Vol.1, 2008 4.2. Interrelation between heavy metals. In surface water statistically significant dependencies of this type were found between Cu and Zn, Fe and Mn ( r = 0,73; 0,78) (Table 3) An important linear correlation in hyporheic water between Cu and Pb (r = 0.96) was found. On testing the heavy metals interrelations in the river sediments, it turned out that the positive linear correlation coefficient was highest between Zn and Fe (r=0.73). While the negative correlation coefficient was highest between Mn and Fe (r = - 0.89). Table 3. Inter correlation matrix of the concentrations of heavy metals in the investigated sites (underlined values are with significant correlation |r| > 0.6) Metal (surface water) Fe
Cu
Pb
Zn
Mn
0,11
0,46
0,04
0,78
0,29
0,73
0,12
0,14
0,40
Cu Pb Zn Metal (hyporheic water) Fe
0,29
0,51
Cu
0,51
-0,20
-0,35
0,96
0,28
-0,21
0,41
-0,08
Pb Zn
0,36
Metal (sediment) Fe Cu
0,07
0,24
0,74
-0,89
0,03
0,18
-0,41
5. Discussion Heavy metals may occur in lotic ecosystems in a wide range of concentrations. (Table 4) The variations in spatial and temporal point of view are considerably high. However the industrial wastewater discharges and mining are major sources of metals in rivers. Significant amounts also enter surface waters in sewage as well as with atmospheric deposition (e.g. lead) [4]. The minimal concentrations of heavy metals in the Iskar (fig.2) are higher than those cited above.
Ecological Engineering and Environmental Protection, Vol.1, 2008 Table 4. World average concentrations of studied heavy metals in unpolluted rivers [4] Heavy metal / Fe Mn Cu Pb Zn Unit of measurement World average values of trace elements carried in solution by major unpolluted rivers mg/l 0,05 0,01 0,0014 0,00004 0,0002 World average values of trace elements in river suspended matter by major unpolluted rivers mg/kg 51,8 1 50 40 110
Since 1988 a decrease in production of Pb, Cu and Zn has been observed and respectively the concentrations of heavy metals in the Bulgarian rivers (including Iskar River) show gradual decline. [12]. A significant increase in heavy metals content in Iskar River just below Elisejna plant is normal tendency, connected with the existence of continuous mining discharge. Site 4 (Lesnovska outflow) was the other critical point, which concerns mostly surface waters. Obviously there is a permanent process of serious industrial pollution. The concentrations of heavy metals at sampling sites to some extent were dependent on interrelations between metals. The interesting correspondence was found between iron and manganese. In surface waters the linear correlation was positive (0.78) while in sediments it was strongly negative (-0.89). It seems that their behavior as regards the river length is absolutely different in these two parts of the lotic ecosystem. Mn-Fe oxides constitute an important transport phase for most metals and the natural pathway by which heavy metals enter into the water system from catchment’s area. Usually the effect of Mn on heavy metals transport is significant only at considerably heavily polluted parts of the rivers [4;16]. In hyporheic zone an important linear correlation between Cu and Pb (r = 0.9) was found. Probably these two heavy metals have a similar sources and processes of transportation in the hyporheal. A comparison of the results at station No 1, which has a negligible anthropogenic source of heavy metals with WHO, European, Canadian and Russian standards shows that, with some exceptions (lead, iron and manganese) the water quality is relatively higher. (table 5) Table 5. Examples of maximum allowable concentrations of selected water quality variables for different uses and comparison with the results from the most clean site (No1) [4] Use Variable Iron (mg l-1) Lead (mg l-1) Manganese (mg l-1) Zinc(mg l-1)
Drinking water WHO1 EU
Canada
USA
0.3 0.01
0.2 0.05
0.3 0.05
0.3 0.015
0.5(P)
0.05
0.05
0.05
3
0.115.01
5.0
5
Fisheries and aquatic life EU Canada Russia 1 0.3 0.1 0.0010.1 0.0078 0.01 0.032.08,10
0.03
0.01
Station 1
0,151 0,026 0,024 0,017
Ecological Engineering and Environmental Protection, Vol.1, 2008 As a result of adsorption and accumulation, the concentration of metals in bottom sediments is much higher than in the water above and this sometimes causes secondary pollution problems. The obtained results in the previous works showed that the most important aqual complex of heavy metals in Iskar River is the association of 4 polluting elements – Pb, Zn, Cu and Cd. From 1999 concentrations of investigated heavy metals in the sediments of Iskar Gorge (including sites 5, 6 and 7) show a gradual decline. The only exception of this tendency is the content of Pb. The higher lead concentration may be due to a complex of factors, including the development of the vehicle transport. Geoecological sustainability remains still disturbed in the highly impaired area of the river valley after “Eliseina” smelting plant. This concerns especially sediments and hyporheic waters. However there is a positive change connected with the decrease of heavy metal concentration through the years 1993-1999-2005. The hyporheic zone is the region beneath and adjacent to streams and rivers where surface and ground water mix [11]. Hyporheic zones link aquatic and terrestrial systems and serve as transition areas between surface water and groundwater systems. The hyporheic zone can also trap heavy metals and other contaminants that absorb to sediments, thus improving surface water quality. From the other hand heavy metals can move from groundwater into surface water through the hyporheic interface [14]. This kind of investigation has been done for the first time in Iskar River. The tendency of variation along the river course is similar to the one that has been found in sediments. From the other point of view the values are several times higher if we compare them with surface water data. Hyporheic zones are dynamic hydrologic ecotones critical for maintaining the health of many river systems. For that reason, further investigations will contribute to the understanding of heavy metal transport process in Bulgarian rivers.
6. Conclusions The results obtained in this study revealed that heavy metal levels in sediments and hyporheic waters exceeded those of the surface waters. The most significant linear correlation was found between iron and manganese. In surface water it was positive (0.78) while in sediments it was strongly negative (-0.89), which means that the transportation of these two elements was quite different in the separate sub-ecosystems. The comparison between recent heavy metals concentrations with previous gathered data reveals that, with the exception of lead content, which shows a serious increase, there is a decrease in the amount of these elements. This shows a partial improvement in the ecological status of the river ecosystem. This study brings an important contribution to the researches on the transportation and distribution of heavy metals in Bulgarian lotic ecosystems.
7. Acknowedgements. We are grateful to R. Hristova for laboratory support. Great part of this work was financed by Ministry of Education and Science (Bulgairia) in the frame the Project U-B-11/2003.
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