Sengupta, M. and Dalwani, R. (Editors). 2008 Proceedings of Taal2007: The 12th World Lake Conference: 1028-1038

Heavy Metal Accumulation by Certain Aquatic Macrophytes from Lake Sevan (Armenia) L. Vardanyan1, K. Schmieder2, H. Sayadyan3, T. Heege4, J. Heblinski2,4, T. Agyemang2 and J. De5, J. Breuer6

1Dept. of Biology, University of Vanevan, #19, Gulbenkyan 29A, Yerevan, Armenia. 2University of Hohenheim, Institute of Landscape and Plant Ecology (320), D - 70593 Stuttgart, Germany, 3State Agrarian University, Dep. of Forestry and Agro-ecology, 74 Teryan, 375079 Yerevan, Armenia, 4EOMAP GmbH & Co KG, Sonderflughafen Oberpfaffenhofen, Geb.319 D - 82205 Gilching, Germany, 5Graduate School of Kuroshio Science, Kochi University, Nankoku, Kochi- 783 8502, Japan, 6State Institute of Agricultural Chemistry, Department of Soil and Fertilizer Analysis, D-70593 Stuttgart, Germany. Email: livag777@yahoo.com, schmied@uni-hohenheim.de, hovik_s@yahoo.com, heege@eomap.de, jaysankarde@yahoo.com, breuerj@uni-hohenheim.de

ABSTRACT General contamination of heavy metals in the environment is a major global concern, which has provoked the emergence of phytoremediation technologies for cleaning aquatic environment. Heavy metals are released into the environment from a wide range of natural and anthropogenic sources. Macrophytes are known as good indicators of heavy metal contamination in aquatic ecosystems and they act as biological filters by accumulating heavy metals from the surrounding environments. Concentrations of heavy metals such as Hg, Cd, Co, Cu, Mo, Ni, Pb, Tl and Zn were measured in macrophytes and water samples from the mouth of five rivers namely; Gavaraget, Argichi, Makenis, Masrik each of them meeting the Lake Sevan, Armenia. The collected plants were Batrachium rionii, Myosotis palustris, Lythrum salicaria, Scrophularia alata, Calamagrostis epigeios, Lepidium latifolium, Glyceria plicata, Veronica anagallis-aquatica, Butomus umbellatus, Sparganium erectum. The highest concentration of Ni (5.5 mg/kg) was observed in Glyceria plicata whereas concentrations (mg/kg) of all other metals were highest (Hg, 0.02; Cd, 0.46; Co, 3; Cu, 18.9; Pb, 6.9; Tl, 0.13 and Zn, 113) in Batrachium rionii. Range and trend in concentrations of Co (

species or populations originating from contaminated areas is the goal of phytoremediation (Baker and Brooks 1989; Salt et al. 1998; McCutcheon and Schnoor 2003). In 1991, Baker et al. concluded that phytoremediation by using certain species could offer a low cost and low technology alternative to current clean up technologies. Best plant candidates for phytoremediation must show accumulating capacities and tolerance to elevated contaminant concentrations to be able to survive and produce biomass. Some trace metals (e.g. Cu, Fe Zn, Mn, Ni, Mo, Se etc.) are essential for normal plant growth although both essential and non-essential metals (e.g. Hg, Cd, Pb, As) can result in growth inhibition and toxicity symptoms (Poschenrieder et al. 2006). Deleterious effects of trace metal pollution on plant at cellular levels might result from binding to proteins sulphydryl groups and thereby ending in the inhibition of enzyme activity and protein function and/or from disruption of cell transport processes. Also, most of the metals induce production of free radicals and active oxygen species (ROS) leading to an oxidative stress (Van Assche et al. 1990; Meharg 1994; Grato et al. 2005). Phytoremediation is a biological process in which living plants are used to remove, accumulate, degrade, or contain environmental contaminants. This passive remediation technique is based on the natural ability of vegetation to utilize nutrients, which are transported by capillary action from the soil and groundwater through a plants root system. The use of a plants own biological mechanisms to contain and reduce concentrations of inorganic and organic contaminants in soils, sediments, and groundwater is a slow process relying on a plants growth rate. However, with advances in biological, chemical, and engineering technologies, phytoremediation has the potential to serve as a sustained, ecologically sound method to remediate contaminated soil and groundwater (Brown et al. 1990). There are few mechanisms helping this process: Phytoextraction - uptake and concentration of substances from the environment into the plant biomass. Phytostabilization - reducing the mobility of substances in the environment, for example by limiting the leaching of substances from the soil. Phytotransformation - chemical modification of environmental substances as a direct result of plant metabolism, often resulting in their inactivation, detoxification (phytodegradation) or immobilization (phytostabilization). Phytostimulation - enhancement of soil microbial activity for the detoxification of contaminants, typically by organisms that associate with roots. This process is also known as rhizosphere detoxification

Phytovolatilization - removal of substances from soil or water with release into the air, sometimes as a result of phytotransformation to more volatile and / or less polluting substances. Rhizofiltration - filtering water through a mass of roots to remove toxic substances or excess nutrients. The pollutants remain absorbed in or adsorbed by the roots.

Aquatic macrophytes have been used for years for this phytoremediation purpose due to their characteristics to accumulate metals and metalloids (Welsh and Denny 1980; Say et al.1981; Heisey and Damman, 1982; Bishop and DeWaters 1986; Brix and Schierup 1989; Gardea-Torresday et al. 2005). Several works have demonstrated that aquatic macrophytes can perform as biological filters and they carry out a purifying function by accumulating dissolved metals and toxins in their tissue (Mejare and Bulow 2001; Prasad et al. 2005; Vardanyan and Ingole 2006). Macrophytes are an important component of aquatic communities due to their roles in oxygen production, nutrient cycling, controlling water quality, sediment stabilization and providing habitat and shelter for aquatic life (Gibbons et al. 1994; Ravera 2001). Hence changes in community dynamics can affect not only other biota but also other uses such as recreational and navigational use of the water body (Lewis 1996). Macrophytes actively take up metals from the sediments through their roots and translocate them to the shoots, which are available for grazing by fish. These may also be available for epiphytic phytoplankton and herbivorous and detritivorous invertebrates (Cardwell et al. 2002), representing a major route of bioaccumulation of heavy metals in the aquatic food chain. It is therefore of interest to assess the levels of heavy metals in macrophytes due to their importance in ecological processes. The immobile nature of macrophytes makes them a particularly effective bioindicator of heavy metal pollution as they represent/reflect the actual environmental contamination prevailing at that site. From an ecological perspective, the apparent lack of translocation of metals from roots to shoots means that the likelihood of bioaccumulation along trophic levels is reduced (Matagi 1998). This is because the higher concentrations of heavy metals are found in plant roots, organs that are unavailable for ingestion and heavy metals are thus tied up, or stored, in areas that are unlikely to be transferred into other areas of the ecosystem and its biota. Studies on the total ecosystem effects involving not only macrophytes but also sediment and other biota are necessary to provide a complete picture of the effects of heavy metals on aquatic ecosystems. Significant differences obtained for the heavy metal concentrations between macrophyte species suggest that the interactions and behaviours of heavy metals with macrophytes are different for each species (Prasad and Frietas 2003).

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Even after years of research on heavy metal accumulation in aquatic plants and water, and its hazardous impacts on environment, major questions still need to be answered. The factors affecting distribution and abundance of submerged aquatic vegetation and the effect of submerged aquatic vegetation on water quality are poorly understood. Also the problem with the selectivity of accumulation of elements by the macrophytes is yet to be studied properly (Monni et al. 2000). The present situation in many coastal waters does not provide an optimistic view (Samecka et al. 2001).

Lake Sevan was once a reservoir of water fit for drinking, according to the physical, chemical, and biological indices. But today, as a result of the intensive exploitation of the lake over the years, its ecological system has been disturbed, with falling water level and resultant swamping bringing about qualitative changes, and the state of its native fish life, the most sensitive index of the health of the lake, has changed.

The Sevan basin has a unique and relatively abundant flora and fauna. The flora of the lake basin is typical to the highlands of the Transcaucasus Region. Here seems to be the greatest diversity in plants (Vardanyan 2002). Along the shoreline of the lake, the greatest artificial woodland of the country is situated which gives a number of interesting examples of natural and human affected successions. Aquatic associations (plankton, benthos and ichthyofauna) are qualitatively poor with only a few dominant species, which simplified studies on ecological relationships (food web etc.).

About 1,600 species of vascular plants (50% of Armenias flora) have been registered in the lake basin. Of them, 48 species are in the Red Data Book of Armenia. The dominant communities of the Sevan basin are mountain steppe, sub-alpine and alpine vegetation (Barseghyan 1990).

Surface water in Armenia, and especially in Sevan Basin, generally seems to be of remarkably high quality, as compared to international standards. Groundwater resources are very well protected from pollution. Spring water usually is of good quality and can be used for drinking without further treatment. However, without proper attention the situation could change easily. The discharge of industrial pollutants, domestic sewerage and agricultural run-off into the lake increases the organic loading. Decomposition of organic matter decreases the oxygen concentrations of the water body. In Lake Sevan in the 1970s oxygen saturation in the bottom water of the profundal during the stratification period were close to analytical zero (Babayan et al. 2003). Worsening of oxygen conditions may seriously contaminate the water, endangering the plant and animals living therein. Dumping of garbage is a big problem for urban areas, especially for Sevan, Gavar, and Martuni.

Taking in consideration the role of macrophyte in Sevan basin and the fact that mentioned issues

have not been elucidated in the region, we proceeded to study the heavy metal accumulation peculiarities in macrophyte elucidation. Such discussions and investigations have become especially urgent over last few years keeping metal pollution of the environment (especially aquatic media) in view. Macrophytes are at the priority level in the list of cleaning and detoxification methods. Important functions of the lake ecosystem include the direct retention of nutrients and toxic substances during the growth period as well as by forming biotic structures for biofilms degrading organic and toxic substances; for epiyphytic algae and macroinvertebrates; and for providing measures for protection and redevelopment of juvenile fishes.

The aim of the present work was to investigate total concentrations of metals in ten of the most abundant aquatic macrophytes existing in the littoral zone of the Lake Sevan. Due to the high sensitivity of the used analytical method (inductively coupled plasma mass spectrometry; ICP-MS) elements not yet determined before in these plants species could be assayed. This study is done under the Sevan Management Information System (SEMIS) project. The project focuses on the fact that shore macrophyte vegetation has decreased immensely due to the direct loss of littoral area by lowering the lake level, the consequential increase of shore erosion and the unstable growing conditions due to the water level fluctuations.

MATERIALS AND METHODS Sampling site

The present study reports on the uptake of heavy metals, by aquatic macrophytes in Lake Sevan area. Lake Sevan is situated in the north-eastern part of Armenia. It is the greatest lake of the Caucasus Region and one of the greatest freshwater high mountain lakes of Eurasia (Fig.1). Before the increased artificial outflow which began in 1933, the surface of Lake Sevan was at an altitude of 1916.20 m above mean sea level with a surface area of 1,416 km2 and volume of 58.5km3 (Babayan et al. 2003). The decrease in water-level (about 20m) influenced an array of hydrological and ecological conditions.

The Lake Sevan watershed is located at the intersection of the Caucasian, Iranian and Mediterranean flora regions, each of which has its own distinctive plant assemblies. The range in altitude, sharp fluctuations in relief and soil variability create numerous landscape types that promote diversity in flora and plant associations. The watershed is known to contain over 1,500 species of flower and seed-producing and more than 250 species of spore-producing plants such as mosses and lichens. In addition, a large number of endemic (local varieties specific to the Sevan Basin) and relict (representatives of old disappearing flora) species can

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Ten plant samples with similar sizes from each species (table 1) were collected at sites. The plants were thoroughly washed at the sampling site with a jet stream of tap water until the surfaces appeared to be clean. The bulk water was removed by vigorous shaking of the plants and then by air-drying for 3 h. Plants were packed into paper bags and transported to the laboratory. There, the samples were washed several times with deionized water, air-dried and then placed in a drying oven at 700C for 6 h. Microscopic inspection of plant surfaces did not show any visible deposits of solid matter on it.

be found in the watershed (Barseghyan 1990). Many of these endemic and endangered plants have highly restricted areas of coverage and are sensitive to changes in environmental conditions.

Concentrations of heavy metals such as Hg, Cd, Co, Cu, Ni, Pb, Tl and Zn were measured in macrophytes and water samples from the mouth of four rivers namely, Gavaraget (sampling site No A), Argichi (site No B), Makenis (site No C), Masrik (site No D), each of them meeting the Lake Sevan (Fig.2). Water and plant samples A composite sample from each group of ten

plants was prepared by mechanically grinding all of them, using a stainless steel grinder, and then by careful homogenization of the powder. Before analysis, aliquots of this powder were again dried overnight at 70

Water samples were collected from four sites (Fig. 2) along the Lake shore: site A (Gavaraget), site B (Argichi), and site C (Makenis) and site D (Masrik) during our field trip on July 15, 2006. All samples were stored in clean polyethylene bottles under freezing temperature until analysis. Measurements of temperature, dissolved oxygen (DO), and pH were performed in the field.

0C.

Figure 1: Location of the Lake Sevan (Armenia).

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Figure 2: Sampling locations in the Lake Sevan Basin. Table 1: Macrophyte samples from Sevan Lake (Armenia) No Name Family Sampling

site 1 Batrachium rionii

(Lagger.) Nym. Ranunculaceae C

2 Myosotis palustris Lam.

Boraginaceae A

3 Lythrum salicaria L.

Lythraceae B

4 Scrophularia alata Gilib.

Scrophulariaceae D

5 Calamagrostis epigeios (L.) Roth.

Poaceae B

6 Lepidium latifolium L.

Brassicaceae B

7 Glyceria plicata Fries.

Gramineae D

8 Veronica anagallis-aquatica L.

Scrophulariaceae C

9 Sparganium erectum L.

Sparganiaceae C

10 Butomus umbellatus L.

Butomaceae A

Digestion of the samples: The acidified and filtered water samples were analyzed directly, whereas plant materials were

submitted to an acid mineralization procedure prior to ICP-MS (Elan 6000, Perkin Elmer-Sciex, Canada) measurements. Glass and plastic ware were decontaminated by immersing them for 2 days in 10% (v/v) Extran R_ solution (MERCK), followed by immersion for 3 days in diluted HNO3 (10% v/v) and finally rinsing with Milli-Q water. All chemical reagents used in this process were of at least analytical grade.

The samples were milled in a metal-free ball mill (ZrO2). An amount of 500 mg sample was weight into PTFE-vessels and 5 ml HNO3 and 1 ml H202 (high analytical grade) were added. The samples in closed vessels were left at room temperature over night, and then the vessels were put into a microwave-heated pressure digestion system (MLS 1200, MLS GmbH, Germany). They were digested for 20 minutes at 800 W and left to cool down to room temperature. After that the digests were transferred to 25-ml volumetric flasks and filled up to the mark with ultra pure water. Measurement of the elements:

The elements Cd, Co, Cu, Ni, Pb, Tl and Zn were measured by ICP-MS. The instrument was equipped with a Scott type Rhyton spray chamber and a quadrupole mass filter. Rh (10g/l) served as an

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internal standard. The samples were diluted as appropriate by 2% HNO3-solution and measured against external calibration curves.

Hg was measured by flow-injection hydride generation Atomic Absorption Spectrometry (AAS). The samples were mixed with a sodium-borohydride solution in an automated system. Elementary Hg formed due to the reduction was removed from the solution by a stream of Ar and transferred to a quartz-cell.

We determined the concentration of metals in water, plant, and sediment samples by Inductive1y Coup1ed Plasma- Optica1 Emission Spectrometry (ICP- OES; EN ISO 11885; for Ni, Zn), ICP-MS (DIN 38406-29; for Cd, Co and Cu) and by Cold Vapour Atomic Emission Spectrometry (CV-AAS; DIN EN 1483; for Hg).

The study on the uptake of heavy metals by plant from contaminated soils is based on the analysis of plant samples after pressure digestion for 20 minutes with 5 ml HNO3- and 1 ml H2O2. Soils were digested with aqua regia (DIN ISO 11466; 1997). RESULTS Water samples General water parameters showed little differences between the four selected sites. The temperature was 15 0.70C and the pH was 7.25-7.95). Details of other parameters are shown in table 2.

Water samples for heavy metal analyses were collected from four rivers namely; Masrik, Argichi, Makenis, and Gavaraget. Concentrations of heavy metals such as Cd, Co, Cu, Ni, Pl, Tl, Zn and Hg were estimated. Concentrations of Co (

maximum in Batrachium rionii. Only Ni (5.50mg/kg) was the maximum in Glyceria plicata (Fig. 4-5). The minimum accumulation of Cd (0.03mg/kg), Co (0.11mg/kg), Ni (0.94mg/kg), Pb (0.22mg/kg) and Tl (0.01mg/kg) were observed in Butomus umbellatus whereas, Cu (3.1mg/kg) and Zn (14 mg/kg) were in its minimum in Lepidium latifolium.

It is quite interesting to note that the macrophytes accumulated toxic heavy metals like Hg, Cd or Tl several hundred folds than that of the water bodies where these metals were always below detection limit. This shows the unique properties of these plants in purifying the water by means of entrapment of the heavy metals in their tissues. DISCUSSION

Factors such as light intensity, oxygen tension and temperature are known to affect the uptake of minerals (Devlin 1967). Moreover, the energy derived from photosynthesis and the oxygen released can improve conditions for the active absorption of elements. However, interactions between metals are often complex, and they are dependent on the metal concentration and pH of the growth medium (Balsberg-Pohlsson 1989).

Figure 4: Concentrations of Hg (upper panel), Co and Ni (middle panel) and Tl (lower panel). in ten plants collected from the Lake Sevan Basin Rivers.

Figure 5: Concentrations of Cd (upper panel), Cu and Pb (middle panel) and Zn (lower panel) in ten plants collected from the Lake Sevan Basin Rivers.

The effects of trace elements in an aquatic

ecosystem can be assessed by changes in the community structure, physiological activity and ultrastructural components of macrophytes (Chester and Stoner 1974; Bohn 1975; Gunterspergen et al. 1989; Blaylock and Huang 2000). However, comparison of metal content in macrophytes is often difficult because of differences in sampling time (age of plants) and presence of pollution sources. Moreover, the metal data cannot be extrapolated from one species to another or even within the same species, largely due to different accumulation rates. Nevertheless, copper (Cu) is known to reduce photosynthesis rates and respiration of aquatic moss, Fontinalis antipyretica (Vazguez et al. 2000). In eutrophic lakes, such as the Sevan Lake, very high local concentrations of metals often occur as a result of the strong reducing environment coupled with industrial and municipal discharges (Vardanyan 2002). Sevan Basin rivers have in and out flow of freshwater that may reduce the rate of metal accumulation in aquatic macrophytes.

Driel and Groot (1974) have studied the metal uptake, translocation and effects in plants growing on

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naturally polluted and unpolluted sediments. Their results suggest that aquatic plants may facilitate the transportation of metals from sediments up into shoots. The metals are thereby made available to grazing mollusks and, thus, reintroduced into the food web via fish to birds and humans (Brown and Chow 1977). In addition, macrophytes in shallow coastal zones function as living filters for nutrients and metals that become bound to living plant material and remain in the inner archipelago areas (Sawidis et al. 1995).

The problem of environment protection and rational utilization is extremely urgent today and its solution requires availability of great amount of ecological information. Hydrochemical and hydrobiological investigations provide the main part of such information. The increasing interest to the lake basin study with respect to the earlier mentioned information is related to eutrophication of the Lake Sevan due anthropogenic activities. Besides hydrological factors anthropogenic impact, recreational load, settlements growth, industry and agricultural development affected the lake water quality and hydrobiont quantitative and qualitative development.

However, one should recall that an increase in the concentration of these microelements in water is toxic for hydrobionts. Many of them produce toxic salts that occur in very low concentrations and therefore for their determination special methods with high determination accuracy, i.e. where determination error ratio is minimal, are required. One of the major properties of heavy metals is their ability to interact with a number of organic compounds that produce relatively strong complex ionic compounds such as cyanide, radonide and thiosulfates by combining with ions (Babayan 1988).

The microelements such as Cu, Zn, by combining with proteins of special type, produce compounds that form bases of several enzyme systems. A decrease in the concentration of Cu or Zn in a nutrient medium may cause different functional disorders, such as choroids. Availability of copper in sufficient levels in plants is essential to provide effect of Zn and Mn in plants (Heisey and Damman 1982). Deficiency of Zn causes a reduction in leaf size effect, yellow pigmentation of leaves, a reduction of fruit size effect, inhibition of young shoot growth (Bryan 1976). Zn is a component of several enzymes. Iron is a part of a number of oxidizing emzyms, plays a leading part in respiration function, and participates in photosynthesis and oxide reducing reactions in cells as a mediator of electrodes (Kamal et al. 2004).

Compared with other heavy metals, copper has the most toxic effects upon the growth and development of plants. A 1 mg/l concentration of copper may cause a withering of a plant (Balsberg-Pohlsson 1989). Copper affects the oxidizing system of a cell and is a compound of several enzyme systems.

It has been revealed that though the microelements Zn, Mo and Cu play a leading part in photosynthesis activity of plants and contribute in transfer of assimilators from leaves to generative organs and roots in plants, even a slight increase in the concentration of these elements in nutrient medium may inhibit mainly the growth and development of plants (Balsberg-Pohlsson 1989; Guilizzoni 1991). The microelements Co, Zn and Cu increase the drought-resistance of plants. Several microelements directly participate in the build-up of enzymes that act as catalysts in protein, carbohydrate and other cellular compounds exchange processes (Vangronsveld and Clijsters 1994).

Heavy metals generally penetrate from aquatic medium into human through waterplanthuman or waterplantanimalhuman biological chains (Smirnova 1984). Therefore finding solution to the problem of toxin tolerance in an aquatic medium is essential for an ecosystem and its components. There are reports with a variety of data detailing the effects of heavy metals on water and water plant structure and their properties, their enzymatic activity and nutrition pattern (Wittman 1979). A negative correlation was revealed between heavy metal content in growth medium and plants submerged organs and green biomass (Zayed et al. 1998). However these peculiarities are not always well-defined and greatly depend on the plant spices and compound forms of certain metals (Clemens et al. 2002.).

The effect of microelements on metabolism process is closely realated with composition of nutrient medium where the plants develop. For instance, our experiments indicate that plants of one species taken from different riverbank sites show different rates of heavy metal content (Vardanyan and Ingole 2006).

High concentration of heavy metal salts in storage reservoirs may depend on both geochemical peculiarities of the area and water inflow. If in the former case, aquatic organisms have developed some properties that are helpful in adaptation to the medium during long evolutionary process, then in the latter case aquatic organisms are exposed to injurious effects because of water pollution by heavy metals from industrial waste.

Water plants, by accumulating heavy metals in their tissues, play an important role in heavy metal transport mechanism. Experiments showed that plants accumulate 2.5 kg zinc from 1 hectare water surface (Fritioff and Greger 2001). Submerged vegetation accumulates heavy metals (Cu and Cr) 4-9 times more than riverside vegetation do. The accumulation ratio of magnesium and copper in respect to/against their content in the medium is the highest about 10 times in moss (Fontinalis). Submerged water plants, particularly hornwort (Ceratophyllum) accumulate mercury, particularly its inorganic compounds and they are so rapid in so

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doing that a balance with the solution is established in after two hours (Vardanyan and Ingole 2006).

Riverside vegetation also take up and accumulate mercury very rapidly, especially by underwater part/segment of the stem. Reed leaves can even evaporate mercury vapour into atmosphere, by taking it up from soil and bottom deposits, especially under optimum lighting and high transpiration factors (James et al. 1980). The accumulation of heavy metals in plants greatly depends on the concentration of these microelements in the medium. Experiments studying microelement accumulating properties of water plants revealed that they 'prefer' Mn, Ni, Cu, Mo, V, Sr, Ba, Fe, Al (Greger 1999). Chemical analysis of higher plants taken from industrial sewage polluted storage reservoirs indicate that accumulation of heavy metals by aquatic plants reduces concentration of these microelements in the water (Samecka et al. 2001).

This study was targeted to gain a better understanding of the importance of aquatic plants in heavy metal accumulation and detoxification mechanisms that may lead to elaboration of new pollution control and prevention facilities aimed to reserve the lakes ecosystem. Many of plant species investigated in the study were recognized as medicinal and edible ones.

CONCLUSION

From the present observations, it is concluded that there is a uniform pattern of heavy metal variation in the macrophytes of Lake Sevan Basin. In general, values of some metals like zinc and lead were high in almost all the specimens. Since the investigations on the heavy metals accumulation in macrophytes of Sevan Lake were carried out after a long time, hence the results presented here could be very useful for environmental monitoring and checking the health of the water body. The data presented here is indispensable information for studies of related nature. The aquatic macrophytes were found to be the potential source for accumulation of heavy metals from water and wetlands. Therefore, such studies should become an integral part of the sustainable development of the ecosystems and pollution assessment program.

Among various future tasks related to habitat technology, priority should be given to the restoration and creation of coastal nurseries such as macrophyte beds. There is an urgent need to study more of those specific macrophytes which are responsible for cleaning the water body from toxic heavy metals. It would be advantageous to understand the similarities and differences between accumulation pathways across different macrophyte for effective deployment in phytoremediation, as well as to identify new macrophytes capable of such activities.

ACKNOWLEDGEMENTS This study was carried out as a part of the SEMIS international project, funded by the Volkswagen Foundation. REFERENCES Babayan, A., Hakobyan, S., Jenderedjian, K., Muradyan, S.,

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