Investigating the mechanisms behind the impact of heavy metal pollution on aquatic ecosystems is urgently required. Due to increasing growth in the mining sector, pollution has become a serious threat to water resources and aquatic biodiversity and is causing unfavorable environmental changes and human health hazards. The aim of the present study was to investigate and assess the environmental risks of heavy metal pollution of river ecosystems in the Lake Sevan and Debed River catchment basins in Armenia, and a thorough study of their qualitative and quantitative parameters. Water samples were taken from the risky river sites of the Sevan and Debed basins in May and August 2013 and 2014. Investigations showed that due to mining and metallurgical industrial activities and the insufficient management of industrial waste and wastewater, the river ecosystems in these territories were exposed to heavy metal pollution, the degree of which in some sites of the Sotq, Masrik (Lake Sevan catchment basin), Debed, Alaverdi, Akhtala, and Chochkan (Debed River catchment basin) rivers may have posed health risks to aquatic life as well as to humans (at least in the case of river water used for drinking purposes). The results of a phytoplankton community study revealed that a decrease in the species diversity of planktonic algae in the investigated rivers was mainly conditioned by the impact of heavy metal pollution induced by mining and metallurgical industrial activities in the Lake Sevan and Debed River catchment basins.

Lake Sevan, Armenia, is the largest freshwater body in the Caucasus region. Cyanobacteria have become increasingly dominant in summer in Lake Sevan, reflecting the eutrophication of the lake and formed a massive bloom event in 2018. These recent observations mark the transition of this previously oligotrophic high mountain lake into an eutrophic lake with scum-forming cyanobacterial blooms. A bloom of Dolichospermum in July caused a sudden increase in chlorophyll-a concentrations up to, on average, 20 µg/L and a strong decrease in water transparency. The cyanobacterial genera Dolichospermum, Aphanizomenon, Anabaena, Cyanobium, and Synechococcus were detected by metagenomic analysis of the lake bacterioplankton. A qualitative and quantitative assessment of peptide-based secondary metabolites revealed the first detection of cyanotoxins in Lake Sevan. Ten types of microcystin congeners were found in Lake Sevan. The total concentration of microcystins in the phytoplankton varied from 0.34 to 2.49 µg/L. This first record of cyanotoxins in the largest lake in the Caucasus region calls for an urgent need for sustainable nutrient management and a systematic assessment of the ultimate causes that lead to the reoccurrence of scum-forming Cyanobacteria in this large Alpine lake.

The concentrations of some heavy metals (Fe, Zn, Mn, Cu, Mo, Pb, Cd) were measured in river waters, macrozoobenthos, and fish (Kura scrapers) from one of the most developed mining areas in Armenia, the Debed River catchment basin. In order to assess heavy metal contamination and its hydro-ecological and health effects, the macrozoobenthos quantitative and qualitative parameters, geo-accumulation index, and hazard index were determined. Microalgal extraction experiments were conducted to assess the microalgal remediation efficiency for heavy metal removal from mining wastewaters. The results showed that the rivers in many sites were polluted with different heavy metals induced by mining activities, which adversely affected macrozoobenthos growth and caused human health risks in the case of waters used for drinking purposes. However, the river fish, particularly Kura scrapers, were determined to be safe for consumption by the local people, as per the conditions of the evaluated fish ingestion rate. The results have shown that microalgal remediation, particularly with Desmodesmus abundans M3456, can be used for the efficient removal ~(62–100%) of certain emerging contaminants (Mn, Pb, Cu, Zn, Cd) from mining wastewater discharged in the Debed catchment basin.

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