The objective of this research is to assess the distribution of heavy metals in the waters and sediments of the Voghji River and its tributaries impacted by mining activity and to reveal the real source of each of the heavy metals in the environment for assessing the pollution level of heavy metals. Voghji River with two main tributaries (Geghi and Norashenik) drain two mining regions. To identify distribution and pollution sources of heavy metals, the water and sediment samples were collected from eight sampling sites. The results of statistical analysis based on data sets of the period 2014–2016 showed that, after the influence of drainage water and wastewater of mining regions, heavy metal contents in the Voghji River basin dramatically increased. The waters of the Voghji River were highly polluted by Mn, Co, Cu, Zn, Mo, Cd, and Pb. The relation of metals content was highly changed due to anthropogenic impact disturbing the geochemical balance of the Voghji River. The water quality based on only heavy metal contents in the source of the Voghji River belongs to “good” chemical status, and in the sources of Geghi and Norashenik Rivers it is “moderate.” The water quality of Voghji and Norashenik Rivers is sharply worsening after the influence of mining activity, becoming “bad” chemical status. The research revealed the pollution sources of each metal.

Lake Sevan (Armenia) is one of the large freshwater high-mountain lakes of Eurasia. Detailed information about the extent and fate of trace elements on lake sediment and water quality has not been published yet. For this reason, surface sediment and water samples were collected from the southern and northern basins of Lake Sevan to determine trace element concentrations and assess the trace element behaviour. Geo-accumulation index, potential ecological risk index, and hazard index were calculated to estimate the environmental risk potential. In comparison to reference values, the investigated sediment samples contained elevated concentrations frequently for V, Cr, Co, Ni, Mo, Cd, Be, Ti, Rb, Sr, Se, Hf, and Th and occasionally for Cu, As, Li, B, Ag, Sb, Tl, Bi, U, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, and Tm. An overall potential ecological risk posed by all the investigated trace elements in the sediments was assessed to be moderate-considerable, however, Mo, Hg, and Cd were the elements with the highest ecological risk potential. The two basins of the lake showed significantly different behaviour according to the investigated trace element contents in the sediments to be higher in the bigger basin compared to the smaller basin. In comparison to reference concentrations in water samples according to the use of the adapted geo-accumulation index, elevated values for Ti, Cr, Cu, Cd, and Pb were observed. Elevated concentration was also observed in the case of B in nearly all water samples in comparison with literature values. Nevertheless, several water samples can be seen as not strongly anthropogenic influenced by Co, Ni, Sn, Sb, Ag, Hg, and Bi. The concentrations of trace elements in the lake water caused health risks to humans particularly children in the case of lake water used for drinking purposes, moreover, As was the main element posing health hazards. The results point out further attention to the sources of elevated trace elements in Lake Sevan, including anthropogenic influences and geological characteristics.

Lake Sevan is the second largest high-mountain lake in the Caucasus, with economic, historical and cultural significance. During the study period of 2015–2019, a total of 209 species of algae and cyanobacteria from eight taxonomic divisions were identified in the phytoplankton of Lake Sevan. Among them, diatoms increased their presence during the study period. The abundance and biomass values increased during the study period, while bloom outbreaks occurred with greater frequency. The Dolichospermum cyanobacterial species causing bloom in the summer, releasing toxins, were noted as posing a threat to the rational use of Lake Sevan. The species number in Big Sevan was generally lower than in Small Sevan. The simultaneous decrease in species richness during the study period from 2015 to 2019 from 53 to 40 species, the Shannon Index from 0.61 to 0.06 and the Saprobic Index from 2.00 to 1.73 reveals a tendency towards restructuring of the ecosystem of Lake Sevan towards simplification. In combination with an increase in quantitative indicators of phytoplankton and the number of species of eutrophic state indicators, these dynamics show an increase in the imbalance of the ecosystem. Redundance Discriminant analysis indicates an increase in water pH and copper concentration as negative factors, and an increase in the total ionic composition and temperature as factors stimulating the development of phytoplankton. Statistical maps revealed points on the coast of Lake Sevan responsible for factors influencing its ecosystem according to various variables, including copper influx. The analysis also revealed sufficient capacity of the ecosystem of Lake Sevan for self-purification during the study period. For the first time, 99 species of diatoms and cyanobacteria with IUCN categories were identified for Lake Sevan, seven of which are considered threatened. The number of threatened species of categories CR and EN decreased between 2015 and 2019, indicating adverse impacts on sensitive ecosystem species. An assessment of the changes occurring in Lake Sevan indicates the need to continue hydroecological monitoring in combination with bioindication and statistical methods and an inventory of all factors affecting the stability of the ecosystem of the high-mountain Lake Sevan.

Lake Sevan, a large, deep, alpine lake in the Lesser Caucasus is the focus of this Special Issue of the Journal of Limnology. It was an outstanding ecosystem 100 years ago characterised by excellent water quality, rich biodiversity with a high level of endemism, wide-ranging beds of macrophytes along the shores and a productive and sustainable fish production. Due to its beauty, natural history, and contributions to social and economic welfare it is also a cultural heritage for the Armenian Nation including its large diaspora.

The UN framework of “Integrated Water Resources Management” recommends countries establish a sustainable management of their water resources, which relies on the availability of proper assessment indexes for the ecological status of surface waters. Such indexes have been developed by many EU countries under the EU Water Framework Directive. Non-EU countries may be interested in adapting such assessment tools. Hence, we describe here a test of three macrophyte-based assessment tools developed in EU countries for use in Armenia. All three indices were tested in a regionally adapted version where local species were entered into reference taxonomic lists, river types were assigned, and matching exercises of the results with benthic macroinvertebrates and physical and chemical parameters of the rivers were performed. The results show that the three tested assessment tools produced similar spatial patterns of ecological status changes, while the adapted version of the MTR index had the highest number of significant correlations with various metrics of macrozoobenthos and hydro-chemical parameters. We conclude that assessment scores for rivers based on macrophytes can be used for rivers of the Caucasus after regional adaptation of the reference macrophyte list. We recommend that the modified MTR index be introduced into the national hydrobiological system of Armenia after some additional adaptations.