High altitude ecosystems have important natural ecological functions but are under increasing impacts from human activities and climate change. A detailed analysis of the water chemistry of Lake Rara, a high mountain lake in western Nepal, was carried out in October 2015 and April 2016. A total of 31 water samples were collected.Major ions (Ca 2+ , Mg 2+ , Na + , K + , SO 4 2−

The aim of this study was to investigate for the first time the morphology, physical and chemical characteristics of three high-altitude lakes in the Gokyo Valley, Everest National Park, Nepal. The moraine-dammed glacial lakes were studied for three seasons to create baseline data. The second, third, and fourth lakes in the Gokyo Valley are deeper than previously assumed. The vertical profiles of temperature and dissolved oxygen indicated that the thermocline zone varied between 10 and 20 m below the surface during the post-monsoon season. Although most of the analyzed metal concentrations were below the level recommended by the WHO for safe drinking water, lead (Pb) and cadmium (Cd) levels exceeded the limits in some of the samples. This has created great concern for human health. The probable route of these two pollutants is monsoon precipitation that carries industrial pollutants along its route. The sedimentation rates of Gokyo Lakes range from 0.069 to 0.089 cm per annum, which is within the limits of other high-altitude lakes. The present findings created a baseline database for some of the remote high-altitude lakes in Nepal that can be used for lake management and for assessing future changes in lake characteristics in the Himalayan region.

High altitude lakes are very sensitive to climate change due to their small catchment area, limited vegetation cover, surface water with low nutrients, and thin soil and low bedrock weathering rates. The present study was focused on high altitude Himalayan Lake Gosainkunda, situated at an elevation of 4300 m in the Langtang National Park, and carried out during the post-monsoon season (October) in 2010. The main aim of the study was to assess the water quality quantitatively considering the anthropogenic as well as natural impacts in the lake. The water samples were collected at six different sites to represent entirely the quality of the lake. The sampling sites were systematically designated as the inlet, outlet, human influence site, littoral zone, middle (central) and the deepest part of the lake.

Background and aims – Two unknown benthic diatom species belonging to the genus Achnanthidium Kütz., and found in French and Nepalese freshwater habitats, were investigated. Both species are here described as new and compared with the original material of Achnanthes minutissima var. macrocephala Hust. [≡ Achnanthidium macrocephalum (Hust.) Round & Bukht.] from Indonesia. Methods – The morphology of three small and capitate Achnanthidium species was investigated using light microscopy (LM) and scanning electron microscopy (SEM). Key results – Achnanthidium coxianum sp. nov. (from the Himalaya) belongs to the group of species with hooked terminal raphe endings, while Achnanthidium peetersianum sp. nov. (from France) has variable terminal raphe endings which are usually slightly bent. Achnanthidium macrocephalum is a much rarer species and illustrations concerning its identity in the literature do not conform to the type studied here. Conclusions – The three species are similar in LM but clearly distinct in SEM. The shape of the areolae and terminal raphe endings separate the species. Achnanthidium macrocephalum has often been misidentified in studies from many areas of the world. It is similar to the new species in valve outline and in its small dimensions.

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